[PATCH 0/2] rebase: add --fixup to fold a range into its oldest commit

[PATCH 0/2] rebase: add --fixup to fold a range into its oldest commit

[Harald Nordgren via GitGitGadget]

Adds git rebase --autosquash --fixup [<upstream>] to fold a range of commits
into its oldest one, reusing that commit's message.

Related idea: https://github.com/gitgitgadget/git/issues/1135

Harald Nordgren (2):
  t3415: remove prepare-commit-msg hook after use
  rebase: add --fixup-all to fold a range

 Documentation/git-rebase.adoc |  11 ++++
 builtin/rebase.c              |  13 ++++-
 sequencer.c                   |  24 +++++++-
 sequencer.h                   |   2 +-
 t/t3415-rebase-autosquash.sh  | 106 ++++++++++++++++++++++++++++++++++
 5 files changed, 152 insertions(+), 4 deletions(-)


base-commit: ea97ad8d017de0c9037451a78008a0fd60abea0c
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v1
Pull-Request: https://github.com/git/git/pull/2337
-- 
gitgitgadget

[PATCH 1/2] t3415: remove prepare-commit-msg hook after use

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

The "pick and fixup respect commit.cleanup" test left its
prepare-commit-msg hook in place, leaking it into later tests. Remove it
with test_when_finished.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 t/t3415-rebase-autosquash.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/t/t3415-rebase-autosquash.sh b/t/t3415-rebase-autosquash.sh
index 5033411a43..8964d1cc88 100755
--- a/t/t3415-rebase-autosquash.sh
+++ b/t/t3415-rebase-autosquash.sh
@@ -490,6 +490,7 @@ test_expect_success 'pick and fixup respect commit.cleanup' '
 	git reset --hard base &&
 	test_commit --no-tag "fixup! second commit" file1 fixup &&
 	test_commit something &&
+	test_when_finished "rm -f .git/hooks/prepare-commit-msg" &&
 	write_script .git/hooks/prepare-commit-msg <<-\EOF &&
 	printf "\n# Prepared\n" >> "$1"
 	EOF
-- 
gitgitgadget

[PATCH 2/2] rebase: add --fixup-all to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git rebase --autosquash --fixup-all [<upstream>]" to do this
directly. It keeps the first commit in the range as a "pick" and turns
every later commit into a "fixup", so the whole range collapses into a
single commit that reuses the first commit's message. With no <upstream>
argument the range is "@{upstream}..HEAD", folding all unpushed commits
into one.

Fold the commits in their original order, so that any fixup!/squash!
commits already present in the range are folded in as well. Allow the
flag only together with --autosquash, and reject --rebase-merges since a
merge commit cannot be folded into another commit.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-rebase.adoc |  11 ++++
 builtin/rebase.c              |  13 ++++-
 sequencer.c                   |  24 +++++++-
 sequencer.h                   |   2 +-
 t/t3415-rebase-autosquash.sh  | 105 ++++++++++++++++++++++++++++++++++
 5 files changed, 151 insertions(+), 4 deletions(-)

diff --git a/Documentation/git-rebase.adoc b/Documentation/git-rebase.adoc
index f6c22d1598..d1a3e4ef64 100644
--- a/Documentation/git-rebase.adoc
+++ b/Documentation/git-rebase.adoc
@@ -602,6 +602,16 @@ option can be used to override that setting.
 +
 See also INCOMPATIBLE OPTIONS below.
 
+--fixup-all::
+	Valid only when used with `--autosquash`.  Keep the first commit in
+	the range as a `pick` and change every later commit to a `fixup`, so
+	the whole range is folded into a single commit that reuses the first
+	commit's message.  With no `<upstream>` argument this folds all commits
+	since `@{upstream}` into one.  The commits are folded in their original
+	order, so any `fixup!`/`squash!` commits already in the range are folded
+	in as well.  Cannot be combined with `--rebase-merges`, as a merge
+	commit cannot be folded into another commit.
+
 --autostash::
 --no-autostash::
 	Automatically create a temporary stash entry before the operation
@@ -652,6 +662,7 @@ are incompatible with the following options:
  * --strategy
  * --strategy-option
  * --autosquash
+ * --fixup-all
  * --rebase-merges
  * --interactive
  * --exec
diff --git a/builtin/rebase.c b/builtin/rebase.c
index fa4f5d9306..a363fbc1f2 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -118,6 +118,7 @@ struct rebase_options {
 	int allow_rerere_autoupdate;
 	int keep_empty;
 	int autosquash;
+	int fixup_all;
 	char *gpg_sign_opt;
 	int autostash;
 	int committer_date_is_author_date;
@@ -329,7 +330,8 @@ static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
 	ret = complete_action(the_repository, &replay, flags,
 		shortrevisions, opts->onto_name, opts->onto,
 		&opts->orig_head->object.oid, &opts->exec,
-		opts->autosquash, opts->update_refs, &todo_list);
+		opts->autosquash, opts->fixup_all, opts->update_refs,
+		&todo_list);
 
 cleanup:
 	replay_opts_release(&replay);
@@ -1205,6 +1207,8 @@ int cmd_rebase(int argc,
 		OPT_BOOL(0, "autosquash", &options.autosquash,
 			 N_("move commits that begin with "
 			    "squash!/fixup! under -i")),
+		OPT_BOOL(0, "fixup-all", &options.fixup_all,
+			 N_("fold all commits in the range into the first one")),
 		OPT_BOOL(0, "update-refs", &options.update_refs,
 			 N_("update branches that point to commits "
 			    "that are being rebased")),
@@ -1594,6 +1598,13 @@ int cmd_rebase(int argc,
 	options.rebase_merges = (options.rebase_merges >= 0) ? options.rebase_merges :
 				((options.config_rebase_merges >= 0) ? options.config_rebase_merges : 0);
 
+	if (options.fixup_all && options.autosquash != 1)
+		die(_("--fixup-all requires --autosquash"));
+
+	if (options.fixup_all && options.rebase_merges)
+		die(_("options '%s' and '%s' cannot be used together"),
+		    "--fixup-all", "--rebase-merges");
+
 	if (options.autosquash == 1) {
 		imply_merge(&options, "--autosquash");
 	} else if (options.autosquash == -1) {
diff --git a/sequencer.c b/sequencer.c
index 57855b0066..eeaf6226fe 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -6554,11 +6554,29 @@ static int todo_list_add_update_ref_commands(struct todo_list *todo_list)
 	return 0;
 }
 
+static void todo_list_fixup_all_but_first(struct todo_list *todo_list)
+{
+	int i, seen_first = 0;
+
+	for (i = 0; i < todo_list->nr; i++) {
+		struct todo_item *item = todo_list->items + i;
+
+		if (!item->commit || item->command == TODO_DROP)
+			continue;
+		if (!seen_first) {
+			seen_first = 1;
+			item->command = TODO_PICK;
+			continue;
+		}
+		item->command = TODO_FIXUP;
+	}
+}
+
 int complete_action(struct repository *r, struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    struct commit *onto, const struct object_id *orig_head,
 		    struct string_list *commands, unsigned autosquash,
-		    unsigned update_refs,
+		    unsigned fixup_all, unsigned update_refs,
 		    struct todo_list *todo_list)
 {
 	char shortonto[GIT_MAX_HEXSZ + 1];
@@ -6581,7 +6599,9 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
 	if (update_refs && todo_list_add_update_ref_commands(todo_list))
 		return -1;
 
-	if (autosquash && todo_list_rearrange_squash(todo_list))
+	if (fixup_all)
+		todo_list_fixup_all_but_first(todo_list);
+	else if (autosquash && todo_list_rearrange_squash(todo_list))
 		return -1;
 
 	if (commands->nr)
diff --git a/sequencer.h b/sequencer.h
index 3164bd437d..9bb6b42c94 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -196,7 +196,7 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
 		    const char *shortrevisions, const char *onto_name,
 		    struct commit *onto, const struct object_id *orig_head,
 		    struct string_list *commands, unsigned autosquash,
-		    unsigned update_refs,
+		    unsigned fixup_all, unsigned update_refs,
 		    struct todo_list *todo_list);
 int todo_list_rearrange_squash(struct todo_list *todo_list);
 
diff --git a/t/t3415-rebase-autosquash.sh b/t/t3415-rebase-autosquash.sh
index 8964d1cc88..21d4159ebd 100755
--- a/t/t3415-rebase-autosquash.sh
+++ b/t/t3415-rebase-autosquash.sh
@@ -511,4 +511,109 @@ test_expect_success 'pick and fixup respect commit.cleanup' '
 	test_commit_message HEAD -m "something"
 '
 
+test_expect_success '--fixup-all folds the range into the first commit' '
+	git reset --hard base &&
+	test_commit --no-tag fold1 file_fold a &&
+	test_commit --no-tag fold2 file_fold b &&
+	test_commit --no-tag fold3 file_fold c &&
+	git rebase --autosquash --fixup-all HEAD~3 &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "fold1" &&
+	echo c >expect &&
+	test_cmp expect file_fold
+'
+
+test_expect_success '--fixup-all folds smoothly when a fixup! commit is in the series' '
+	git reset --hard base &&
+	test_commit --no-tag foldA file_fold a &&
+	test_commit --no-tag foldB file_fold b &&
+	git commit --allow-empty --fixup HEAD~1 &&
+	git rebase --autosquash --fixup-all HEAD~3 &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "foldA" &&
+	echo b >expect &&
+	test_cmp expect file_fold
+'
+
+test_expect_success '--fixup-all picks the first commit even if it is a fixup!' '
+	git reset --hard base &&
+	test_commit --no-tag fixupbase file_fix a &&
+	git commit --allow-empty --fixup HEAD &&
+	test_commit --no-tag fixuptail file_fix b &&
+	git rebase --autosquash --fixup-all HEAD~3 &&
+	test_cmp_rev base HEAD~1 &&
+	echo b >expect &&
+	test_cmp expect file_fix
+'
+
+test_expect_success '--fixup-all with a single commit in range is a no-op' '
+	git reset --hard base &&
+	test_commit --no-tag solo file_solo a &&
+	git rev-parse HEAD >expect &&
+	git rebase --autosquash --fixup-all HEAD~1 &&
+	git rev-parse HEAD >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--fixup-all with an empty range succeeds' '
+	git reset --hard base &&
+	git rebase --autosquash --fixup-all HEAD &&
+	test_cmp_rev base HEAD
+'
+
+test_expect_success '--fixup-all skips a dropped commit in the range' '
+	git reset --hard base &&
+	test_commit --no-tag fixdrop1 file_drop a &&
+	git commit --allow-empty -m "empty in the middle" &&
+	test_commit --no-tag fixdrop3 file_drop b &&
+	git rebase --autosquash --empty=drop --fixup-all HEAD~3 &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "fixdrop1" &&
+	echo b >expect &&
+	test_cmp expect file_drop
+'
+
+test_expect_success '--fixup-all folds a merge commit in the middle of the range' '
+	git reset --hard base &&
+	test_commit --no-tag mid-first &&
+	git checkout -b mid-side &&
+	test_commit --no-tag mid-merged &&
+	git checkout - &&
+	git merge --no-ff -m "merge mid-side" mid-side &&
+	test_commit --no-tag mid-last &&
+	git rebase --autosquash --fixup-all base &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "mid-first" &&
+	test_path_is_file mid-merged.t
+'
+
+test_expect_success '--fixup-all keeps the first flattened commit when a merge sorts first' '
+	git reset --hard base &&
+	git checkout -b head-side &&
+	test_commit --no-tag head-merged &&
+	git checkout - &&
+	git merge --no-ff -m "merge head-side" head-side &&
+	test_commit --no-tag head-last &&
+	git rebase --autosquash --fixup-all base &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "head-merged" &&
+	test_path_is_file head-merged.t
+'
+
+test_expect_success '--fixup-all requires --autosquash' '
+	git reset --hard base &&
+	test_must_fail git rebase --fixup-all HEAD~1 2>err &&
+	test_grep "fixup-all requires --autosquash" err &&
+	test_must_fail git rebase --no-autosquash --fixup-all HEAD~1 2>err &&
+	test_grep "fixup-all requires --autosquash" err
+'
+
+test_expect_success '--fixup-all and --rebase-merges cannot be combined' '
+	git reset --hard base &&
+	test_must_fail git rebase --autosquash --rebase-merges \
+		--fixup-all HEAD~1 2>err &&
+	test_grep "cannot be used together" err &&
+	test_path_is_missing .git/rebase-merge
+'
+
 test_done
-- 
gitgitgadget

Re: [PATCH 0/2] rebase: add --fixup to fold a range into its oldest commit

[Junio C Hamano]

"Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:

> Adds git rebase --autosquash --fixup [<upstream>] to fold a range of commits
> into its oldest one, reusing that commit's message.

[2/2] seems to add "--fixup-all" but I agree with the "related idea"
that naming it and modelling it after "merge --squash" would be
easier to understand.

> Related idea: https://github.com/gitgitgadget/git/issues/1135

I also wonder if we can do something like this without adding any
new option or command.  E.g., if you have four patch series, where
the initial implementation HEAD~3 is followed by "oops it was still
wrong" fix-up HEAD~2, HEAD~1 and HEAD, then

    git reset --soft HEAD~3 && git commit --amend --no-edit

is what the user wants to do, no?

Re: [PATCH 0/2] rebase: add --fixup to fold a range into its oldest commit

[Harald Nordgren]

> > Adds git rebase --autosquash --fixup [<upstream>] to fold a range of commits
> > into its oldest one, reusing that commit's message.
>
> [2/2] seems to add "--fixup-all" but I agree with the "related idea"
> that naming it and modelling it after "merge --squash" would be
> easier to understand.

Sounds reasonable.

> I also wonder if we can do something like this without adding any
> new option or command.  E.g., if you have four patch series, where
> the initial implementation HEAD~3 is followed by "oops it was still
> wrong" fix-up HEAD~2, HEAD~1 and HEAD, then
>
>     git reset --soft HEAD~3 && git commit --amend --no-edit
>
> is what the user wants to do, no?

I don't think it's enough. First of all the user has to know the N for
HEAD~N, and then 'git reset --soft HEAD~N && git commit --amend
--no-edit' is still quite ugly.


Harald

Re: [PATCH 0/2] rebase: add --fixup to fold a range into its oldest commit

[D. Ben Knoble]

On Mon, Jun 15, 2026 at 4:22 AM Harald Nordgren
<haraldnordgren@gmail.com> wrote:
> > > Adds git rebase --autosquash --fixup [<upstream>] to fold a range of commits
> > > into its oldest one, reusing that commit's message.
[snip]
> > I also wonder if we can do something like this without adding any
> > new option or command.  E.g., if you have four patch series, where
> > the initial implementation HEAD~3 is followed by "oops it was still
> > wrong" fix-up HEAD~2, HEAD~1 and HEAD, then
> >
> >     git reset --soft HEAD~3 && git commit --amend --no-edit
> >
> > is what the user wants to do, no?
>
> I don't think it's enough. First of all the user has to know the N for
> HEAD~N, and then 'git reset --soft HEAD~N && git commit --amend
> --no-edit' is still quite ugly.

Well, there are a few ways to get this more easily than counting; for example,

- git rev-list @{u}.. | tail -n1
- the lovely ":/<pattern>" or "@^{/<pattern>}" revision notations
- etc.

---

Stepping back a moment and assuming that the important thing you want
is the "squash" (and not necessarily the "rebase" moving commits onto
a new base), I wonder about

     git history squash <range>

which would squash all commits in the (now arbitrary!) range into the
first. That makes it somewhat more versatile at selecting commits, I
think, at the cost that re-basing is somewhat harder. That is, you
could then do

    git history squash @~3..

and things like

    git history squash @~5..@~2

As a future extension, I think we could support merge commits: merges
could be replayed as a merge into the final squash instead (creating
an octopus merge if there are multiple merges to replay), though I'm
hand-waving what we should do for conflicts. (We _do_ know what the
final tree should look like—the same as the final commit in the
range—so maybe we can actually avoid all conflicts?)

Anyway, I've cc'd Patrick for his opinion about whether this fits in
"git-history".

-- 
D. Ben Knoble

Re: [PATCH 0/2] rebase: add --fixup to fold a range into its oldest commit

[Patrick Steinhardt]

On Mon, Jun 15, 2026 at 11:17:21AM -0400, D. Ben Knoble wrote:
> On Mon, Jun 15, 2026 at 4:22 AM Harald Nordgren
> <haraldnordgren@gmail.com> wrote:
> > > > Adds git rebase --autosquash --fixup [<upstream>] to fold a range of commits
> > > > into its oldest one, reusing that commit's message.
> [snip]
> > > I also wonder if we can do something like this without adding any
> > > new option or command.  E.g., if you have four patch series, where
> > > the initial implementation HEAD~3 is followed by "oops it was still
> > > wrong" fix-up HEAD~2, HEAD~1 and HEAD, then
> > >
> > >     git reset --soft HEAD~3 && git commit --amend --no-edit
> > >
> > > is what the user wants to do, no?
> >
> > I don't think it's enough. First of all the user has to know the N for
> > HEAD~N, and then 'git reset --soft HEAD~N && git commit --amend
> > --no-edit' is still quite ugly.
> 
> Well, there are a few ways to get this more easily than counting; for example,
> 
> - git rev-list @{u}.. | tail -n1
> - the lovely ":/<pattern>" or "@^{/<pattern>}" revision notations
> - etc.
> 
> ---
> 
> Stepping back a moment and assuming that the important thing you want
> is the "squash" (and not necessarily the "rebase" moving commits onto
> a new base), I wonder about
> 
>      git history squash <range>
> 
> which would squash all commits in the (now arbitrary!) range into the
> first. That makes it somewhat more versatile at selecting commits, I
> think, at the cost that re-basing is somewhat harder. That is, you
> could then do
> 
>     git history squash @~3..
> 
> and things like
> 
>     git history squash @~5..@~2
> 
> As a future extension, I think we could support merge commits: merges
> could be replayed as a merge into the final squash instead (creating
> an octopus merge if there are multiple merges to replay), though I'm
> hand-waving what we should do for conflicts. (We _do_ know what the
> final tree should look like—the same as the final commit in the
> range—so maybe we can actually avoid all conflicts?)
> 
> Anyway, I've cc'd Patrick for his opinion about whether this fits in
> "git-history".

Yes, it does fit into git-history(1), and I do indeed already have plans
to implement such a command going forward. I wouldn't mind at all though
if somebody else beat me to it, I want to implement at least one more
command before I get to this.

Patrick

Re: [PATCH 0/2] rebase: add --fixup to fold a range into its oldest commit

[Harald Nordgren]

> Yes, it does fit into git-history(1), and I do indeed already have plans
> to implement such a command going forward. I wouldn't mind at all though
> if somebody else beat me to it, I want to implement at least one more
> command before I get to this.

What I like about 'git rebase --squash' is that when upstream is set
up, it understands the commit range automatically, whereas history
feels more removed from the current upstream. Maybe I'm wrong about
that.


Harald

[PATCH v2 0/2] rebase: add --squash to fold a range into its first commit

[Harald Nordgren via GitGitGadget]

Rename to rebase --squash.

Harald Nordgren (2):
  t3415: remove prepare-commit-msg hook after use
  rebase: add --squash to fold a range

 Documentation/git-rebase.adoc |  11 ++++
 builtin/rebase.c              |  16 ++++-
 sequencer.c                   |  24 ++++++-
 sequencer.h                   |   2 +-
 t/t3415-rebase-autosquash.sh  | 118 ++++++++++++++++++++++++++++++++++
 5 files changed, 166 insertions(+), 5 deletions(-)


base-commit: ea97ad8d017de0c9037451a78008a0fd60abea0c
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v2
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v1:

 1:  c55b9cd6f7 = 1:  c55b9cd6f7 t3415: remove prepare-commit-msg hook after use
 2:  bd1bc62aa8 ! 2:  22d4276ff5 rebase: add --fixup-all to fold a range
     @@ Metadata
      Author: Harald Nordgren <haraldnordgren@gmail.com>
      
       ## Commit message ##
     -    rebase: add --fixup-all to fold a range
     +    rebase: add --squash to fold a range
      
          Folding a series of commits into one required either an interactive
          rebase where each commit after the first was hand-edited to "fixup", or
          a "git reset --soft" to the merge base followed by "git commit --amend".
      
     -    Add "git rebase --autosquash --fixup-all [<upstream>]" to do this
     -    directly. It keeps the first commit in the range as a "pick" and turns
     -    every later commit into a "fixup", so the whole range collapses into a
     -    single commit that reuses the first commit's message. With no <upstream>
     -    argument the range is "@{upstream}..HEAD", folding all unpushed commits
     -    into one.
     +    Add "git rebase --squash [<upstream>]" to do this directly. It keeps
     +    the first commit in the range as a "pick" and turns every later commit
     +    into a "fixup", so the whole range collapses into a single commit that
     +    reuses the first commit's message. With no <upstream> argument the range
     +    is "@{upstream}..HEAD", folding all unpushed commits into one.
      
     -    Fold the commits in their original order, so that any fixup!/squash!
     -    commits already present in the range are folded in as well. Allow the
     -    flag only together with --autosquash, and reject --rebase-merges since a
     -    merge commit cannot be folded into another commit.
     +    The option implies the merge backend, so it works on its own without
     +    --autosquash. Fold the commits in their original order, so that any
     +    fixup!/squash! commits already present in the range are folded in as
     +    well. Reject --rebase-merges since a merge commit cannot be folded into
     +    another commit.
      
     +    Inspired-by: Sergey Chernov <serega.morph@gmail.com>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
       ## Documentation/git-rebase.adoc ##
     @@ Documentation/git-rebase.adoc: option can be used to override that setting.
       +
       See also INCOMPATIBLE OPTIONS below.
       
     -+--fixup-all::
     -+	Valid only when used with `--autosquash`.  Keep the first commit in
     -+	the range as a `pick` and change every later commit to a `fixup`, so
     -+	the whole range is folded into a single commit that reuses the first
     -+	commit's message.  With no `<upstream>` argument this folds all commits
     -+	since `@{upstream}` into one.  The commits are folded in their original
     -+	order, so any `fixup!`/`squash!` commits already in the range are folded
     -+	in as well.  Cannot be combined with `--rebase-merges`, as a merge
     -+	commit cannot be folded into another commit.
     ++--squash::
     ++	Keep the first commit in the range as a `pick` and change every later
     ++	commit to a `fixup`, so the whole range is folded into a single commit
     ++	that reuses the first commit's message.  With no `<upstream>` argument
     ++	this folds all commits since `@{upstream}` into one.  The commits are
     ++	folded in their original order, so any `fixup!`/`squash!` commits
     ++	already in the range are folded in as well.  Cannot be combined with
     ++	`--rebase-merges`, as a merge commit cannot be folded into another
     ++	commit.
      +
       --autostash::
       --no-autostash::
     @@ Documentation/git-rebase.adoc: are incompatible with the following options:
        * --strategy
        * --strategy-option
        * --autosquash
     -+ * --fixup-all
     ++ * --squash
        * --rebase-merges
        * --interactive
        * --exec
     @@ builtin/rebase.c: struct rebase_options {
       	int allow_rerere_autoupdate;
       	int keep_empty;
       	int autosquash;
     -+	int fixup_all;
     ++	int squash;
       	char *gpg_sign_opt;
       	int autostash;
       	int committer_date_is_author_date;
     @@ builtin/rebase.c: static int do_interactive_rebase(struct rebase_options *opts,
       		shortrevisions, opts->onto_name, opts->onto,
       		&opts->orig_head->object.oid, &opts->exec,
      -		opts->autosquash, opts->update_refs, &todo_list);
     -+		opts->autosquash, opts->fixup_all, opts->update_refs,
     ++		opts->autosquash, opts->squash, opts->update_refs,
      +		&todo_list);
       
       cleanup:
     @@ builtin/rebase.c: int cmd_rebase(int argc,
       		OPT_BOOL(0, "autosquash", &options.autosquash,
       			 N_("move commits that begin with "
       			    "squash!/fixup! under -i")),
     -+		OPT_BOOL(0, "fixup-all", &options.fixup_all,
     ++		OPT_BOOL(0, "squash", &options.squash,
      +			 N_("fold all commits in the range into the first one")),
       		OPT_BOOL(0, "update-refs", &options.update_refs,
       			 N_("update branches that point to commits "
       			    "that are being rebased")),
     +@@ builtin/rebase.c: int cmd_rebase(int argc,
     + 	if ((options.flags & REBASE_INTERACTIVE_EXPLICIT) ||
     + 	    (options.action != ACTION_NONE) ||
     + 	    (options.exec.nr > 0) ||
     +-	    options.autosquash == 1) {
     ++	    options.autosquash == 1 ||
     ++	    options.squash) {
     + 		allow_preemptive_ff = 0;
     + 	}
     + 	if (options.committer_date_is_author_date || options.ignore_date)
      @@ builtin/rebase.c: int cmd_rebase(int argc,
       	options.rebase_merges = (options.rebase_merges >= 0) ? options.rebase_merges :
       				((options.config_rebase_merges >= 0) ? options.config_rebase_merges : 0);
       
     -+	if (options.fixup_all && options.autosquash != 1)
     -+		die(_("--fixup-all requires --autosquash"));
     -+
     -+	if (options.fixup_all && options.rebase_merges)
     ++	if (options.squash && options.rebase_merges)
      +		die(_("options '%s' and '%s' cannot be used together"),
     -+		    "--fixup-all", "--rebase-merges");
     ++		    "--squash", "--rebase-merges");
     ++
     ++	if (options.squash)
     ++		imply_merge(&options, "--squash");
      +
       	if (options.autosquash == 1) {
       		imply_merge(&options, "--autosquash");
     @@ sequencer.c: static int todo_list_add_update_ref_commands(struct todo_list *todo
       		    struct commit *onto, const struct object_id *orig_head,
       		    struct string_list *commands, unsigned autosquash,
      -		    unsigned update_refs,
     -+		    unsigned fixup_all, unsigned update_refs,
     ++		    unsigned squash, unsigned update_refs,
       		    struct todo_list *todo_list)
       {
       	char shortonto[GIT_MAX_HEXSZ + 1];
     @@ sequencer.c: int complete_action(struct repository *r, struct replay_opts *opts,
       		return -1;
       
      -	if (autosquash && todo_list_rearrange_squash(todo_list))
     -+	if (fixup_all)
     ++	if (squash)
      +		todo_list_fixup_all_but_first(todo_list);
      +	else if (autosquash && todo_list_rearrange_squash(todo_list))
       		return -1;
     @@ sequencer.h: int complete_action(struct repository *r, struct replay_opts *opts,
       		    struct commit *onto, const struct object_id *orig_head,
       		    struct string_list *commands, unsigned autosquash,
      -		    unsigned update_refs,
     -+		    unsigned fixup_all, unsigned update_refs,
     ++		    unsigned squash, unsigned update_refs,
       		    struct todo_list *todo_list);
       int todo_list_rearrange_squash(struct todo_list *todo_list);
       
     @@ t/t3415-rebase-autosquash.sh: test_expect_success 'pick and fixup respect commit
       	test_commit_message HEAD -m "something"
       '
       
     -+test_expect_success '--fixup-all folds the range into the first commit' '
     ++test_expect_success '--squash folds the range into the first commit' '
      +	git reset --hard base &&
      +	test_commit --no-tag fold1 file_fold a &&
      +	test_commit --no-tag fold2 file_fold b &&
      +	test_commit --no-tag fold3 file_fold c &&
     -+	git rebase --autosquash --fixup-all HEAD~3 &&
     ++	git rebase --squash HEAD~3 &&
      +	test_cmp_rev base HEAD~1 &&
      +	test_commit_message HEAD -m "fold1" &&
      +	echo c >expect &&
      +	test_cmp expect file_fold
      +'
      +
     -+test_expect_success '--fixup-all folds smoothly when a fixup! commit is in the series' '
     ++test_expect_success '--squash folds smoothly when a fixup! commit is in the series' '
      +	git reset --hard base &&
      +	test_commit --no-tag foldA file_fold a &&
      +	test_commit --no-tag foldB file_fold b &&
      +	git commit --allow-empty --fixup HEAD~1 &&
     -+	git rebase --autosquash --fixup-all HEAD~3 &&
     ++	git rebase --squash HEAD~3 &&
      +	test_cmp_rev base HEAD~1 &&
      +	test_commit_message HEAD -m "foldA" &&
      +	echo b >expect &&
      +	test_cmp expect file_fold
      +'
      +
     -+test_expect_success '--fixup-all picks the first commit even if it is a fixup!' '
     ++test_expect_success '--squash picks the first commit even if it is a fixup!' '
      +	git reset --hard base &&
      +	test_commit --no-tag fixupbase file_fix a &&
      +	git commit --allow-empty --fixup HEAD &&
      +	test_commit --no-tag fixuptail file_fix b &&
     -+	git rebase --autosquash --fixup-all HEAD~3 &&
     ++	git rebase --squash HEAD~3 &&
      +	test_cmp_rev base HEAD~1 &&
      +	echo b >expect &&
      +	test_cmp expect file_fix
      +'
      +
     -+test_expect_success '--fixup-all with a single commit in range is a no-op' '
     ++test_expect_success '--squash with a single commit in range is a no-op' '
      +	git reset --hard base &&
      +	test_commit --no-tag solo file_solo a &&
      +	git rev-parse HEAD >expect &&
     -+	git rebase --autosquash --fixup-all HEAD~1 &&
     ++	git rebase --squash HEAD~1 &&
      +	git rev-parse HEAD >actual &&
      +	test_cmp expect actual
      +'
      +
     -+test_expect_success '--fixup-all with an empty range succeeds' '
     ++test_expect_success '--squash with an empty range succeeds' '
      +	git reset --hard base &&
     -+	git rebase --autosquash --fixup-all HEAD &&
     ++	git rebase --squash HEAD &&
      +	test_cmp_rev base HEAD
      +'
      +
     -+test_expect_success '--fixup-all skips a dropped commit in the range' '
     ++test_expect_success '--squash skips a dropped commit in the range' '
      +	git reset --hard base &&
      +	test_commit --no-tag fixdrop1 file_drop a &&
      +	git commit --allow-empty -m "empty in the middle" &&
      +	test_commit --no-tag fixdrop3 file_drop b &&
     -+	git rebase --autosquash --empty=drop --fixup-all HEAD~3 &&
     ++	git rebase --squash --empty=drop HEAD~3 &&
      +	test_cmp_rev base HEAD~1 &&
      +	test_commit_message HEAD -m "fixdrop1" &&
      +	echo b >expect &&
      +	test_cmp expect file_drop
      +'
      +
     -+test_expect_success '--fixup-all folds a merge commit in the middle of the range' '
     ++test_expect_success '--squash folds a merge commit in the middle of the range' '
      +	git reset --hard base &&
      +	test_commit --no-tag mid-first &&
      +	git checkout -b mid-side &&
     @@ t/t3415-rebase-autosquash.sh: test_expect_success 'pick and fixup respect commit
      +	git checkout - &&
      +	git merge --no-ff -m "merge mid-side" mid-side &&
      +	test_commit --no-tag mid-last &&
     -+	git rebase --autosquash --fixup-all base &&
     ++	git rebase --squash base &&
      +	test_cmp_rev base HEAD~1 &&
      +	test_commit_message HEAD -m "mid-first" &&
      +	test_path_is_file mid-merged.t
      +'
      +
     -+test_expect_success '--fixup-all keeps the first flattened commit when a merge sorts first' '
     ++test_expect_success '--squash keeps the first flattened commit when a merge sorts first' '
      +	git reset --hard base &&
      +	git checkout -b head-side &&
      +	test_commit --no-tag head-merged &&
      +	git checkout - &&
      +	git merge --no-ff -m "merge head-side" head-side &&
      +	test_commit --no-tag head-last &&
     -+	git rebase --autosquash --fixup-all base &&
     ++	git rebase --squash base &&
      +	test_cmp_rev base HEAD~1 &&
      +	test_commit_message HEAD -m "head-merged" &&
      +	test_path_is_file head-merged.t
      +'
      +
     -+test_expect_success '--fixup-all requires --autosquash' '
     ++test_expect_success '--squash takes precedence over --autosquash' '
      +	git reset --hard base &&
     -+	test_must_fail git rebase --fixup-all HEAD~1 2>err &&
     -+	test_grep "fixup-all requires --autosquash" err &&
     -+	test_must_fail git rebase --no-autosquash --fixup-all HEAD~1 2>err &&
     -+	test_grep "fixup-all requires --autosquash" err
     ++	test_commit --no-tag combo-first &&
     ++	test_commit --no-tag combo-mid &&
     ++	git commit --allow-empty --fixup HEAD~1 &&
     ++	test_commit --no-tag combo-last &&
     ++	git rebase --autosquash --squash base &&
     ++	test_cmp_rev base HEAD~1 &&
     ++	test_commit_message HEAD -m "combo-first"
     ++'
     ++
     ++test_expect_success '--squash folds the range with rebase.autosquash set' '
     ++	test_config rebase.autosquash true &&
     ++	git reset --hard base &&
     ++	test_commit --no-tag cfg-first &&
     ++	test_commit --no-tag cfg-last &&
     ++	git rebase --squash base &&
     ++	test_cmp_rev base HEAD~1 &&
     ++	test_commit_message HEAD -m "cfg-first"
      +'
      +
     -+test_expect_success '--fixup-all and --rebase-merges cannot be combined' '
     ++test_expect_success '--squash and --rebase-merges cannot be combined' '
      +	git reset --hard base &&
     -+	test_must_fail git rebase --autosquash --rebase-merges \
     -+		--fixup-all HEAD~1 2>err &&
     ++	test_must_fail git rebase --rebase-merges --squash HEAD~1 2>err &&
      +	test_grep "cannot be used together" err &&
      +	test_path_is_missing .git/rebase-merge
      +'

-- 
gitgitgadget

[PATCH v2 1/2] t3415: remove prepare-commit-msg hook after use

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

The "pick and fixup respect commit.cleanup" test left its
prepare-commit-msg hook in place, leaking it into later tests. Remove it
with test_when_finished.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 t/t3415-rebase-autosquash.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/t/t3415-rebase-autosquash.sh b/t/t3415-rebase-autosquash.sh
index 5033411a43..8964d1cc88 100755
--- a/t/t3415-rebase-autosquash.sh
+++ b/t/t3415-rebase-autosquash.sh
@@ -490,6 +490,7 @@ test_expect_success 'pick and fixup respect commit.cleanup' '
 	git reset --hard base &&
 	test_commit --no-tag "fixup! second commit" file1 fixup &&
 	test_commit something &&
+	test_when_finished "rm -f .git/hooks/prepare-commit-msg" &&
 	write_script .git/hooks/prepare-commit-msg <<-\EOF &&
 	printf "\n# Prepared\n" >> "$1"
 	EOF
-- 
gitgitgadget

[PATCH v2 2/2] rebase: add --squash to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git rebase --squash [<upstream>]" to do this directly. It keeps
the first commit in the range as a "pick" and turns every later commit
into a "fixup", so the whole range collapses into a single commit that
reuses the first commit's message. With no <upstream> argument the range
is "@{upstream}..HEAD", folding all unpushed commits into one.

The option implies the merge backend, so it works on its own without
--autosquash. Fold the commits in their original order, so that any
fixup!/squash! commits already present in the range are folded in as
well. Reject --rebase-merges since a merge commit cannot be folded into
another commit.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-rebase.adoc |  11 ++++
 builtin/rebase.c              |  16 ++++-
 sequencer.c                   |  24 ++++++-
 sequencer.h                   |   2 +-
 t/t3415-rebase-autosquash.sh  | 117 ++++++++++++++++++++++++++++++++++
 5 files changed, 165 insertions(+), 5 deletions(-)

diff --git a/Documentation/git-rebase.adoc b/Documentation/git-rebase.adoc
index f6c22d1598..4244288148 100644
--- a/Documentation/git-rebase.adoc
+++ b/Documentation/git-rebase.adoc
@@ -602,6 +602,16 @@ option can be used to override that setting.
 +
 See also INCOMPATIBLE OPTIONS below.
 
+--squash::
+	Keep the first commit in the range as a `pick` and change every later
+	commit to a `fixup`, so the whole range is folded into a single commit
+	that reuses the first commit's message.  With no `<upstream>` argument
+	this folds all commits since `@{upstream}` into one.  The commits are
+	folded in their original order, so any `fixup!`/`squash!` commits
+	already in the range are folded in as well.  Cannot be combined with
+	`--rebase-merges`, as a merge commit cannot be folded into another
+	commit.
+
 --autostash::
 --no-autostash::
 	Automatically create a temporary stash entry before the operation
@@ -652,6 +662,7 @@ are incompatible with the following options:
  * --strategy
  * --strategy-option
  * --autosquash
+ * --squash
  * --rebase-merges
  * --interactive
  * --exec
diff --git a/builtin/rebase.c b/builtin/rebase.c
index fa4f5d9306..2df9f04728 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -118,6 +118,7 @@ struct rebase_options {
 	int allow_rerere_autoupdate;
 	int keep_empty;
 	int autosquash;
+	int squash;
 	char *gpg_sign_opt;
 	int autostash;
 	int committer_date_is_author_date;
@@ -329,7 +330,8 @@ static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
 	ret = complete_action(the_repository, &replay, flags,
 		shortrevisions, opts->onto_name, opts->onto,
 		&opts->orig_head->object.oid, &opts->exec,
-		opts->autosquash, opts->update_refs, &todo_list);
+		opts->autosquash, opts->squash, opts->update_refs,
+		&todo_list);
 
 cleanup:
 	replay_opts_release(&replay);
@@ -1205,6 +1207,8 @@ int cmd_rebase(int argc,
 		OPT_BOOL(0, "autosquash", &options.autosquash,
 			 N_("move commits that begin with "
 			    "squash!/fixup! under -i")),
+		OPT_BOOL(0, "squash", &options.squash,
+			 N_("fold all commits in the range into the first one")),
 		OPT_BOOL(0, "update-refs", &options.update_refs,
 			 N_("update branches that point to commits "
 			    "that are being rebased")),
@@ -1471,7 +1475,8 @@ int cmd_rebase(int argc,
 	if ((options.flags & REBASE_INTERACTIVE_EXPLICIT) ||
 	    (options.action != ACTION_NONE) ||
 	    (options.exec.nr > 0) ||
-	    options.autosquash == 1) {
+	    options.autosquash == 1 ||
+	    options.squash) {
 		allow_preemptive_ff = 0;
 	}
 	if (options.committer_date_is_author_date || options.ignore_date)
@@ -1594,6 +1599,13 @@ int cmd_rebase(int argc,
 	options.rebase_merges = (options.rebase_merges >= 0) ? options.rebase_merges :
 				((options.config_rebase_merges >= 0) ? options.config_rebase_merges : 0);
 
+	if (options.squash && options.rebase_merges)
+		die(_("options '%s' and '%s' cannot be used together"),
+		    "--squash", "--rebase-merges");
+
+	if (options.squash)
+		imply_merge(&options, "--squash");
+
 	if (options.autosquash == 1) {
 		imply_merge(&options, "--autosquash");
 	} else if (options.autosquash == -1) {
diff --git a/sequencer.c b/sequencer.c
index 57855b0066..bb42b40796 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -6554,11 +6554,29 @@ static int todo_list_add_update_ref_commands(struct todo_list *todo_list)
 	return 0;
 }
 
+static void todo_list_fixup_all_but_first(struct todo_list *todo_list)
+{
+	int i, seen_first = 0;
+
+	for (i = 0; i < todo_list->nr; i++) {
+		struct todo_item *item = todo_list->items + i;
+
+		if (!item->commit || item->command == TODO_DROP)
+			continue;
+		if (!seen_first) {
+			seen_first = 1;
+			item->command = TODO_PICK;
+			continue;
+		}
+		item->command = TODO_FIXUP;
+	}
+}
+
 int complete_action(struct repository *r, struct replay_opts *opts, unsigned flags,
 		    const char *shortrevisions, const char *onto_name,
 		    struct commit *onto, const struct object_id *orig_head,
 		    struct string_list *commands, unsigned autosquash,
-		    unsigned update_refs,
+		    unsigned squash, unsigned update_refs,
 		    struct todo_list *todo_list)
 {
 	char shortonto[GIT_MAX_HEXSZ + 1];
@@ -6581,7 +6599,9 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
 	if (update_refs && todo_list_add_update_ref_commands(todo_list))
 		return -1;
 
-	if (autosquash && todo_list_rearrange_squash(todo_list))
+	if (squash)
+		todo_list_fixup_all_but_first(todo_list);
+	else if (autosquash && todo_list_rearrange_squash(todo_list))
 		return -1;
 
 	if (commands->nr)
diff --git a/sequencer.h b/sequencer.h
index 3164bd437d..1d5a164f02 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -196,7 +196,7 @@ int complete_action(struct repository *r, struct replay_opts *opts, unsigned fla
 		    const char *shortrevisions, const char *onto_name,
 		    struct commit *onto, const struct object_id *orig_head,
 		    struct string_list *commands, unsigned autosquash,
-		    unsigned update_refs,
+		    unsigned squash, unsigned update_refs,
 		    struct todo_list *todo_list);
 int todo_list_rearrange_squash(struct todo_list *todo_list);
 
diff --git a/t/t3415-rebase-autosquash.sh b/t/t3415-rebase-autosquash.sh
index 8964d1cc88..ce9abe5147 100755
--- a/t/t3415-rebase-autosquash.sh
+++ b/t/t3415-rebase-autosquash.sh
@@ -511,4 +511,121 @@ test_expect_success 'pick and fixup respect commit.cleanup' '
 	test_commit_message HEAD -m "something"
 '
 
+test_expect_success '--squash folds the range into the first commit' '
+	git reset --hard base &&
+	test_commit --no-tag fold1 file_fold a &&
+	test_commit --no-tag fold2 file_fold b &&
+	test_commit --no-tag fold3 file_fold c &&
+	git rebase --squash HEAD~3 &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "fold1" &&
+	echo c >expect &&
+	test_cmp expect file_fold
+'
+
+test_expect_success '--squash folds smoothly when a fixup! commit is in the series' '
+	git reset --hard base &&
+	test_commit --no-tag foldA file_fold a &&
+	test_commit --no-tag foldB file_fold b &&
+	git commit --allow-empty --fixup HEAD~1 &&
+	git rebase --squash HEAD~3 &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "foldA" &&
+	echo b >expect &&
+	test_cmp expect file_fold
+'
+
+test_expect_success '--squash picks the first commit even if it is a fixup!' '
+	git reset --hard base &&
+	test_commit --no-tag fixupbase file_fix a &&
+	git commit --allow-empty --fixup HEAD &&
+	test_commit --no-tag fixuptail file_fix b &&
+	git rebase --squash HEAD~3 &&
+	test_cmp_rev base HEAD~1 &&
+	echo b >expect &&
+	test_cmp expect file_fix
+'
+
+test_expect_success '--squash with a single commit in range is a no-op' '
+	git reset --hard base &&
+	test_commit --no-tag solo file_solo a &&
+	git rev-parse HEAD >expect &&
+	git rebase --squash HEAD~1 &&
+	git rev-parse HEAD >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--squash with an empty range succeeds' '
+	git reset --hard base &&
+	git rebase --squash HEAD &&
+	test_cmp_rev base HEAD
+'
+
+test_expect_success '--squash skips a dropped commit in the range' '
+	git reset --hard base &&
+	test_commit --no-tag fixdrop1 file_drop a &&
+	git commit --allow-empty -m "empty in the middle" &&
+	test_commit --no-tag fixdrop3 file_drop b &&
+	git rebase --squash --empty=drop HEAD~3 &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "fixdrop1" &&
+	echo b >expect &&
+	test_cmp expect file_drop
+'
+
+test_expect_success '--squash folds a merge commit in the middle of the range' '
+	git reset --hard base &&
+	test_commit --no-tag mid-first &&
+	git checkout -b mid-side &&
+	test_commit --no-tag mid-merged &&
+	git checkout - &&
+	git merge --no-ff -m "merge mid-side" mid-side &&
+	test_commit --no-tag mid-last &&
+	git rebase --squash base &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "mid-first" &&
+	test_path_is_file mid-merged.t
+'
+
+test_expect_success '--squash keeps the first flattened commit when a merge sorts first' '
+	git reset --hard base &&
+	git checkout -b head-side &&
+	test_commit --no-tag head-merged &&
+	git checkout - &&
+	git merge --no-ff -m "merge head-side" head-side &&
+	test_commit --no-tag head-last &&
+	git rebase --squash base &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "head-merged" &&
+	test_path_is_file head-merged.t
+'
+
+test_expect_success '--squash takes precedence over --autosquash' '
+	git reset --hard base &&
+	test_commit --no-tag combo-first &&
+	test_commit --no-tag combo-mid &&
+	git commit --allow-empty --fixup HEAD~1 &&
+	test_commit --no-tag combo-last &&
+	git rebase --autosquash --squash base &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "combo-first"
+'
+
+test_expect_success '--squash folds the range with rebase.autosquash set' '
+	test_config rebase.autosquash true &&
+	git reset --hard base &&
+	test_commit --no-tag cfg-first &&
+	test_commit --no-tag cfg-last &&
+	git rebase --squash base &&
+	test_cmp_rev base HEAD~1 &&
+	test_commit_message HEAD -m "cfg-first"
+'
+
+test_expect_success '--squash and --rebase-merges cannot be combined' '
+	git reset --hard base &&
+	test_must_fail git rebase --rebase-merges --squash HEAD~1 2>err &&
+	test_grep "cannot be used together" err &&
+	test_path_is_missing .git/rebase-merge
+'
+
 test_done
-- 
gitgitgadget

Re: [PATCH v2 0/2] rebase: add --squash to fold a range into its first commit

[Phillip Wood]

Hi Harald

On 15/06/2026 09:37, Harald Nordgren via GitGitGadget wrote:
> Rename to rebase --squash.

Please include the original cover letter as well so people who have not 
read the previous version know what the series is about.

I agree that git-history might be a better place for this but I'm not 
opposed to adding a --squash option to git-rebase. However I do think we 
need to think about the implementation - picking consecutive commits 
when we want to squash them together is inefficient and if we're 
changing the base risks the user having to stop to resolve conflicts 
multiple times. Regardless of whether this ends up in git-rebase or 
git-history I think the implementation should cherry-pick the whole 
commit range by doing the equivalent of

   git merge-tree --merge-base $(git merge-base HEAD @{upstream}) \
                  @{upstream} HEAD

We should also let the user edit the commit message to reflect the 
changes that are being squashed in. We should think about what support 
we want for "amend!" commits that replace the commit message when rebasing.

Thanks

Phillip

> Harald Nordgren (2):
>    t3415: remove prepare-commit-msg hook after use
>    rebase: add --squash to fold a range
> 
>   Documentation/git-rebase.adoc |  11 ++++
>   builtin/rebase.c              |  16 ++++-
>   sequencer.c                   |  24 ++++++-
>   sequencer.h                   |   2 +-
>   t/t3415-rebase-autosquash.sh  | 118 ++++++++++++++++++++++++++++++++++
>   5 files changed, 166 insertions(+), 5 deletions(-)
> 
> 
> base-commit: ea97ad8d017de0c9037451a78008a0fd60abea0c
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v2
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v2
> Pull-Request: https://github.com/git/git/pull/2337
> 
> Range-diff vs v1:
> 
>   1:  c55b9cd6f7 = 1:  c55b9cd6f7 t3415: remove prepare-commit-msg hook after use
>   2:  bd1bc62aa8 ! 2:  22d4276ff5 rebase: add --fixup-all to fold a range
>       @@ Metadata
>        Author: Harald Nordgren <haraldnordgren@gmail.com>
>        
>         ## Commit message ##
>       -    rebase: add --fixup-all to fold a range
>       +    rebase: add --squash to fold a range
>        
>            Folding a series of commits into one required either an interactive
>            rebase where each commit after the first was hand-edited to "fixup", or
>            a "git reset --soft" to the merge base followed by "git commit --amend".
>        
>       -    Add "git rebase --autosquash --fixup-all [<upstream>]" to do this
>       -    directly. It keeps the first commit in the range as a "pick" and turns
>       -    every later commit into a "fixup", so the whole range collapses into a
>       -    single commit that reuses the first commit's message. With no <upstream>
>       -    argument the range is "@{upstream}..HEAD", folding all unpushed commits
>       -    into one.
>       +    Add "git rebase --squash [<upstream>]" to do this directly. It keeps
>       +    the first commit in the range as a "pick" and turns every later commit
>       +    into a "fixup", so the whole range collapses into a single commit that
>       +    reuses the first commit's message. With no <upstream> argument the range
>       +    is "@{upstream}..HEAD", folding all unpushed commits into one.
>        
>       -    Fold the commits in their original order, so that any fixup!/squash!
>       -    commits already present in the range are folded in as well. Allow the
>       -    flag only together with --autosquash, and reject --rebase-merges since a
>       -    merge commit cannot be folded into another commit.
>       +    The option implies the merge backend, so it works on its own without
>       +    --autosquash. Fold the commits in their original order, so that any
>       +    fixup!/squash! commits already present in the range are folded in as
>       +    well. Reject --rebase-merges since a merge commit cannot be folded into
>       +    another commit.
>        
>       +    Inspired-by: Sergey Chernov <serega.morph@gmail.com>
>            Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
>        
>         ## Documentation/git-rebase.adoc ##
>       @@ Documentation/git-rebase.adoc: option can be used to override that setting.
>         +
>         See also INCOMPATIBLE OPTIONS below.
>         
>       -+--fixup-all::
>       -+	Valid only when used with `--autosquash`.  Keep the first commit in
>       -+	the range as a `pick` and change every later commit to a `fixup`, so
>       -+	the whole range is folded into a single commit that reuses the first
>       -+	commit's message.  With no `<upstream>` argument this folds all commits
>       -+	since `@{upstream}` into one.  The commits are folded in their original
>       -+	order, so any `fixup!`/`squash!` commits already in the range are folded
>       -+	in as well.  Cannot be combined with `--rebase-merges`, as a merge
>       -+	commit cannot be folded into another commit.
>       ++--squash::
>       ++	Keep the first commit in the range as a `pick` and change every later
>       ++	commit to a `fixup`, so the whole range is folded into a single commit
>       ++	that reuses the first commit's message.  With no `<upstream>` argument
>       ++	this folds all commits since `@{upstream}` into one.  The commits are
>       ++	folded in their original order, so any `fixup!`/`squash!` commits
>       ++	already in the range are folded in as well.  Cannot be combined with
>       ++	`--rebase-merges`, as a merge commit cannot be folded into another
>       ++	commit.
>        +
>         --autostash::
>         --no-autostash::
>       @@ Documentation/git-rebase.adoc: are incompatible with the following options:
>          * --strategy
>          * --strategy-option
>          * --autosquash
>       -+ * --fixup-all
>       ++ * --squash
>          * --rebase-merges
>          * --interactive
>          * --exec
>       @@ builtin/rebase.c: struct rebase_options {
>         	int allow_rerere_autoupdate;
>         	int keep_empty;
>         	int autosquash;
>       -+	int fixup_all;
>       ++	int squash;
>         	char *gpg_sign_opt;
>         	int autostash;
>         	int committer_date_is_author_date;
>       @@ builtin/rebase.c: static int do_interactive_rebase(struct rebase_options *opts,
>         		shortrevisions, opts->onto_name, opts->onto,
>         		&opts->orig_head->object.oid, &opts->exec,
>        -		opts->autosquash, opts->update_refs, &todo_list);
>       -+		opts->autosquash, opts->fixup_all, opts->update_refs,
>       ++		opts->autosquash, opts->squash, opts->update_refs,
>        +		&todo_list);
>         
>         cleanup:
>       @@ builtin/rebase.c: int cmd_rebase(int argc,
>         		OPT_BOOL(0, "autosquash", &options.autosquash,
>         			 N_("move commits that begin with "
>         			    "squash!/fixup! under -i")),
>       -+		OPT_BOOL(0, "fixup-all", &options.fixup_all,
>       ++		OPT_BOOL(0, "squash", &options.squash,
>        +			 N_("fold all commits in the range into the first one")),
>         		OPT_BOOL(0, "update-refs", &options.update_refs,
>         			 N_("update branches that point to commits "
>         			    "that are being rebased")),
>       +@@ builtin/rebase.c: int cmd_rebase(int argc,
>       + 	if ((options.flags & REBASE_INTERACTIVE_EXPLICIT) ||
>       + 	    (options.action != ACTION_NONE) ||
>       + 	    (options.exec.nr > 0) ||
>       +-	    options.autosquash == 1) {
>       ++	    options.autosquash == 1 ||
>       ++	    options.squash) {
>       + 		allow_preemptive_ff = 0;
>       + 	}
>       + 	if (options.committer_date_is_author_date || options.ignore_date)
>        @@ builtin/rebase.c: int cmd_rebase(int argc,
>         	options.rebase_merges = (options.rebase_merges >= 0) ? options.rebase_merges :
>         				((options.config_rebase_merges >= 0) ? options.config_rebase_merges : 0);
>         
>       -+	if (options.fixup_all && options.autosquash != 1)
>       -+		die(_("--fixup-all requires --autosquash"));
>       -+
>       -+	if (options.fixup_all && options.rebase_merges)
>       ++	if (options.squash && options.rebase_merges)
>        +		die(_("options '%s' and '%s' cannot be used together"),
>       -+		    "--fixup-all", "--rebase-merges");
>       ++		    "--squash", "--rebase-merges");
>       ++
>       ++	if (options.squash)
>       ++		imply_merge(&options, "--squash");
>        +
>         	if (options.autosquash == 1) {
>         		imply_merge(&options, "--autosquash");
>       @@ sequencer.c: static int todo_list_add_update_ref_commands(struct todo_list *todo
>         		    struct commit *onto, const struct object_id *orig_head,
>         		    struct string_list *commands, unsigned autosquash,
>        -		    unsigned update_refs,
>       -+		    unsigned fixup_all, unsigned update_refs,
>       ++		    unsigned squash, unsigned update_refs,
>         		    struct todo_list *todo_list)
>         {
>         	char shortonto[GIT_MAX_HEXSZ + 1];
>       @@ sequencer.c: int complete_action(struct repository *r, struct replay_opts *opts,
>         		return -1;
>         
>        -	if (autosquash && todo_list_rearrange_squash(todo_list))
>       -+	if (fixup_all)
>       ++	if (squash)
>        +		todo_list_fixup_all_but_first(todo_list);
>        +	else if (autosquash && todo_list_rearrange_squash(todo_list))
>         		return -1;
>       @@ sequencer.h: int complete_action(struct repository *r, struct replay_opts *opts,
>         		    struct commit *onto, const struct object_id *orig_head,
>         		    struct string_list *commands, unsigned autosquash,
>        -		    unsigned update_refs,
>       -+		    unsigned fixup_all, unsigned update_refs,
>       ++		    unsigned squash, unsigned update_refs,
>         		    struct todo_list *todo_list);
>         int todo_list_rearrange_squash(struct todo_list *todo_list);
>         
>       @@ t/t3415-rebase-autosquash.sh: test_expect_success 'pick and fixup respect commit
>         	test_commit_message HEAD -m "something"
>         '
>         
>       -+test_expect_success '--fixup-all folds the range into the first commit' '
>       ++test_expect_success '--squash folds the range into the first commit' '
>        +	git reset --hard base &&
>        +	test_commit --no-tag fold1 file_fold a &&
>        +	test_commit --no-tag fold2 file_fold b &&
>        +	test_commit --no-tag fold3 file_fold c &&
>       -+	git rebase --autosquash --fixup-all HEAD~3 &&
>       ++	git rebase --squash HEAD~3 &&
>        +	test_cmp_rev base HEAD~1 &&
>        +	test_commit_message HEAD -m "fold1" &&
>        +	echo c >expect &&
>        +	test_cmp expect file_fold
>        +'
>        +
>       -+test_expect_success '--fixup-all folds smoothly when a fixup! commit is in the series' '
>       ++test_expect_success '--squash folds smoothly when a fixup! commit is in the series' '
>        +	git reset --hard base &&
>        +	test_commit --no-tag foldA file_fold a &&
>        +	test_commit --no-tag foldB file_fold b &&
>        +	git commit --allow-empty --fixup HEAD~1 &&
>       -+	git rebase --autosquash --fixup-all HEAD~3 &&
>       ++	git rebase --squash HEAD~3 &&
>        +	test_cmp_rev base HEAD~1 &&
>        +	test_commit_message HEAD -m "foldA" &&
>        +	echo b >expect &&
>        +	test_cmp expect file_fold
>        +'
>        +
>       -+test_expect_success '--fixup-all picks the first commit even if it is a fixup!' '
>       ++test_expect_success '--squash picks the first commit even if it is a fixup!' '
>        +	git reset --hard base &&
>        +	test_commit --no-tag fixupbase file_fix a &&
>        +	git commit --allow-empty --fixup HEAD &&
>        +	test_commit --no-tag fixuptail file_fix b &&
>       -+	git rebase --autosquash --fixup-all HEAD~3 &&
>       ++	git rebase --squash HEAD~3 &&
>        +	test_cmp_rev base HEAD~1 &&
>        +	echo b >expect &&
>        +	test_cmp expect file_fix
>        +'
>        +
>       -+test_expect_success '--fixup-all with a single commit in range is a no-op' '
>       ++test_expect_success '--squash with a single commit in range is a no-op' '
>        +	git reset --hard base &&
>        +	test_commit --no-tag solo file_solo a &&
>        +	git rev-parse HEAD >expect &&
>       -+	git rebase --autosquash --fixup-all HEAD~1 &&
>       ++	git rebase --squash HEAD~1 &&
>        +	git rev-parse HEAD >actual &&
>        +	test_cmp expect actual
>        +'
>        +
>       -+test_expect_success '--fixup-all with an empty range succeeds' '
>       ++test_expect_success '--squash with an empty range succeeds' '
>        +	git reset --hard base &&
>       -+	git rebase --autosquash --fixup-all HEAD &&
>       ++	git rebase --squash HEAD &&
>        +	test_cmp_rev base HEAD
>        +'
>        +
>       -+test_expect_success '--fixup-all skips a dropped commit in the range' '
>       ++test_expect_success '--squash skips a dropped commit in the range' '
>        +	git reset --hard base &&
>        +	test_commit --no-tag fixdrop1 file_drop a &&
>        +	git commit --allow-empty -m "empty in the middle" &&
>        +	test_commit --no-tag fixdrop3 file_drop b &&
>       -+	git rebase --autosquash --empty=drop --fixup-all HEAD~3 &&
>       ++	git rebase --squash --empty=drop HEAD~3 &&
>        +	test_cmp_rev base HEAD~1 &&
>        +	test_commit_message HEAD -m "fixdrop1" &&
>        +	echo b >expect &&
>        +	test_cmp expect file_drop
>        +'
>        +
>       -+test_expect_success '--fixup-all folds a merge commit in the middle of the range' '
>       ++test_expect_success '--squash folds a merge commit in the middle of the range' '
>        +	git reset --hard base &&
>        +	test_commit --no-tag mid-first &&
>        +	git checkout -b mid-side &&
>       @@ t/t3415-rebase-autosquash.sh: test_expect_success 'pick and fixup respect commit
>        +	git checkout - &&
>        +	git merge --no-ff -m "merge mid-side" mid-side &&
>        +	test_commit --no-tag mid-last &&
>       -+	git rebase --autosquash --fixup-all base &&
>       ++	git rebase --squash base &&
>        +	test_cmp_rev base HEAD~1 &&
>        +	test_commit_message HEAD -m "mid-first" &&
>        +	test_path_is_file mid-merged.t
>        +'
>        +
>       -+test_expect_success '--fixup-all keeps the first flattened commit when a merge sorts first' '
>       ++test_expect_success '--squash keeps the first flattened commit when a merge sorts first' '
>        +	git reset --hard base &&
>        +	git checkout -b head-side &&
>        +	test_commit --no-tag head-merged &&
>        +	git checkout - &&
>        +	git merge --no-ff -m "merge head-side" head-side &&
>        +	test_commit --no-tag head-last &&
>       -+	git rebase --autosquash --fixup-all base &&
>       ++	git rebase --squash base &&
>        +	test_cmp_rev base HEAD~1 &&
>        +	test_commit_message HEAD -m "head-merged" &&
>        +	test_path_is_file head-merged.t
>        +'
>        +
>       -+test_expect_success '--fixup-all requires --autosquash' '
>       ++test_expect_success '--squash takes precedence over --autosquash' '
>        +	git reset --hard base &&
>       -+	test_must_fail git rebase --fixup-all HEAD~1 2>err &&
>       -+	test_grep "fixup-all requires --autosquash" err &&
>       -+	test_must_fail git rebase --no-autosquash --fixup-all HEAD~1 2>err &&
>       -+	test_grep "fixup-all requires --autosquash" err
>       ++	test_commit --no-tag combo-first &&
>       ++	test_commit --no-tag combo-mid &&
>       ++	git commit --allow-empty --fixup HEAD~1 &&
>       ++	test_commit --no-tag combo-last &&
>       ++	git rebase --autosquash --squash base &&
>       ++	test_cmp_rev base HEAD~1 &&
>       ++	test_commit_message HEAD -m "combo-first"
>       ++'
>       ++
>       ++test_expect_success '--squash folds the range with rebase.autosquash set' '
>       ++	test_config rebase.autosquash true &&
>       ++	git reset --hard base &&
>       ++	test_commit --no-tag cfg-first &&
>       ++	test_commit --no-tag cfg-last &&
>       ++	git rebase --squash base &&
>       ++	test_cmp_rev base HEAD~1 &&
>       ++	test_commit_message HEAD -m "cfg-first"
>        +'
>        +
>       -+test_expect_success '--fixup-all and --rebase-merges cannot be combined' '
>       ++test_expect_success '--squash and --rebase-merges cannot be combined' '
>        +	git reset --hard base &&
>       -+	test_must_fail git rebase --autosquash --rebase-merges \
>       -+		--fixup-all HEAD~1 2>err &&
>       ++	test_must_fail git rebase --rebase-merges --squash HEAD~1 2>err &&
>        +	test_grep "cannot be used together" err &&
>        +	test_path_is_missing .git/rebase-merge
>        +'
> 

Re: [PATCH v2 0/2] rebase: add --squash to fold a range into its first commit

[Harald Nordgren]

On Tue, Jun 16, 2026 at 12:10 PM Phillip Wood <phillip.wood123@gmail.com> wrote:
>
> Hi Harald
>
> On 15/06/2026 09:37, Harald Nordgren via GitGitGadget wrote:
> > Rename to rebase --squash.
>
> Please include the original cover letter as well so people who have not
> read the previous version know what the series is about.

So you mean this one, should that be included in each version, and
append each subsequent one:

```
Adds `git rebase --autosquash --fixup [<upstream>]` to fold a range of
commits into its oldest one, reusing that commit's message.

Related idea: https://github.com/gitgitgadget/git/issues/1135
```

Or make each message a full cover letter instead of just a diff?




Harald

Re: [PATCH v2 0/2] rebase: add --squash to fold a range into its first commit

[Phillip Wood]

On 17/06/2026 10:11, Harald Nordgren wrote:
> On Tue, Jun 16, 2026 at 12:10 PM Phillip Wood <phillip.wood123@gmail.com> wrote:
>> On 15/06/2026 09:37, Harald Nordgren via GitGitGadget wrote:
>>> Rename to rebase --squash.
>>
>> Please include the original cover letter as well so people who have not
>> read the previous version know what the series is about.
> 
> So you mean this one, should that be included in each version, and
> append each subsequent one:
> 
> ```
> Adds `git rebase --autosquash --fixup [<upstream>]` to fold a range of
> commits into its oldest one, reusing that commit's message.

Yes, see 
https://lore.kernel.org/20260615-b4-pks-history-drop-v6-0-2e329e536d78@pks.im 
for an example and the "Cover Letter" section of 
Documentation/SubmittingPatches

Thanks

Phillip

> 
> Related idea: https://github.com/gitgitgadget/git/issues/1135
> ```
> 
> Or make each message a full cover letter instead of just a diff?
> 
> 
> 
> 
> Harald
> 

[PATCH v3 0/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits into its
oldest one, reusing that commit's message and replaying any descendants on
top.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (4):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  history: add squash subcommand to fold a range
  history: re-edit a squash with every message

 Documentation/git-history.adoc |  21 +++
 builtin/history.c              | 287 ++++++++++++++++++++++++++++-----
 t/meson.build                  |   1 +
 t/t3454-history-squash.sh      | 250 ++++++++++++++++++++++++++++
 4 files changed, 521 insertions(+), 38 deletions(-)
 create mode 100755 t/t3454-history-squash.sh


base-commit: 95e20213faefeb95df29277c58ac1980ab68f701
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v3
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v2:

 1:  c55b9cd6f7 < -:  ---------- t3415: remove prepare-commit-msg hook after use
 2:  22d4276ff5 < -:  ---------- rebase: add --squash to fold a range
 -:  ---------- > 1:  1e31474ef6 history: extract helper for a commit's parent tree
 -:  ---------- > 2:  498da64046 history: give commit_tree_ext a message template
 -:  ---------- > 3:  66b2f49fb4 history: add squash subcommand to fold a range
 -:  ---------- > 4:  43e4270614 history: re-edit a squash with every message

-- 
gitgitgadget

[PATCH v3 1/4] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 091465a59e..f95f26e684 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -157,6 +157,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -164,21 +183,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -444,18 +453,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -799,16 +800,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v3 2/4] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index f95f26e684..305bde3102 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -101,6 +101,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -130,13 +131,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -189,7 +193,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -644,7 +648,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -855,7 +859,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -872,7 +876,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v3 3/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git history squash <revision-range>" to do this directly. It folds
every commit in the range into the oldest one, keeping that commit's
message and authorship and taking the tree of the newest commit, so the
range collapses into a single commit. Commits above the range are
replayed on top of the result.

The range is given as <base>..<tip>, so "git history squash @~3.."
folds the three most recent commits and "git history squash @~5..@~2"
squashes an interior range. A merge inside the range is folded like any
other commit, but the range must have a single base, so a range with
more than one entry point is rejected.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  20 ++++
 builtin/history.c              | 154 ++++++++++++++++++++++++
 t/meson.build                  |   1 +
 t/t3454-history-squash.sh      | 213 +++++++++++++++++++++++++++++++++
 4 files changed, 388 insertions(+)
 create mode 100755 t/t3454-history-squash.sh

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 2ba8121795..d3a5ad28a3 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -11,6 +11,7 @@ SYNOPSIS
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]
 
 DESCRIPTION
 -----------
@@ -97,6 +98,25 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's message and
+	authorship and takes the tree of the range's newest commit, so the
+	whole range collapses into a single commit. Commits above the range
+	are replayed on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash @~3..` folds the three most recent commits into one, and
+`git history squash @~5..@~2` squashes an interior range while leaving
+the two newest commits in place.
++
+The oldest commit's message and authorship are preserved by default,
+unless you specify `--reedit-message`. A merge commit inside the range is
+folded like any other, but the range must have a single base, so a range
+that reaches more than one entry point (for example a side branch that
+forked before the range and was later merged into it) is rejected.
+
 OPTIONS
 -------
 
diff --git a/builtin/history.c b/builtin/history.c
index 305bde3102..9d9416870f 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -30,6 +30,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -973,6 +975,156 @@ out:
 	return ret;
 }
 
+/*
+ * Resolve a "<base>..<tip>" revision range into the base commit just outside
+ * the range (which becomes the parent of the squashed commit), the oldest
+ * commit contained in the range (whose message the squash reuses), and the
+ * range tip (whose tree becomes the result). A merge inside the range is fine,
+ * but the range must have a single base and must not reach a root commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				const char *range,
+				struct commit **base_out,
+				struct commit **oldest_out,
+				struct commit **tip_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
+	struct strvec args = STRVEC_INIT;
+	int ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_push(&args, "--boundary");
+	strvec_push(&args, range);
+	setup_revisions_from_strvec(&args, &revs, NULL);
+	if (args.nr != 1) {
+		ret = error(_("'%s' does not name a revision range"), range);
+		goto out;
+	}
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs))) {
+		if (commit->object.flags & BOUNDARY) {
+			if (base) {
+				ret = error(_("range '%s' has more than one base; "
+					      "cannot squash"), range);
+				goto out;
+			}
+			base = commit;
+			continue;
+		}
+		if (!oldest)
+			oldest = commit;
+		tip = commit;
+	}
+
+	if (!oldest) {
+		ret = error(_("the range '%s' is empty"), range);
+		goto out;
+	}
+
+	if (!base) {
+		ret = error(_("cannot squash the root commit"));
+		goto out;
+	}
+
+	*base_out = base;
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	enum commit_tree_flags flags = 0;
+	int dry_run = 0;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BIT(0, "reedit-message", &flags,
+			N_("open an editor to modify the commit message"),
+			COMMIT_TREE_EDIT_MESSAGE),
+		OPT_END(),
+	};
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct commit *base, *oldest, *tip, *rewritten;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	struct commit_list *parents = NULL;
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+	if (argc != 1) {
+		ret = error(_("command expects a single revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
+
+	ret = resolve_squash_range(repo, argv[0], &base, &oldest, &tip);
+	if (ret < 0)
+		goto out;
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+	commit_list_append(base, &parents);
+
+	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
+			      base_tree_oid, tip_tree_oid, &rewritten, flags);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	strbuf_addf(&reflog_msg, "squash: updating %s", argv[0]);
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	commit_list_free(parents);
+	release_revisions(&revs);
+	return ret;
+}
+
 int cmd_history(int argc,
 		const char **argv,
 		const char *prefix,
@@ -982,6 +1134,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -989,6 +1142,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
diff --git a/t/meson.build b/t/meson.build
index 3219264fe7..d7ae5a46ef 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -399,6 +399,7 @@ integration_tests = [
   't3451-history-reword.sh',
   't3452-history-split.sh',
   't3453-history-fixup.sh',
+  't3454-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3454-history-squash.sh b/t/t3454-history-squash.sh
new file mode 100755
index 0000000000..6c6a75bf00
--- /dev/null
+++ b/t/t3454-history-squash.sh
@@ -0,0 +1,213 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+test_expect_success 'setup linear history touching two files' '
+	test_commit base file a &&
+	git tag start &&
+	test_commit one other x &&
+	test_commit two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "command expects a single revision range" err
+'
+
+test_expect_success 'errors on too many arguments' '
+	test_must_fail git history squash start.. HEAD 2>err &&
+	test_grep "command expects a single revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the range .* is empty" err
+'
+
+test_expect_success 'errors when the range includes the root commit' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "cannot squash the root commit" err
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	git log --format="%s" -1 >subject &&
+	echo one >expect &&
+	test_cmp expect subject &&
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..@~1 &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	three
+	one
+	EOF
+	test_cmp expect actual &&
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$root.." &&
+
+	git rev-list --count "$root..HEAD" >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashing a single-commit range replays the rest' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..@~2 &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	three
+	two
+	one
+	EOF
+	test_cmp expect actual &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'reuses the message of a fixup! commit in the range' '
+	git reset --hard start &&
+	test_commit reg1 file b &&
+	git commit --allow-empty -m "fixup! reg1" &&
+	test_commit reg2 file c &&
+
+	git history squash start.. &&
+
+	git log --format="%s" -1 >actual &&
+	echo reg1 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'keeps the oldest message even if it is a fixup!' '
+	git reset --hard start &&
+	test_commit --no-tag "fixup! something" file b &&
+	test_commit tail file c &&
+
+	git history squash start.. &&
+
+	git log --format="%s" -1 >actual &&
+	echo "fixup! something" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'preserves authorship of the oldest commit' '
+	git reset --hard start &&
+	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
+		test_commit oldest file b &&
+	test_commit newest file c &&
+
+	git history squash start.. &&
+
+	git log -1 --format="%an <%ae>" >actual &&
+	echo "Squasher <squash@example.com>" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--dry-run predicts the rewrite without performing it' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	git history squash --dry-run start.. >out &&
+	grep "^update refs/heads/" out >update &&
+	predicted=$(awk "{print \$3}" update) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash start.. &&
+	test "$predicted" = "$(git rev-parse HEAD)"
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --update-refs=head start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success '--update-refs=branches moves a branch pointing into the range' '
+	git reset --hard three &&
+	git branch -f mid HEAD~2 &&
+	mid_before=$(git rev-parse mid) &&
+
+	git history squash start..@~1 &&
+
+	test_cmp_rev "$mid_before" mid &&
+	test_commit_message mid -m one
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	test_commit before-side file b &&
+	git checkout -b inner-side &&
+	test_commit on-inner-side inner x &&
+	git checkout - &&
+	test_commit after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	test_commit after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	git log --format="%s" -1 >subject &&
+	echo before-side >expect &&
+	test_cmp expect subject &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'refuses to squash a range with more than one base' '
+	git reset --hard start &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b forked-before &&
+	test_commit forked-side fside x &&
+	git checkout - &&
+	test_commit forked-main file b &&
+	git merge --no-ff -m merge forked-before &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash forked-main.. 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_done
-- 
gitgitgadget

Re: [PATCH v3 3/4] history: add squash subcommand to fold a range

[Junio C Hamano]

"Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:

> +static int cmd_history_squash(int argc,
> +			      const char **argv,
> +			      const char *prefix,
> +			      struct repository *repo)
> +{
> +	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
> +	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
> +	commit_list_append(base, &parents);
> +
> +	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
> +			      base_tree_oid, tip_tree_oid, &rewritten, flags);

We use the tree object taken from the commit at the top end of the
range, and create a new commit directly on top of the boundary
commit beyond the bottom of the range, using the message from the
commit at the bottom of the range.  No need to go through the
rigmarole of replaying commits in the range stepwise like sequencer
does, since we are not transplanting the history on top of a
different tree at all.  Very nice.

When I do drunken-walk development to build many commits, making
detour to arrive at an ideal state, the key message is often not in
the bottommost commit but somewhere in the middle where I discovered
why my initial attempt were wrong and discovered a much better
solution, so using only the message from the oldest limits the
usefulness of this feature, but I guess for certain people the
bottommost commit would be a good default.

I see you have already an option to grab messages from all the
commits in the range (many of which may have useless "oops, that was
wrong" single-liner) in a way similar to how "git rebase --squash"
or "squash" insn in the "git rebase -i" todo list lets you use them
in the next step, which is workable.  It is plausible that we would
later want to offer an option to name the single commit that may not
be the bottommost one and use the message only from that commit.

But we'd need to start from somewhere, and "use the bottommost
commit and nothing else" and "we will give you messages from all the
commits, just rearrange them in your editor" may be a good place to
start.

As t3454 is taken by another topic already in flight, I've queued a
trivial "rename it to t3455" patch on top before queuing the topic.

Thanks.

Re: [PATCH v3 3/4] history: add squash subcommand to fold a range

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> As t3454 is taken by another topic already in flight, I've queued a
> trivial "rename it to t3455" patch on top before queuing the topic.

Another tweak I had to make was to replace "grep" with "test_grep"
to avoid triggering test lint added by another topic in flight.

For the one in the second hunk, it may be much better to rewrite it
to process "out" directly with the awk script without preprocessing
it with "grep", as awk is a programming language capable enough to
recognize a line that matches a pattern and process only those
matching lines by itself.

--- >8 ---
Author: Junio C Hamano <gitster@pobox.com>
Date:   Thu Jun 18 13:44:36 2026 -0700

    SQUASH??? avoid test_grep lint triggering on uses of raw grep

diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index 1edd148295..20370c0136 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -150,10 +150,10 @@ test_expect_success '--reedit-message offers every folded-in message' '
 	test_set_editor "$(pwd)/editor" &&
 	git history squash --reedit-message start.. &&
 
-	grep "re-one subject" buffer &&
-	grep "re-one body line" buffer &&
-	grep re-two buffer &&
-	grep re-three buffer &&
+	test_grep "re-one subject" buffer &&
+	test_grep "re-one body line" buffer &&
+	test_grep re-two buffer &&
+	test_grep re-three buffer &&
 	git log --format="%s" -1 >actual &&
 	echo combined >expect &&
 	test_cmp expect actual
@@ -177,7 +177,7 @@ test_expect_success '--dry-run predicts the rewrite without performing it' '
 	head_before=$(git rev-parse HEAD) &&
 
 	git history squash --dry-run start.. >out &&
-	grep "^update refs/heads/" out >update &&
+	test_grep "^update refs/heads/" out >update &&
 	predicted=$(awk "{print \$3}" update) &&
 	test_cmp_rev "$head_before" HEAD &&
 

Re: [PATCH v3 3/4] history: add squash subcommand to fold a range

[D. Ben Knoble]

On Thu, Jun 18, 2026 at 5:25 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> Junio C Hamano <gitster@pobox.com> writes:
>
> > As t3454 is taken by another topic already in flight, I've queued a
> > trivial "rename it to t3455" patch on top before queuing the topic.
>
> Another tweak I had to make was to replace "grep" with "test_grep"
> to avoid triggering test lint added by another topic in flight.
>
> For the one in the second hunk, it may be much better to rewrite it
> to process "out" directly with the awk script without preprocessing
> it with "grep", as awk is a programming language capable enough to
> recognize a line that matches a pattern and process only those
> matching lines by itself.
>
> --- >8 ---
> Author: Junio C Hamano <gitster@pobox.com>
> Date:   Thu Jun 18 13:44:36 2026 -0700
>
>     SQUASH??? avoid test_grep lint triggering on uses of raw grep
>
> diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
> index 1edd148295..20370c0136 100755
> --- a/t/t3455-history-squash.sh
> +++ b/t/t3455-history-squash.sh
[snip]
> @@ -177,7 +177,7 @@ test_expect_success '--dry-run predicts the rewrite without performing it' '
>         head_before=$(git rev-parse HEAD) &&
>
>         git history squash --dry-run start.. >out &&
> -       grep "^update refs/heads/" out >update &&
> +       test_grep "^update refs/heads/" out >update &&
>         predicted=$(awk "{print \$3}" update) &&
>         test_cmp_rev "$head_before" HEAD &&

Odd: I thought the other topic acknowledged that bare grep as a filter
(here, with stdout redirected) was fine. My memory must not be right
:)

-- 
D. Ben Knoble

Re: [PATCH v3 3/4] history: add squash subcommand to fold a range

[Patrick Steinhardt]

On Thu, Jun 18, 2026 at 07:17:05PM +0000, Harald Nordgren via GitGitGadget wrote:
> diff --git a/builtin/history.c b/builtin/history.c
> index 305bde3102..9d9416870f 100644
> --- a/builtin/history.c
> +++ b/builtin/history.c
> @@ -973,6 +975,156 @@ out:
>  	return ret;
>  }
>  
> +/*
> + * Resolve a "<base>..<tip>" revision range into the base commit just outside
> + * the range (which becomes the parent of the squashed commit), the oldest
> + * commit contained in the range (whose message the squash reuses), and the
> + * range tip (whose tree becomes the result). A merge inside the range is fine,
> + * but the range must have a single base and must not reach a root commit.
> + */
> +static int resolve_squash_range(struct repository *repo,
> +				const char *range,
> +				struct commit **base_out,
> +				struct commit **oldest_out,
> +				struct commit **tip_out)
> +{
> +	struct rev_info revs;
> +	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
> +	struct strvec args = STRVEC_INIT;
> +	int ret;
> +
> +	repo_init_revisions(repo, &revs, NULL);
> +	strvec_push(&args, "ignored");
> +	strvec_push(&args, "--reverse");
> +	strvec_push(&args, "--topo-order");
> +	strvec_push(&args, "--boundary");
> +	strvec_push(&args, range);

We don't have any kind of input verification for "range". So in theory,
the user could pass whatever string here, and this may or may not work.

Also, should we use "--ancestry-path" with the first commit of the range
here? Otherwise we may incldue commits that aren't descendants of A in a
range "A..B". If not I wonder whether we might see multiple boundaries
even though we would be able to resolve the boundary unambiguously in
some cases.

> +	setup_revisions_from_strvec(&args, &revs, NULL);
> +	if (args.nr != 1) {
> +		ret = error(_("'%s' does not name a revision range"), range);
> +		goto out;
> +	}
> +
> +	if (prepare_revision_walk(&revs) < 0) {
> +		ret = error(_("error preparing revisions"));
> +		goto out;
> +	}
> +
> +	while ((commit = get_revision(&revs))) {
> +		if (commit->object.flags & BOUNDARY) {
> +			if (base) {
> +				ret = error(_("range '%s' has more than one base; "
> +					      "cannot squash"), range);
> +				goto out;
> +			}
> +			base = commit;
> +			continue;
> +		}
> +		if (!oldest)
> +			oldest = commit;
> +		tip = commit;
> +	}

Hmm. I really wonder whether we should also restrict merges. It might be
somewhat obvious that intermediate merge commits should just be
discarded. But is that equally obvious for HEAD and the base commit?

> +	if (!oldest) {
> +		ret = error(_("the range '%s' is empty"), range);
> +		goto out;
> +	}
> +
> +	if (!base) {
> +		ret = error(_("cannot squash the root commit"));
> +		goto out;
> +	}

In theory we can by squashing onto an empty tree. But it's fine to not
care about this edge case, we can still address it at a later point in
time if we ever feel the need to.

> +	*base_out = base;
> +	*oldest_out = oldest;
> +	*tip_out = tip;
> +	ret = 0;
> +
> +out:
> +	reset_revision_walk();
> +	release_revisions(&revs);
> +	strvec_clear(&args);
> +	return ret;
> +}
> +
> +static int cmd_history_squash(int argc,
> +			      const char **argv,
> +			      const char *prefix,
> +			      struct repository *repo)
> +{
> +	const char * const usage[] = {
> +		GIT_HISTORY_SQUASH_USAGE,
> +		NULL,
> +	};
> +	enum ref_action action = REF_ACTION_DEFAULT;
> +	enum commit_tree_flags flags = 0;
> +	int dry_run = 0;
> +	struct option options[] = {
> +		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
> +			       N_("control which refs should be updated"),
> +			       PARSE_OPT_NONEG, parse_ref_action),
> +		OPT_BOOL('n', "dry-run", &dry_run,
> +			 N_("perform a dry-run without updating any refs")),
> +		OPT_BIT(0, "reedit-message", &flags,
> +			N_("open an editor to modify the commit message"),
> +			COMMIT_TREE_EDIT_MESSAGE),
> +		OPT_END(),
> +	};
> +	struct strbuf reflog_msg = STRBUF_INIT;
> +	struct commit *base, *oldest, *tip, *rewritten;
> +	const struct object_id *base_tree_oid, *tip_tree_oid;
> +	struct commit_list *parents = NULL;
> +	struct rev_info revs = { 0 };
> +	int ret;
> +
> +	argc = parse_options(argc, argv, prefix, options, usage, 0);
> +	if (argc != 1) {
> +		ret = error(_("command expects a single revision range"));
> +		goto out;
> +	}
> +	repo_config(repo, git_default_config, NULL);
> +
> +	if (action == REF_ACTION_DEFAULT)
> +		action = REF_ACTION_BRANCHES;
> +
> +	ret = resolve_squash_range(repo, argv[0], &base, &oldest, &tip);
> +	if (ret < 0)
> +		goto out;
> +
> +	ret = setup_revwalk(repo, action, tip, &revs);
> +	if (ret < 0)
> +		goto out;

Oh, you already use `setup_revwalk()` here. Wouldn't that keep us from
accepting merge commits?

Patrick

[PATCH v3 4/4] history: re-edit a squash with every message

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

By default "git history squash" reuses the oldest commit's message.
When --reedit-message is given it only reopened that one message, so the
messages of the folded-in commits were lost.

Gather the messages of every commit in the range, oldest first, and use
them as the editor template when re-editing, mirroring how "git rebase
-i" presents a squash. The combined message is built before the
descendant walk so it is not disturbed by the flags that walk leaves on
the commits.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  5 +--
 builtin/history.c              | 61 +++++++++++++++++++++++++++++++++-
 t/t3454-history-squash.sh      | 37 +++++++++++++++++++++
 3 files changed, 100 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index d3a5ad28a3..dd3544832d 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -111,8 +111,9 @@ history squash @~3..` folds the three most recent commits into one, and
 `git history squash @~5..@~2` squashes an interior range while leaving
 the two newest commits in place.
 +
-The oldest commit's message and authorship are preserved by default,
-unless you specify `--reedit-message`. A merge commit inside the range is
+The oldest commit's message and authorship are preserved by default. With
+`--reedit-message`, an editor opens pre-filled with the messages of all the
+folded commits so you can combine them. A merge commit inside the range is
 folded like any other, but the range must have a single base, so a range
 that reaches more than one entry point (for example a side branch that
 forked before the range and was later merged into it) is rejected.
diff --git a/builtin/history.c b/builtin/history.c
index 9d9416870f..eb12a5d7e8 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1047,6 +1047,56 @@ out:
 	return ret;
 }
 
+static int build_squash_message(struct repository *repo,
+				struct commit *base,
+				struct commit *tip,
+				struct strbuf *out)
+{
+	struct rev_info revs;
+	struct commit *commit;
+	struct strvec args = STRVEC_INIT;
+	int n = 0, ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs))) {
+		const char *message, *body;
+		struct strbuf one = STRBUF_INIT;
+
+		message = repo_logmsg_reencode(repo, commit, NULL, NULL);
+		find_commit_subject(message, &body);
+		strbuf_addstr(&one, body);
+		strbuf_trim_trailing_newline(&one);
+
+		if (n++)
+			strbuf_addch(out, '\n');
+		strbuf_addbuf(out, &one);
+		strbuf_addch(out, '\n');
+
+		strbuf_release(&one);
+		repo_unuse_commit_buffer(repo, commit, message);
+	}
+
+	ret = 0;
+
+out:
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1071,6 +1121,7 @@ static int cmd_history_squash(int argc,
 		OPT_END(),
 	};
 	struct strbuf reflog_msg = STRBUF_INIT;
+	struct strbuf message = STRBUF_INIT;
 	struct commit *base, *oldest, *tip, *rewritten;
 	const struct object_id *base_tree_oid, *tip_tree_oid;
 	struct commit_list *parents = NULL;
@@ -1091,6 +1142,12 @@ static int cmd_history_squash(int argc,
 	if (ret < 0)
 		goto out;
 
+	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
+		ret = build_squash_message(repo, base, tip, &message);
+		if (ret < 0)
+			goto out;
+	}
+
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
 		goto out;
@@ -1099,7 +1156,8 @@ static int cmd_history_squash(int argc,
 	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
 	commit_list_append(base, &parents);
 
-	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
+	ret = commit_tree_ext(repo, "squash", oldest,
+			      message.len ? message.buf : NULL, parents,
 			      base_tree_oid, tip_tree_oid, &rewritten, flags);
 	if (ret < 0) {
 		ret = error(_("failed writing squashed commit"));
@@ -1120,6 +1178,7 @@ static int cmd_history_squash(int argc,
 
 out:
 	strbuf_release(&reflog_msg);
+	strbuf_release(&message);
 	commit_list_free(parents);
 	release_revisions(&revs);
 	return ret;
diff --git a/t/t3454-history-squash.sh b/t/t3454-history-squash.sh
index 6c6a75bf00..1edd148295 100755
--- a/t/t3454-history-squash.sh
+++ b/t/t3454-history-squash.sh
@@ -135,6 +135,43 @@ test_expect_success 'preserves authorship of the oldest commit' '
 	test_cmp expect actual
 '
 
+test_expect_success '--reedit-message offers every folded-in message' '
+	git reset --hard start &&
+	echo b >file &&
+	git add file &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit re-two file c &&
+	test_commit re-three file d &&
+
+	write_script editor <<-\EOF &&
+	cp "$1" buffer &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	grep "re-one subject" buffer &&
+	grep "re-one body line" buffer &&
+	grep re-two buffer &&
+	grep re-three buffer &&
+	git log --format="%s" -1 >actual &&
+	echo combined >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--reedit-message aborts on an empty message' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	test_must_fail git history squash --reedit-message start.. &&
+
+	test_cmp_rev "$head_before" HEAD
+'
+
 test_expect_success '--dry-run predicts the rewrite without performing it' '
 	git reset --hard three &&
 	head_before=$(git rev-parse HEAD) &&
-- 
gitgitgadget

Re: [PATCH v3 0/4] history: add squash subcommand to fold a range

[D. Ben Knoble]

On Thu, Jun 18, 2026 at 3:17 PM Harald Nordgren via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> Adds git history squash <revision-range> to fold a range of commits into its
> oldest one, reusing that commit's message and replaying any descendants on
> top.
>
> Changes in v3:
>
>  * Moved the feature out of git rebase and into a new git history squash
>    <revision-range> subcommand, per the list discussion. git rebase --squash
>    is dropped.
>  * Takes an arbitrary range (git history squash @~3.., git history squash
>    @~5..@~2), folding it into the oldest commit and replaying any
>    descendants on top.
>  * Implemented as a single tree operation rather than picking each commit,
>    so there are no repeated conflict stops (addresses Phillip's efficiency
>    point).

I think I mentioned this, too, albeit indirectly. I'm not concerned
about credit, though. Just excited to have this.

Thanks!

>  * A merge inside the range is folded fine, only a range with more than one
>    base is rejected.
>  * --reedit-message seeds the editor with every folded-in message, not just
>    the oldest.
>
> Harald Nordgren (4):
>   history: extract helper for a commit's parent tree
>   history: give commit_tree_ext a message template
>   history: add squash subcommand to fold a range
>   history: re-edit a squash with every message

Re: [PATCH v3 0/4] history: add squash subcommand to fold a range

[Junio C Hamano]

"Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:

> Adds git history squash <revision-range> to fold a range of commits into its
> oldest one, reusing that commit's message and replaying any descendants on
> top.

One thing that just occurred to me.

When you have a linear history

    o---A---B---C

you run "git history squash A..C" and come to

    o---X

where the tree of X is the same as C, with the log message of A
reused for it.  That is simple, clean, and easy to explain.

But what should happen to refs (i.e., branch head) that point at A
or B?

I am adressing this message to Patrick as this question relates to
the grand vision for the "git history" command.  I think "git
replay" wants to rewrite all the refs that are involved in the
rewrite operation, while "git rebase" (without "--update-refs")
wants to leave all others refs intact and update only the branch it
was told to rewrite.  Is it the same design as "rebase" and
"--update-refs" controls if we update _other_ refs that happened to
be in the range that are rewritten?

Now, assuming that there do exist a mode where the command can
update these refs that point into the history that got rewritten,
there probably are at least two possibilities.

On one hand, I think it is reasonable to _remove_ these refs that
used to point at a section of history that disappeared (like the one
that were pointing at A or B).  Perhaps A and B were pointed at by
two branches or tags that were used to mark "up to this point things
are broken" and "from here on things are fixed" (i.e., imagine a
manual bisection).  After squashing all of the commits in this
section of history, the result no longer has such transition points.

It also is plausible that users may want these refs that used to
point at A or B to point at X, just like the ref that used to point
at C would now point at X, even though I cannot offhand think of a
good story (like "there used to be transtion points, now there
isn't" I said above to explain why these refs should disappear) to
support such a behaviour.

Thoughts?

Re: [PATCH v3 0/4] history: add squash subcommand to fold a range

[Patrick Steinhardt]

On Thu, Jun 18, 2026 at 05:34:44PM -0700, Junio C Hamano wrote:
> "Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
> > Adds git history squash <revision-range> to fold a range of commits into its
> > oldest one, reusing that commit's message and replaying any descendants on
> > top.
> 
> One thing that just occurred to me.
> 
> When you have a linear history
> 
>     o---A---B---C
> 
> you run "git history squash A..C" and come to
> 
>     o---X
> 
> where the tree of X is the same as C, with the log message of A
> reused for it.  That is simple, clean, and easy to explain.
> 
> But what should happen to refs (i.e., branch head) that point at A
> or B?

It's a very good question. I had `git history squash` in my backlog for
a while, and this very question made me defer that topic repeatedly.

> I am adressing this message to Patrick as this question relates to
> the grand vision for the "git history" command.  I think "git
> replay" wants to rewrite all the refs that are involved in the
> rewrite operation, while "git rebase" (without "--update-refs")
> wants to leave all others refs intact and update only the branch it
> was told to rewrite.  Is it the same design as "rebase" and
> "--update-refs" controls if we update _other_ refs that happened to
> be in the range that are rewritten?

Yeah.

> Now, assuming that there do exist a mode where the command can
> update these refs that point into the history that got rewritten,
> there probably are at least two possibilities.
> 
> On one hand, I think it is reasonable to _remove_ these refs that
> used to point at a section of history that disappeared (like the one
> that were pointing at A or B).  Perhaps A and B were pointed at by
> two branches or tags that were used to mark "up to this point things
> are broken" and "from here on things are fixed" (i.e., imagine a
> manual bisection).  After squashing all of the commits in this
> section of history, the result no longer has such transition points.

I think just pruning references would be extremely surprising to our
users.

> It also is plausible that users may want these refs that used to
> point at A or B to point at X, just like the ref that used to point
> at C would now point at X, even though I cannot offhand think of a
> good story (like "there used to be transtion points, now there
> isn't" I said above to explain why these refs should disappear) to
> support such a behaviour.
>
> Thoughts?

There are two more modes:

  - If a reference points at an intermediate commit then it stays there.

  - We detect this case and reject the update. Optionally, we may ask
    the user what they intend to do with those other refs.

It really is kind of ambiguous what is supposed to happen, and I can
think of different scenarios where each of the possibilities would be
the best choice. So ultimately, I think the last option is the best one,
as it also gives us a way to iterate.

If so, a user would already be able to achieve that other refs keep
pointing at X by saying `git history squash --update-refs=head`. The
other modes can then be added at a later point in time as the need
arises.

Patrick

Re: [PATCH v3 0/4] history: add squash subcommand to fold a range

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

> There are two more modes:
>
>   - If a reference points at an intermediate commit then it stays there.
>
>   - We detect this case and reject the update. Optionally, we may ask
>     the user what they intend to do with those other refs.
>
> It really is kind of ambiguous what is supposed to happen, and I can
> think of different scenarios where each of the possibilities would be
> the best choice. So ultimately, I think the last option is the best one,
> as it also gives us a way to iterate.
>
> If so, a user would already be able to achieve that other refs keep
> pointing at X by saying `git history squash --update-refs=head`. The
> other modes can then be added at a later point in time as the need
> arises.

Yeah, sounds like we should detect and fail this case, with advice()
to use --update-refs.

[PATCH v4 0/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (4):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  history: add squash subcommand to fold a range
  history: re-edit a squash with every message

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  26 +++
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 328 +++++++++++++++++++++++++----
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 340 +++++++++++++++++++++++++++++++
 7 files changed, 663 insertions(+), 38 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: 8d96f09e9245ddf80c1981476fcbac8c4bb4125f
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v4
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v3:

 1:  1e31474ef6 = 1:  fc2801c0b1 history: extract helper for a commit's parent tree
 2:  498da64046 = 2:  ee591e83b4 history: give commit_tree_ext a message template
 3:  66b2f49fb4 ! 3:  80bfea642e history: add squash subcommand to fold a range
     @@ Commit message
          other commit, but the range must have a single base, so a range with
          more than one entry point is rejected.
      
     +    The folded commits leave the history, so by default the command refuses
     +    when another ref points at one of them. Use "--update-refs=head" to
     +    rewrite only the current branch and leave those refs untouched.
     +
          Inspired-by: Sergey Chernov <serega.morph@gmail.com>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
     + ## Documentation/config/advice.adoc ##
     +@@ Documentation/config/advice.adoc: all advice messages.
     + 	forceDeleteBranch::
     + 		Shown when the user tries to delete a not fully merged
     + 		branch without the force option set.
     ++	historyUpdateRefs::
     ++		Shown when `git history squash` refuses because a ref points
     ++		into the range being folded, to tell the user about
     ++		`--update-refs=head`.
     + 	ignoredHook::
     + 		Shown when a hook is ignored because the hook is not
     + 		set as executable.
     +
       ## Documentation/git-history.adoc ##
      @@ Documentation/git-history.adoc: SYNOPSIS
       git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      +folded like any other, but the range must have a single base, so a range
      +that reaches more than one entry point (for example a side branch that
      +forked before the range and was later merged into it) is rejected.
     +++
     ++The folded commits disappear from the history, so with the default
     ++`--update-refs=branches` the command refuses when another ref points at
     ++one of them. Rerun with `--update-refs=head` to rewrite only the current
     ++branch and leave those refs pointing at the old commits.
      +
       OPTIONS
       -------
       
      
     + ## advice.c ##
     +@@ advice.c: static struct {
     + 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
     + 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
     + 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
     ++	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
     + 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
     + 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
     + 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
     +
     + ## advice.h ##
     +@@ advice.h: enum advice_type {
     + 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
     + 	ADVICE_FORCE_DELETE_BRANCH,
     + 	ADVICE_GRAFT_FILE_DEPRECATED,
     ++	ADVICE_HISTORY_UPDATE_REFS,
     + 	ADVICE_IGNORED_HOOK,
     + 	ADVICE_IMPLICIT_IDENTITY,
     + 	ADVICE_MERGE_CONFLICT,
     +
       ## builtin/history.c ##
     +@@
     + #define USE_THE_REPOSITORY_VARIABLE
     + 
     + #include "builtin.h"
     ++#include "advice.h"
     + #include "cache-tree.h"
     + #include "commit.h"
     + #include "commit-reach.h"
      @@
       	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
       #define GIT_HISTORY_SPLIT_USAGE \
     @@ builtin/history.c: out:
      +				const char *range,
      +				struct commit **base_out,
      +				struct commit **oldest_out,
     -+				struct commit **tip_out)
     ++				struct commit **tip_out,
     ++				struct oidset *interior_out)
      +{
      +	struct rev_info revs;
      +	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
     @@ builtin/history.c: out:
      +		}
      +		if (!oldest)
      +			oldest = commit;
     ++		if (tip)
     ++			oidset_insert(interior_out, &tip->object.oid);
      +		tip = commit;
      +	}
      +
     @@ builtin/history.c: out:
      +	return ret;
      +}
      +
     ++struct interior_ref_cb {
     ++	const struct oidset *interior;
     ++	const char *name;
     ++};
     ++
     ++static int find_interior_ref(const struct reference *ref, void *cb_data)
     ++{
     ++	struct interior_ref_cb *data = cb_data;
     ++
     ++	if (oidset_contains(data->interior, ref->oid)) {
     ++		data->name = xstrdup(ref->name);
     ++		return 1;
     ++	}
     ++
     ++	return 0;
     ++}
     ++
      +static int cmd_history_squash(int argc,
      +			      const char **argv,
      +			      const char *prefix,
     @@ builtin/history.c: out:
      +		OPT_END(),
      +	};
      +	struct strbuf reflog_msg = STRBUF_INIT;
     ++	struct oidset interior = OIDSET_INIT;
      +	struct commit *base, *oldest, *tip, *rewritten;
      +	const struct object_id *base_tree_oid, *tip_tree_oid;
      +	struct commit_list *parents = NULL;
     @@ builtin/history.c: out:
      +	if (action == REF_ACTION_DEFAULT)
      +		action = REF_ACTION_BRANCHES;
      +
     -+	ret = resolve_squash_range(repo, argv[0], &base, &oldest, &tip);
     ++	ret = resolve_squash_range(repo, argv[0], &base, &oldest, &tip,
     ++				   &interior);
      +	if (ret < 0)
      +		goto out;
      +
     ++	if (action == REF_ACTION_BRANCHES) {
     ++		struct interior_ref_cb cb = { .interior = &interior };
     ++
     ++		refs_for_each_ref(get_main_ref_store(repo),
     ++				  find_interior_ref, &cb);
     ++		if (cb.name) {
     ++			ret = error(_("'%s' points into the squashed range"),
     ++				    cb.name);
     ++			advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
     ++					  _("Use --update-refs=head to rewrite only "
     ++					    "the current branch and leave such refs "
     ++					    "untouched."));
     ++			free((char *)cb.name);
     ++			goto out;
     ++		}
     ++	}
     ++
      +	ret = setup_revwalk(repo, action, tip, &revs);
      +	if (ret < 0)
      +		goto out;
     @@ builtin/history.c: out:
      +
      +out:
      +	strbuf_release(&reflog_msg);
     ++	oidset_clear(&interior);
      +	commit_list_free(parents);
      +	release_revisions(&revs);
      +	return ret;
     @@ t/meson.build: integration_tests = [
         't3451-history-reword.sh',
         't3452-history-split.sh',
         't3453-history-fixup.sh',
     -+  't3454-history-squash.sh',
     ++  't3455-history-squash.sh',
         't3500-cherry.sh',
         't3501-revert-cherry-pick.sh',
         't3502-cherry-pick-merge.sh',
      
     - ## t/t3454-history-squash.sh (new) ##
     + ## t/t3455-history-squash.sh (new) ##
      @@
      +#!/bin/sh
      +
     @@ t/t3454-history-squash.sh (new)
      +test_expect_success 'setup linear history touching two files' '
      +	test_commit base file a &&
      +	git tag start &&
     -+	test_commit one other x &&
     -+	test_commit two file c &&
     ++	test_commit --no-tag one other x &&
     ++	test_commit --no-tag two file c &&
      +	test_commit three file d
      +'
      +
     @@ t/t3454-history-squash.sh (new)
      +
      +test_expect_success 'reuses the message of a fixup! commit in the range' '
      +	git reset --hard start &&
     -+	test_commit reg1 file b &&
     ++	test_commit --no-tag reg1 file b &&
      +	git commit --allow-empty -m "fixup! reg1" &&
      +	test_commit reg2 file c &&
      +
     @@ t/t3454-history-squash.sh (new)
      +test_expect_success 'preserves authorship of the oldest commit' '
      +	git reset --hard start &&
      +	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
     -+		test_commit oldest file b &&
     ++		test_commit --no-tag oldest file b &&
      +	test_commit newest file c &&
      +
      +	git history squash start.. &&
     @@ t/t3454-history-squash.sh (new)
      +test_expect_success '--dry-run predicts the rewrite without performing it' '
      +	git reset --hard three &&
      +	head_before=$(git rev-parse HEAD) &&
     ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
      +	git history squash --dry-run start.. >out &&
     -+	grep "^update refs/heads/" out >update &&
     -+	predicted=$(awk "{print \$3}" update) &&
     ++	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
      +	test_cmp_rev "$head_before" HEAD &&
      +
      +	git history squash start.. &&
     -+	test "$predicted" = "$(git rev-parse HEAD)"
     ++	test "$predicted" = "$(git rev-parse HEAD)" &&
     ++	git rev-list --count start..HEAD >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
     ++	test_cmp_rev start HEAD^ &&
     ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
      +'
      +
      +test_expect_success '--update-refs=head only moves HEAD' '
     @@ t/t3454-history-squash.sh (new)
      +	test_cmp_rev "$other_before" other
      +'
      +
     -+test_expect_success '--update-refs=branches moves a branch pointing into the range' '
     ++test_expect_success 'refuses to fold a range a ref points into' '
     ++	git reset --hard three &&
     ++	git branch -f mid HEAD~1 &&
     ++	head_before=$(git rev-parse HEAD) &&
     ++
     ++	test_must_fail git history squash start.. 2>err &&
     ++	test_grep "error: .* points into the squashed range" err &&
     ++	test_grep "hint: .*--update-refs=head" err &&
     ++	test_cmp_rev "$head_before" HEAD &&
     ++
     ++	git branch -D mid
     ++'
     ++
     ++test_expect_success 'advice.historyUpdateRefs silences the hint' '
     ++	git reset --hard three &&
     ++	git branch -f mid HEAD~1 &&
     ++
     ++	test_must_fail git -c advice.historyUpdateRefs=false \
     ++		history squash start.. 2>err &&
     ++	test_grep "points into the squashed range" err &&
     ++	test_grep ! "hint:" err &&
     ++
     ++	git branch -D mid
     ++'
     ++
     ++test_expect_success '--update-refs=head folds past a ref pointing into the range' '
      +	git reset --hard three &&
     -+	git branch -f mid HEAD~2 &&
     ++	git branch -f mid HEAD~1 &&
      +	mid_before=$(git rev-parse mid) &&
      +
     -+	git history squash start..@~1 &&
     ++	git history squash --update-refs=head start.. &&
      +
     ++	git rev-list --count start..HEAD >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
      +	test_cmp_rev "$mid_before" mid &&
     -+	test_commit_message mid -m one
     ++
     ++	git branch -D mid
     ++'
     ++
     ++test_expect_success 'refuses to fold a range a tag points into' '
     ++	git reset --hard three &&
     ++	git tag -f mark HEAD~1 &&
     ++	head_before=$(git rev-parse HEAD) &&
     ++
     ++	test_must_fail git history squash start.. 2>err &&
     ++	test_grep "refs/tags/mark" err &&
     ++	test_grep "points into the squashed range" err &&
     ++	test_cmp_rev "$head_before" HEAD &&
     ++
     ++	git tag -d mark
      +'
      +
      +test_expect_success 'squashes a range whose internal merge has a single base' '
      +	git reset --hard start &&
     -+	test_commit before-side file b &&
     ++	test_commit --no-tag before-side file b &&
      +	git checkout -b inner-side &&
     -+	test_commit on-inner-side inner x &&
     ++	test_commit --no-tag on-inner-side inner x &&
      +	git checkout - &&
     -+	test_commit after-side file c &&
     ++	test_commit --no-tag after-side file c &&
      +	git merge --no-ff -m merge inner-side &&
     -+	test_commit after-merge file d &&
     ++	git branch -D inner-side &&
     ++	test_commit --no-tag after-merge file d &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
      +	git history squash start.. &&
     @@ t/t3454-history-squash.sh (new)
      +	test_path_is_file inner
      +'
      +
     ++test_expect_success 'folds a range whose tip is a merge commit' '
     ++	git reset --hard start &&
     ++	test_commit --no-tag tipmerge-base file b &&
     ++	git checkout -b tipmerge-side &&
     ++	test_commit --no-tag tipmerge-side side x &&
     ++	git checkout - &&
     ++	test_commit --no-tag tipmerge-main file c &&
     ++	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
     ++	git branch -D tipmerge-side &&
     ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
     ++
     ++	git history squash start.. &&
     ++
     ++	git rev-list --count start..HEAD >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
     ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     ++	test_path_is_file side
     ++'
     ++
     ++test_expect_success 'folds a range whose base is a merge commit' '
     ++	git reset --hard start &&
     ++	git checkout -b basemerge-side &&
     ++	test_commit --no-tag basemerge-side side x &&
     ++	git checkout - &&
     ++	test_commit --no-tag basemerge-main file b &&
     ++	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
     ++	git branch -D basemerge-side &&
     ++	base=$(git rev-parse HEAD) &&
     ++	test_commit --no-tag basemerge-one file c &&
     ++	test_commit --no-tag basemerge-two file d &&
     ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
     ++
     ++	git history squash "$base.." &&
     ++
     ++	git rev-list --count "$base..HEAD" >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
     ++	test_cmp_rev "$base" HEAD^ &&
     ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
     ++'
     ++
      +test_expect_success 'refuses to squash a range with more than one base' '
      +	git reset --hard start &&
      +	head_before=$(git rev-parse HEAD) &&
 4:  43e4270614 ! 4:  85c7817d7e history: re-edit a squash with every message
     @@ Documentation/git-history.adoc: history squash @~3..` folds the three most recen
       forked before the range and was later merged into it) is rejected.
      
       ## builtin/history.c ##
     -@@ builtin/history.c: out:
     - 	return ret;
     +@@ builtin/history.c: static int find_interior_ref(const struct reference *ref, void *cb_data)
     + 	return 0;
       }
       
      +static int build_squash_message(struct repository *repo,
     @@ builtin/history.c: static int cmd_history_squash(int argc,
       	};
       	struct strbuf reflog_msg = STRBUF_INIT;
      +	struct strbuf message = STRBUF_INIT;
     + 	struct oidset interior = OIDSET_INIT;
       	struct commit *base, *oldest, *tip, *rewritten;
       	const struct object_id *base_tree_oid, *tip_tree_oid;
     - 	struct commit_list *parents = NULL;
      @@ builtin/history.c: static int cmd_history_squash(int argc,
     - 	if (ret < 0)
     - 		goto out;
     + 		}
     + 	}
       
      +	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
      +		ret = build_squash_message(repo, base, tip, &message);
     @@ builtin/history.c: static int cmd_history_squash(int argc,
       out:
       	strbuf_release(&reflog_msg);
      +	strbuf_release(&message);
     + 	oidset_clear(&interior);
       	commit_list_free(parents);
       	release_revisions(&revs);
     - 	return ret;
      
     - ## t/t3454-history-squash.sh ##
     -@@ t/t3454-history-squash.sh: test_expect_success 'preserves authorship of the oldest commit' '
     + ## t/t3455-history-squash.sh ##
     +@@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the oldest commit' '
       	test_cmp expect actual
       '
       
     @@ t/t3454-history-squash.sh: test_expect_success 'preserves authorship of the olde
      +	echo b >file &&
      +	git add file &&
      +	git commit -m "re-one subject" -m "re-one body line" &&
     -+	test_commit re-two file c &&
     ++	test_commit --no-tag re-two file c &&
      +	test_commit re-three file d &&
      +
      +	write_script editor <<-\EOF &&
     @@ t/t3454-history-squash.sh: test_expect_success 'preserves authorship of the olde
      +	test_set_editor "$(pwd)/editor" &&
      +	git history squash --reedit-message start.. &&
      +
     -+	grep "re-one subject" buffer &&
     -+	grep "re-one body line" buffer &&
     -+	grep re-two buffer &&
     -+	grep re-three buffer &&
     ++	test_grep "re-one subject" buffer &&
     ++	test_grep "re-one body line" buffer &&
     ++	test_grep re-two buffer &&
     ++	test_grep re-three buffer &&
      +	git log --format="%s" -1 >actual &&
      +	echo combined >expect &&
      +	test_cmp expect actual

-- 
gitgitgadget

[PATCH v4 1/4] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 091465a59e..f95f26e684 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -157,6 +157,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -164,21 +183,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -444,18 +453,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -799,16 +800,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v4 2/4] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index f95f26e684..305bde3102 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -101,6 +101,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -130,13 +131,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -189,7 +193,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -644,7 +648,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -855,7 +859,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -872,7 +876,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v4 3/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git history squash <revision-range>" to do this directly. It folds
every commit in the range into the oldest one, keeping that commit's
message and authorship and taking the tree of the newest commit, so the
range collapses into a single commit. Commits above the range are
replayed on top of the result.

The range is given as <base>..<tip>, so "git history squash @~3.."
folds the three most recent commits and "git history squash @~5..@~2"
squashes an interior range. A merge inside the range is folded like any
other commit, but the range must have a single base, so a range with
more than one entry point is rejected.

The folded commits leave the history, so by default the command refuses
when another ref points at one of them. Use "--update-refs=head" to
rewrite only the current branch and leave those refs untouched.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  25 +++
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 195 ++++++++++++++++++++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 303 +++++++++++++++++++++++++++++++
 7 files changed, 530 insertions(+)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 257db58918..f4d692d136 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -55,6 +55,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a ref points
+		into the range being folded, to tell the user about
+		`--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 2ba8121795..6716749cde 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -11,6 +11,7 @@ SYNOPSIS
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]
 
 DESCRIPTION
 -----------
@@ -97,6 +98,30 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's message and
+	authorship and takes the tree of the range's newest commit, so the
+	whole range collapses into a single commit. Commits above the range
+	are replayed on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash @~3..` folds the three most recent commits into one, and
+`git history squash @~5..@~2` squashes an interior range while leaving
+the two newest commits in place.
++
+The oldest commit's message and authorship are preserved by default,
+unless you specify `--reedit-message`. A merge commit inside the range is
+folded like any other, but the range must have a single base, so a range
+that reaches more than one entry point (for example a side branch that
+forked before the range and was later merged into it) is rejected.
++
+The folded commits disappear from the history, so with the default
+`--update-refs=branches` the command refuses when another ref points at
+one of them. Rerun with `--update-refs=head` to rewrite only the current
+branch and leave those refs pointing at the old commits.
+
 OPTIONS
 -------
 
diff --git a/advice.c b/advice.c
index 0018501b7b..5c6ff95e31 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 8def280688..911b4e4643 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index 305bde3102..4f1baea56c 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -30,6 +31,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -973,6 +976,196 @@ out:
 	return ret;
 }
 
+/*
+ * Resolve a "<base>..<tip>" revision range into the base commit just outside
+ * the range (which becomes the parent of the squashed commit), the oldest
+ * commit contained in the range (whose message the squash reuses), and the
+ * range tip (whose tree becomes the result). A merge inside the range is fine,
+ * but the range must have a single base and must not reach a root commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				const char *range,
+				struct commit **base_out,
+				struct commit **oldest_out,
+				struct commit **tip_out,
+				struct oidset *interior_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
+	struct strvec args = STRVEC_INIT;
+	int ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_push(&args, "--boundary");
+	strvec_push(&args, range);
+	setup_revisions_from_strvec(&args, &revs, NULL);
+	if (args.nr != 1) {
+		ret = error(_("'%s' does not name a revision range"), range);
+		goto out;
+	}
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs))) {
+		if (commit->object.flags & BOUNDARY) {
+			if (base) {
+				ret = error(_("range '%s' has more than one base; "
+					      "cannot squash"), range);
+				goto out;
+			}
+			base = commit;
+			continue;
+		}
+		if (!oldest)
+			oldest = commit;
+		if (tip)
+			oidset_insert(interior_out, &tip->object.oid);
+		tip = commit;
+	}
+
+	if (!oldest) {
+		ret = error(_("the range '%s' is empty"), range);
+		goto out;
+	}
+
+	if (!base) {
+		ret = error(_("cannot squash the root commit"));
+		goto out;
+	}
+
+	*base_out = base;
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+struct interior_ref_cb {
+	const struct oidset *interior;
+	const char *name;
+};
+
+static int find_interior_ref(const struct reference *ref, void *cb_data)
+{
+	struct interior_ref_cb *data = cb_data;
+
+	if (oidset_contains(data->interior, ref->oid)) {
+		data->name = xstrdup(ref->name);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	enum commit_tree_flags flags = 0;
+	int dry_run = 0;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BIT(0, "reedit-message", &flags,
+			N_("open an editor to modify the commit message"),
+			COMMIT_TREE_EDIT_MESSAGE),
+		OPT_END(),
+	};
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct oidset interior = OIDSET_INIT;
+	struct commit *base, *oldest, *tip, *rewritten;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	struct commit_list *parents = NULL;
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+	if (argc != 1) {
+		ret = error(_("command expects a single revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
+
+	ret = resolve_squash_range(repo, argv[0], &base, &oldest, &tip,
+				   &interior);
+	if (ret < 0)
+		goto out;
+
+	if (action == REF_ACTION_BRANCHES) {
+		struct interior_ref_cb cb = { .interior = &interior };
+
+		refs_for_each_ref(get_main_ref_store(repo),
+				  find_interior_ref, &cb);
+		if (cb.name) {
+			ret = error(_("'%s' points into the squashed range"),
+				    cb.name);
+			advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+					  _("Use --update-refs=head to rewrite only "
+					    "the current branch and leave such refs "
+					    "untouched."));
+			free((char *)cb.name);
+			goto out;
+		}
+	}
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+	commit_list_append(base, &parents);
+
+	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
+			      base_tree_oid, tip_tree_oid, &rewritten, flags);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	strbuf_addf(&reflog_msg, "squash: updating %s", argv[0]);
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	oidset_clear(&interior);
+	commit_list_free(parents);
+	release_revisions(&revs);
+	return ret;
+}
+
 int cmd_history(int argc,
 		const char **argv,
 		const char *prefix,
@@ -982,6 +1175,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -989,6 +1183,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
diff --git a/t/meson.build b/t/meson.build
index 3219264fe7..63ea26b8ed 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -399,6 +399,7 @@ integration_tests = [
   't3451-history-reword.sh',
   't3452-history-split.sh',
   't3453-history-fixup.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..821c801153
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,303 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+test_expect_success 'setup linear history touching two files' '
+	test_commit base file a &&
+	git tag start &&
+	test_commit --no-tag one other x &&
+	test_commit --no-tag two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "command expects a single revision range" err
+'
+
+test_expect_success 'errors on too many arguments' '
+	test_must_fail git history squash start.. HEAD 2>err &&
+	test_grep "command expects a single revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the range .* is empty" err
+'
+
+test_expect_success 'errors when the range includes the root commit' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "cannot squash the root commit" err
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	git log --format="%s" -1 >subject &&
+	echo one >expect &&
+	test_cmp expect subject &&
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..@~1 &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	three
+	one
+	EOF
+	test_cmp expect actual &&
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$root.." &&
+
+	git rev-list --count "$root..HEAD" >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashing a single-commit range replays the rest' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..@~2 &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	three
+	two
+	one
+	EOF
+	test_cmp expect actual &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'reuses the message of a fixup! commit in the range' '
+	git reset --hard start &&
+	test_commit --no-tag reg1 file b &&
+	git commit --allow-empty -m "fixup! reg1" &&
+	test_commit reg2 file c &&
+
+	git history squash start.. &&
+
+	git log --format="%s" -1 >actual &&
+	echo reg1 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'keeps the oldest message even if it is a fixup!' '
+	git reset --hard start &&
+	test_commit --no-tag "fixup! something" file b &&
+	test_commit tail file c &&
+
+	git history squash start.. &&
+
+	git log --format="%s" -1 >actual &&
+	echo "fixup! something" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'preserves authorship of the oldest commit' '
+	git reset --hard start &&
+	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
+		test_commit --no-tag oldest file b &&
+	test_commit newest file c &&
+
+	git history squash start.. &&
+
+	git log -1 --format="%an <%ae>" >actual &&
+	echo "Squasher <squash@example.com>" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--dry-run predicts the rewrite without performing it' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash start.. &&
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --update-refs=head start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success 'refuses to fold a range a ref points into' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "error: .* points into the squashed range" err &&
+	test_grep "hint: .*--update-refs=head" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D mid
+'
+
+test_expect_success 'advice.historyUpdateRefs silences the hint' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "points into the squashed range" err &&
+	test_grep ! "hint:" err &&
+
+	git branch -D mid
+'
+
+test_expect_success '--update-refs=head folds past a ref pointing into the range' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	mid_before=$(git rev-parse mid) &&
+
+	git history squash --update-refs=head start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$mid_before" mid &&
+
+	git branch -D mid
+'
+
+test_expect_success 'refuses to fold a range a tag points into' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "refs/tags/mark" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git tag -d mark
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout - &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	test_commit --no-tag after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	git log --format="%s" -1 >subject &&
+	echo before-side >expect &&
+	test_cmp expect subject &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout - &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout - &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$base.." &&
+
+	git rev-list --count "$base..HEAD" >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'refuses to squash a range with more than one base' '
+	git reset --hard start &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b forked-before &&
+	test_commit forked-side fside x &&
+	git checkout - &&
+	test_commit forked-main file b &&
+	git merge --no-ff -m merge forked-before &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash forked-main.. 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_done
-- 
gitgitgadget

[PATCH v4 4/4] history: re-edit a squash with every message

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

By default "git history squash" reuses the oldest commit's message.
When --reedit-message is given it only reopened that one message, so the
messages of the folded-in commits were lost.

Gather the messages of every commit in the range, oldest first, and use
them as the editor template when re-editing, mirroring how "git rebase
-i" presents a squash. The combined message is built before the
descendant walk so it is not disturbed by the flags that walk leaves on
the commits.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  5 +--
 builtin/history.c              | 61 +++++++++++++++++++++++++++++++++-
 t/t3455-history-squash.sh      | 37 +++++++++++++++++++++
 3 files changed, 100 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 6716749cde..df389015aa 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -111,8 +111,9 @@ history squash @~3..` folds the three most recent commits into one, and
 `git history squash @~5..@~2` squashes an interior range while leaving
 the two newest commits in place.
 +
-The oldest commit's message and authorship are preserved by default,
-unless you specify `--reedit-message`. A merge commit inside the range is
+The oldest commit's message and authorship are preserved by default. With
+`--reedit-message`, an editor opens pre-filled with the messages of all the
+folded commits so you can combine them. A merge commit inside the range is
 folded like any other, but the range must have a single base, so a range
 that reaches more than one entry point (for example a side branch that
 forked before the range and was later merged into it) is rejected.
diff --git a/builtin/history.c b/builtin/history.c
index 4f1baea56c..ff3bc9f945 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1068,6 +1068,56 @@ static int find_interior_ref(const struct reference *ref, void *cb_data)
 	return 0;
 }
 
+static int build_squash_message(struct repository *repo,
+				struct commit *base,
+				struct commit *tip,
+				struct strbuf *out)
+{
+	struct rev_info revs;
+	struct commit *commit;
+	struct strvec args = STRVEC_INIT;
+	int n = 0, ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs))) {
+		const char *message, *body;
+		struct strbuf one = STRBUF_INIT;
+
+		message = repo_logmsg_reencode(repo, commit, NULL, NULL);
+		find_commit_subject(message, &body);
+		strbuf_addstr(&one, body);
+		strbuf_trim_trailing_newline(&one);
+
+		if (n++)
+			strbuf_addch(out, '\n');
+		strbuf_addbuf(out, &one);
+		strbuf_addch(out, '\n');
+
+		strbuf_release(&one);
+		repo_unuse_commit_buffer(repo, commit, message);
+	}
+
+	ret = 0;
+
+out:
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1092,6 +1142,7 @@ static int cmd_history_squash(int argc,
 		OPT_END(),
 	};
 	struct strbuf reflog_msg = STRBUF_INIT;
+	struct strbuf message = STRBUF_INIT;
 	struct oidset interior = OIDSET_INIT;
 	struct commit *base, *oldest, *tip, *rewritten;
 	const struct object_id *base_tree_oid, *tip_tree_oid;
@@ -1131,6 +1182,12 @@ static int cmd_history_squash(int argc,
 		}
 	}
 
+	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
+		ret = build_squash_message(repo, base, tip, &message);
+		if (ret < 0)
+			goto out;
+	}
+
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
 		goto out;
@@ -1139,7 +1196,8 @@ static int cmd_history_squash(int argc,
 	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
 	commit_list_append(base, &parents);
 
-	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
+	ret = commit_tree_ext(repo, "squash", oldest,
+			      message.len ? message.buf : NULL, parents,
 			      base_tree_oid, tip_tree_oid, &rewritten, flags);
 	if (ret < 0) {
 		ret = error(_("failed writing squashed commit"));
@@ -1160,6 +1218,7 @@ static int cmd_history_squash(int argc,
 
 out:
 	strbuf_release(&reflog_msg);
+	strbuf_release(&message);
 	oidset_clear(&interior);
 	commit_list_free(parents);
 	release_revisions(&revs);
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index 821c801153..1fb3b9b63e 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -135,6 +135,43 @@ test_expect_success 'preserves authorship of the oldest commit' '
 	test_cmp expect actual
 '
 
+test_expect_success '--reedit-message offers every folded-in message' '
+	git reset --hard start &&
+	echo b >file &&
+	git add file &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+
+	write_script editor <<-\EOF &&
+	cp "$1" buffer &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	test_grep "re-one subject" buffer &&
+	test_grep "re-one body line" buffer &&
+	test_grep re-two buffer &&
+	test_grep re-three buffer &&
+	git log --format="%s" -1 >actual &&
+	echo combined >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--reedit-message aborts on an empty message' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	test_must_fail git history squash --reedit-message start.. &&
+
+	test_cmp_rev "$head_before" HEAD
+'
+
 test_expect_success '--dry-run predicts the rewrite without performing it' '
 	git reset --hard three &&
 	head_before=$(git rev-parse HEAD) &&
-- 
gitgitgadget

Re: [PATCH v4 0/4] history: add squash subcommand to fold a range

[Patrick Steinhardt]

On Sun, Jun 21, 2026 at 05:53:11AM +0000, Harald Nordgren via GitGitGadget wrote:
> Adds git history squash <revision-range> to fold a range of commits.
> 
> Changes in v4:
> 
>  * git history squash now detects when another ref points at a commit inside
>    the range being folded and refuses, with an advice.historyUpdateRefs hint
>    to use --update-refs=head.
>  * A merge inside the range is folded fine as long as the range has a single
>    base; a range with merge commit at the tip or base also folds correctly.
>    Only a range with more than one base is rejected.

Some of the conceptual questions on v3 are still open, like for example
whether we should be using "--ancestry=". Please make sure that you are
replying to questions like that when rerolling, especially when you
don't plan to address them. Otherwise the reviewer will not know why you
didn't take feedback into account. See also the thread at [1] for
guidance.

I'll wait for open questions to be addressed before reviewing this (or
any subsequent) version.

Thanks!

Patrick

[1]: <xmqqv7bhxiby.fsf@gitster.g>

Re: [PATCH v4 0/4] history: add squash subcommand to fold a range

[Harald Nordgren]

Sorry about that.

I skipped the ancestry question because I felt the implementation
would get too complex and was hoping we could do without it. Probably
would have been better to be explicit about that instead of just
skipping it. I don't want to balloon the code more than necessary, but
I'll take a look at it now.


Harald

[PATCH v5 0/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v5:

 * The range walk now uses --ancestry-path, so only commits descended from
   the base are folded; a single revision such as HEAD or HEAD~1 is now
   rejected as "not a <base>..<tip> range" rather than treated as a squash
   down to the root.
 * This adopts the --ancestry-path suggestion; the multi-base rejection is
   unchanged, so a side branch that forked before the base and merged in is
   still refused.
 * Added tests covering more merge topologies: two interior merges, a nested
   merge, an octopus merge, an octopus arm forked before the base, a merge
   among the descendants replayed above the range, and a ref pointing at an
   interior merge commit.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (4):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  history: add squash subcommand to fold a range
  history: re-edit a squash with every message

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  26 ++
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 341 ++++++++++++++++++---
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 497 +++++++++++++++++++++++++++++++
 7 files changed, 833 insertions(+), 38 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: 26d8d94e94df5535eecd036f16627493506a0614
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v5
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v4:

 1:  fc2801c0b1 = 1:  0f1ae9b05a history: extract helper for a commit's parent tree
 2:  ee591e83b4 = 2:  a97ffab1e6 history: give commit_tree_ext a message template
 3:  80bfea642e ! 3:  04e18ef979 history: add squash subcommand to fold a range
     @@ builtin/history.c: out:
      +	struct rev_info revs;
      +	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
      +	struct strvec args = STRVEC_INIT;
     ++	size_t i;
      +	int ret;
      +
      +	repo_init_revisions(repo, &revs, NULL);
     @@ builtin/history.c: out:
      +	strvec_push(&args, "--reverse");
      +	strvec_push(&args, "--topo-order");
      +	strvec_push(&args, "--boundary");
     ++	strvec_push(&args, "--ancestry-path");
      +	strvec_push(&args, range);
      +	setup_revisions_from_strvec(&args, &revs, NULL);
      +	if (args.nr != 1) {
     @@ builtin/history.c: out:
      +		goto out;
      +	}
      +
     ++	/*
     ++	 * A squash needs a base to reparent onto, so the argument has to
     ++	 * exclude something, as in "<base>..<tip>". A single revision has no
     ++	 * such bottom commit and cannot be squashed.
     ++	 */
     ++	for (i = 0; i < revs.cmdline.nr; i++)
     ++		if (revs.cmdline.rev[i].flags & UNINTERESTING)
     ++			break;
     ++	if (i == revs.cmdline.nr) {
     ++		ret = error(_("'%s' is not a '<base>..<tip>' range"), range);
     ++		goto out;
     ++	}
     ++
      +	if (prepare_revision_walk(&revs) < 0) {
      +		ret = error(_("error preparing revisions"));
      +		goto out;
     @@ builtin/history.c: out:
      +		goto out;
      +	}
      +
     -+	if (!base) {
     -+		ret = error(_("cannot squash the root commit"));
     -+		goto out;
     -+	}
     ++	if (!base)
     ++		BUG("a non-empty range must have a boundary commit");
      +
      +	*base_out = base;
      +	*oldest_out = oldest;
     @@ t/t3455-history-squash.sh (new)
      +	test_grep "the range .* is empty" err
      +'
      +
     -+test_expect_success 'errors when the range includes the root commit' '
     ++test_expect_success 'errors on a single revision that is not a range' '
      +	test_must_fail git history squash HEAD 2>err &&
     -+	test_grep "cannot squash the root commit" err
     ++	test_grep "is not a .*range" err &&
     ++	test_must_fail git history squash HEAD~1 2>err &&
     ++	test_grep "is not a .*range" err
      +'
      +
      +test_expect_success 'squashes a range into a single commit without changing the tree' '
     @@ t/t3455-history-squash.sh (new)
      +	test_path_is_file inner
      +'
      +
     ++test_expect_success 'folds a merge of a branch that forked at the base' '
     ++	git reset --hard start &&
     ++	git checkout -b base-fork-side &&
     ++	test_commit --no-tag base-fork-side side x &&
     ++	git checkout - &&
     ++	test_commit --no-tag base-fork-main file b &&
     ++	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
     ++	git branch -D base-fork-side &&
     ++	test_commit --no-tag base-fork-tail file c &&
     ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
     ++
     ++	git history squash start.. &&
     ++
     ++	git rev-list --count start..HEAD >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
     ++	test_cmp_rev start HEAD^ &&
     ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     ++	test_path_is_file side
     ++'
     ++
      +test_expect_success 'folds a range whose tip is a merge commit' '
      +	git reset --hard start &&
      +	test_commit --no-tag tipmerge-base file b &&
     @@ t/t3455-history-squash.sh (new)
      +	test_cmp_rev "$merged" HEAD
      +'
      +
     ++test_expect_success 'folds a range with two interior merges' '
     ++	git reset --hard start &&
     ++	test_commit --no-tag two-merge-a file a1 &&
     ++	git checkout -b two-merge-s1 &&
     ++	test_commit --no-tag two-merge-s1 s1 x &&
     ++	git checkout - &&
     ++	git merge --no-ff -m "merge s1" two-merge-s1 &&
     ++	test_commit --no-tag two-merge-b file b1 &&
     ++	git checkout -b two-merge-s2 &&
     ++	test_commit --no-tag two-merge-s2 s2 y &&
     ++	git checkout - &&
     ++	git merge --no-ff -m "merge s2" two-merge-s2 &&
     ++	git branch -D two-merge-s1 two-merge-s2 &&
     ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
     ++
     ++	git history squash start.. &&
     ++
     ++	git rev-list --count start..HEAD >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
     ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     ++	test_path_is_file s1 &&
     ++	test_path_is_file s2
     ++'
     ++
     ++test_expect_success 'folds a range with a nested merge' '
     ++	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
     ++	git checkout -b nested-outer &&
     ++	test_commit --no-tag nested-outer outer x &&
     ++	git checkout -b nested-inner &&
     ++	test_commit --no-tag nested-inner inner y &&
     ++	git checkout nested-outer &&
     ++	git merge --no-ff -m "merge inner" nested-inner &&
     ++	git checkout "$main" &&
     ++	test_commit --no-tag nested-main file b1 &&
     ++	git merge --no-ff -m "merge outer" nested-outer &&
     ++	git branch -D nested-outer nested-inner &&
     ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
     ++
     ++	git history squash start.. &&
     ++
     ++	git rev-list --count start..HEAD >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
     ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     ++	test_path_is_file outer &&
     ++	test_path_is_file inner
     ++'
     ++
     ++test_expect_success 'folds a range with an octopus merge' '
     ++	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
     ++	test_commit --no-tag octo-base file a1 &&
     ++	git checkout -b octo-1 &&
     ++	test_commit --no-tag octo-1 o1 x &&
     ++	git checkout "$main" &&
     ++	git checkout -b octo-2 &&
     ++	test_commit --no-tag octo-2 o2 y &&
     ++	git checkout "$main" &&
     ++	git merge --no-ff -m octopus octo-1 octo-2 &&
     ++	git branch -D octo-1 octo-2 &&
     ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
     ++
     ++	git history squash start.. &&
     ++
     ++	git rev-list --count start..HEAD >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
     ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     ++	test_path_is_file o1 &&
     ++	test_path_is_file o2
     ++'
     ++
     ++test_expect_success 'refuses an octopus merge with an arm forked before the base' '
     ++	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
     ++	git checkout -b octo-pre &&
     ++	test_commit octo-pre-side pside x &&
     ++	git checkout "$main" &&
     ++	test_commit octo-pre-main file b1 &&
     ++	octo_base=$(git rev-parse HEAD) &&
     ++	git checkout -b octo-within &&
     ++	test_commit --no-tag octo-within wside y &&
     ++	git checkout "$main" &&
     ++	git merge --no-ff -m octopus octo-pre octo-within &&
     ++	merged=$(git rev-parse HEAD) &&
     ++	git branch -D octo-pre octo-within &&
     ++
     ++	test_must_fail git history squash "$octo_base.." 2>err &&
     ++	test_grep "more than one base" err &&
     ++	test_cmp_rev "$merged" HEAD
     ++'
     ++
     ++test_expect_success 'refuses when a descendant above the range is a merge' '
     ++	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
     ++	test_commit --no-tag desc-base file b &&
     ++	git tag desc-tip &&
     ++	git checkout -b desc-above &&
     ++	test_commit --no-tag desc-above above x &&
     ++	git checkout "$main" &&
     ++	test_commit --no-tag desc-main file c &&
     ++	git merge --no-ff -m "merge desc-above" desc-above &&
     ++	git branch -D desc-above &&
     ++	head_before=$(git rev-parse HEAD) &&
     ++
     ++	test_must_fail git history squash start..desc-tip 2>err &&
     ++	test_grep "merge commits is not supported" err &&
     ++	test_cmp_rev "$head_before" HEAD
     ++'
     ++
     ++test_expect_success 'refuses to fold a range a ref points into at a merge' '
     ++	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
     ++	test_commit --no-tag refmerge-base file b &&
     ++	git checkout -b refmerge-side &&
     ++	test_commit --no-tag refmerge-side side x &&
     ++	git checkout "$main" &&
     ++	test_commit --no-tag refmerge-main file c &&
     ++	git merge --no-ff -m "interior merge" refmerge-side &&
     ++	git branch -D refmerge-side &&
     ++	git branch at-merge HEAD &&
     ++	test_commit --no-tag refmerge-tail file d &&
     ++	head_before=$(git rev-parse HEAD) &&
     ++
     ++	test_must_fail git history squash start.. 2>err &&
     ++	test_grep "at-merge" err &&
     ++	test_grep "points into the squashed range" err &&
     ++	test_cmp_rev "$head_before" HEAD &&
     ++
     ++	git branch -D at-merge
     ++'
     ++
      +test_done
 4:  85c7817d7e = 4:  a758e1f084 history: re-edit a squash with every message

-- 
gitgitgadget

[PATCH v5 1/4] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 091465a59e..f95f26e684 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -157,6 +157,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -164,21 +183,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -444,18 +453,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -799,16 +800,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v5 2/4] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index f95f26e684..305bde3102 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -101,6 +101,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -130,13 +131,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -189,7 +193,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -644,7 +648,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -855,7 +859,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -872,7 +876,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v5 3/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git history squash <revision-range>" to do this directly. It folds
every commit in the range into the oldest one, keeping that commit's
message and authorship and taking the tree of the newest commit, so the
range collapses into a single commit. Commits above the range are
replayed on top of the result.

The range is given as <base>..<tip>, so "git history squash @~3.."
folds the three most recent commits and "git history squash @~5..@~2"
squashes an interior range. A merge inside the range is folded like any
other commit, but the range must have a single base, so a range with
more than one entry point is rejected.

The folded commits leave the history, so by default the command refuses
when another ref points at one of them. Use "--update-refs=head" to
rewrite only the current branch and leave those refs untouched.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  25 ++
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 208 ++++++++++++++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 460 +++++++++++++++++++++++++++++++
 7 files changed, 700 insertions(+)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 257db58918..f4d692d136 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -55,6 +55,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a ref points
+		into the range being folded, to tell the user about
+		`--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 2ba8121795..6716749cde 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -11,6 +11,7 @@ SYNOPSIS
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]
 
 DESCRIPTION
 -----------
@@ -97,6 +98,30 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's message and
+	authorship and takes the tree of the range's newest commit, so the
+	whole range collapses into a single commit. Commits above the range
+	are replayed on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash @~3..` folds the three most recent commits into one, and
+`git history squash @~5..@~2` squashes an interior range while leaving
+the two newest commits in place.
++
+The oldest commit's message and authorship are preserved by default,
+unless you specify `--reedit-message`. A merge commit inside the range is
+folded like any other, but the range must have a single base, so a range
+that reaches more than one entry point (for example a side branch that
+forked before the range and was later merged into it) is rejected.
++
+The folded commits disappear from the history, so with the default
+`--update-refs=branches` the command refuses when another ref points at
+one of them. Rerun with `--update-refs=head` to rewrite only the current
+branch and leave those refs pointing at the old commits.
+
 OPTIONS
 -------
 
diff --git a/advice.c b/advice.c
index 0018501b7b..5c6ff95e31 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 8def280688..911b4e4643 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index 305bde3102..0acfabed66 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -30,6 +31,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -973,6 +976,209 @@ out:
 	return ret;
 }
 
+/*
+ * Resolve a "<base>..<tip>" revision range into the base commit just outside
+ * the range (which becomes the parent of the squashed commit), the oldest
+ * commit contained in the range (whose message the squash reuses), and the
+ * range tip (whose tree becomes the result). A merge inside the range is fine,
+ * but the range must have a single base and must not reach a root commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				const char *range,
+				struct commit **base_out,
+				struct commit **oldest_out,
+				struct commit **tip_out,
+				struct oidset *interior_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
+	struct strvec args = STRVEC_INIT;
+	size_t i;
+	int ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_push(&args, "--boundary");
+	strvec_push(&args, "--ancestry-path");
+	strvec_push(&args, range);
+	setup_revisions_from_strvec(&args, &revs, NULL);
+	if (args.nr != 1) {
+		ret = error(_("'%s' does not name a revision range"), range);
+		goto out;
+	}
+
+	/*
+	 * A squash needs a base to reparent onto, so the argument has to
+	 * exclude something, as in "<base>..<tip>". A single revision has no
+	 * such bottom commit and cannot be squashed.
+	 */
+	for (i = 0; i < revs.cmdline.nr; i++)
+		if (revs.cmdline.rev[i].flags & UNINTERESTING)
+			break;
+	if (i == revs.cmdline.nr) {
+		ret = error(_("'%s' is not a '<base>..<tip>' range"), range);
+		goto out;
+	}
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs))) {
+		if (commit->object.flags & BOUNDARY) {
+			if (base) {
+				ret = error(_("range '%s' has more than one base; "
+					      "cannot squash"), range);
+				goto out;
+			}
+			base = commit;
+			continue;
+		}
+		if (!oldest)
+			oldest = commit;
+		if (tip)
+			oidset_insert(interior_out, &tip->object.oid);
+		tip = commit;
+	}
+
+	if (!oldest) {
+		ret = error(_("the range '%s' is empty"), range);
+		goto out;
+	}
+
+	if (!base)
+		BUG("a non-empty range must have a boundary commit");
+
+	*base_out = base;
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+struct interior_ref_cb {
+	const struct oidset *interior;
+	const char *name;
+};
+
+static int find_interior_ref(const struct reference *ref, void *cb_data)
+{
+	struct interior_ref_cb *data = cb_data;
+
+	if (oidset_contains(data->interior, ref->oid)) {
+		data->name = xstrdup(ref->name);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	enum commit_tree_flags flags = 0;
+	int dry_run = 0;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BIT(0, "reedit-message", &flags,
+			N_("open an editor to modify the commit message"),
+			COMMIT_TREE_EDIT_MESSAGE),
+		OPT_END(),
+	};
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct oidset interior = OIDSET_INIT;
+	struct commit *base, *oldest, *tip, *rewritten;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	struct commit_list *parents = NULL;
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+	if (argc != 1) {
+		ret = error(_("command expects a single revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
+
+	ret = resolve_squash_range(repo, argv[0], &base, &oldest, &tip,
+				   &interior);
+	if (ret < 0)
+		goto out;
+
+	if (action == REF_ACTION_BRANCHES) {
+		struct interior_ref_cb cb = { .interior = &interior };
+
+		refs_for_each_ref(get_main_ref_store(repo),
+				  find_interior_ref, &cb);
+		if (cb.name) {
+			ret = error(_("'%s' points into the squashed range"),
+				    cb.name);
+			advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+					  _("Use --update-refs=head to rewrite only "
+					    "the current branch and leave such refs "
+					    "untouched."));
+			free((char *)cb.name);
+			goto out;
+		}
+	}
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+	commit_list_append(base, &parents);
+
+	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
+			      base_tree_oid, tip_tree_oid, &rewritten, flags);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	strbuf_addf(&reflog_msg, "squash: updating %s", argv[0]);
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	oidset_clear(&interior);
+	commit_list_free(parents);
+	release_revisions(&revs);
+	return ret;
+}
+
 int cmd_history(int argc,
 		const char **argv,
 		const char *prefix,
@@ -982,6 +1188,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -989,6 +1196,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
diff --git a/t/meson.build b/t/meson.build
index 3219264fe7..63ea26b8ed 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -399,6 +399,7 @@ integration_tests = [
   't3451-history-reword.sh',
   't3452-history-split.sh',
   't3453-history-fixup.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..7227c5c90f
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,460 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+test_expect_success 'setup linear history touching two files' '
+	test_commit base file a &&
+	git tag start &&
+	test_commit --no-tag one other x &&
+	test_commit --no-tag two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "command expects a single revision range" err
+'
+
+test_expect_success 'errors on too many arguments' '
+	test_must_fail git history squash start.. HEAD 2>err &&
+	test_grep "command expects a single revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the range .* is empty" err
+'
+
+test_expect_success 'errors on a single revision that is not a range' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "is not a .*range" err &&
+	test_must_fail git history squash HEAD~1 2>err &&
+	test_grep "is not a .*range" err
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	git log --format="%s" -1 >subject &&
+	echo one >expect &&
+	test_cmp expect subject &&
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..@~1 &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	three
+	one
+	EOF
+	test_cmp expect actual &&
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$root.." &&
+
+	git rev-list --count "$root..HEAD" >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashing a single-commit range replays the rest' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..@~2 &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	three
+	two
+	one
+	EOF
+	test_cmp expect actual &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'reuses the message of a fixup! commit in the range' '
+	git reset --hard start &&
+	test_commit --no-tag reg1 file b &&
+	git commit --allow-empty -m "fixup! reg1" &&
+	test_commit reg2 file c &&
+
+	git history squash start.. &&
+
+	git log --format="%s" -1 >actual &&
+	echo reg1 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'keeps the oldest message even if it is a fixup!' '
+	git reset --hard start &&
+	test_commit --no-tag "fixup! something" file b &&
+	test_commit tail file c &&
+
+	git history squash start.. &&
+
+	git log --format="%s" -1 >actual &&
+	echo "fixup! something" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'preserves authorship of the oldest commit' '
+	git reset --hard start &&
+	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
+		test_commit --no-tag oldest file b &&
+	test_commit newest file c &&
+
+	git history squash start.. &&
+
+	git log -1 --format="%an <%ae>" >actual &&
+	echo "Squasher <squash@example.com>" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--dry-run predicts the rewrite without performing it' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash start.. &&
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --update-refs=head start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success 'refuses to fold a range a ref points into' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "error: .* points into the squashed range" err &&
+	test_grep "hint: .*--update-refs=head" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D mid
+'
+
+test_expect_success 'advice.historyUpdateRefs silences the hint' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "points into the squashed range" err &&
+	test_grep ! "hint:" err &&
+
+	git branch -D mid
+'
+
+test_expect_success '--update-refs=head folds past a ref pointing into the range' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	mid_before=$(git rev-parse mid) &&
+
+	git history squash --update-refs=head start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$mid_before" mid &&
+
+	git branch -D mid
+'
+
+test_expect_success 'refuses to fold a range a tag points into' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "refs/tags/mark" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git tag -d mark
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout - &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	test_commit --no-tag after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	git log --format="%s" -1 >subject &&
+	echo before-side >expect &&
+	test_cmp expect subject &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a merge of a branch that forked at the base' '
+	git reset --hard start &&
+	git checkout -b base-fork-side &&
+	test_commit --no-tag base-fork-side side x &&
+	git checkout - &&
+	test_commit --no-tag base-fork-main file b &&
+	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
+	git branch -D base-fork-side &&
+	test_commit --no-tag base-fork-tail file c &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout - &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout - &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$base.." &&
+
+	git rev-list --count "$base..HEAD" >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'refuses to squash a range with more than one base' '
+	git reset --hard start &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b forked-before &&
+	test_commit forked-side fside x &&
+	git checkout - &&
+	test_commit forked-main file b &&
+	git merge --no-ff -m merge forked-before &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash forked-main.. 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range with two interior merges' '
+	git reset --hard start &&
+	test_commit --no-tag two-merge-a file a1 &&
+	git checkout -b two-merge-s1 &&
+	test_commit --no-tag two-merge-s1 s1 x &&
+	git checkout - &&
+	git merge --no-ff -m "merge s1" two-merge-s1 &&
+	test_commit --no-tag two-merge-b file b1 &&
+	git checkout -b two-merge-s2 &&
+	test_commit --no-tag two-merge-s2 s2 y &&
+	git checkout - &&
+	git merge --no-ff -m "merge s2" two-merge-s2 &&
+	git branch -D two-merge-s1 two-merge-s2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file s1 &&
+	test_path_is_file s2
+'
+
+test_expect_success 'folds a range with a nested merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b nested-outer &&
+	test_commit --no-tag nested-outer outer x &&
+	git checkout -b nested-inner &&
+	test_commit --no-tag nested-inner inner y &&
+	git checkout nested-outer &&
+	git merge --no-ff -m "merge inner" nested-inner &&
+	git checkout "$main" &&
+	test_commit --no-tag nested-main file b1 &&
+	git merge --no-ff -m "merge outer" nested-outer &&
+	git branch -D nested-outer nested-inner &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file outer &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range with an octopus merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag octo-base file a1 &&
+	git checkout -b octo-1 &&
+	test_commit --no-tag octo-1 o1 x &&
+	git checkout "$main" &&
+	git checkout -b octo-2 &&
+	test_commit --no-tag octo-2 o2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-1 octo-2 &&
+	git branch -D octo-1 octo-2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file o1 &&
+	test_path_is_file o2
+'
+
+test_expect_success 'refuses an octopus merge with an arm forked before the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b octo-pre &&
+	test_commit octo-pre-side pside x &&
+	git checkout "$main" &&
+	test_commit octo-pre-main file b1 &&
+	octo_base=$(git rev-parse HEAD) &&
+	git checkout -b octo-within &&
+	test_commit --no-tag octo-within wside y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-pre octo-within &&
+	merged=$(git rev-parse HEAD) &&
+	git branch -D octo-pre octo-within &&
+
+	test_must_fail git history squash "$octo_base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'refuses when a descendant above the range is a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag desc-base file b &&
+	git tag desc-tip &&
+	git checkout -b desc-above &&
+	test_commit --no-tag desc-above above x &&
+	git checkout "$main" &&
+	test_commit --no-tag desc-main file c &&
+	git merge --no-ff -m "merge desc-above" desc-above &&
+	git branch -D desc-above &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start..desc-tip 2>err &&
+	test_grep "merge commits is not supported" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'refuses to fold a range a ref points into at a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag refmerge-base file b &&
+	git checkout -b refmerge-side &&
+	test_commit --no-tag refmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag refmerge-main file c &&
+	git merge --no-ff -m "interior merge" refmerge-side &&
+	git branch -D refmerge-side &&
+	git branch at-merge HEAD &&
+	test_commit --no-tag refmerge-tail file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "at-merge" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D at-merge
+'
+
+test_done
-- 
gitgitgadget

[PATCH v5 4/4] history: re-edit a squash with every message

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

By default "git history squash" reuses the oldest commit's message.
When --reedit-message is given it only reopened that one message, so the
messages of the folded-in commits were lost.

Gather the messages of every commit in the range, oldest first, and use
them as the editor template when re-editing, mirroring how "git rebase
-i" presents a squash. The combined message is built before the
descendant walk so it is not disturbed by the flags that walk leaves on
the commits.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  5 +--
 builtin/history.c              | 61 +++++++++++++++++++++++++++++++++-
 t/t3455-history-squash.sh      | 37 +++++++++++++++++++++
 3 files changed, 100 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 6716749cde..df389015aa 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -111,8 +111,9 @@ history squash @~3..` folds the three most recent commits into one, and
 `git history squash @~5..@~2` squashes an interior range while leaving
 the two newest commits in place.
 +
-The oldest commit's message and authorship are preserved by default,
-unless you specify `--reedit-message`. A merge commit inside the range is
+The oldest commit's message and authorship are preserved by default. With
+`--reedit-message`, an editor opens pre-filled with the messages of all the
+folded commits so you can combine them. A merge commit inside the range is
 folded like any other, but the range must have a single base, so a range
 that reaches more than one entry point (for example a side branch that
 forked before the range and was later merged into it) is rejected.
diff --git a/builtin/history.c b/builtin/history.c
index 0acfabed66..e93f8398e6 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1081,6 +1081,56 @@ static int find_interior_ref(const struct reference *ref, void *cb_data)
 	return 0;
 }
 
+static int build_squash_message(struct repository *repo,
+				struct commit *base,
+				struct commit *tip,
+				struct strbuf *out)
+{
+	struct rev_info revs;
+	struct commit *commit;
+	struct strvec args = STRVEC_INIT;
+	int n = 0, ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs))) {
+		const char *message, *body;
+		struct strbuf one = STRBUF_INIT;
+
+		message = repo_logmsg_reencode(repo, commit, NULL, NULL);
+		find_commit_subject(message, &body);
+		strbuf_addstr(&one, body);
+		strbuf_trim_trailing_newline(&one);
+
+		if (n++)
+			strbuf_addch(out, '\n');
+		strbuf_addbuf(out, &one);
+		strbuf_addch(out, '\n');
+
+		strbuf_release(&one);
+		repo_unuse_commit_buffer(repo, commit, message);
+	}
+
+	ret = 0;
+
+out:
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1105,6 +1155,7 @@ static int cmd_history_squash(int argc,
 		OPT_END(),
 	};
 	struct strbuf reflog_msg = STRBUF_INIT;
+	struct strbuf message = STRBUF_INIT;
 	struct oidset interior = OIDSET_INIT;
 	struct commit *base, *oldest, *tip, *rewritten;
 	const struct object_id *base_tree_oid, *tip_tree_oid;
@@ -1144,6 +1195,12 @@ static int cmd_history_squash(int argc,
 		}
 	}
 
+	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
+		ret = build_squash_message(repo, base, tip, &message);
+		if (ret < 0)
+			goto out;
+	}
+
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
 		goto out;
@@ -1152,7 +1209,8 @@ static int cmd_history_squash(int argc,
 	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
 	commit_list_append(base, &parents);
 
-	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
+	ret = commit_tree_ext(repo, "squash", oldest,
+			      message.len ? message.buf : NULL, parents,
 			      base_tree_oid, tip_tree_oid, &rewritten, flags);
 	if (ret < 0) {
 		ret = error(_("failed writing squashed commit"));
@@ -1173,6 +1231,7 @@ static int cmd_history_squash(int argc,
 
 out:
 	strbuf_release(&reflog_msg);
+	strbuf_release(&message);
 	oidset_clear(&interior);
 	commit_list_free(parents);
 	release_revisions(&revs);
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index 7227c5c90f..af59ddf6e3 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -137,6 +137,43 @@ test_expect_success 'preserves authorship of the oldest commit' '
 	test_cmp expect actual
 '
 
+test_expect_success '--reedit-message offers every folded-in message' '
+	git reset --hard start &&
+	echo b >file &&
+	git add file &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+
+	write_script editor <<-\EOF &&
+	cp "$1" buffer &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	test_grep "re-one subject" buffer &&
+	test_grep "re-one body line" buffer &&
+	test_grep re-two buffer &&
+	test_grep re-three buffer &&
+	git log --format="%s" -1 >actual &&
+	echo combined >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--reedit-message aborts on an empty message' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	test_must_fail git history squash --reedit-message start.. &&
+
+	test_cmp_rev "$head_before" HEAD
+'
+
 test_expect_success '--dry-run predicts the rewrite without performing it' '
 	git reset --hard three &&
 	head_before=$(git rev-parse HEAD) &&
-- 
gitgitgadget

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Phillip Wood]

Hi Harald

On 24/06/2026 22:54, Harald Nordgren via GitGitGadget wrote:
> Adds git history squash <revision-range> to fold a range of commits.

It would be helpful to give a bit more detail here about the command so 
that the reader has an overview of what is actually being implemented.

  - what does it do with fixup!, squash! and amend! commits? Can it use
    the message from amend! commits to reword the commit?
  - can the user reword the commit message?
  - what happens if a merge commit inside the range has a parent outside
    the range?
  - what happens to branches that point to commits inside the range?

I had a quick play and found that it accepts ranges that containing a 
single commit (e.g. @^!) where there is nothing to squash. It also 
accepts ranges that are not ancestors of HEAD (e.g. checkout master and 
run "git history squash --dry-run origin/seen^2^!") without printing an 
error message. Only accepting a single argument is quite limiting as one 
cannot say

	git history squash ^:/base :/tip

Thanks

Phillip


> Changes in v5:
> 
>   * The range walk now uses --ancestry-path, so only commits descended from
>     the base are folded; a single revision such as HEAD or HEAD~1 is now
>     rejected as "not a <base>..<tip> range" rather than treated as a squash
>     down to the root.
>   * This adopts the --ancestry-path suggestion; the multi-base rejection is
>     unchanged, so a side branch that forked before the base and merged in is
>     still refused.
>   * Added tests covering more merge topologies: two interior merges, a nested
>     merge, an octopus merge, an octopus arm forked before the base, a merge
>     among the descendants replayed above the range, and a ref pointing at an
>     interior merge commit.
> 
> Changes in v4:
> 
>   * git history squash now detects when another ref points at a commit inside
>     the range being folded and refuses, with an advice.historyUpdateRefs hint
>     to use --update-refs=head.
>   * A merge inside the range is folded fine as long as the range has a single
>     base; a range with merge commit at the tip or base also folds correctly.
>     Only a range with more than one base is rejected.
> 
> Changes in v3:
> 
>   * Moved the feature out of git rebase and into a new git history squash
>     <revision-range> subcommand, per the list discussion. git rebase --squash
>     is dropped.
>   * Takes an arbitrary range (git history squash @~3.., git history squash
>     @~5..@~2), folding it into the oldest commit and replaying any
>     descendants on top.
>   * Implemented as a single tree operation rather than picking each commit,
>     so there are no repeated conflict stops (addresses Phillip's efficiency
>     point).
>   * A merge inside the range is folded fine, only a range with more than one
>     base is rejected.
>   * --reedit-message seeds the editor with every folded-in message, not just
>     the oldest.
> 
> Harald Nordgren (4):
>    history: extract helper for a commit's parent tree
>    history: give commit_tree_ext a message template
>    history: add squash subcommand to fold a range
>    history: re-edit a squash with every message
> 
>   Documentation/config/advice.adoc |   4 +
>   Documentation/git-history.adoc   |  26 ++
>   advice.c                         |   1 +
>   advice.h                         |   1 +
>   builtin/history.c                | 341 ++++++++++++++++++---
>   t/meson.build                    |   1 +
>   t/t3455-history-squash.sh        | 497 +++++++++++++++++++++++++++++++
>   7 files changed, 833 insertions(+), 38 deletions(-)
>   create mode 100755 t/t3455-history-squash.sh
> 
> 
> base-commit: 26d8d94e94df5535eecd036f16627493506a0614
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v5
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v5
> Pull-Request: https://github.com/git/git/pull/2337
> 
> Range-diff vs v4:
> 
>   1:  fc2801c0b1 = 1:  0f1ae9b05a history: extract helper for a commit's parent tree
>   2:  ee591e83b4 = 2:  a97ffab1e6 history: give commit_tree_ext a message template
>   3:  80bfea642e ! 3:  04e18ef979 history: add squash subcommand to fold a range
>       @@ builtin/history.c: out:
>        +	struct rev_info revs;
>        +	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
>        +	struct strvec args = STRVEC_INIT;
>       ++	size_t i;
>        +	int ret;
>        +
>        +	repo_init_revisions(repo, &revs, NULL);
>       @@ builtin/history.c: out:
>        +	strvec_push(&args, "--reverse");
>        +	strvec_push(&args, "--topo-order");
>        +	strvec_push(&args, "--boundary");
>       ++	strvec_push(&args, "--ancestry-path");
>        +	strvec_push(&args, range);
>        +	setup_revisions_from_strvec(&args, &revs, NULL);
>        +	if (args.nr != 1) {
>       @@ builtin/history.c: out:
>        +		goto out;
>        +	}
>        +
>       ++	/*
>       ++	 * A squash needs a base to reparent onto, so the argument has to
>       ++	 * exclude something, as in "<base>..<tip>". A single revision has no
>       ++	 * such bottom commit and cannot be squashed.
>       ++	 */
>       ++	for (i = 0; i < revs.cmdline.nr; i++)
>       ++		if (revs.cmdline.rev[i].flags & UNINTERESTING)
>       ++			break;
>       ++	if (i == revs.cmdline.nr) {
>       ++		ret = error(_("'%s' is not a '<base>..<tip>' range"), range);
>       ++		goto out;
>       ++	}
>       ++
>        +	if (prepare_revision_walk(&revs) < 0) {
>        +		ret = error(_("error preparing revisions"));
>        +		goto out;
>       @@ builtin/history.c: out:
>        +		goto out;
>        +	}
>        +
>       -+	if (!base) {
>       -+		ret = error(_("cannot squash the root commit"));
>       -+		goto out;
>       -+	}
>       ++	if (!base)
>       ++		BUG("a non-empty range must have a boundary commit");
>        +
>        +	*base_out = base;
>        +	*oldest_out = oldest;
>       @@ t/t3455-history-squash.sh (new)
>        +	test_grep "the range .* is empty" err
>        +'
>        +
>       -+test_expect_success 'errors when the range includes the root commit' '
>       ++test_expect_success 'errors on a single revision that is not a range' '
>        +	test_must_fail git history squash HEAD 2>err &&
>       -+	test_grep "cannot squash the root commit" err
>       ++	test_grep "is not a .*range" err &&
>       ++	test_must_fail git history squash HEAD~1 2>err &&
>       ++	test_grep "is not a .*range" err
>        +'
>        +
>        +test_expect_success 'squashes a range into a single commit without changing the tree' '
>       @@ t/t3455-history-squash.sh (new)
>        +	test_path_is_file inner
>        +'
>        +
>       ++test_expect_success 'folds a merge of a branch that forked at the base' '
>       ++	git reset --hard start &&
>       ++	git checkout -b base-fork-side &&
>       ++	test_commit --no-tag base-fork-side side x &&
>       ++	git checkout - &&
>       ++	test_commit --no-tag base-fork-main file b &&
>       ++	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
>       ++	git branch -D base-fork-side &&
>       ++	test_commit --no-tag base-fork-tail file c &&
>       ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
>       ++
>       ++	git history squash start.. &&
>       ++
>       ++	git rev-list --count start..HEAD >count &&
>       ++	echo 1 >expect &&
>       ++	test_cmp expect count &&
>       ++	test_cmp_rev start HEAD^ &&
>       ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
>       ++	test_path_is_file side
>       ++'
>       ++
>        +test_expect_success 'folds a range whose tip is a merge commit' '
>        +	git reset --hard start &&
>        +	test_commit --no-tag tipmerge-base file b &&
>       @@ t/t3455-history-squash.sh (new)
>        +	test_cmp_rev "$merged" HEAD
>        +'
>        +
>       ++test_expect_success 'folds a range with two interior merges' '
>       ++	git reset --hard start &&
>       ++	test_commit --no-tag two-merge-a file a1 &&
>       ++	git checkout -b two-merge-s1 &&
>       ++	test_commit --no-tag two-merge-s1 s1 x &&
>       ++	git checkout - &&
>       ++	git merge --no-ff -m "merge s1" two-merge-s1 &&
>       ++	test_commit --no-tag two-merge-b file b1 &&
>       ++	git checkout -b two-merge-s2 &&
>       ++	test_commit --no-tag two-merge-s2 s2 y &&
>       ++	git checkout - &&
>       ++	git merge --no-ff -m "merge s2" two-merge-s2 &&
>       ++	git branch -D two-merge-s1 two-merge-s2 &&
>       ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
>       ++
>       ++	git history squash start.. &&
>       ++
>       ++	git rev-list --count start..HEAD >count &&
>       ++	echo 1 >expect &&
>       ++	test_cmp expect count &&
>       ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
>       ++	test_path_is_file s1 &&
>       ++	test_path_is_file s2
>       ++'
>       ++
>       ++test_expect_success 'folds a range with a nested merge' '
>       ++	git reset --hard start &&
>       ++	main=$(git symbolic-ref --short HEAD) &&
>       ++	git checkout -b nested-outer &&
>       ++	test_commit --no-tag nested-outer outer x &&
>       ++	git checkout -b nested-inner &&
>       ++	test_commit --no-tag nested-inner inner y &&
>       ++	git checkout nested-outer &&
>       ++	git merge --no-ff -m "merge inner" nested-inner &&
>       ++	git checkout "$main" &&
>       ++	test_commit --no-tag nested-main file b1 &&
>       ++	git merge --no-ff -m "merge outer" nested-outer &&
>       ++	git branch -D nested-outer nested-inner &&
>       ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
>       ++
>       ++	git history squash start.. &&
>       ++
>       ++	git rev-list --count start..HEAD >count &&
>       ++	echo 1 >expect &&
>       ++	test_cmp expect count &&
>       ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
>       ++	test_path_is_file outer &&
>       ++	test_path_is_file inner
>       ++'
>       ++
>       ++test_expect_success 'folds a range with an octopus merge' '
>       ++	git reset --hard start &&
>       ++	main=$(git symbolic-ref --short HEAD) &&
>       ++	test_commit --no-tag octo-base file a1 &&
>       ++	git checkout -b octo-1 &&
>       ++	test_commit --no-tag octo-1 o1 x &&
>       ++	git checkout "$main" &&
>       ++	git checkout -b octo-2 &&
>       ++	test_commit --no-tag octo-2 o2 y &&
>       ++	git checkout "$main" &&
>       ++	git merge --no-ff -m octopus octo-1 octo-2 &&
>       ++	git branch -D octo-1 octo-2 &&
>       ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
>       ++
>       ++	git history squash start.. &&
>       ++
>       ++	git rev-list --count start..HEAD >count &&
>       ++	echo 1 >expect &&
>       ++	test_cmp expect count &&
>       ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
>       ++	test_path_is_file o1 &&
>       ++	test_path_is_file o2
>       ++'
>       ++
>       ++test_expect_success 'refuses an octopus merge with an arm forked before the base' '
>       ++	git reset --hard start &&
>       ++	main=$(git symbolic-ref --short HEAD) &&
>       ++	git checkout -b octo-pre &&
>       ++	test_commit octo-pre-side pside x &&
>       ++	git checkout "$main" &&
>       ++	test_commit octo-pre-main file b1 &&
>       ++	octo_base=$(git rev-parse HEAD) &&
>       ++	git checkout -b octo-within &&
>       ++	test_commit --no-tag octo-within wside y &&
>       ++	git checkout "$main" &&
>       ++	git merge --no-ff -m octopus octo-pre octo-within &&
>       ++	merged=$(git rev-parse HEAD) &&
>       ++	git branch -D octo-pre octo-within &&
>       ++
>       ++	test_must_fail git history squash "$octo_base.." 2>err &&
>       ++	test_grep "more than one base" err &&
>       ++	test_cmp_rev "$merged" HEAD
>       ++'
>       ++
>       ++test_expect_success 'refuses when a descendant above the range is a merge' '
>       ++	git reset --hard start &&
>       ++	main=$(git symbolic-ref --short HEAD) &&
>       ++	test_commit --no-tag desc-base file b &&
>       ++	git tag desc-tip &&
>       ++	git checkout -b desc-above &&
>       ++	test_commit --no-tag desc-above above x &&
>       ++	git checkout "$main" &&
>       ++	test_commit --no-tag desc-main file c &&
>       ++	git merge --no-ff -m "merge desc-above" desc-above &&
>       ++	git branch -D desc-above &&
>       ++	head_before=$(git rev-parse HEAD) &&
>       ++
>       ++	test_must_fail git history squash start..desc-tip 2>err &&
>       ++	test_grep "merge commits is not supported" err &&
>       ++	test_cmp_rev "$head_before" HEAD
>       ++'
>       ++
>       ++test_expect_success 'refuses to fold a range a ref points into at a merge' '
>       ++	git reset --hard start &&
>       ++	main=$(git symbolic-ref --short HEAD) &&
>       ++	test_commit --no-tag refmerge-base file b &&
>       ++	git checkout -b refmerge-side &&
>       ++	test_commit --no-tag refmerge-side side x &&
>       ++	git checkout "$main" &&
>       ++	test_commit --no-tag refmerge-main file c &&
>       ++	git merge --no-ff -m "interior merge" refmerge-side &&
>       ++	git branch -D refmerge-side &&
>       ++	git branch at-merge HEAD &&
>       ++	test_commit --no-tag refmerge-tail file d &&
>       ++	head_before=$(git rev-parse HEAD) &&
>       ++
>       ++	test_must_fail git history squash start.. 2>err &&
>       ++	test_grep "at-merge" err &&
>       ++	test_grep "points into the squashed range" err &&
>       ++	test_cmp_rev "$head_before" HEAD &&
>       ++
>       ++	git branch -D at-merge
>       ++'
>       ++
>        +test_done
>   4:  85c7817d7e = 4:  a758e1f084 history: re-edit a squash with every message
> 

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Harald Nordgren]

On Fri, Jun 26, 2026 at 10:53 AM Phillip Wood <phillip.wood123@gmail.com> wrote:
>
> Hi Harald
>
> On 24/06/2026 22:54, Harald Nordgren via GitGitGadget wrote:
> > Adds git history squash <revision-range> to fold a range of commits.
>
> It would be helpful to give a bit more detail here about the command so
> that the reader has an overview of what is actually being implemented.
>
>   - what does it do with fixup!, squash! and amend! commits? Can it use
>     the message from amend! commits to reword the commit?
>   - can the user reword the commit message?
>   - what happens if a merge commit inside the range has a parent outside
>     the range?
>   - what happens to branches that point to commits inside the range?
>
> I had a quick play and found that it accepts ranges that containing a
> single commit (e.g. @^!) where there is nothing to squash. It also
> accepts ranges that are not ancestors of HEAD (e.g. checkout master and
> run "git history squash --dry-run origin/seen^2^!") without printing an
> error message.

Good points, I will take a look at clarifying or giving an error (like
in the case of ancestor not in history of HEAD).

Only accepting a single argument is quite limiting as one
> cannot say
>
>         git history squash ^:/base :/tip

I don't understand why this is limiting? It thought it was clear that
it should be one argument REF1..REF2 ? What does '^:/base :/tip'
achieve that '^:/base..:/tip' cannot?


Harald

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Phillip Wood]

On 26/06/2026 10:57, Harald Nordgren wrote:
> On Fri, Jun 26, 2026 at 10:53 AM Phillip Wood <phillip.wood123@gmail.com> wrote:>> >> Only accepting a single argument is quite limiting as one
>> cannot say
>>
>>          git history squash ^:/base :/tip
> 
> I don't understand why this is limiting? It thought it was clear that
> it should be one argument REF1..REF2 ? What does '^:/base :/tip'
> achieve that '^:/base..:/tip' cannot?

'^/:base..:/tip' is not a range - everything after the first '/:' is 
treated as a regular expression to search for.

Thanks

Phillip

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Junio C Hamano]

Phillip Wood <phillip.wood123@gmail.com> writes:

> On 26/06/2026 10:57, Harald Nordgren wrote:
>> On Fri, Jun 26, 2026 at 10:53 AM Phillip Wood <phillip.wood123@gmail.com> wrote:>> >> Only accepting a single argument is quite limiting as one
>>> cannot say
>>>
>>>          git history squash ^:/base :/tip
>> 
>> I don't understand why this is limiting? It thought it was clear that
>> it should be one argument REF1..REF2 ? What does '^:/base :/tip'
>> achieve that '^:/base..:/tip' cannot?
>
> '^/:base..:/tip' is not a range - everything after the first '/:' is 
> treated as a regular expression to search for.

This particular case you can do

	HEAD^{/base}..HEAD^{/tip}

(or even go "HEAD^{/tip}~43" and fancier other forms, the point
being with matching {} pair, you can do more than what the lazy
short-hand form can).

But I think your point still stands, I think, as

	git history squash HEAD^{/base}..:/tip ^main

may be something you would want to do to express additional
constraints, like "I want this range squashed, but I should never
ever touch what is already in main".

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Harald Nordgren]

Interesting, I will take a look at handling multiple args.


Harald

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Patrick Steinhardt]

On Fri, Jun 26, 2026 at 09:52:57AM +0100, Phillip Wood wrote:
> Hi Harald
> 
> On 24/06/2026 22:54, Harald Nordgren via GitGitGadget wrote:
> > Adds git history squash <revision-range> to fold a range of commits.
> 
> It would be helpful to give a bit more detail here about the command so that
> the reader has an overview of what is actually being implemented.
> 
>  - what does it do with fixup!, squash! and amend! commits? Can it use
>    the message from amend! commits to reword the commit?
>  - can the user reword the commit message?

Good things to document/discuss.

>  - what happens if a merge commit inside the range has a parent outside
>    the range?

Yeah, I agree that we should punt on merge commits for now. They are a
can of worms, and I'm not sure that we should just squash them. I would
at least like the user to ask a flag that tells us that it's fine
squashing those.

>  - what happens to branches that point to commits inside the range?

Yeah, this should be documented indeed.

> I had a quick play and found that it accepts ranges that containing a single
> commit (e.g. @^!) where there is nothing to squash. It also accepts ranges
> that are not ancestors of HEAD (e.g. checkout master and run "git history
> squash --dry-run origin/seen^2^!") without printing an error message. Only
> accepting a single argument is quite limiting as one cannot say
> 
> 	git history squash ^:/base :/tip

Note that it is intentional that you can rewrite branches that are not
currently checked out, and the other subcommands work the same. So I'd
argue this should also be the case for "squash".

Patrick

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Phillip Wood]

Hi Harald and Patrick

On 29/06/2026 07:26, Patrick Steinhardt wrote:
> On Fri, Jun 26, 2026 at 09:52:57AM +0100, Phillip Wood wrote:
>> Hi Harald
>>
>> On 24/06/2026 22:54, Harald Nordgren via GitGitGadget wrote:
>>> Adds git history squash <revision-range> to fold a range of commits.
>>
>> It would be helpful to give a bit more detail here about the command so that
>> the reader has an overview of what is actually being implemented.
>>
>>   - what does it do with fixup!, squash! and amend! commits? Can it use
>>     the message from amend! commits to reword the commit?
>>   - can the user reword the commit message?
> 
> Good things to document/discuss.

Thanks, I was disappointed that these questions were not addressed in 
the cover letter for v6 which contains no more detail than this one.

We should make rewording the commit as easy as possible to encourage 
users to create useful commit histories. I think that means having some 
support for fixup! style commits. We could just do what rebase does and 
comment out the fixup! style commit subjects and the commit messages 
replaced by amend! commits but I think we have the opportunity to do 
something nicer (I find the commented-out messages annoying). We could 
have a comment saying "this is the combination of the following commits" 
followed by a list of the subject lines and then in the template message 
we'd simply omit the useless fixup! subjects when the commit body is 
empty and also omit the original commit messages that have been replaced 
by an amend! commit.

So instead of

     # This is the combination of 4 commits
     # This is the first commit message
     Base subject

     Base body

     # This is the second commit message
     # Another subject

     # Another body

     # This is the third commit message
     # fixup! Base subject

     # This is the fourth commit message
     # amend! Another subject
     A better subject

     A better body

We'd have

     # This is the combination of 4 commits
     # 123 Base subject
     # 456 Another subject
     # 789 fixup! Base subject
     # abc amend! Another subject

     Base Subject

     Base Body

     Another subject

     Another Body

Possibly with a comment before each message saying where it came from.

It would be good to error out if the user tries squash a fixup! style 
commit and range does not contain its target commit.

In the long run we should provide a way to squash an arbitrary list of 
commits rather than just a range.

> 
>>   - what happens if a merge commit inside the range has a parent outside
>>     the range?
> 
> Yeah, I agree that we should punt on merge commits for now. They are a
> can of worms, and I'm not sure that we should just squash them. I would
> at least like the user to ask a flag that tells us that it's fine
> squashing those.

There does seem to be some support for merges in this patch series which 
I think behaves pretty sensibly. If we have

           C - D
          /     \
   - A - B - E - F - G

Then squashing A..G should be fine because the parents of F are in the 
range and it looks like we support that. Squashing should B..G without 
--ancestry-path should be safe as well because B ends up as the parent 
of the squashed commit but we don't have a way to disable 
--ancestry-path (and maybe we don't want to add one). Squashing F^@..G 
might be useful to fixup a merge (though perhaps amending F rather than 
creating G is a simpler way to fix a broken merge). Squashing E..G does 
not make sense because the range does not include one of the merge parents.

>>   - what happens to branches that point to commits inside the range?
> 
> Yeah, this should be documented indeed.
> 
>> I had a quick play and found that it accepts ranges that containing a single
>> commit (e.g. @^!) where there is nothing to squash. It also accepts ranges
>> that are not ancestors of HEAD (e.g. checkout master and run "git history
>> squash --dry-run origin/seen^2^!") without printing an error message. Only
>> accepting a single argument is quite limiting as one cannot say
>>
>> 	git history squash ^:/base :/tip

We should sanitize what the user passes though - we do not want to 
accept arbitrary rev-list options. Off the top of my head "--left-only" 
and "--right-only" would allow the use of "A...B" and allowing "--not" 
seems reasonable.

> Note that it is intentional that you can rewrite branches that are not
> currently checked out, and the other subcommands work the same. So I'd
> argue this should also be the case for "squash".

Ah, thanks for clarifying that - it does not seem to check that there is 
a branch to be rewritten though if I do

     ./git checkout origin/master
     ./git history squash --dry-run origin/seen^2^^..origin/seen^2

there is no error message and it exits 0. If I create a branch pointing 
at origin/seen^2 then it does print a sensible ref-update.

Thanks

Phillip

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Junio C Hamano]

Phillip Wood <phillip.wood123@gmail.com> writes:

> It would be good to error out if the user tries squash a fixup! style 
> commit and range does not contain its target commit.

That's interesting.  It at least deserves a warning, even though the
choice to leave them out, with intentions to make it a separate fix
on top, may be deliberate.  If such a change-of-mind-in-the-middle
is rare, then erroring out would be perfect.  The user can first
reword the !fixup to make it a separate fix and then squash the
range in quesiton.

> We should sanitize what the user passes though - we do not want to 
> accept arbitrary rev-list options. Off the top of my head "--left-only" 
> and "--right-only" would allow the use of "A...B" and allowing "--not" 
> seems reasonable.

I would not recommend guessing what these rev-list "expressions"
would produce and blacklist some of the operations and notations.
It would be a more robust approach to let the machinery do its thing
to determine the set of commits, *and* inspect the shape of the
history these commits represent.  Are they connected?  Do they have
a single "bottom" that is just outside and below the range so that
we can replace it with the result of squashing everything together?
Do they have a single "top" whose children can be rewritten to have
the resulting single commit as one of their parents?  Starting from
the acceptable shape of the history we want to deal with, rather
than trying to enumerate rev-list operations and notations that
would prevent the resulting set of commits to fall outside the
acceptable shape of the history (and I am reasonably sure anybody
who attempts to do so would either end up with unusablly narrow
subset of what we can reasonably handle, or miss some cases that we
do not want to handle), would be a better approach.

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Phillip Wood]

Hi Junio

On 29/06/2026 17:54, Junio C Hamano wrote:
> Phillip Wood <phillip.wood123@gmail.com> writes:
> 
>> We should sanitize what the user passes though - we do not want to
>> accept arbitrary rev-list options. Off the top of my head "--left-only"
>> and "--right-only" would allow the use of "A...B" and allowing "--not"
>> seems reasonable.
> 
> I would not recommend guessing what these rev-list "expressions"
> would produce and blacklist some of the operations and notations.
> It would be a more robust approach to let the machinery do its thing
> to determine the set of commits, *and* inspect the shape of the
> history these commits represent.  Are they connected?  Do they have
> a single "bottom" that is just outside and below the range so that
> we can replace it with the result of squashing everything together?
> Do they have a single "top" whose children can be rewritten to have
> the resulting single commit as one of their parents?  Starting from
> the acceptable shape of the history we want to deal with, rather
> than trying to enumerate rev-list operations and notations that
> would prevent the resulting set of commits to fall outside the
> acceptable shape of the history (and I am reasonably sure anybody
> who attempts to do so would either end up with unusablly narrow
> subset of what we can reasonably handle, or miss some cases that we
> do not want to handle), would be a better approach.

I think we still want some sanity checks similar to "git replay" though 
to ensure the user has not overridden "--reverse", "--topo-order", and 
"--boundary". It will be easier to sanity check the list of commits if 
we can at least rely on those options being set as we know what order to 
expect them in and can detect merge parents that are outside the range 
by looking for BOUNDARY commits.

Thanks

Phillip

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Harald Nordgren]

> So instead of
>
>      # This is the combination of 4 commits
>      # This is the first commit message
>      Base subject
>
>      Base body
>
>      # This is the second commit message
>      # Another subject
>
>      # Another body
>
>      # This is the third commit message
>      # fixup! Base subject
>
>      # This is the fourth commit message
>      # amend! Another subject
>      A better subject
>
>      A better body
>
> We'd have
>
>      # This is the combination of 4 commits
>      # 123 Base subject
>      # 456 Another subject
>      # 789 fixup! Base subject
>      # abc amend! Another subject
>
>      Base Subject
>
>      Base Body
>
>      Another subject
>
>      Another Body

I think this makes it a lot harder to read. If every commit body was
always just a single paragraph it could make sense, but it's generally
not. Look at the commits in this series, with no delimiter of where
one commit message ends and the next one starts, it would be very
confusing.

> It would be good to error out if the user tries squash a fixup! style
> commit and range does not contain its target commit.

Good point, I don't see a good reason to allow this.

> There does seem to be some support for merges in this patch series which
> I think behaves pretty sensibly. If we have
>
>            C - D
>           /     \
>    - A - B - E - F - G
>
> Then squashing A..G should be fine because the parents of F are in the
> range and it looks like we support that. Squashing should B..G without
> --ancestry-path should be safe as well because B ends up as the parent
> of the squashed commit but we don't have a way to disable
> --ancestry-path (and maybe we don't want to add one). Squashing F^@..G
> might be useful to fixup a merge (though perhaps amending F rather than
> creating G is a simpler way to fix a broken merge). Squashing E..G does
> not make sense because the range does not include one of the merge parents.

Thanks for a good explanation here!


Harald

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Phillip Wood]

On 29/06/2026 19:03, Harald Nordgren wrote:
>> So instead of
>>
>>       # This is the combination of 4 commits
>>       # This is the first commit message
>>       Base subject
>>
>>       Base body
>>
>>       # This is the second commit message
>>       # Another subject
>>
>>       # Another body
>>
>>       # This is the third commit message
>>       # fixup! Base subject
>>
>>       # This is the fourth commit message
>>       # amend! Another subject
>>       A better subject
>>
>>       A better body
>>
>> We'd have
>>
>>       # This is the combination of 4 commits
>>       # 123 Base subject
>>       # 456 Another subject
>>       # 789 fixup! Base subject
>>       # abc amend! Another subject
>>
>>       Base Subject
>>
>>       Base Body
>>
>>       Another subject
>>
>>       Another Body
> 
> I think this makes it a lot harder to read. If every commit body was
> always just a single paragraph it could make sense, but it's generally
> not. Look at the commits in this series, with no delimiter of where
> one commit message ends and the next one starts, it would be very
> confusing.

You've trimmed the line where I said

 >> Possibly with a comment before each message saying where it came
 >> from.

So I'm not against adding a comment before each message, but I do think 
we should omit any messages that would be commented out completely. If 
you look at the rebase example above you can see there is a mass of 
comments between the two pieces of text that make up the new message. 
That makes it hard to see what is actually going to be included in the 
new message.

Thanks

Phillip

>> It would be good to error out if the user tries squash a fixup! style
>> commit and range does not contain its target commit.
> 
> Good point, I don't see a good reason to allow this.
> 
>> There does seem to be some support for merges in this patch series which
>> I think behaves pretty sensibly. If we have
>>
>>             C - D
>>            /     \
>>     - A - B - E - F - G
>>
>> Then squashing A..G should be fine because the parents of F are in the
>> range and it looks like we support that. Squashing should B..G without
>> --ancestry-path should be safe as well because B ends up as the parent
>> of the squashed commit but we don't have a way to disable
>> --ancestry-path (and maybe we don't want to add one). Squashing F^@..G
>> might be useful to fixup a merge (though perhaps amending F rather than
>> creating G is a simpler way to fix a broken merge). Squashing E..G does
>> not make sense because the range does not include one of the merge parents.
> 
> Thanks for a good explanation here!
> 
> 
> Harald
> 

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Harald Nordgren]

> You've trimmed the line where I said
>
>  >> Possibly with a comment before each message saying where it came
>  >> from.

Sorry about that! Can you show me the example of what it would look
like? It's much easier for me to reason about it then.


Harald

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Phillip Wood]

On 29/06/2026 22:13, Harald Nordgren wrote:
>> You've trimmed the line where I said
>>
>>   >> Possibly with a comment before each message saying where it came
>>   >> from.
> 
> Sorry about that! Can you show me the example of what it would look
> like? It's much easier for me to reason about it then.

For the commits

     123 Commit one
     456 Commit two
     789 fixup! Commit one
     abc squash! Commit two
     def amend! Commit one

It would look something like

     # This is the combination of the following commits:
     #   123 Commit one
     #   789 fixup! Commit one
     #   def amend! Commit one
     #   456 Commit two
     #   abc squash! Commit two

     A better commit one subject

     A better commit one body

     # ------------------------------------

     Commit two

     Commit two body

     # squash! Commit two

     More text for commit two

I've rearranged the commits in the summary to keep fixup commits with 
their targets instead of listing them in the same order of "git log 
--reverse". As we're dropping uninteresting messages I not sure there is 
much point in numbering them[1] so I've just used a plain separator to 
show where a message ends. For squash! commits commenting out the 
subject shows where the original message ends and the message from the 
squash! commit begins. I'm on the fence as to whether it is worth having

     # amend! Commit one

above the first message

Thanks

Phillip

[1] If we really want to number things we could number each commit in
     the summary and then use that to label it in the message template
     with separators like

         # This is the message from commit <n>

     instead of separating them with

         # ----------------------------

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Harald Nordgren]

I want to avoid creating drift between this and the format of 'git
rebase -i', so if we want to change this, maybe better to change both
at a later point instead?


Harald

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Phillip Wood]

Hi Harald

On 30/06/2026 19:38, Harald Nordgren wrote:
> I want to avoid creating drift between this and the format of 'git
> rebase -i', so if we want to change this, maybe better to change both
> at a later point instead?

The reason we're introducing the history command is to experiment with 
providing a better user interface for rewriting history without being 
bound by the limitations of "git rebase". So I think it would entirely 
appropriate to try a different format for the squash message here. If it 
turns out to be a success then we can see if we want to use it in "git 
rebase" as well.

Thanks

Phillip

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Junio C Hamano]

Phillip Wood <phillip.wood123@gmail.com> writes:

> The reason we're introducing the history command is to experiment with 
> providing a better user interface for rewriting history without being 
> bound by the limitations of "git rebase". So I think it would entirely 
> appropriate to try a different format for the squash message here. If it 
> turns out to be a success then we can see if we want to use it in "git 
> rebase" as well.

Do we know concretely things that are bad in the current way "rebase
-i" works, so that we can experiment deviation from?  If not, the
above is going backwards, I'm afraind.

Thanks

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Phillip Wood]

On 01/07/2026 14:47, Junio C Hamano wrote:
> Phillip Wood <phillip.wood123@gmail.com> writes:
> 
>> The reason we're introducing the history command is to experiment with
>> providing a better user interface for rewriting history without being
>> bound by the limitations of "git rebase". So I think it would entirely
>> appropriate to try a different format for the squash message here. If it
>> turns out to be a success then we can see if we want to use it in "git
>> rebase" as well.
> 
> Do we know concretely things that are bad in the current way "rebase
> -i" works, so that we can experiment deviation from? 

Yes - if you apply the way "rebase -i" works to multiple commits you can 
end up with a message template that has a screen full of commented lines 
between uncommitted parts of the message. See the example below from 
earlier in the thread. It is not so much of a problem in "rebase -i" 
because it only fixes up a single commit at a time so all the commented 
messages end up at the top of the buffer and at worst you have a few "# 
fixup! ..." or "# squash! ..." lines mixed in with the uncommitted text.

     # This is the combination of 4 commits
     # This is the first commit message
     Base subject

     Base body

     # This is the second commit message
     # Another subject

     # Another body

     # This is the third commit message
     # fixup! Base subject

     # This is the fourth commit message
     # amend! Another subject
     A better subject

     A better body

Thanks

Phillip

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Junio C Hamano]

Phillip Wood <phillip.wood123@gmail.com> writes:

> Yes - if you apply the way "rebase -i" works to multiple commits you can 
> end up with a message template that has a screen full of commented lines 
> between uncommitted parts of the message. See the example below from 
> earlier in the thread. It is not so much of a problem in "rebase -i" 
> because it only fixes up a single commit at a time so all the commented 
> messages end up at the top of the buffer and at worst you have a few "# 
> fixup! ..." or "# squash! ..." lines mixed in with the uncommitted text.
>
>      # This is the combination of 4 commits
>      # This is the first commit message
>      Base subject
>
>      Base body
>
>      # This is the second commit message
>      # Another subject
>
>      # Another body
>
>      # This is the third commit message
>      # fixup! Base subject
>
>      # This is the fourth commit message
>      # amend! Another subject
>      A better subject
>
>      A better body

In the example, the second one becomes completely empty?

Is the proposal not to show any messages that will be discarded
anyway and not even show them in commented form?  I think that makes
sense, and leaving only commit titles for these commits that would
not contribute to the text in the editor given to the user to edit
would indeed be an improvement.  For the same reason, as "# amend!"
will replace the message wholesale, it would also be a good idea for
the first commit to be hidden like all the other commits that would
not contribute to the text, so an improved version of the above may
be:

    # This is the combination fo 4 commits
    # 1. Base subject
    # 2. Another subject
    # 3. fixup! Base subject
    # 4. amend! Another subject
    A better subject

    A better body.

or something?  Is that the direction you want us to take?

Thanks.

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Phillip Wood]

On 01/07/2026 18:41, Junio C Hamano wrote:
> Phillip Wood <phillip.wood123@gmail.com> writes:
> 
>> Yes - if you apply the way "rebase -i" works to multiple commits you can
>> end up with a message template that has a screen full of commented lines
>> between uncommitted parts of the message. See the example below from
>> earlier in the thread. It is not so much of a problem in "rebase -i"
>> because it only fixes up a single commit at a time so all the commented
>> messages end up at the top of the buffer and at worst you have a few "#
>> fixup! ..." or "# squash! ..." lines mixed in with the uncommitted text.
>>
>>       # This is the combination of 4 commits
>>       # This is the first commit message
>>       Base subject
>>
>>       Base body
>>
>>       # This is the second commit message
>>       # Another subject
>>
>>       # Another body
>>
>>       # This is the third commit message
>>       # fixup! Base subject
>>
>>       # This is the fourth commit message
>>       # amend! Another subject
>>       A better subject
>>
>>       A better body
> 
> In the example, the second one becomes completely empty?

Yes because there is an amend! commit that replaces its message
> Is the proposal not to show any messages that will be discarded
> anyway and not even show them in commented form?  I think that makes
> sense, and leaving only commit titles for these commits that would
> not contribute to the text in the editor given to the user to edit
> would indeed be an improvement.  For the same reason, as "# amend!"
> will replace the message wholesale, it would also be a good idea for
> the first commit to be hidden like all the other commits that would
> not contribute to the text,

But the amend! commit does not target the first commit - it replaces the 
message of the second commit so I think we should keep the first message 
as shown below. You can see a different example with a squash! message 
at [1]
>      # This is the combination fo 4 commits
>      # 1. Base subject
>      # 2. Another subject
>      # 3. fixup! Base subject
>      # 4. amend! Another subject

        Base subject

        Base body

        # -------------------------------------
	
>      A better subject
> 
>      A better body.

Thanks

Phillip

[1] 
https://lore.kernel.org/git/4b505228-4846-4a48-9255-e249f4e70a1f@gmail.com

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Matt Hunter]

Hi!

I haven't experimented much with the new 'git history' commands, but
this discussion caught my eye and wanted to chime in.  (aka: please
forgive my stupid questions)

Note: I have built and am testing with v6 of this topic.

On Mon Jun 29, 2026 at 3:48 PM EDT, Phillip Wood wrote:
> On 29/06/2026 19:03, Harald Nordgren wrote:
>>> So instead of
>>>
>>>       # This is the combination of 4 commits
>>>       # This is the first commit message
>>>       Base subject
>>>
>>>       Base body
>>>
>>>       # This is the second commit message
>>>       # Another subject
>>>
>>>       # Another body
>>>
>>>       # This is the third commit message
>>>       # fixup! Base subject
>>>
>>>       # This is the fourth commit message
>>>       # amend! Another subject
>>>       A better subject
>>>
>>>       A better body
>>>
>>> We'd have
>>>
>>>       # This is the combination of 4 commits
>>>       # 123 Base subject
>>>       # 456 Another subject
>>>       # 789 fixup! Base subject
>>>       # abc amend! Another subject
>>>
>>>       Base Subject
>>>
>>>       Base Body
>>>
>>>       Another subject
>>>
>>>       Another Body
>> 
>> I think this makes it a lot harder to read. If every commit body was
>> always just a single paragraph it could make sense, but it's generally
>> not. Look at the commits in this series, with no delimiter of where
>> one commit message ends and the next one starts, it would be very
>> confusing.
>
> You've trimmed the line where I said
>
>  >> Possibly with a comment before each message saying where it came
>  >> from.
>
> So I'm not against adding a comment before each message, but I do think 
> we should omit any messages that would be commented out completely. If 
> you look at the rebase example above you can see there is a mass of 
> comments between the two pieces of text that make up the new message. 
> That makes it hard to see what is actually going to be included in the 
> new message.

I agree with this idea as well.  And letting fixup! messages completely
fall out makes more sense here than I want to say in git rebase.  The
commented list of commits at the top is a nice compromise for the todo
list you would have seen had you run 'git rebase -i' instead, and a
glance at the list would confirm that the fixup!s you thought you
included _actually are_ in the squash range.

I assume the same treatment would _not_ be completely given to squash!
messages, since there is at least some expectation that they carry an
additional remark that the author might want to reword into the base
commit?

>
> Thanks
> Phillip

Given the above, and how 'git rebase' usually works, I'm suprised that
--reedit-message isn't the default behavior.  This may be my bias
towards rebase showing...  Perhaps the typical use of this command is to
just work fast, and expect a follow up 'git history reword' if needed -
when the original just needs a little extra context?

This is probably a larger question, since (according to the man page) it
affects the other 'git history' commands as well.  When I run
'git history ...' and discover that I made a mistake after inspecting
the results, is there a fool-proof way to undo the change and return to
the previous state?  My first thought was to run 'git reset --hard ...',
but the default behavior of --update-refs (moving other branches) can
make this more complicated.

Thanks

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Harald Nordgren]

> This is probably a larger question, since (according to the man page) it
> affects the other 'git history' commands as well.  When I run
> 'git history ...' and discover that I made a mistake after inspecting
> the results, is there a fool-proof way to undo the change and return to
> the previous state?  My first thought was to run 'git reset --hard ...',
> but the default behavior of --update-refs (moving other branches) can
> make this more complicated.

This is a larger question: But I would love to have a reflog that is
more human-centered. When e.g. rebasing a series with N commits, it's
very tricky in the reflog to find what was the state before that.

I feel like branch switching is given too much space in the reflog,
since it's not a destructive action, I don't care about it.

And when handling multiple commits in on go (squashing, rebasing), I
would love to see a visual hierarchy (with indentation for sub-steps)
instead of treating each action as equally important when it isn't.


Harald

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Matt Hunter]

On Tue Jun 30, 2026 at 3:19 AM EDT, Harald Nordgren wrote:
>> This is probably a larger question, since (according to the man page) it
>> affects the other 'git history' commands as well.  When I run
>> 'git history ...' and discover that I made a mistake after inspecting
>> the results, is there a fool-proof way to undo the change and return to
>> the previous state?  My first thought was to run 'git reset --hard ...',
>> but the default behavior of --update-refs (moving other branches) can
>> make this more complicated.
>
> This is a larger question: But I would love to have a reflog that is
> more human-centered. When e.g. rebasing a series with N commits, it's
> very tricky in the reflog to find what was the state before that.
>
> I feel like branch switching is given too much space in the reflog,
> since it's not a destructive action, I don't care about it.

I share these headaches to an extent.  When dealing with the first
problem (seeing an atomic entry in the reflog), I usually look at the
branch's own reflog instead of HEAD's

But my question is about doing a comprehensive reset from a botched
operation.  If any history operation updates branch refs besides the
current one.  I don't think there's an obvious way to see which other
ones were affected, and a naive 'git reset --hard my-branch@{1}' leaves
them pointed at unwanted commits.  Is this right?

tangent:  I'm pretty sure that git-status relies on checkout / branch
switching reflog entries in order to know which tag your detached HEAD
started from, eg: when it says something like

    HEAD detached from v2.55.0-rc2
    nothing to commit, working tree clean

>
> And when handling multiple commits in on go (squashing, rebasing), I
> would love to see a visual hierarchy (with indentation for sub-steps)
> instead of treating each action as equally important when it isn't.

Sounds compelling!

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Phillip Wood]

Hi Matt

On 30/06/2026 03:55, Matt Hunter wrote:
> I haven't experimented much with the new 'git history' commands, but
> this discussion caught my eye and wanted to chime in.  (aka: please
> forgive my stupid questions)
> 
> Note: I have built and am testing with v6 of this topic.

Thanks for testing it, and also for your questions - it is always 
helpful to get the perspective of someone using the command, especially 
while we're still designing it.

> [...] 
> I agree with this idea as well.  And letting fixup! messages completely
> fall out makes more sense here than I want to say in git rebase.  The
> commented list of commits at the top is a nice compromise for the todo
> list you would have seen had you run 'git rebase -i' instead, and a
> glance at the list would confirm that the fixup!s you thought you
> included _actually are_ in the squash range.
> 
> I assume the same treatment would _not_ be completely given to squash!
> messages, since there is at least some expectation that they carry an
> additional remark that the author might want to reword into the base
> commit?

Yes for "squash! Some commit" I think we'd want to have

     Some commit

     Some commit body

     # squash! Some commit

     The body of the squash! commit

> Given the above, and how 'git rebase' usually works, I'm suprised that
> --reedit-message isn't the default behavior.  This may be my bias
> towards rebase showing...  Perhaps the typical use of this command is to
> just work fast, and expect a follow up 'git history reword' if needed -
> when the original just needs a little extra context?

That's a good point - if we want to encourage good commit histories then 
opening the editor by default gives the user an opportunity to double 
check which commits are being squashed and edit the message as appropriate.

"--reedit-message" is a bit of a mouthful - maybe we should call it 
"--edit" (or "--no-edit" if we want to open the editor by default) like 
"git commit"

> This is probably a larger question, since (according to the man page) it
> affects the other 'git history' commands as well.  When I run
> 'git history ...' and discover that I made a mistake after inspecting
> the results, is there a fool-proof way to undo the change and return to
> the previous state?  My first thought was to run 'git reset --hard ...',
> but the default behavior of --update-refs (moving other branches) can
> make this more complicated.

Yes this is a problem to which we don't have a good solution at the 
moment. I believe Jujitsu and git-branchless both have some kind of 
operations log that lets you revert a whole operation rather than just a 
single ref-update. We'd need some way to tie all the ref updates from a 
single ref transaction together either by logging the separately or 
adding some form of transaction id to the reflog. That would be a big 
change.

Thanks

Phillip

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Patrick Steinhardt]

On Tue, Jun 30, 2026 at 03:01:43PM +0100, Phillip Wood wrote:
> On 30/06/2026 03:55, Matt Hunter wrote:
[?nip]
> > This is probably a larger question, since (according to the man page) it
> > affects the other 'git history' commands as well.  When I run
> > 'git history ...' and discover that I made a mistake after inspecting
> > the results, is there a fool-proof way to undo the change and return to
> > the previous state?  My first thought was to run 'git reset --hard ...',
> > but the default behavior of --update-refs (moving other branches) can
> > make this more complicated.
> 
> Yes this is a problem to which we don't have a good solution at the moment.
> I believe Jujitsu and git-branchless both have some kind of operations log
> that lets you revert a whole operation rather than just a single ref-update.
> We'd need some way to tie all the ref updates from a single ref transaction
> together either by logging the separately or adding some form of transaction
> id to the reflog. That would be a big change.

Yeah, agreed. I think that the reflog is insufficient for a lot of Git's
operations and that it is way too hard to reason about. It's both too
detailed and not detailed enough at the same time:

  - It provides way too much detail about individual reference updates
    when all the user cares about is the high-level operation on the
    logical level.

  - It does not provide enough detail to give information about what the
    high-level operation even was.

I don't think that we can fix the reflog to work properly in this case.
But I certainly think that we should explore whether we can eventually
introduce something like an oplog, as well, so that we can easily have
the equivalent of `jj undo`.

It's something that I'd eventually want to get to, but it'll take a
while. So if anybody else beats me to it then please go ahead :)

Patrick

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Junio C Hamano]

Patrick Steinhardt <ps@pks.im> writes:

> Yeah, agreed. I think that the reflog is insufficient for a lot of Git's
> operations and that it is way too hard to reason about.

As the reflog has never been about undoing, this is understandable.

Things like @{-N} notation and "git push --force-if-includes" make
good use of the "what was this ref pointing at historically?"
information, so they give us a proof that it is possible to
programmatically go back and find the necessary state, though.

Re: [PATCH v5 0/4] history: add squash subcommand to fold a range

[Harald Nordgren]

> Yeah, I agree that we should punt on merge commits for now. They are a
> can of worms, and I'm not sure that we should just squash them. I would
> at least like the user to ask a flag that tells us that it's fine
> squashing those.

Do you mean not even handling simple merges that are fully within the
range? I'm already handling those, so remove?


Harald

[PATCH v6 0/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v6:

 * git history squash now accepts multiple revision arguments, read like the
   arguments to git-rev-list, so a compound range such as @~3.. ^topic
   works.
 * The base to reparent onto is now the oldest in-range commit's parent; a
   boundary other than that base means the range has more than one base and
   is rejected. This also fixes the earlier overly-restrictive handling of
   merges and side branches.
 * A single-commit range (e.g. @^!) is rejected with "nothing to squash"
   (this also covers the @^!-style example that previously succeeded
   silently).
 * Commit messages reworded: the squash commit now gives an overview of
   fixup!/squash!/amend! handling, rewording, merge-parent and ref behavior.

Changes in v5:

 * The range walk now uses --ancestry-path, so only commits descended from
   the base are folded; a single revision such as HEAD or HEAD~1 is now
   rejected as "not a <base>..<tip> range" rather than treated as a squash
   down to the root.
 * This adopts the --ancestry-path suggestion; the multi-base rejection is
   unchanged, so a side branch that forked before the base and merged in is
   still refused.
 * Added tests covering more merge topologies: two interior merges, a nested
   merge, an octopus merge, an octopus arm forked before the base, a merge
   among the descendants replayed above the range, and a ref pointing at an
   interior merge commit.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (4):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  history: add squash subcommand to fold a range
  history: re-edit a squash with every message

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  29 ++
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 357 +++++++++++++++++---
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 550 +++++++++++++++++++++++++++++++
 7 files changed, 905 insertions(+), 38 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: 6c3d7b73556db708feb3b16232fab1efc4353428
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v6
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v6
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v5:

 1:  0f1ae9b05a = 1:  fea6b79e60 history: extract helper for a commit's parent tree
 2:  a97ffab1e6 = 2:  e2674e0bc4 history: give commit_tree_ext a message template
 3:  04e18ef979 ! 3:  811e393ab4 history: add squash subcommand to fold a range
     @@ Commit message
      
          Add "git history squash <revision-range>" to do this directly. It folds
          every commit in the range into the oldest one, keeping that commit's
     -    message and authorship and taking the tree of the newest commit, so the
     -    range collapses into a single commit. Commits above the range are
     -    replayed on top of the result.
     +    message and authorship and taking the tree of the newest commit, then
     +    replays the commits above the range on top. fixup!, squash! and amend!
     +    commits are folded like any other and are not interpreted, so the
     +    squashed message comes from the oldest commit, or from an editor with
     +    --reedit-message.
      
     -    The range is given as <base>..<tip>, so "git history squash @~3.."
     -    folds the three most recent commits and "git history squash @~5..@~2"
     -    squashes an interior range. A merge inside the range is folded like any
     -    other commit, but the range must have a single base, so a range with
     -    more than one entry point is rejected.
     -
     -    The folded commits leave the history, so by default the command refuses
     -    when another ref points at one of them. Use "--update-refs=head" to
     -    rewrite only the current branch and leave those refs untouched.
     +    The range is read like the arguments to "git rev-list", so several
     +    arguments such as "@~3.. ^topic" are allowed. A merge inside the range
     +    is folded when its other parent is reachable from the base, otherwise
     +    the range has more than one base and is rejected. By default the command
     +    also refuses when a ref points at a commit that the fold would discard.
     +    Use --update-refs=head to rewrite only the current branch instead.
      
          Inspired-by: Sergey Chernov <serega.morph@gmail.com>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      +the commit just below the oldest commit to squash. For example, `git
      +history squash @~3..` folds the three most recent commits into one, and
      +`git history squash @~5..@~2` squashes an interior range while leaving
     -+the two newest commits in place.
     ++the two newest commits in place. _<revision-range>_ is read like the
     ++arguments to linkgit:git-rev-list[1], so several arguments may be given,
     ++for example `@~3.. ^topic` to additionally exclude what is already on
     ++`topic`.
      ++
      +The oldest commit's message and authorship are preserved by default,
      +unless you specify `--reedit-message`. A merge commit inside the range is
     @@ builtin/history.c: out:
      + * but the range must have a single base and must not reach a root commit.
      + */
      +static int resolve_squash_range(struct repository *repo,
     -+				const char *range,
     ++				const char **argv,
      +				struct commit **base_out,
      +				struct commit **oldest_out,
      +				struct commit **tip_out,
     @@ builtin/history.c: out:
      +{
      +	struct rev_info revs;
      +	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
     ++	struct commit_list *boundaries = NULL, *b;
      +	struct strvec args = STRVEC_INIT;
      +	size_t i;
      +	int ret;
     @@ builtin/history.c: out:
      +	strvec_push(&args, "--topo-order");
      +	strvec_push(&args, "--boundary");
      +	strvec_push(&args, "--ancestry-path");
     -+	strvec_push(&args, range);
     ++	strvec_pushv(&args, argv);
      +	setup_revisions_from_strvec(&args, &revs, NULL);
      +	if (args.nr != 1) {
     -+		ret = error(_("'%s' does not name a revision range"), range);
     ++		ret = error(_("unrecognized argument: %s"), args.v[1]);
      +		goto out;
      +	}
      +
      +	/*
     -+	 * A squash needs a base to reparent onto, so the argument has to
     -+	 * exclude something, as in "<base>..<tip>". A single revision has no
     -+	 * such bottom commit and cannot be squashed.
     ++	 * A squash needs a base to reparent onto, so the range has to exclude
     ++	 * something, as in "<base>..<tip>". A revision range with no such
     ++	 * bottom commit cannot be squashed.
      +	 */
      +	for (i = 0; i < revs.cmdline.nr; i++)
      +		if (revs.cmdline.rev[i].flags & UNINTERESTING)
      +			break;
      +	if (i == revs.cmdline.nr) {
     -+		ret = error(_("'%s' is not a '<base>..<tip>' range"), range);
     ++		ret = error(_("not a '<base>..<tip>' revision range"));
      +		goto out;
      +	}
      +
     @@ builtin/history.c: out:
      +
      +	while ((commit = get_revision(&revs))) {
      +		if (commit->object.flags & BOUNDARY) {
     -+			if (base) {
     -+				ret = error(_("range '%s' has more than one base; "
     -+					      "cannot squash"), range);
     -+				goto out;
     -+			}
     -+			base = commit;
     ++			commit_list_insert(commit, &boundaries);
      +			continue;
      +		}
      +		if (!oldest)
     @@ builtin/history.c: out:
      +	}
      +
      +	if (!oldest) {
     -+		ret = error(_("the range '%s' is empty"), range);
     ++		ret = error(_("the revision range is empty"));
     ++		goto out;
     ++	}
     ++
     ++	if (oldest == tip) {
     ++		ret = error(_("the revision range holds a single commit; "
     ++			      "nothing to squash"));
      +		goto out;
      +	}
      +
     -+	if (!base)
     -+		BUG("a non-empty range must have a boundary commit");
     ++	if (!oldest->parents)
     ++		BUG("an in-range commit must have a parent");
     ++	base = oldest->parents->item;
     ++
     ++	/*
     ++	 * A boundary other than the base is an in-range commit reaching a
     ++	 * commit outside the range, so the range has more than one base.
     ++	 */
     ++	for (b = boundaries; b; b = b->next) {
     ++		if (b->item != base) {
     ++			ret = error(_("the revision range has more than one base; "
     ++				      "cannot squash"));
     ++			goto out;
     ++		}
     ++	}
      +
      +	*base_out = base;
      +	*oldest_out = oldest;
     @@ builtin/history.c: out:
      +	ret = 0;
      +
      +out:
     ++	commit_list_free(boundaries);
      +	reset_revision_walk();
      +	release_revisions(&revs);
      +	strvec_clear(&args);
     @@ builtin/history.c: out:
      +	int ret;
      +
      +	argc = parse_options(argc, argv, prefix, options, usage, 0);
     -+	if (argc != 1) {
     -+		ret = error(_("command expects a single revision range"));
     ++	if (!argc) {
     ++		ret = error(_("command expects a revision range"));
      +		goto out;
      +	}
      +	repo_config(repo, git_default_config, NULL);
     @@ builtin/history.c: out:
      +	if (action == REF_ACTION_DEFAULT)
      +		action = REF_ACTION_BRANCHES;
      +
     -+	ret = resolve_squash_range(repo, argv[0], &base, &oldest, &tip,
     ++	ret = resolve_squash_range(repo, argv, &base, &oldest, &tip,
      +				   &interior);
      +	if (ret < 0)
      +		goto out;
     @@ t/t3455-history-squash.sh (new)
      +
      +test_expect_success 'errors on missing range argument' '
      +	test_must_fail git history squash 2>err &&
     -+	test_grep "command expects a single revision range" err
     -+'
     -+
     -+test_expect_success 'errors on too many arguments' '
     -+	test_must_fail git history squash start.. HEAD 2>err &&
     -+	test_grep "command expects a single revision range" err
     ++	test_grep "expects a revision range" err
      +'
      +
      +test_expect_success 'errors on an empty range' '
      +	test_must_fail git history squash HEAD..HEAD 2>err &&
     -+	test_grep "the range .* is empty" err
     ++	test_grep "the revision range is empty" err
      +'
      +
      +test_expect_success 'errors on a single revision that is not a range' '
      +	test_must_fail git history squash HEAD 2>err &&
     -+	test_grep "is not a .*range" err &&
     ++	test_grep "not a .*range" err &&
      +	test_must_fail git history squash HEAD~1 2>err &&
     -+	test_grep "is not a .*range" err
     ++	test_grep "not a .*range" err
     ++'
     ++
     ++test_expect_success 'errors on a range holding a single commit' '
     ++	git reset --hard three &&
     ++	head_before=$(git rev-parse HEAD) &&
     ++
     ++	test_must_fail git history squash "HEAD^!" 2>err &&
     ++	test_grep "single commit; nothing to squash" err &&
     ++	test_cmp_rev "$head_before" HEAD
     ++'
     ++
     ++test_expect_success 'accepts multiple revision arguments with an exclusion' '
     ++	git reset --hard three &&
     ++	git branch -f keep HEAD~2 &&
     ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
     ++
     ++	git history squash start..HEAD ^keep &&
     ++
     ++	git log --format="%s" start..HEAD >actual &&
     ++	cat >expect <<-\EOF &&
     ++	two
     ++	one
     ++	EOF
     ++	test_cmp expect actual &&
     ++	test_cmp_rev keep HEAD~1 &&
     ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     ++
     ++	git branch -D keep
     ++'
     ++
     ++test_expect_success 'squashes a branch the current branch is not on' '
     ++	git reset --hard three &&
     ++	main=$(git symbolic-ref --short HEAD) &&
     ++	head_before=$(git rev-parse HEAD) &&
     ++	git checkout -b off-history start &&
     ++	test_commit --no-tag off-one off a &&
     ++	test_commit --no-tag off-two off b &&
     ++	git checkout "$main" &&
     ++
     ++	git history squash start..off-history &&
     ++
     ++	git rev-list --count start..off-history >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
     ++	test_cmp_rev "$head_before" HEAD &&
     ++
     ++	git branch -D off-history
      +'
      +
      +test_expect_success 'squashes a range into a single commit without changing the tree' '
     @@ t/t3455-history-squash.sh (new)
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
      +'
      +
     -+test_expect_success 'squashing a single-commit range replays the rest' '
     -+	git reset --hard three &&
     -+	tip_tree=$(git rev-parse HEAD^{tree}) &&
     -+
     -+	git history squash start..@~2 &&
     -+
     -+	git log --format="%s" start..HEAD >actual &&
     -+	cat >expect <<-\EOF &&
     -+	three
     -+	two
     -+	one
     -+	EOF
     -+	test_cmp expect actual &&
     -+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
     -+'
      +
      +test_expect_success 'reuses the message of a fixup! commit in the range' '
      +	git reset --hard start &&
     @@ t/t3455-history-squash.sh (new)
      +
      +test_expect_success 'squashes a range whose internal merge has a single base' '
      +	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
      +	test_commit --no-tag before-side file b &&
      +	git checkout -b inner-side &&
      +	test_commit --no-tag on-inner-side inner x &&
     -+	git checkout - &&
     ++	git checkout "$main" &&
      +	test_commit --no-tag after-side file c &&
      +	git merge --no-ff -m merge inner-side &&
      +	git branch -D inner-side &&
     @@ t/t3455-history-squash.sh (new)
      +
      +test_expect_success 'folds a merge of a branch that forked at the base' '
      +	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
      +	git checkout -b base-fork-side &&
      +	test_commit --no-tag base-fork-side side x &&
     -+	git checkout - &&
     ++	git checkout "$main" &&
      +	test_commit --no-tag base-fork-main file b &&
      +	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
      +	git branch -D base-fork-side &&
     @@ t/t3455-history-squash.sh (new)
      +	test_path_is_file side
      +'
      +
     ++test_expect_success 'refuses a merge whose other parent is outside the range' '
     ++	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
     ++	git checkout -b outside-parent &&
     ++	test_commit --no-tag outside-parent outside x &&
     ++	git checkout "$main" &&
     ++	test_commit --no-tag outside-main file b &&
     ++	base=$(git rev-parse HEAD) &&
     ++	test_commit --no-tag outside-mid file c &&
     ++	git merge --no-ff -m "merge outside-parent" outside-parent &&
     ++	git branch -D outside-parent &&
     ++	merged=$(git rev-parse HEAD) &&
     ++
     ++	test_must_fail git history squash "$base.." 2>err &&
     ++	test_grep "more than one base" err &&
     ++	test_cmp_rev "$merged" HEAD
     ++'
     ++
      +test_expect_success 'folds a range whose tip is a merge commit' '
      +	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
      +	test_commit --no-tag tipmerge-base file b &&
      +	git checkout -b tipmerge-side &&
      +	test_commit --no-tag tipmerge-side side x &&
     -+	git checkout - &&
     ++	git checkout "$main" &&
      +	test_commit --no-tag tipmerge-main file c &&
      +	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
      +	git branch -D tipmerge-side &&
     @@ t/t3455-history-squash.sh (new)
      +
      +test_expect_success 'folds a range whose base is a merge commit' '
      +	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
      +	git checkout -b basemerge-side &&
      +	test_commit --no-tag basemerge-side side x &&
     -+	git checkout - &&
     ++	git checkout "$main" &&
      +	test_commit --no-tag basemerge-main file b &&
      +	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
      +	git branch -D basemerge-side &&
     @@ t/t3455-history-squash.sh (new)
      +
      +test_expect_success 'refuses to squash a range with more than one base' '
      +	git reset --hard start &&
     -+	head_before=$(git rev-parse HEAD) &&
     ++	main=$(git symbolic-ref --short HEAD) &&
      +	git checkout -b forked-before &&
      +	test_commit forked-side fside x &&
     -+	git checkout - &&
     -+	test_commit forked-main file b &&
     ++	git checkout "$main" &&
     ++	test_commit forked-base file b &&
     ++	base=$(git rev-parse HEAD) &&
     ++	test_commit forked-main file c &&
      +	git merge --no-ff -m merge forked-before &&
      +	merged=$(git rev-parse HEAD) &&
      +
     -+	test_must_fail git history squash forked-main.. 2>err &&
     ++	test_must_fail git history squash "$base.." 2>err &&
      +	test_grep "more than one base" err &&
      +	test_cmp_rev "$merged" HEAD
      +'
      +
      +test_expect_success 'folds a range with two interior merges' '
      +	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
      +	test_commit --no-tag two-merge-a file a1 &&
      +	git checkout -b two-merge-s1 &&
      +	test_commit --no-tag two-merge-s1 s1 x &&
     -+	git checkout - &&
     ++	git checkout "$main" &&
      +	git merge --no-ff -m "merge s1" two-merge-s1 &&
      +	test_commit --no-tag two-merge-b file b1 &&
      +	git checkout -b two-merge-s2 &&
      +	test_commit --no-tag two-merge-s2 s2 y &&
     -+	git checkout - &&
     ++	git checkout "$main" &&
      +	git merge --no-ff -m "merge s2" two-merge-s2 &&
      +	git branch -D two-merge-s1 two-merge-s2 &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
     @@ t/t3455-history-squash.sh (new)
      +test_expect_success 'refuses when a descendant above the range is a merge' '
      +	git reset --hard start &&
      +	main=$(git symbolic-ref --short HEAD) &&
     -+	test_commit --no-tag desc-base file b &&
     ++	test_commit --no-tag desc-one file b &&
     ++	test_commit --no-tag desc-two file c &&
      +	git tag desc-tip &&
      +	git checkout -b desc-above &&
      +	test_commit --no-tag desc-above above x &&
      +	git checkout "$main" &&
     -+	test_commit --no-tag desc-main file c &&
     ++	test_commit --no-tag desc-main file d &&
      +	git merge --no-ff -m "merge desc-above" desc-above &&
      +	git branch -D desc-above &&
      +	head_before=$(git rev-parse HEAD) &&
 4:  a758e1f084 ! 4:  4edf012b77 history: re-edit a squash with every message
     @@ Commit message
      
          Gather the messages of every commit in the range, oldest first, and use
          them as the editor template when re-editing, mirroring how "git rebase
     -    -i" presents a squash. The combined message is built before the
     -    descendant walk so it is not disturbed by the flags that walk leaves on
     -    the commits.
     +    -i" presents a squash.
      
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
       ## Documentation/git-history.adoc ##
     -@@ Documentation/git-history.adoc: history squash @~3..` folds the three most recent commits into one, and
     - `git history squash @~5..@~2` squashes an interior range while leaving
     - the two newest commits in place.
     +@@ Documentation/git-history.adoc: arguments to linkgit:git-rev-list[1], so several arguments may be given,
     + for example `@~3.. ^topic` to additionally exclude what is already on
     + `topic`.
       +
      -The oldest commit's message and authorship are preserved by default,
      -unless you specify `--reedit-message`. A merge commit inside the range is

-- 
gitgitgadget

[PATCH v6 1/4] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 091465a59e..f95f26e684 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -157,6 +157,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -164,21 +183,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -444,18 +453,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -799,16 +800,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v6 2/4] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index f95f26e684..305bde3102 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -101,6 +101,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -130,13 +131,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -189,7 +193,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -644,7 +648,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -855,7 +859,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -872,7 +876,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v6 3/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git history squash <revision-range>" to do this directly. It folds
every commit in the range into the oldest one, keeping that commit's
message and authorship and taking the tree of the newest commit, then
replays the commits above the range on top. fixup!, squash! and amend!
commits are folded like any other and are not interpreted, so the
squashed message comes from the oldest commit, or from an editor with
--reedit-message.

The range is read like the arguments to "git rev-list", so several
arguments such as "@~3.. ^topic" are allowed. A merge inside the range
is folded when its other parent is reachable from the base, otherwise
the range has more than one base and is rejected. By default the command
also refuses when a ref points at a commit that the fold would discard.
Use --update-refs=head to rewrite only the current branch instead.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  28 ++
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 224 ++++++++++++++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 513 +++++++++++++++++++++++++++++++
 7 files changed, 772 insertions(+)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 257db58918..f4d692d136 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -55,6 +55,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a ref points
+		into the range being folded, to tell the user about
+		`--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 2ba8121795..123ad5d4bc 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -11,6 +11,7 @@ SYNOPSIS
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]
 
 DESCRIPTION
 -----------
@@ -97,6 +98,33 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's message and
+	authorship and takes the tree of the range's newest commit, so the
+	whole range collapses into a single commit. Commits above the range
+	are replayed on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash @~3..` folds the three most recent commits into one, and
+`git history squash @~5..@~2` squashes an interior range while leaving
+the two newest commits in place. _<revision-range>_ is read like the
+arguments to linkgit:git-rev-list[1], so several arguments may be given,
+for example `@~3.. ^topic` to additionally exclude what is already on
+`topic`.
++
+The oldest commit's message and authorship are preserved by default,
+unless you specify `--reedit-message`. A merge commit inside the range is
+folded like any other, but the range must have a single base, so a range
+that reaches more than one entry point (for example a side branch that
+forked before the range and was later merged into it) is rejected.
++
+The folded commits disappear from the history, so with the default
+`--update-refs=branches` the command refuses when another ref points at
+one of them. Rerun with `--update-refs=head` to rewrite only the current
+branch and leave those refs pointing at the old commits.
+
 OPTIONS
 -------
 
diff --git a/advice.c b/advice.c
index 0018501b7b..5c6ff95e31 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 8def280688..911b4e4643 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index 305bde3102..5a1b42c063 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -30,6 +31,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -973,6 +976,225 @@ out:
 	return ret;
 }
 
+/*
+ * Resolve a "<base>..<tip>" revision range into the base commit just outside
+ * the range (which becomes the parent of the squashed commit), the oldest
+ * commit contained in the range (whose message the squash reuses), and the
+ * range tip (whose tree becomes the result). A merge inside the range is fine,
+ * but the range must have a single base and must not reach a root commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				const char **argv,
+				struct commit **base_out,
+				struct commit **oldest_out,
+				struct commit **tip_out,
+				struct oidset *interior_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
+	struct commit_list *boundaries = NULL, *b;
+	struct strvec args = STRVEC_INIT;
+	size_t i;
+	int ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_push(&args, "--boundary");
+	strvec_push(&args, "--ancestry-path");
+	strvec_pushv(&args, argv);
+	setup_revisions_from_strvec(&args, &revs, NULL);
+	if (args.nr != 1) {
+		ret = error(_("unrecognized argument: %s"), args.v[1]);
+		goto out;
+	}
+
+	/*
+	 * A squash needs a base to reparent onto, so the range has to exclude
+	 * something, as in "<base>..<tip>". A revision range with no such
+	 * bottom commit cannot be squashed.
+	 */
+	for (i = 0; i < revs.cmdline.nr; i++)
+		if (revs.cmdline.rev[i].flags & UNINTERESTING)
+			break;
+	if (i == revs.cmdline.nr) {
+		ret = error(_("not a '<base>..<tip>' revision range"));
+		goto out;
+	}
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs))) {
+		if (commit->object.flags & BOUNDARY) {
+			commit_list_insert(commit, &boundaries);
+			continue;
+		}
+		if (!oldest)
+			oldest = commit;
+		if (tip)
+			oidset_insert(interior_out, &tip->object.oid);
+		tip = commit;
+	}
+
+	if (!oldest) {
+		ret = error(_("the revision range is empty"));
+		goto out;
+	}
+
+	if (oldest == tip) {
+		ret = error(_("the revision range holds a single commit; "
+			      "nothing to squash"));
+		goto out;
+	}
+
+	if (!oldest->parents)
+		BUG("an in-range commit must have a parent");
+	base = oldest->parents->item;
+
+	/*
+	 * A boundary other than the base is an in-range commit reaching a
+	 * commit outside the range, so the range has more than one base.
+	 */
+	for (b = boundaries; b; b = b->next) {
+		if (b->item != base) {
+			ret = error(_("the revision range has more than one base; "
+				      "cannot squash"));
+			goto out;
+		}
+	}
+
+	*base_out = base;
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	commit_list_free(boundaries);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+struct interior_ref_cb {
+	const struct oidset *interior;
+	const char *name;
+};
+
+static int find_interior_ref(const struct reference *ref, void *cb_data)
+{
+	struct interior_ref_cb *data = cb_data;
+
+	if (oidset_contains(data->interior, ref->oid)) {
+		data->name = xstrdup(ref->name);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	enum commit_tree_flags flags = 0;
+	int dry_run = 0;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BIT(0, "reedit-message", &flags,
+			N_("open an editor to modify the commit message"),
+			COMMIT_TREE_EDIT_MESSAGE),
+		OPT_END(),
+	};
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct oidset interior = OIDSET_INIT;
+	struct commit *base, *oldest, *tip, *rewritten;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	struct commit_list *parents = NULL;
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+	if (!argc) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
+
+	ret = resolve_squash_range(repo, argv, &base, &oldest, &tip,
+				   &interior);
+	if (ret < 0)
+		goto out;
+
+	if (action == REF_ACTION_BRANCHES) {
+		struct interior_ref_cb cb = { .interior = &interior };
+
+		refs_for_each_ref(get_main_ref_store(repo),
+				  find_interior_ref, &cb);
+		if (cb.name) {
+			ret = error(_("'%s' points into the squashed range"),
+				    cb.name);
+			advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+					  _("Use --update-refs=head to rewrite only "
+					    "the current branch and leave such refs "
+					    "untouched."));
+			free((char *)cb.name);
+			goto out;
+		}
+	}
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+	commit_list_append(base, &parents);
+
+	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
+			      base_tree_oid, tip_tree_oid, &rewritten, flags);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	strbuf_addf(&reflog_msg, "squash: updating %s", argv[0]);
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	oidset_clear(&interior);
+	commit_list_free(parents);
+	release_revisions(&revs);
+	return ret;
+}
+
 int cmd_history(int argc,
 		const char **argv,
 		const char *prefix,
@@ -982,6 +1204,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -989,6 +1212,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
diff --git a/t/meson.build b/t/meson.build
index 3219264fe7..63ea26b8ed 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -399,6 +399,7 @@ integration_tests = [
   't3451-history-reword.sh',
   't3452-history-split.sh',
   't3453-history-fixup.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..94ee54eb24
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,513 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+test_expect_success 'setup linear history touching two files' '
+	test_commit base file a &&
+	git tag start &&
+	test_commit --no-tag one other x &&
+	test_commit --no-tag two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "expects a revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the revision range is empty" err
+'
+
+test_expect_success 'errors on a single revision that is not a range' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "not a .*range" err &&
+	test_must_fail git history squash HEAD~1 2>err &&
+	test_grep "not a .*range" err
+'
+
+test_expect_success 'errors on a range holding a single commit' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "HEAD^!" 2>err &&
+	test_grep "single commit; nothing to squash" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'accepts multiple revision arguments with an exclusion' '
+	git reset --hard three &&
+	git branch -f keep HEAD~2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..HEAD ^keep &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	two
+	one
+	EOF
+	test_cmp expect actual &&
+	test_cmp_rev keep HEAD~1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git branch -D keep
+'
+
+test_expect_success 'squashes a branch the current branch is not on' '
+	git reset --hard three &&
+	main=$(git symbolic-ref --short HEAD) &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b off-history start &&
+	test_commit --no-tag off-one off a &&
+	test_commit --no-tag off-two off b &&
+	git checkout "$main" &&
+
+	git history squash start..off-history &&
+
+	git rev-list --count start..off-history >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D off-history
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	git log --format="%s" -1 >subject &&
+	echo one >expect &&
+	test_cmp expect subject &&
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..@~1 &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	three
+	one
+	EOF
+	test_cmp expect actual &&
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$root.." &&
+
+	git rev-list --count "$root..HEAD" >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+
+test_expect_success 'reuses the message of a fixup! commit in the range' '
+	git reset --hard start &&
+	test_commit --no-tag reg1 file b &&
+	git commit --allow-empty -m "fixup! reg1" &&
+	test_commit reg2 file c &&
+
+	git history squash start.. &&
+
+	git log --format="%s" -1 >actual &&
+	echo reg1 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'keeps the oldest message even if it is a fixup!' '
+	git reset --hard start &&
+	test_commit --no-tag "fixup! something" file b &&
+	test_commit tail file c &&
+
+	git history squash start.. &&
+
+	git log --format="%s" -1 >actual &&
+	echo "fixup! something" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'preserves authorship of the oldest commit' '
+	git reset --hard start &&
+	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
+		test_commit --no-tag oldest file b &&
+	test_commit newest file c &&
+
+	git history squash start.. &&
+
+	git log -1 --format="%an <%ae>" >actual &&
+	echo "Squasher <squash@example.com>" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--dry-run predicts the rewrite without performing it' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash start.. &&
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --update-refs=head start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success 'refuses to fold a range a ref points into' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "error: .* points into the squashed range" err &&
+	test_grep "hint: .*--update-refs=head" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D mid
+'
+
+test_expect_success 'advice.historyUpdateRefs silences the hint' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "points into the squashed range" err &&
+	test_grep ! "hint:" err &&
+
+	git branch -D mid
+'
+
+test_expect_success '--update-refs=head folds past a ref pointing into the range' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	mid_before=$(git rev-parse mid) &&
+
+	git history squash --update-refs=head start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$mid_before" mid &&
+
+	git branch -D mid
+'
+
+test_expect_success 'refuses to fold a range a tag points into' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "refs/tags/mark" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git tag -d mark
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout "$main" &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	test_commit --no-tag after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	git log --format="%s" -1 >subject &&
+	echo before-side >expect &&
+	test_cmp expect subject &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a merge of a branch that forked at the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b base-fork-side &&
+	test_commit --no-tag base-fork-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag base-fork-main file b &&
+	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
+	git branch -D base-fork-side &&
+	test_commit --no-tag base-fork-tail file c &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'refuses a merge whose other parent is outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$base.." &&
+
+	git rev-list --count "$base..HEAD" >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'refuses to squash a range with more than one base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b forked-before &&
+	test_commit forked-side fside x &&
+	git checkout "$main" &&
+	test_commit forked-base file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit forked-main file c &&
+	git merge --no-ff -m merge forked-before &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range with two interior merges' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag two-merge-a file a1 &&
+	git checkout -b two-merge-s1 &&
+	test_commit --no-tag two-merge-s1 s1 x &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s1" two-merge-s1 &&
+	test_commit --no-tag two-merge-b file b1 &&
+	git checkout -b two-merge-s2 &&
+	test_commit --no-tag two-merge-s2 s2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s2" two-merge-s2 &&
+	git branch -D two-merge-s1 two-merge-s2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file s1 &&
+	test_path_is_file s2
+'
+
+test_expect_success 'folds a range with a nested merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b nested-outer &&
+	test_commit --no-tag nested-outer outer x &&
+	git checkout -b nested-inner &&
+	test_commit --no-tag nested-inner inner y &&
+	git checkout nested-outer &&
+	git merge --no-ff -m "merge inner" nested-inner &&
+	git checkout "$main" &&
+	test_commit --no-tag nested-main file b1 &&
+	git merge --no-ff -m "merge outer" nested-outer &&
+	git branch -D nested-outer nested-inner &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file outer &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range with an octopus merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag octo-base file a1 &&
+	git checkout -b octo-1 &&
+	test_commit --no-tag octo-1 o1 x &&
+	git checkout "$main" &&
+	git checkout -b octo-2 &&
+	test_commit --no-tag octo-2 o2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-1 octo-2 &&
+	git branch -D octo-1 octo-2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file o1 &&
+	test_path_is_file o2
+'
+
+test_expect_success 'refuses an octopus merge with an arm forked before the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b octo-pre &&
+	test_commit octo-pre-side pside x &&
+	git checkout "$main" &&
+	test_commit octo-pre-main file b1 &&
+	octo_base=$(git rev-parse HEAD) &&
+	git checkout -b octo-within &&
+	test_commit --no-tag octo-within wside y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-pre octo-within &&
+	merged=$(git rev-parse HEAD) &&
+	git branch -D octo-pre octo-within &&
+
+	test_must_fail git history squash "$octo_base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'refuses when a descendant above the range is a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag desc-one file b &&
+	test_commit --no-tag desc-two file c &&
+	git tag desc-tip &&
+	git checkout -b desc-above &&
+	test_commit --no-tag desc-above above x &&
+	git checkout "$main" &&
+	test_commit --no-tag desc-main file d &&
+	git merge --no-ff -m "merge desc-above" desc-above &&
+	git branch -D desc-above &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start..desc-tip 2>err &&
+	test_grep "merge commits is not supported" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'refuses to fold a range a ref points into at a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag refmerge-base file b &&
+	git checkout -b refmerge-side &&
+	test_commit --no-tag refmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag refmerge-main file c &&
+	git merge --no-ff -m "interior merge" refmerge-side &&
+	git branch -D refmerge-side &&
+	git branch at-merge HEAD &&
+	test_commit --no-tag refmerge-tail file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "at-merge" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D at-merge
+'
+
+test_done
-- 
gitgitgadget

Re: [PATCH v6 3/4] history: add squash subcommand to fold a range

[Junio C Hamano]

"Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:

> @@ -11,6 +11,7 @@ SYNOPSIS
>  git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
>  git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
>  git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
> +git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]

Not your fault at all, as there are existing violators but the
gitcli tells us that the canonical order of arguments on the command
line is to have dashed options early before any real arguments.

Seeing <commit> followed by --dry-run, --update-refs, etc. with the
existing subcommands should also be corrected and this new command
should not spread the existing violation by mimicking.  The revision
range (which is not just a single token A..B, but the usual range
notation that rev-list takes, like ^A B..C) should come after all
these dashed options.

> +The range is given in the usual `<base>..<tip>` form, where _<base>_ is
> +the commit just below the oldest commit to squash. For example, `git
> +history squash @~3..` folds the three most recent commits into one, and

It is OK to use in your personal development, but in the official
documentation, avoid cryptic @ and always spell HEAD (except for a
single place that explain that @ can stand in for HEAD, for obvious
reasons).  It is extremely annoying and confusing to read as these
look so similar to reflog notation for the current branch, e.g., @~1
vs @{1}.

So "squash HEAD~3..HEAD" specifies a range of commits HEAD~2, HEAD~1
and HEAD (three commits), these are squashed into one commit on top
of HEAD~3, creating a sibling to HEAD~2 whose tree matches HEAD.

OK.  Looking good.

[PATCH v6 4/4] history: re-edit a squash with every message

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

By default "git history squash" reuses the oldest commit's message.
When --reedit-message is given it only reopened that one message, so the
messages of the folded-in commits were lost.

Gather the messages of every commit in the range, oldest first, and use
them as the editor template when re-editing, mirroring how "git rebase
-i" presents a squash.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  5 +--
 builtin/history.c              | 61 +++++++++++++++++++++++++++++++++-
 t/t3455-history-squash.sh      | 37 +++++++++++++++++++++
 3 files changed, 100 insertions(+), 3 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 123ad5d4bc..8d4398ab1b 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -114,8 +114,9 @@ arguments to linkgit:git-rev-list[1], so several arguments may be given,
 for example `@~3.. ^topic` to additionally exclude what is already on
 `topic`.
 +
-The oldest commit's message and authorship are preserved by default,
-unless you specify `--reedit-message`. A merge commit inside the range is
+The oldest commit's message and authorship are preserved by default. With
+`--reedit-message`, an editor opens pre-filled with the messages of all the
+folded commits so you can combine them. A merge commit inside the range is
 folded like any other, but the range must have a single base, so a range
 that reaches more than one entry point (for example a side branch that
 forked before the range and was later merged into it) is rejected.
diff --git a/builtin/history.c b/builtin/history.c
index 5a1b42c063..1c31ea9118 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1097,6 +1097,56 @@ static int find_interior_ref(const struct reference *ref, void *cb_data)
 	return 0;
 }
 
+static int build_squash_message(struct repository *repo,
+				struct commit *base,
+				struct commit *tip,
+				struct strbuf *out)
+{
+	struct rev_info revs;
+	struct commit *commit;
+	struct strvec args = STRVEC_INIT;
+	int n = 0, ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs))) {
+		const char *message, *body;
+		struct strbuf one = STRBUF_INIT;
+
+		message = repo_logmsg_reencode(repo, commit, NULL, NULL);
+		find_commit_subject(message, &body);
+		strbuf_addstr(&one, body);
+		strbuf_trim_trailing_newline(&one);
+
+		if (n++)
+			strbuf_addch(out, '\n');
+		strbuf_addbuf(out, &one);
+		strbuf_addch(out, '\n');
+
+		strbuf_release(&one);
+		repo_unuse_commit_buffer(repo, commit, message);
+	}
+
+	ret = 0;
+
+out:
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1121,6 +1171,7 @@ static int cmd_history_squash(int argc,
 		OPT_END(),
 	};
 	struct strbuf reflog_msg = STRBUF_INIT;
+	struct strbuf message = STRBUF_INIT;
 	struct oidset interior = OIDSET_INIT;
 	struct commit *base, *oldest, *tip, *rewritten;
 	const struct object_id *base_tree_oid, *tip_tree_oid;
@@ -1160,6 +1211,12 @@ static int cmd_history_squash(int argc,
 		}
 	}
 
+	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
+		ret = build_squash_message(repo, base, tip, &message);
+		if (ret < 0)
+			goto out;
+	}
+
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
 		goto out;
@@ -1168,7 +1225,8 @@ static int cmd_history_squash(int argc,
 	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
 	commit_list_append(base, &parents);
 
-	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
+	ret = commit_tree_ext(repo, "squash", oldest,
+			      message.len ? message.buf : NULL, parents,
 			      base_tree_oid, tip_tree_oid, &rewritten, flags);
 	if (ret < 0) {
 		ret = error(_("failed writing squashed commit"));
@@ -1189,6 +1247,7 @@ static int cmd_history_squash(int argc,
 
 out:
 	strbuf_release(&reflog_msg);
+	strbuf_release(&message);
 	oidset_clear(&interior);
 	commit_list_free(parents);
 	release_revisions(&revs);
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index 94ee54eb24..5ef6768826 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -164,6 +164,43 @@ test_expect_success 'preserves authorship of the oldest commit' '
 	test_cmp expect actual
 '
 
+test_expect_success '--reedit-message offers every folded-in message' '
+	git reset --hard start &&
+	echo b >file &&
+	git add file &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+
+	write_script editor <<-\EOF &&
+	cp "$1" buffer &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	test_grep "re-one subject" buffer &&
+	test_grep "re-one body line" buffer &&
+	test_grep re-two buffer &&
+	test_grep re-three buffer &&
+	git log --format="%s" -1 >actual &&
+	echo combined >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--reedit-message aborts on an empty message' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	test_must_fail git history squash --reedit-message start.. &&
+
+	test_cmp_rev "$head_before" HEAD
+'
+
 test_expect_success '--dry-run predicts the rewrite without performing it' '
 	git reset --hard three &&
 	head_before=$(git rev-parse HEAD) &&
-- 
gitgitgadget

Re: [PATCH v6 4/4] history: re-edit a squash with every message

[Junio C Hamano]

"Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Harald Nordgren <haraldnordgren@gmail.com>
>
> By default "git history squash" reuses the oldest commit's message.
> When --reedit-message is given it only reopened that one message, so the
> messages of the folded-in commits were lost.
>
> Gather the messages of every commit in the range, oldest first, and use
> them as the editor template when re-editing, mirroring how "git rebase
> -i" presents a squash.

I doubt it would make practical difference, but one thing I notice
is that unlike "git rebase -i", this one does not intersperse
markers like "# This is the 1st commit message" in between the
messages taken from the squashed commits, so it is not exactly
"mirroring".

Re: [PATCH v6 4/4] history: re-edit a squash with every message

[Harald Nordgren]

> I doubt it would make practical difference, but one thing I notice
> is that unlike "git rebase -i", this one does not intersperse
> markers like "# This is the 1st commit message" in between the
> messages taken from the squashed commits, so it is not exactly
> "mirroring".

I wouldn't mind extracting that logic from 'rebase -i' to show it
here. It would be nice to have.


Harald

Re: [PATCH v6 4/4] history: re-edit a squash with every message

[Junio C Hamano]

Harald Nordgren <haraldnordgren@gmail.com> writes:

>> I doubt it would make practical difference, but one thing I notice
>> is that unlike "git rebase -i", this one does not intersperse
>> markers like "# This is the 1st commit message" in between the
>> messages taken from the squashed commits, so it is not exactly
>> "mirroring".
>
> I wouldn't mind extracting that logic from 'rebase -i' to show it
> here. It would be nice to have.

If we can share more code (not necessarily the exact existing
code---after cleaning it up if needed is perfectly fine and may even
be better) across codebaes that would be excellent.  Thanks.

Re: [PATCH v6 4/4] history: re-edit a squash with every message

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> Harald Nordgren <haraldnordgren@gmail.com> writes:
>
>>> I doubt it would make practical difference, but one thing I notice
>>> is that unlike "git rebase -i", this one does not intersperse
>>> markers like "# This is the 1st commit message" in between the
>>> messages taken from the squashed commits, so it is not exactly
>>> "mirroring".
>>
>> I wouldn't mind extracting that logic from 'rebase -i' to show it
>> here. It would be nice to have.
>
> If we can share more code (not necessarily the exact existing
> code---after cleaning it up if needed is perfectly fine and may even
> be better) across codebaes that would be excellent.  Thanks.

After looking at what Phillip said in a side thread (look for "So
instead of ... We'd have") [*], I retract my "I doubt it would make
practical difference".  Without boundary that shows where each
message begins, the result is much harder to look at.


[Reference]

 * https://lore.kernel.org/git/3b3af3ef-a043-4af9-964e-429237789c97@gmail.com/

[PATCH v7 0/5] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v7:

 * --reedit-message now builds the same editor template git rebase -i shows
   for a squash (a combination of N commits banner with each folded message
   under its own header) and follows autosquash for markers: a fixup!
   message falls out (commented under a will be skipped header), while a
   squash! or amend! keeps its body with only the marker subject commented
   so its remark can be reworded in. Only the message text is affected,
   every commit's changes are always folded in.
 * Reuse git rebase -i's squash-message code: a preparatory sequencer:
   commit extracts the banner, header and marker-comment helpers so both
   rebase and git history squash build the identical template from one
   source.
 * Refuse a range whose oldest commit is a fixup!, squash! or amend!, since
   the marker's target cannot be inside the range.
 * Reorder the squash usage so dashed options come before <revision-range>,
   and spell out HEAD instead of @ in the documentation and examples.
 * Expand the squash commit message and documentation with this overview,
   and scope the merge limitation so it no longer contradicts squash folding
   a single-base interior merge.

Changes in v6:

 * git history squash now accepts multiple revision arguments, read like the
   arguments to git-rev-list, so a compound range such as @~3.. ^topic
   works.
 * The base to reparent onto is now the oldest in-range commit's parent; a
   boundary other than that base means the range has more than one base and
   is rejected. This also fixes the earlier overly-restrictive handling of
   merges and side branches.
 * A single-commit range (e.g. @^!) is rejected with "nothing to squash"
   (this also covers the @^!-style example that previously succeeded
   silently).
 * Commit messages reworded: the squash commit now gives an overview of
   fixup!/squash!/amend! handling, rewording, merge-parent and ref behavior.

Changes in v5:

 * The range walk now uses --ancestry-path, so only commits descended from
   the base are folded; a single revision such as HEAD or HEAD~1 is now
   rejected as "not a <base>..<tip> range" rather than treated as a squash
   down to the root.
 * This adopts the --ancestry-path suggestion; the multi-base rejection is
   unchanged, so a side branch that forked before the base and merged in is
   still refused.
 * Added tests covering more merge topologies: two interior merges, a nested
   merge, an octopus merge, an octopus arm forked before the base, a merge
   among the descendants replayed above the range, and a ref pointing at an
   interior merge commit.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (5):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  history: add squash subcommand to fold a range
  sequencer: extract helpers for the squash message markers
  history: re-edit a squash with every message

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  49 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 390 +++++++++++++++++--
 sequencer.c                      |  64 ++--
 sequencer.h                      |  23 ++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 632 +++++++++++++++++++++++++++++++
 9 files changed, 1099 insertions(+), 66 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: e9019fcafe0040228b8631c30f97ae1adb61bcdc
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v7
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v7
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v6:

 1:  fea6b79e60 = 1:  56ed8fadbb history: extract helper for a commit's parent tree
 2:  e2674e0bc4 = 2:  212e9c228f history: give commit_tree_ext a message template
 3:  811e393ab4 ! 3:  cf3346a1cd history: add squash subcommand to fold a range
     @@ Commit message
          Add "git history squash <revision-range>" to do this directly. It folds
          every commit in the range into the oldest one, keeping that commit's
          message and authorship and taking the tree of the newest commit, then
     -    replays the commits above the range on top. fixup!, squash! and amend!
     -    commits are folded like any other and are not interpreted, so the
     -    squashed message comes from the oldest commit, or from an editor with
     -    --reedit-message.
     +    replays the commits above the range on top. The squashed message comes
     +    from the oldest commit, or from an editor with --reedit-message. As that
     +    message is reused, a range whose oldest commit is a fixup!, squash! or
     +    amend! is refused, since the marker's target cannot be in the range.
      
          The range is read like the arguments to "git rev-list", so several
     -    arguments such as "@~3.. ^topic" are allowed. A merge inside the range
     -    is folded when its other parent is reachable from the base, otherwise
     -    the range has more than one base and is rejected. By default the command
     -    also refuses when a ref points at a commit that the fold would discard.
     -    Use --update-refs=head to rewrite only the current branch instead.
     +    arguments such as "HEAD~3..HEAD ^topic" are allowed. A merge inside the
     +    range is folded when its other parent is reachable from the base,
     +    otherwise the range has more than one base and is rejected. By default
     +    the command also refuses when a ref points at a commit that the fold
     +    would discard. Use --update-refs=head to rewrite only the current branch
     +    instead.
      
          Inspired-by: Sergey Chernov <serega.morph@gmail.com>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
     @@ Documentation/git-history.adoc: SYNOPSIS
       git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
       git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
       git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
     -+git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]
     ++git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>
       
       DESCRIPTION
       -----------
     +@@ Documentation/git-history.adoc: at once.
     + LIMITATIONS
     + -----------
     + 
     +-This command does not (yet) work with histories that contain merges. You
     +-should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
     ++This command does not (yet) replay merge commits onto the rewritten
     ++history: if a commit that would be replayed is a merge, the operation is
     ++rejected, and you should use linkgit:git-rebase[1] with the
     ++`--rebase-merges` flag instead. The `squash` subcommand can still fold a
     ++merge that lies inside the range, as long as the range has a single base.
     + 
     + Furthermore, the command does not support operations that can result in merge
     + conflicts. This limitation is by design as history rewrites are not intended to
      @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
       It is invalid to select either all or no hunks, as that would lead to
       one of the commits becoming empty.
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      ++
      +The range is given in the usual `<base>..<tip>` form, where _<base>_ is
      +the commit just below the oldest commit to squash. For example, `git
     -+history squash @~3..` folds the three most recent commits into one, and
     -+`git history squash @~5..@~2` squashes an interior range while leaving
     -+the two newest commits in place. _<revision-range>_ is read like the
     -+arguments to linkgit:git-rev-list[1], so several arguments may be given,
     -+for example `@~3.. ^topic` to additionally exclude what is already on
     -+`topic`.
     ++history squash HEAD~3..HEAD` folds the three most recent commits into
     ++one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
     ++while leaving the two newest commits in place. _<revision-range>_ is read
     ++like the arguments to linkgit:git-rev-list[1], so several arguments may be
     ++given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
     ++already on `topic`.
      ++
      +The oldest commit's message and authorship are preserved by default,
      +unless you specify `--reedit-message`. A merge commit inside the range is
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      +that reaches more than one entry point (for example a side branch that
      +forked before the range and was later merged into it) is rejected.
      ++
     -+The folded commits disappear from the history, so with the default
     -+`--update-refs=branches` the command refuses when another ref points at
     -+one of them. Rerun with `--update-refs=head` to rewrite only the current
     -+branch and leave those refs pointing at the old commits.
     ++Because the oldest commit's message is reused, the range may not begin
     ++with a `fixup!`, `squash!`, or `amend!` commit, whose target is
     ++necessarily outside the range.
     +++
     ++A branch or tag that points at a commit inside the range would be left
     ++dangling once those commits are folded away, so with the default
     ++`--update-refs=branches` the command refuses. Rerun with
     ++`--update-refs=head` to rewrite only the current branch and leave such
     ++refs pointing at the old commits.
      +
       OPTIONS
       -------
       
     +@@ Documentation/git-history.adoc: OPTIONS
     + 	ref updates is generally safe.
     + 
     + `--reedit-message`::
     +-	Open an editor to modify the target commit's message.
     ++	Open an editor to modify the rewritten commit's message. For `squash`
     ++	the editor is pre-filled with the messages of all the folded commits.
     + 
     + `--empty=(drop|keep|abort)`::
     + 	Control what happens when a commit becomes empty as a result of the
      
       ## advice.c ##
      @@ advice.c: static struct {
     @@ builtin/history.c
       #define GIT_HISTORY_SPLIT_USAGE \
       	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
      +#define GIT_HISTORY_SQUASH_USAGE \
     -+	N_("git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]")
     ++	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>")
       
       static void change_data_free(void *util, const char *str UNUSED)
       {
     @@ builtin/history.c: out:
      +	return ret;
      +}
      +
     ++static int reject_fixupish_oldest(struct repository *repo,
     ++				  struct commit *oldest)
     ++{
     ++	const char *message, *subject;
     ++	int ret = 0;
     ++
     ++	message = repo_logmsg_reencode(repo, oldest, NULL, NULL);
     ++	find_commit_subject(message, &subject);
     ++	if (starts_with(subject, "fixup! ") ||
     ++	    starts_with(subject, "squash! ") ||
     ++	    starts_with(subject, "amend! "))
     ++		ret = error(_("the range begins with a fixup!, squash! or amend! "
     ++			      "commit whose target is not in the range"));
     ++	repo_unuse_commit_buffer(repo, oldest, message);
     ++	return ret;
     ++}
     ++
      +struct interior_ref_cb {
      +	const struct oidset *interior;
      +	const char *name;
     @@ builtin/history.c: out:
      +	if (ret < 0)
      +		goto out;
      +
     ++	ret = reject_fixupish_oldest(repo, oldest);
     ++	if (ret < 0)
     ++		goto out;
     ++
      +	if (action == REF_ACTION_BRANCHES) {
      +		struct interior_ref_cb cb = { .interior = &interior };
      +
     @@ t/t3455-history-squash.sh (new)
      +
      +test_expect_success 'squashes a range into a single commit without changing the tree' '
      +	git reset --hard three &&
     ++	head_before=$(git rev-parse HEAD) &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     ++	git history squash --dry-run start.. >out &&
     ++	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
     ++	test_cmp_rev "$head_before" HEAD &&
     ++
      +	git history squash start.. &&
      +
     ++	test "$predicted" = "$(git rev-parse HEAD)" &&
      +	git rev-list --count start..HEAD >count &&
      +	echo 1 >expect &&
      +	test_cmp expect count &&
     @@ t/t3455-history-squash.sh (new)
      +	test_cmp expect actual
      +'
      +
     -+test_expect_success 'keeps the oldest message even if it is a fixup!' '
     ++test_expect_success 'refuses a range whose oldest commit is a fixup!' '
      +	git reset --hard start &&
      +	test_commit --no-tag "fixup! something" file b &&
     -+	test_commit tail file c &&
     ++	test_commit --no-tag tail file c &&
     ++	head_before=$(git rev-parse HEAD) &&
     ++
     ++	test_must_fail git history squash start.. 2>err &&
     ++	test_grep "target is not in the range" err &&
     ++	test_cmp_rev "$head_before" HEAD
     ++'
     ++
     ++test_expect_success 'does not interpret squash! or amend! markers' '
     ++	git reset --hard start &&
     ++	test_commit --no-tag marker-oldest file b &&
     ++	git commit --allow-empty -m "squash! marker-oldest" &&
     ++	git commit --allow-empty -m "amend! marker-oldest" &&
     ++	test_commit --no-tag marker-newest file c &&
      +
      +	git history squash start.. &&
      +
     ++	git rev-list --count start..HEAD >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
      +	git log --format="%s" -1 >actual &&
     -+	echo "fixup! something" >expect &&
     ++	echo marker-oldest >expect &&
      +	test_cmp expect actual
      +'
      +
     @@ t/t3455-history-squash.sh (new)
      +	test_cmp expect actual
      +'
      +
     -+test_expect_success '--dry-run predicts the rewrite without performing it' '
     -+	git reset --hard three &&
     -+	head_before=$(git rev-parse HEAD) &&
     -+	tip_tree=$(git rev-parse HEAD^{tree}) &&
     -+
     -+	git history squash --dry-run start.. >out &&
     -+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
     -+	test_cmp_rev "$head_before" HEAD &&
     -+
     -+	git history squash start.. &&
     -+	test "$predicted" = "$(git rev-parse HEAD)" &&
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     -+	test_cmp_rev start HEAD^ &&
     -+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
     -+'
     -+
      +test_expect_success '--update-refs=head only moves HEAD' '
      +	git reset --hard three &&
      +	git branch -f other HEAD &&
 -:  ---------- > 4:  001356db93 sequencer: extract helpers for the squash message markers
 4:  4edf012b77 ! 5:  615fe4dd3f history: re-edit a squash with every message
     @@ Commit message
          When --reedit-message is given it only reopened that one message, so the
          messages of the folded-in commits were lost.
      
     -    Gather the messages of every commit in the range, oldest first, and use
     -    them as the editor template when re-editing, mirroring how "git rebase
     -    -i" presents a squash.
     +    Gather the messages of every commit in the range, oldest first, and build
     +    the same editor template that "git rebase -i" shows for a squash, using
     +    add_squash_combination_header(), add_squash_message_header() and
     +    squash_subject_comment_len(). Only the message text differs, the changes
     +    are always folded in. Following autosquash, a fixup!'s message is
     +    commented out in full under a "will be skipped" header, while a squash! or
     +    amend! keeps its body with only the marker subject commented.
      
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
       ## Documentation/git-history.adoc ##
     -@@ Documentation/git-history.adoc: arguments to linkgit:git-rev-list[1], so several arguments may be given,
     - for example `@~3.. ^topic` to additionally exclude what is already on
     - `topic`.
     +@@ Documentation/git-history.adoc: like the arguments to linkgit:git-rev-list[1], so several arguments may be
     + given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
     + already on `topic`.
       +
      -The oldest commit's message and authorship are preserved by default,
      -unless you specify `--reedit-message`. A merge commit inside the range is
     @@ Documentation/git-history.adoc: arguments to linkgit:git-rev-list[1], so several
       folded like any other, but the range must have a single base, so a range
       that reaches more than one entry point (for example a side branch that
       forked before the range and was later merged into it) is rejected.
     + +
     + Because the oldest commit's message is reused, the range may not begin
     + with a `fixup!`, `squash!`, or `amend!` commit, whose target is
     +-necessarily outside the range.
     ++necessarily outside the range. The changes from every commit in the range
     ++are always folded in. Only the message text differs. With
     ++`--reedit-message` the template mirrors `git rebase -i`: the message of a
     ++`fixup!` elsewhere in the range is commented out in full, while a
     ++`squash!` or `amend!` keeps its message body with only the marker subject
     ++commented, so you can fold the remark into the result.
     + +
     + A branch or tag that points at a commit inside the range would be left
     + dangling once those commits are folded away, so with the default
      
       ## builtin/history.c ##
      @@ builtin/history.c: static int find_interior_ref(const struct reference *ref, void *cb_data)
     @@ builtin/history.c: static int find_interior_ref(const struct reference *ref, voi
      +				struct commit *tip,
      +				struct strbuf *out)
      +{
     ++	struct commit_list *commits = NULL, **tail = &commits, *c;
      +	struct rev_info revs;
      +	struct commit *commit;
      +	struct strvec args = STRVEC_INIT;
     -+	int n = 0, ret;
     ++	int n = 0, total, ret;
      +
      +	repo_init_revisions(repo, &revs, NULL);
      +	strvec_push(&args, "ignored");
     @@ builtin/history.c: static int find_interior_ref(const struct reference *ref, voi
      +		goto out;
      +	}
      +
     -+	while ((commit = get_revision(&revs))) {
     ++	while ((commit = get_revision(&revs)))
     ++		tail = &commit_list_insert(commit, tail)->next;
     ++	total = commit_list_count(commits);
     ++
     ++	for (c = commits; c; c = c->next) {
      +		const char *message, *body;
     -+		struct strbuf one = STRBUF_INIT;
     ++		size_t commented_len;
     ++		int skip;
      +
     -+		message = repo_logmsg_reencode(repo, commit, NULL, NULL);
     ++		message = repo_logmsg_reencode(repo, c->item, NULL, NULL);
      +		find_commit_subject(message, &body);
     -+		strbuf_addstr(&one, body);
     -+		strbuf_trim_trailing_newline(&one);
      +
     -+		if (n++)
     -+			strbuf_addch(out, '\n');
     -+		strbuf_addbuf(out, &one);
     ++		skip = starts_with(body, "fixup! ");
     ++		commented_len = skip ? strlen(body) :
     ++			squash_subject_comment_len(body, 1);
     ++
     ++		if (!n)
     ++			add_squash_combination_header(out, total);
      +		strbuf_addch(out, '\n');
     ++		add_squash_message_header(out, ++n, skip);
     ++		strbuf_addstr(out, "\n\n");
     ++		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
     ++		strbuf_addstr(out, body + commented_len);
     ++		strbuf_complete_line(out);
      +
     -+		strbuf_release(&one);
     -+		repo_unuse_commit_buffer(repo, commit, message);
     ++		repo_unuse_commit_buffer(repo, c->item, message);
      +	}
      +
      +	ret = 0;
      +
      +out:
     ++	commit_list_free(commits);
      +	reset_revision_walk();
      +	release_revisions(&revs);
      +	strvec_clear(&args);
     @@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the olde
      +	test_commit re-three file d &&
      +
      +	write_script editor <<-\EOF &&
     -+	cp "$1" buffer &&
     ++	cat "$1" >edited &&
      +	echo combined >"$1"
      +	EOF
      +	test_set_editor "$(pwd)/editor" &&
      +	git history squash --reedit-message start.. &&
      +
     -+	test_grep "re-one subject" buffer &&
     -+	test_grep "re-one body line" buffer &&
     -+	test_grep re-two buffer &&
     -+	test_grep re-three buffer &&
     -+	git log --format="%s" -1 >actual &&
     ++	cat >expect <<-EOF &&
     ++	# This is a combination of 3 commits.
     ++	# This is the 1st commit message:
     ++
     ++	re-one subject
     ++
     ++	re-one body line
     ++
     ++	# This is the commit message #2:
     ++
     ++	re-two
     ++
     ++	# This is the commit message #3:
     ++
     ++	re-three
     ++
     ++	# Please enter the commit message for the squash changes. Lines starting
     ++	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     ++	# Changes to be committed:
     ++	#	modified:   file
     ++	#
     ++	EOF
     ++	test_cmp expect edited &&
      +	echo combined >expect &&
     ++	git log --format="%s" -1 >actual &&
      +	test_cmp expect actual
      +'
      +
     ++test_expect_success '--reedit-message handles fixup!, squash! and amend! like rebase' '
     ++	git reset --hard start &&
     ++	test_commit --no-tag mark-base file b &&
     ++	printf "fixup! mark-base\n\nfixup body\n" >msg &&
     ++	echo c >file &&
     ++	git add file &&
     ++	git commit -qF msg &&
     ++	printf "squash! mark-base\n\nsquash remark\n" >msg &&
     ++	echo d >file &&
     ++	git add file &&
     ++	git commit -qF msg &&
     ++	printf "amend! mark-base\n\namended message\n" >msg &&
     ++	echo e >file &&
     ++	git add file &&
     ++	git commit -qF msg &&
     ++
     ++	write_script editor <<-\EOF &&
     ++	cat "$1" >edited
     ++	EOF
     ++	test_set_editor "$(pwd)/editor" &&
     ++	git history squash --reedit-message start.. &&
     ++
     ++	cat >expect <<-EOF &&
     ++	# This is a combination of 4 commits.
     ++	# This is the 1st commit message:
     ++
     ++	mark-base
     ++
     ++	# The commit message #2 will be skipped:
     ++
     ++	# fixup! mark-base
     ++	#
     ++	# fixup body
     ++
     ++	# This is the commit message #3:
     ++
     ++	# squash! mark-base
     ++
     ++	squash remark
     ++
     ++	# This is the commit message #4:
     ++
     ++	# amend! mark-base
     ++
     ++	amended message
     ++
     ++	# Please enter the commit message for the squash changes. Lines starting
     ++	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     ++	# Changes to be committed:
     ++	#	modified:   file
     ++	#
     ++	EOF
     ++	test_cmp expect edited &&
     ++	git log -1 --format="%B" >final &&
     ++	test_grep ! "fixup body" final &&
     ++	test_grep "squash remark" final &&
     ++	test_grep "amended message" final
     ++'
     ++
      +test_expect_success '--reedit-message aborts on an empty message' '
      +	git reset --hard three &&
      +	head_before=$(git rev-parse HEAD) &&
     @@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the olde
      +	test_cmp_rev "$head_before" HEAD
      +'
      +
     - test_expect_success '--dry-run predicts the rewrite without performing it' '
     + test_expect_success '--update-refs=head only moves HEAD' '
       	git reset --hard three &&
     - 	head_before=$(git rev-parse HEAD) &&
     + 	git branch -f other HEAD &&

-- 
gitgitgadget

[PATCH v7 1/5] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 091465a59e..f95f26e684 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -157,6 +157,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -164,21 +183,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -444,18 +453,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -799,16 +800,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v7 2/5] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index f95f26e684..305bde3102 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -101,6 +101,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -130,13 +131,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -189,7 +193,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -644,7 +648,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -855,7 +859,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -872,7 +876,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v7 3/5] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git history squash <revision-range>" to do this directly. It folds
every commit in the range into the oldest one, keeping that commit's
message and authorship and taking the tree of the newest commit, then
replays the commits above the range on top. The squashed message comes
from the oldest commit, or from an editor with --reedit-message. As that
message is reused, a range whose oldest commit is a fixup!, squash! or
amend! is refused, since the marker's target cannot be in the range.

The range is read like the arguments to "git rev-list", so several
arguments such as "HEAD~3..HEAD ^topic" are allowed. A merge inside the
range is folded when its other parent is reachable from the base,
otherwise the range has more than one base and is rejected. By default
the command also refuses when a ref points at a commit that the fold
would discard. Use --update-refs=head to rewrite only the current branch
instead.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  43 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 245 +++++++++++++++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 517 +++++++++++++++++++++++++++++++
 7 files changed, 809 insertions(+), 3 deletions(-)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 257db58918..f4d692d136 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -55,6 +55,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a ref points
+		into the range being folded, to tell the user about
+		`--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 2ba8121795..783ddf4a51 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -11,6 +11,7 @@ SYNOPSIS
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>
 
 DESCRIPTION
 -----------
@@ -42,8 +43,11 @@ at once.
 LIMITATIONS
 -----------
 
-This command does not (yet) work with histories that contain merges. You
-should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
+This command does not (yet) replay merge commits onto the rewritten
+history: if a commit that would be replayed is a merge, the operation is
+rejected, and you should use linkgit:git-rebase[1] with the
+`--rebase-merges` flag instead. The `squash` subcommand can still fold a
+merge that lies inside the range, as long as the range has a single base.
 
 Furthermore, the command does not support operations that can result in merge
 conflicts. This limitation is by design as history rewrites are not intended to
@@ -97,6 +101,38 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's message and
+	authorship and takes the tree of the range's newest commit, so the
+	whole range collapses into a single commit. Commits above the range
+	are replayed on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash HEAD~3..HEAD` folds the three most recent commits into
+one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
+while leaving the two newest commits in place. _<revision-range>_ is read
+like the arguments to linkgit:git-rev-list[1], so several arguments may be
+given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
+already on `topic`.
++
+The oldest commit's message and authorship are preserved by default,
+unless you specify `--reedit-message`. A merge commit inside the range is
+folded like any other, but the range must have a single base, so a range
+that reaches more than one entry point (for example a side branch that
+forked before the range and was later merged into it) is rejected.
++
+Because the oldest commit's message is reused, the range may not begin
+with a `fixup!`, `squash!`, or `amend!` commit, whose target is
+necessarily outside the range.
++
+A branch or tag that points at a commit inside the range would be left
+dangling once those commits are folded away, so with the default
+`--update-refs=branches` the command refuses. Rerun with
+`--update-refs=head` to rewrite only the current branch and leave such
+refs pointing at the old commits.
+
 OPTIONS
 -------
 
@@ -107,7 +143,8 @@ OPTIONS
 	ref updates is generally safe.
 
 `--reedit-message`::
-	Open an editor to modify the target commit's message.
+	Open an editor to modify the rewritten commit's message. For `squash`
+	the editor is pre-filled with the messages of all the folded commits.
 
 `--empty=(drop|keep|abort)`::
 	Control what happens when a commit becomes empty as a result of the
diff --git a/advice.c b/advice.c
index 0018501b7b..5c6ff95e31 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 8def280688..911b4e4643 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index 305bde3102..63911a493d 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -30,6 +31,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -973,6 +976,246 @@ out:
 	return ret;
 }
 
+/*
+ * Resolve a "<base>..<tip>" revision range into the base commit just outside
+ * the range (which becomes the parent of the squashed commit), the oldest
+ * commit contained in the range (whose message the squash reuses), and the
+ * range tip (whose tree becomes the result). A merge inside the range is fine,
+ * but the range must have a single base and must not reach a root commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				const char **argv,
+				struct commit **base_out,
+				struct commit **oldest_out,
+				struct commit **tip_out,
+				struct oidset *interior_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
+	struct commit_list *boundaries = NULL, *b;
+	struct strvec args = STRVEC_INIT;
+	size_t i;
+	int ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_push(&args, "--boundary");
+	strvec_push(&args, "--ancestry-path");
+	strvec_pushv(&args, argv);
+	setup_revisions_from_strvec(&args, &revs, NULL);
+	if (args.nr != 1) {
+		ret = error(_("unrecognized argument: %s"), args.v[1]);
+		goto out;
+	}
+
+	/*
+	 * A squash needs a base to reparent onto, so the range has to exclude
+	 * something, as in "<base>..<tip>". A revision range with no such
+	 * bottom commit cannot be squashed.
+	 */
+	for (i = 0; i < revs.cmdline.nr; i++)
+		if (revs.cmdline.rev[i].flags & UNINTERESTING)
+			break;
+	if (i == revs.cmdline.nr) {
+		ret = error(_("not a '<base>..<tip>' revision range"));
+		goto out;
+	}
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs))) {
+		if (commit->object.flags & BOUNDARY) {
+			commit_list_insert(commit, &boundaries);
+			continue;
+		}
+		if (!oldest)
+			oldest = commit;
+		if (tip)
+			oidset_insert(interior_out, &tip->object.oid);
+		tip = commit;
+	}
+
+	if (!oldest) {
+		ret = error(_("the revision range is empty"));
+		goto out;
+	}
+
+	if (oldest == tip) {
+		ret = error(_("the revision range holds a single commit; "
+			      "nothing to squash"));
+		goto out;
+	}
+
+	if (!oldest->parents)
+		BUG("an in-range commit must have a parent");
+	base = oldest->parents->item;
+
+	/*
+	 * A boundary other than the base is an in-range commit reaching a
+	 * commit outside the range, so the range has more than one base.
+	 */
+	for (b = boundaries; b; b = b->next) {
+		if (b->item != base) {
+			ret = error(_("the revision range has more than one base; "
+				      "cannot squash"));
+			goto out;
+		}
+	}
+
+	*base_out = base;
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	commit_list_free(boundaries);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+static int reject_fixupish_oldest(struct repository *repo,
+				  struct commit *oldest)
+{
+	const char *message, *subject;
+	int ret = 0;
+
+	message = repo_logmsg_reencode(repo, oldest, NULL, NULL);
+	find_commit_subject(message, &subject);
+	if (starts_with(subject, "fixup! ") ||
+	    starts_with(subject, "squash! ") ||
+	    starts_with(subject, "amend! "))
+		ret = error(_("the range begins with a fixup!, squash! or amend! "
+			      "commit whose target is not in the range"));
+	repo_unuse_commit_buffer(repo, oldest, message);
+	return ret;
+}
+
+struct interior_ref_cb {
+	const struct oidset *interior;
+	const char *name;
+};
+
+static int find_interior_ref(const struct reference *ref, void *cb_data)
+{
+	struct interior_ref_cb *data = cb_data;
+
+	if (oidset_contains(data->interior, ref->oid)) {
+		data->name = xstrdup(ref->name);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	enum commit_tree_flags flags = 0;
+	int dry_run = 0;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BIT(0, "reedit-message", &flags,
+			N_("open an editor to modify the commit message"),
+			COMMIT_TREE_EDIT_MESSAGE),
+		OPT_END(),
+	};
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct oidset interior = OIDSET_INIT;
+	struct commit *base, *oldest, *tip, *rewritten;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	struct commit_list *parents = NULL;
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+	if (!argc) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
+
+	ret = resolve_squash_range(repo, argv, &base, &oldest, &tip,
+				   &interior);
+	if (ret < 0)
+		goto out;
+
+	ret = reject_fixupish_oldest(repo, oldest);
+	if (ret < 0)
+		goto out;
+
+	if (action == REF_ACTION_BRANCHES) {
+		struct interior_ref_cb cb = { .interior = &interior };
+
+		refs_for_each_ref(get_main_ref_store(repo),
+				  find_interior_ref, &cb);
+		if (cb.name) {
+			ret = error(_("'%s' points into the squashed range"),
+				    cb.name);
+			advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+					  _("Use --update-refs=head to rewrite only "
+					    "the current branch and leave such refs "
+					    "untouched."));
+			free((char *)cb.name);
+			goto out;
+		}
+	}
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+	commit_list_append(base, &parents);
+
+	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
+			      base_tree_oid, tip_tree_oid, &rewritten, flags);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	strbuf_addf(&reflog_msg, "squash: updating %s", argv[0]);
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	oidset_clear(&interior);
+	commit_list_free(parents);
+	release_revisions(&revs);
+	return ret;
+}
+
 int cmd_history(int argc,
 		const char **argv,
 		const char *prefix,
@@ -982,6 +1225,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -989,6 +1233,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
diff --git a/t/meson.build b/t/meson.build
index 3219264fe7..63ea26b8ed 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -399,6 +399,7 @@ integration_tests = [
   't3451-history-reword.sh',
   't3452-history-split.sh',
   't3453-history-fixup.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..6598649971
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,517 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+test_expect_success 'setup linear history touching two files' '
+	test_commit base file a &&
+	git tag start &&
+	test_commit --no-tag one other x &&
+	test_commit --no-tag two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "expects a revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the revision range is empty" err
+'
+
+test_expect_success 'errors on a single revision that is not a range' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "not a .*range" err &&
+	test_must_fail git history squash HEAD~1 2>err &&
+	test_grep "not a .*range" err
+'
+
+test_expect_success 'errors on a range holding a single commit' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "HEAD^!" 2>err &&
+	test_grep "single commit; nothing to squash" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'accepts multiple revision arguments with an exclusion' '
+	git reset --hard three &&
+	git branch -f keep HEAD~2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..HEAD ^keep &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	two
+	one
+	EOF
+	test_cmp expect actual &&
+	test_cmp_rev keep HEAD~1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git branch -D keep
+'
+
+test_expect_success 'squashes a branch the current branch is not on' '
+	git reset --hard three &&
+	main=$(git symbolic-ref --short HEAD) &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b off-history start &&
+	test_commit --no-tag off-one off a &&
+	test_commit --no-tag off-two off b &&
+	git checkout "$main" &&
+
+	git history squash start..off-history &&
+
+	git rev-list --count start..off-history >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D off-history
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash start.. &&
+
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	git log --format="%s" -1 >subject &&
+	echo one >expect &&
+	test_cmp expect subject &&
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..@~1 &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	three
+	one
+	EOF
+	test_cmp expect actual &&
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$root.." &&
+
+	git rev-list --count "$root..HEAD" >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+
+test_expect_success 'reuses the message of a fixup! commit in the range' '
+	git reset --hard start &&
+	test_commit --no-tag reg1 file b &&
+	git commit --allow-empty -m "fixup! reg1" &&
+	test_commit reg2 file c &&
+
+	git history squash start.. &&
+
+	git log --format="%s" -1 >actual &&
+	echo reg1 >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'refuses a range whose oldest commit is a fixup!' '
+	git reset --hard start &&
+	test_commit --no-tag "fixup! something" file b &&
+	test_commit --no-tag tail file c &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "target is not in the range" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'does not interpret squash! or amend! markers' '
+	git reset --hard start &&
+	test_commit --no-tag marker-oldest file b &&
+	git commit --allow-empty -m "squash! marker-oldest" &&
+	git commit --allow-empty -m "amend! marker-oldest" &&
+	test_commit --no-tag marker-newest file c &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	git log --format="%s" -1 >actual &&
+	echo marker-oldest >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'preserves authorship of the oldest commit' '
+	git reset --hard start &&
+	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
+		test_commit --no-tag oldest file b &&
+	test_commit newest file c &&
+
+	git history squash start.. &&
+
+	git log -1 --format="%an <%ae>" >actual &&
+	echo "Squasher <squash@example.com>" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --update-refs=head start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success 'refuses to fold a range a ref points into' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "error: .* points into the squashed range" err &&
+	test_grep "hint: .*--update-refs=head" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D mid
+'
+
+test_expect_success 'advice.historyUpdateRefs silences the hint' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "points into the squashed range" err &&
+	test_grep ! "hint:" err &&
+
+	git branch -D mid
+'
+
+test_expect_success '--update-refs=head folds past a ref pointing into the range' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	mid_before=$(git rev-parse mid) &&
+
+	git history squash --update-refs=head start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$mid_before" mid &&
+
+	git branch -D mid
+'
+
+test_expect_success 'refuses to fold a range a tag points into' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "refs/tags/mark" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git tag -d mark
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout "$main" &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	test_commit --no-tag after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	git log --format="%s" -1 >subject &&
+	echo before-side >expect &&
+	test_cmp expect subject &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a merge of a branch that forked at the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b base-fork-side &&
+	test_commit --no-tag base-fork-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag base-fork-main file b &&
+	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
+	git branch -D base-fork-side &&
+	test_commit --no-tag base-fork-tail file c &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'refuses a merge whose other parent is outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$base.." &&
+
+	git rev-list --count "$base..HEAD" >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'refuses to squash a range with more than one base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b forked-before &&
+	test_commit forked-side fside x &&
+	git checkout "$main" &&
+	test_commit forked-base file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit forked-main file c &&
+	git merge --no-ff -m merge forked-before &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range with two interior merges' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag two-merge-a file a1 &&
+	git checkout -b two-merge-s1 &&
+	test_commit --no-tag two-merge-s1 s1 x &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s1" two-merge-s1 &&
+	test_commit --no-tag two-merge-b file b1 &&
+	git checkout -b two-merge-s2 &&
+	test_commit --no-tag two-merge-s2 s2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s2" two-merge-s2 &&
+	git branch -D two-merge-s1 two-merge-s2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file s1 &&
+	test_path_is_file s2
+'
+
+test_expect_success 'folds a range with a nested merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b nested-outer &&
+	test_commit --no-tag nested-outer outer x &&
+	git checkout -b nested-inner &&
+	test_commit --no-tag nested-inner inner y &&
+	git checkout nested-outer &&
+	git merge --no-ff -m "merge inner" nested-inner &&
+	git checkout "$main" &&
+	test_commit --no-tag nested-main file b1 &&
+	git merge --no-ff -m "merge outer" nested-outer &&
+	git branch -D nested-outer nested-inner &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file outer &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range with an octopus merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag octo-base file a1 &&
+	git checkout -b octo-1 &&
+	test_commit --no-tag octo-1 o1 x &&
+	git checkout "$main" &&
+	git checkout -b octo-2 &&
+	test_commit --no-tag octo-2 o2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-1 octo-2 &&
+	git branch -D octo-1 octo-2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file o1 &&
+	test_path_is_file o2
+'
+
+test_expect_success 'refuses an octopus merge with an arm forked before the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b octo-pre &&
+	test_commit octo-pre-side pside x &&
+	git checkout "$main" &&
+	test_commit octo-pre-main file b1 &&
+	octo_base=$(git rev-parse HEAD) &&
+	git checkout -b octo-within &&
+	test_commit --no-tag octo-within wside y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-pre octo-within &&
+	merged=$(git rev-parse HEAD) &&
+	git branch -D octo-pre octo-within &&
+
+	test_must_fail git history squash "$octo_base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'refuses when a descendant above the range is a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag desc-one file b &&
+	test_commit --no-tag desc-two file c &&
+	git tag desc-tip &&
+	git checkout -b desc-above &&
+	test_commit --no-tag desc-above above x &&
+	git checkout "$main" &&
+	test_commit --no-tag desc-main file d &&
+	git merge --no-ff -m "merge desc-above" desc-above &&
+	git branch -D desc-above &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start..desc-tip 2>err &&
+	test_grep "merge commits is not supported" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'refuses to fold a range a ref points into at a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag refmerge-base file b &&
+	git checkout -b refmerge-side &&
+	test_commit --no-tag refmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag refmerge-main file c &&
+	git merge --no-ff -m "interior merge" refmerge-side &&
+	git branch -D refmerge-side &&
+	git branch at-merge HEAD &&
+	test_commit --no-tag refmerge-tail file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "at-merge" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D at-merge
+'
+
+test_done
-- 
gitgitgadget

[PATCH v7 4/5] sequencer: extract helpers for the squash message markers

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

When "git rebase -i" squashes commits it builds an editor template with a
"This is a combination of N commits." banner, a "This is the 1st/Nth
commit message:" header above each kept message (or a "will be skipped"
header for a dropped one), and a commented-out subject for any fixup!,
squash! or amend! commit. The banner, the headers and the
subject-commenting all live in static helpers in sequencer.c wired to the
rebase state, so no other command can present a squash the same way.

Pull the three pieces out into add_squash_combination_header(),
add_squash_message_header() (which takes a flag for the "will be skipped"
variant) and squash_subject_comment_len(), and use them from
update_squash_messages() and append_squash_message(). A later change
reuses them to give "git history squash --reedit-message" the same
template.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 sequencer.c | 64 ++++++++++++++++++++++++++++++++---------------------
 sequencer.h | 23 +++++++++++++++++++
 2 files changed, 62 insertions(+), 25 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 57855b0066..f4893e8f40 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1892,6 +1892,32 @@ static const char skip_first_commit_msg_str[] = N_("The 1st commit message will
 static const char skip_nth_commit_msg_fmt[] = N_("The commit message #%d will be skipped:");
 static const char combined_commit_msg_fmt[] = N_("This is a combination of %d commits.");
 
+void add_squash_combination_header(struct strbuf *buf, int n)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	strbuf_addf(buf, _(combined_commit_msg_fmt), n);
+}
+
+void add_squash_message_header(struct strbuf *buf, int n, int skip)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	if (n == 1)
+		strbuf_addstr(buf, skip ? _(skip_first_commit_msg_str) :
+				   _(first_commit_msg_str));
+	else
+		strbuf_addf(buf, skip ? _(skip_nth_commit_msg_fmt) :
+			    _(nth_commit_msg_fmt), n);
+}
+
+size_t squash_subject_comment_len(const char *body, int squashing)
+{
+	if (starts_with(body, "amend!") ||
+	    (squashing && (starts_with(body, "squash!") ||
+			   starts_with(body, "fixup!"))))
+		return commit_subject_length(body);
+	return 0;
+}
+
 static int is_fixup_flag(enum todo_command command, unsigned flag)
 {
 	return command == TODO_FIXUP && ((flag & TODO_REPLACE_FIXUP_MSG) ||
@@ -2005,20 +2031,13 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 {
 	struct replay_ctx *ctx = opts->ctx;
 	const char *fixup_msg;
-	size_t commented_len = 0, fixup_off;
-	/*
-	 * amend is non-interactive and not normally used with fixup!
-	 * or squash! commits, so only comment out those subjects when
-	 * squashing commit messages.
-	 */
-	if (starts_with(body, "amend!") ||
-	    ((command == TODO_SQUASH || seen_squash(ctx)) &&
-	     (starts_with(body, "squash!") || starts_with(body, "fixup!"))))
-		commented_len = commit_subject_length(body);
+	size_t commented_len, fixup_off;
+
+	commented_len = squash_subject_comment_len(body,
+				command == TODO_SQUASH || seen_squash(ctx));
 
-	strbuf_addf(buf, "\n%s ", comment_line_str);
-	strbuf_addf(buf, _(nth_commit_msg_fmt),
-		    ++ctx->current_fixup_count + 1);
+	strbuf_addch(buf, '\n');
+	add_squash_message_header(buf, ++ctx->current_fixup_count + 1, 0);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len, comment_line_str);
 	/* buf->buf may be reallocated so store an offset into the buffer */
@@ -2083,9 +2102,8 @@ static int update_squash_messages(struct repository *r,
 		eol = !starts_with(buf.buf, comment_line_str) ?
 			buf.buf : strchrnul(buf.buf, '\n');
 
-		strbuf_addf(&header, "%s ", comment_line_str);
-		strbuf_addf(&header, _(combined_commit_msg_fmt),
-			    ctx->current_fixup_count + 2);
+		add_squash_combination_header(&header,
+					      ctx->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);
 		if (is_fixup_flag(command, flag) && !seen_squash(ctx))
@@ -2109,12 +2127,9 @@ static int update_squash_messages(struct repository *r,
 			repo_unuse_commit_buffer(r, head_commit, head_message);
 			return error(_("cannot write '%s'"), rebase_path_fixup_msg());
 		}
-		strbuf_addf(&buf, "%s ", comment_line_str);
-		strbuf_addf(&buf, _(combined_commit_msg_fmt), 2);
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addstr(&buf, is_fixup_flag(command, flag) ?
-			      _(skip_first_commit_msg_str) :
-			      _(first_commit_msg_str));
+		add_squash_combination_header(&buf, 2);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, 1, is_fixup_flag(command, flag));
 		strbuf_addstr(&buf, "\n\n");
 		if (is_fixup_flag(command, flag))
 			strbuf_add_commented_lines(&buf, body, strlen(body),
@@ -2133,9 +2148,8 @@ static int update_squash_messages(struct repository *r,
 	if (command == TODO_SQUASH || is_fixup_flag(command, flag)) {
 		res = append_squash_message(&buf, body, command, opts, flag);
 	} else if (command == TODO_FIXUP) {
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),
-			    ++ctx->current_fixup_count + 1);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, ++ctx->current_fixup_count + 1, 1);
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body),
 					   comment_line_str);
diff --git a/sequencer.h b/sequencer.h
index 3164bd437d..feed0e9de3 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -208,6 +208,29 @@ int todo_list_rearrange_squash(struct todo_list *todo_list);
  */
 void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
 
+/*
+ * Append the "This is a combination of N commits." banner that "git rebase
+ * -i" writes at the top of a squashed commit's message, commented out with
+ * the comment character.
+ */
+void add_squash_combination_header(struct strbuf *buf, int n);
+
+/*
+ * Append the header (1-based N) that "git rebase -i" writes above each message
+ * when squashing, commented out with the comment character. With SKIP it reads
+ * "The ... commit message will be skipped" for a message that is dropped (a
+ * fixup), otherwise "This is the ... commit message".
+ */
+void add_squash_message_header(struct strbuf *buf, int n, int skip);
+
+/*
+ * Return the length of the leading subject of BODY when it should be commented
+ * out in a squash message, or 0 otherwise. An "amend!" subject always
+ * qualifies; "squash!" and "fixup!" subjects only when SQUASHING, since a
+ * plain fixup chain keeps them.
+ */
+size_t squash_subject_comment_len(const char *body, int squashing);
+
 void append_conflicts_hint(struct index_state *istate,
 		struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
 enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,
-- 
gitgitgadget

[PATCH v7 5/5] history: re-edit a squash with every message

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

By default "git history squash" reuses the oldest commit's message.
When --reedit-message is given it only reopened that one message, so the
messages of the folded-in commits were lost.

Gather the messages of every commit in the range, oldest first, and build
the same editor template that "git rebase -i" shows for a squash, using
add_squash_combination_header(), add_squash_message_header() and
squash_subject_comment_len(). Only the message text differs, the changes
are always folded in. Following autosquash, a fixup!'s message is
commented out in full under a "will be skipped" header, while a squash! or
amend! keeps its body with only the marker subject commented.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  12 +++-
 builtin/history.c              |  73 ++++++++++++++++++++-
 t/t3455-history-squash.sh      | 115 +++++++++++++++++++++++++++++++++
 3 files changed, 196 insertions(+), 4 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 783ddf4a51..f51332e731 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -117,15 +117,21 @@ like the arguments to linkgit:git-rev-list[1], so several arguments may be
 given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
 already on `topic`.
 +
-The oldest commit's message and authorship are preserved by default,
-unless you specify `--reedit-message`. A merge commit inside the range is
+The oldest commit's message and authorship are preserved by default. With
+`--reedit-message`, an editor opens pre-filled with the messages of all the
+folded commits so you can combine them. A merge commit inside the range is
 folded like any other, but the range must have a single base, so a range
 that reaches more than one entry point (for example a side branch that
 forked before the range and was later merged into it) is rejected.
 +
 Because the oldest commit's message is reused, the range may not begin
 with a `fixup!`, `squash!`, or `amend!` commit, whose target is
-necessarily outside the range.
+necessarily outside the range. The changes from every commit in the range
+are always folded in. Only the message text differs. With
+`--reedit-message` the template mirrors `git rebase -i`: the message of a
+`fixup!` elsewhere in the range is commented out in full, while a
+`squash!` or `amend!` keeps its message body with only the marker subject
+commented, so you can fold the remark into the result.
 +
 A branch or tag that points at a commit inside the range would be left
 dangling once those commits are folded away, so with the default
diff --git a/builtin/history.c b/builtin/history.c
index 63911a493d..8999ba9533 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1114,6 +1114,68 @@ static int find_interior_ref(const struct reference *ref, void *cb_data)
 	return 0;
 }
 
+static int build_squash_message(struct repository *repo,
+				struct commit *base,
+				struct commit *tip,
+				struct strbuf *out)
+{
+	struct commit_list *commits = NULL, **tail = &commits, *c;
+	struct rev_info revs;
+	struct commit *commit;
+	struct strvec args = STRVEC_INIT;
+	int n = 0, total, ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs)))
+		tail = &commit_list_insert(commit, tail)->next;
+	total = commit_list_count(commits);
+
+	for (c = commits; c; c = c->next) {
+		const char *message, *body;
+		size_t commented_len;
+		int skip;
+
+		message = repo_logmsg_reencode(repo, c->item, NULL, NULL);
+		find_commit_subject(message, &body);
+
+		skip = starts_with(body, "fixup! ");
+		commented_len = skip ? strlen(body) :
+			squash_subject_comment_len(body, 1);
+
+		if (!n)
+			add_squash_combination_header(out, total);
+		strbuf_addch(out, '\n');
+		add_squash_message_header(out, ++n, skip);
+		strbuf_addstr(out, "\n\n");
+		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
+		strbuf_addstr(out, body + commented_len);
+		strbuf_complete_line(out);
+
+		repo_unuse_commit_buffer(repo, c->item, message);
+	}
+
+	ret = 0;
+
+out:
+	commit_list_free(commits);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1138,6 +1200,7 @@ static int cmd_history_squash(int argc,
 		OPT_END(),
 	};
 	struct strbuf reflog_msg = STRBUF_INIT;
+	struct strbuf message = STRBUF_INIT;
 	struct oidset interior = OIDSET_INIT;
 	struct commit *base, *oldest, *tip, *rewritten;
 	const struct object_id *base_tree_oid, *tip_tree_oid;
@@ -1181,6 +1244,12 @@ static int cmd_history_squash(int argc,
 		}
 	}
 
+	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
+		ret = build_squash_message(repo, base, tip, &message);
+		if (ret < 0)
+			goto out;
+	}
+
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
 		goto out;
@@ -1189,7 +1258,8 @@ static int cmd_history_squash(int argc,
 	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
 	commit_list_append(base, &parents);
 
-	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
+	ret = commit_tree_ext(repo, "squash", oldest,
+			      message.len ? message.buf : NULL, parents,
 			      base_tree_oid, tip_tree_oid, &rewritten, flags);
 	if (ret < 0) {
 		ret = error(_("failed writing squashed commit"));
@@ -1210,6 +1280,7 @@ static int cmd_history_squash(int argc,
 
 out:
 	strbuf_release(&reflog_msg);
+	strbuf_release(&message);
 	oidset_clear(&interior);
 	commit_list_free(parents);
 	release_revisions(&revs);
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index 6598649971..1985c83fbb 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -186,6 +186,121 @@ test_expect_success 'preserves authorship of the oldest commit' '
 	test_cmp expect actual
 '
 
+test_expect_success '--reedit-message offers every folded-in message' '
+	git reset --hard start &&
+	echo b >file &&
+	git add file &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# This is the 1st commit message:
+
+	re-one subject
+
+	re-one body line
+
+	# This is the commit message #2:
+
+	re-two
+
+	# This is the commit message #3:
+
+	re-three
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	echo combined >expect &&
+	git log --format="%s" -1 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--reedit-message handles fixup!, squash! and amend! like rebase' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	printf "fixup! mark-base\n\nfixup body\n" >msg &&
+	echo c >file &&
+	git add file &&
+	git commit -qF msg &&
+	printf "squash! mark-base\n\nsquash remark\n" >msg &&
+	echo d >file &&
+	git add file &&
+	git commit -qF msg &&
+	printf "amend! mark-base\n\namended message\n" >msg &&
+	echo e >file &&
+	git add file &&
+	git commit -qF msg &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	mark-base
+
+	# The commit message #2 will be skipped:
+
+	# fixup! mark-base
+	#
+	# fixup body
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# This is the commit message #4:
+
+	# amend! mark-base
+
+	amended message
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	git log -1 --format="%B" >final &&
+	test_grep ! "fixup body" final &&
+	test_grep "squash remark" final &&
+	test_grep "amended message" final
+'
+
+test_expect_success '--reedit-message aborts on an empty message' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	test_must_fail git history squash --reedit-message start.. &&
+
+	test_cmp_rev "$head_before" HEAD
+'
+
 test_expect_success '--update-refs=head only moves HEAD' '
 	git reset --hard three &&
 	git branch -f other HEAD &&
-- 
gitgitgadget

Re: [PATCH v7 0/5] history: add squash subcommand to fold a range

[Phillip Wood]

Hi Harald

On 06/07/2026 09:50, Harald Nordgren via GitGitGadget wrote:
> Adds git history squash <revision-range> to fold a range of commits.
> 
> Changes in v7:
> 
>   * --reedit-message

There was some discussion [1] about making that the default and renaming 
it - was that overlooked? If not it would be helpful to comment on those 
discussions to explain why you don't think it is a good idea.

>     now builds the same editor template git rebase -i shows
>     for a squash (a combination of N commits banner with each folded message
>     under its own header) and follows autosquash for markers: a fixup!
>     message falls out (commented under a will be skipped header), while a
>     squash! or amend! keeps its body with only the marker subject commented
>     so its remark can be reworded in. Only the message text is affected,
>     every commit's changes are always folded in.

Rebase re-orders commits so that fixups immediately follow their target 
- do you do that here? I think that is very relevant because here we may 
be dealing with several different commits each being targeted by a set 
of fixups and presenting them mixed together will be confusing. When 
rebase sees an "amend!" commit it comments out the message that is being 
replaced - it is not clear from this description whether that happens here.

As I've said before I think we would be better off with a summary of the 
commits that are being squashed and a more compact template message that 
only contains the messages we want to keep [2]. What are the advantages 
of having lots of commented lines (or redundant messages if you don't 
comment out the original when there is an amend! commit) in the middle 
of the template message?

>   * Reuse git rebase -i's squash-message code: a preparatory sequencer:
>     commit extracts the banner, header and marker-comment helpers so both
>     rebase and git history squash build the identical template from one
>     source.
>   * Refuse a range whose oldest commit is a fixup!, squash! or amend!, since
>     the marker's target cannot be inside the range.

I think it should allow squashing a bunch of fixups together though. I 
thought there was a plan [3] to refuse to squash a fixup unless the 
range included its target.

The range-diff does not show any input sanitization - what happens when 
the user passes "--reverse" for example? As I said in [4] we should copy 
what "git replay" does to sanity check the rev-list options, otherwise 
we've got no idea whether the parent of the first commit returned by 
get_revision() is the commit we want to use as the parent of the 
squashed commit.

Thanks

Phillip

[1] 
https://lore.kernel.org/git/3c35bd17-e884-432d-a400-36a89964ed89@gmail.com/
[2] 
https://lore.kernel.org/git/4b505228-4846-4a48-9255-e249f4e70a1f@gmail.com
[3] 
https://lore.kernel.org/git/CAHwyqnWQmObWr3N81_EU6F13iyKp3FfY8KSNFfoAjS4r_0qJrQ@mail.gmail.com/
[4] 
https://lore.kernel.org/git/f3fe7ff2-3ce9-4e90-95e7-8c620de5628a@gmail.com/

>   * Reorder the squash usage so dashed options come before <revision-range>,
>     and spell out HEAD instead of @ in the documentation and examples.
>   * Expand the squash commit message and documentation with this overview,
>     and scope the merge limitation so it no longer contradicts squash folding
>     a single-base interior merge.
> 
> Changes in v6:
> 
>   * git history squash now accepts multiple revision arguments, read like the
>     arguments to git-rev-list, so a compound range such as @~3.. ^topic
>     works.
>   * The base to reparent onto is now the oldest in-range commit's parent; a
>     boundary other than that base means the range has more than one base and
>     is rejected. This also fixes the earlier overly-restrictive handling of
>     merges and side branches.
>   * A single-commit range (e.g. @^!) is rejected with "nothing to squash"
>     (this also covers the @^!-style example that previously succeeded
>     silently).
>   * Commit messages reworded: the squash commit now gives an overview of
>     fixup!/squash!/amend! handling, rewording, merge-parent and ref behavior.
> 
> Changes in v5:
> 
>   * The range walk now uses --ancestry-path, so only commits descended from
>     the base are folded; a single revision such as HEAD or HEAD~1 is now
>     rejected as "not a <base>..<tip> range" rather than treated as a squash
>     down to the root.
>   * This adopts the --ancestry-path suggestion; the multi-base rejection is
>     unchanged, so a side branch that forked before the base and merged in is
>     still refused.
>   * Added tests covering more merge topologies: two interior merges, a nested
>     merge, an octopus merge, an octopus arm forked before the base, a merge
>     among the descendants replayed above the range, and a ref pointing at an
>     interior merge commit.
> 
> Changes in v4:
> 
>   * git history squash now detects when another ref points at a commit inside
>     the range being folded and refuses, with an advice.historyUpdateRefs hint
>     to use --update-refs=head.
>   * A merge inside the range is folded fine as long as the range has a single
>     base; a range with merge commit at the tip or base also folds correctly.
>     Only a range with more than one base is rejected.
> 
> Changes in v3:
> 
>   * Moved the feature out of git rebase and into a new git history squash
>     <revision-range> subcommand, per the list discussion. git rebase --squash
>     is dropped.
>   * Takes an arbitrary range (git history squash @~3.., git history squash
>     @~5..@~2), folding it into the oldest commit and replaying any
>     descendants on top.
>   * Implemented as a single tree operation rather than picking each commit,
>     so there are no repeated conflict stops (addresses Phillip's efficiency
>     point).
>   * A merge inside the range is folded fine, only a range with more than one
>     base is rejected.
>   * --reedit-message seeds the editor with every folded-in message, not just
>     the oldest.
> 
> Harald Nordgren (5):
>    history: extract helper for a commit's parent tree
>    history: give commit_tree_ext a message template
>    history: add squash subcommand to fold a range
>    sequencer: extract helpers for the squash message markers
>    history: re-edit a squash with every message
> 
>   Documentation/config/advice.adoc |   4 +
>   Documentation/git-history.adoc   |  49 ++-
>   advice.c                         |   1 +
>   advice.h                         |   1 +
>   builtin/history.c                | 390 +++++++++++++++++--
>   sequencer.c                      |  64 ++--
>   sequencer.h                      |  23 ++
>   t/meson.build                    |   1 +
>   t/t3455-history-squash.sh        | 632 +++++++++++++++++++++++++++++++
>   9 files changed, 1099 insertions(+), 66 deletions(-)
>   create mode 100755 t/t3455-history-squash.sh
> 
> 
> base-commit: e9019fcafe0040228b8631c30f97ae1adb61bcdc
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v7
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v7
> Pull-Request: https://github.com/git/git/pull/2337
> 
> Range-diff vs v6:
> 
>   1:  fea6b79e60 = 1:  56ed8fadbb history: extract helper for a commit's parent tree
>   2:  e2674e0bc4 = 2:  212e9c228f history: give commit_tree_ext a message template
>   3:  811e393ab4 ! 3:  cf3346a1cd history: add squash subcommand to fold a range
>       @@ Commit message
>            Add "git history squash <revision-range>" to do this directly. It folds
>            every commit in the range into the oldest one, keeping that commit's
>            message and authorship and taking the tree of the newest commit, then
>       -    replays the commits above the range on top. fixup!, squash! and amend!
>       -    commits are folded like any other and are not interpreted, so the
>       -    squashed message comes from the oldest commit, or from an editor with
>       -    --reedit-message.
>       +    replays the commits above the range on top. The squashed message comes
>       +    from the oldest commit, or from an editor with --reedit-message. As that
>       +    message is reused, a range whose oldest commit is a fixup!, squash! or
>       +    amend! is refused, since the marker's target cannot be in the range.
>        
>            The range is read like the arguments to "git rev-list", so several
>       -    arguments such as "@~3.. ^topic" are allowed. A merge inside the range
>       -    is folded when its other parent is reachable from the base, otherwise
>       -    the range has more than one base and is rejected. By default the command
>       -    also refuses when a ref points at a commit that the fold would discard.
>       -    Use --update-refs=head to rewrite only the current branch instead.
>       +    arguments such as "HEAD~3..HEAD ^topic" are allowed. A merge inside the
>       +    range is folded when its other parent is reachable from the base,
>       +    otherwise the range has more than one base and is rejected. By default
>       +    the command also refuses when a ref points at a commit that the fold
>       +    would discard. Use --update-refs=head to rewrite only the current branch
>       +    instead.
>        
>            Inspired-by: Sergey Chernov <serega.morph@gmail.com>
>            Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
>       @@ Documentation/git-history.adoc: SYNOPSIS
>         git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
>         git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
>         git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
>       -+git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]
>       ++git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>
>         
>         DESCRIPTION
>         -----------
>       +@@ Documentation/git-history.adoc: at once.
>       + LIMITATIONS
>       + -----------
>       +
>       +-This command does not (yet) work with histories that contain merges. You
>       +-should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
>       ++This command does not (yet) replay merge commits onto the rewritten
>       ++history: if a commit that would be replayed is a merge, the operation is
>       ++rejected, and you should use linkgit:git-rebase[1] with the
>       ++`--rebase-merges` flag instead. The `squash` subcommand can still fold a
>       ++merge that lies inside the range, as long as the range has a single base.
>       +
>       + Furthermore, the command does not support operations that can result in merge
>       + conflicts. This limitation is by design as history rewrites are not intended to
>        @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
>         It is invalid to select either all or no hunks, as that would lead to
>         one of the commits becoming empty.
>       @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
>        ++
>        +The range is given in the usual `<base>..<tip>` form, where _<base>_ is
>        +the commit just below the oldest commit to squash. For example, `git
>       -+history squash @~3..` folds the three most recent commits into one, and
>       -+`git history squash @~5..@~2` squashes an interior range while leaving
>       -+the two newest commits in place. _<revision-range>_ is read like the
>       -+arguments to linkgit:git-rev-list[1], so several arguments may be given,
>       -+for example `@~3.. ^topic` to additionally exclude what is already on
>       -+`topic`.
>       ++history squash HEAD~3..HEAD` folds the three most recent commits into
>       ++one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
>       ++while leaving the two newest commits in place. _<revision-range>_ is read
>       ++like the arguments to linkgit:git-rev-list[1], so several arguments may be
>       ++given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
>       ++already on `topic`.
>        ++
>        +The oldest commit's message and authorship are preserved by default,
>        +unless you specify `--reedit-message`. A merge commit inside the range is
>       @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
>        +that reaches more than one entry point (for example a side branch that
>        +forked before the range and was later merged into it) is rejected.
>        ++
>       -+The folded commits disappear from the history, so with the default
>       -+`--update-refs=branches` the command refuses when another ref points at
>       -+one of them. Rerun with `--update-refs=head` to rewrite only the current
>       -+branch and leave those refs pointing at the old commits.
>       ++Because the oldest commit's message is reused, the range may not begin
>       ++with a `fixup!`, `squash!`, or `amend!` commit, whose target is
>       ++necessarily outside the range.
>       +++
>       ++A branch or tag that points at a commit inside the range would be left
>       ++dangling once those commits are folded away, so with the default
>       ++`--update-refs=branches` the command refuses. Rerun with
>       ++`--update-refs=head` to rewrite only the current branch and leave such
>       ++refs pointing at the old commits.
>        +
>         OPTIONS
>         -------
>         
>       +@@ Documentation/git-history.adoc: OPTIONS
>       + 	ref updates is generally safe.
>       +
>       + `--reedit-message`::
>       +-	Open an editor to modify the target commit's message.
>       ++	Open an editor to modify the rewritten commit's message. For `squash`
>       ++	the editor is pre-filled with the messages of all the folded commits.
>       +
>       + `--empty=(drop|keep|abort)`::
>       + 	Control what happens when a commit becomes empty as a result of the
>        
>         ## advice.c ##
>        @@ advice.c: static struct {
>       @@ builtin/history.c
>         #define GIT_HISTORY_SPLIT_USAGE \
>         	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
>        +#define GIT_HISTORY_SQUASH_USAGE \
>       -+	N_("git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]")
>       ++	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>")
>         
>         static void change_data_free(void *util, const char *str UNUSED)
>         {
>       @@ builtin/history.c: out:
>        +	return ret;
>        +}
>        +
>       ++static int reject_fixupish_oldest(struct repository *repo,
>       ++				  struct commit *oldest)
>       ++{
>       ++	const char *message, *subject;
>       ++	int ret = 0;
>       ++
>       ++	message = repo_logmsg_reencode(repo, oldest, NULL, NULL);
>       ++	find_commit_subject(message, &subject);
>       ++	if (starts_with(subject, "fixup! ") ||
>       ++	    starts_with(subject, "squash! ") ||
>       ++	    starts_with(subject, "amend! "))
>       ++		ret = error(_("the range begins with a fixup!, squash! or amend! "
>       ++			      "commit whose target is not in the range"));
>       ++	repo_unuse_commit_buffer(repo, oldest, message);
>       ++	return ret;
>       ++}
>       ++
>        +struct interior_ref_cb {
>        +	const struct oidset *interior;
>        +	const char *name;
>       @@ builtin/history.c: out:
>        +	if (ret < 0)
>        +		goto out;
>        +
>       ++	ret = reject_fixupish_oldest(repo, oldest);
>       ++	if (ret < 0)
>       ++		goto out;
>       ++
>        +	if (action == REF_ACTION_BRANCHES) {
>        +		struct interior_ref_cb cb = { .interior = &interior };
>        +
>       @@ t/t3455-history-squash.sh (new)
>        +
>        +test_expect_success 'squashes a range into a single commit without changing the tree' '
>        +	git reset --hard three &&
>       ++	head_before=$(git rev-parse HEAD) &&
>        +	tip_tree=$(git rev-parse HEAD^{tree}) &&
>        +
>       ++	git history squash --dry-run start.. >out &&
>       ++	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
>       ++	test_cmp_rev "$head_before" HEAD &&
>       ++
>        +	git history squash start.. &&
>        +
>       ++	test "$predicted" = "$(git rev-parse HEAD)" &&
>        +	git rev-list --count start..HEAD >count &&
>        +	echo 1 >expect &&
>        +	test_cmp expect count &&
>       @@ t/t3455-history-squash.sh (new)
>        +	test_cmp expect actual
>        +'
>        +
>       -+test_expect_success 'keeps the oldest message even if it is a fixup!' '
>       ++test_expect_success 'refuses a range whose oldest commit is a fixup!' '
>        +	git reset --hard start &&
>        +	test_commit --no-tag "fixup! something" file b &&
>       -+	test_commit tail file c &&
>       ++	test_commit --no-tag tail file c &&
>       ++	head_before=$(git rev-parse HEAD) &&
>       ++
>       ++	test_must_fail git history squash start.. 2>err &&
>       ++	test_grep "target is not in the range" err &&
>       ++	test_cmp_rev "$head_before" HEAD
>       ++'
>       ++
>       ++test_expect_success 'does not interpret squash! or amend! markers' '
>       ++	git reset --hard start &&
>       ++	test_commit --no-tag marker-oldest file b &&
>       ++	git commit --allow-empty -m "squash! marker-oldest" &&
>       ++	git commit --allow-empty -m "amend! marker-oldest" &&
>       ++	test_commit --no-tag marker-newest file c &&
>        +
>        +	git history squash start.. &&
>        +
>       ++	git rev-list --count start..HEAD >count &&
>       ++	echo 1 >expect &&
>       ++	test_cmp expect count &&
>        +	git log --format="%s" -1 >actual &&
>       -+	echo "fixup! something" >expect &&
>       ++	echo marker-oldest >expect &&
>        +	test_cmp expect actual
>        +'
>        +
>       @@ t/t3455-history-squash.sh (new)
>        +	test_cmp expect actual
>        +'
>        +
>       -+test_expect_success '--dry-run predicts the rewrite without performing it' '
>       -+	git reset --hard three &&
>       -+	head_before=$(git rev-parse HEAD) &&
>       -+	tip_tree=$(git rev-parse HEAD^{tree}) &&
>       -+
>       -+	git history squash --dry-run start.. >out &&
>       -+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
>       -+	test_cmp_rev "$head_before" HEAD &&
>       -+
>       -+	git history squash start.. &&
>       -+	test "$predicted" = "$(git rev-parse HEAD)" &&
>       -+	git rev-list --count start..HEAD >count &&
>       -+	echo 1 >expect &&
>       -+	test_cmp expect count &&
>       -+	test_cmp_rev start HEAD^ &&
>       -+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
>       -+'
>       -+
>        +test_expect_success '--update-refs=head only moves HEAD' '
>        +	git reset --hard three &&
>        +	git branch -f other HEAD &&
>   -:  ---------- > 4:  001356db93 sequencer: extract helpers for the squash message markers
>   4:  4edf012b77 ! 5:  615fe4dd3f history: re-edit a squash with every message
>       @@ Commit message
>            When --reedit-message is given it only reopened that one message, so the
>            messages of the folded-in commits were lost.
>        
>       -    Gather the messages of every commit in the range, oldest first, and use
>       -    them as the editor template when re-editing, mirroring how "git rebase
>       -    -i" presents a squash.
>       +    Gather the messages of every commit in the range, oldest first, and build
>       +    the same editor template that "git rebase -i" shows for a squash, using
>       +    add_squash_combination_header(), add_squash_message_header() and
>       +    squash_subject_comment_len(). Only the message text differs, the changes
>       +    are always folded in. Following autosquash, a fixup!'s message is
>       +    commented out in full under a "will be skipped" header, while a squash! or
>       +    amend! keeps its body with only the marker subject commented.
>        
>            Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
>        
>         ## Documentation/git-history.adoc ##
>       -@@ Documentation/git-history.adoc: arguments to linkgit:git-rev-list[1], so several arguments may be given,
>       - for example `@~3.. ^topic` to additionally exclude what is already on
>       - `topic`.
>       +@@ Documentation/git-history.adoc: like the arguments to linkgit:git-rev-list[1], so several arguments may be
>       + given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
>       + already on `topic`.
>         +
>        -The oldest commit's message and authorship are preserved by default,
>        -unless you specify `--reedit-message`. A merge commit inside the range is
>       @@ Documentation/git-history.adoc: arguments to linkgit:git-rev-list[1], so several
>         folded like any other, but the range must have a single base, so a range
>         that reaches more than one entry point (for example a side branch that
>         forked before the range and was later merged into it) is rejected.
>       + +
>       + Because the oldest commit's message is reused, the range may not begin
>       + with a `fixup!`, `squash!`, or `amend!` commit, whose target is
>       +-necessarily outside the range.
>       ++necessarily outside the range. The changes from every commit in the range
>       ++are always folded in. Only the message text differs. With
>       ++`--reedit-message` the template mirrors `git rebase -i`: the message of a
>       ++`fixup!` elsewhere in the range is commented out in full, while a
>       ++`squash!` or `amend!` keeps its message body with only the marker subject
>       ++commented, so you can fold the remark into the result.
>       + +
>       + A branch or tag that points at a commit inside the range would be left
>       + dangling once those commits are folded away, so with the default
>        
>         ## builtin/history.c ##
>        @@ builtin/history.c: static int find_interior_ref(const struct reference *ref, void *cb_data)
>       @@ builtin/history.c: static int find_interior_ref(const struct reference *ref, voi
>        +				struct commit *tip,
>        +				struct strbuf *out)
>        +{
>       ++	struct commit_list *commits = NULL, **tail = &commits, *c;
>        +	struct rev_info revs;
>        +	struct commit *commit;
>        +	struct strvec args = STRVEC_INIT;
>       -+	int n = 0, ret;
>       ++	int n = 0, total, ret;
>        +
>        +	repo_init_revisions(repo, &revs, NULL);
>        +	strvec_push(&args, "ignored");
>       @@ builtin/history.c: static int find_interior_ref(const struct reference *ref, voi
>        +		goto out;
>        +	}
>        +
>       -+	while ((commit = get_revision(&revs))) {
>       ++	while ((commit = get_revision(&revs)))
>       ++		tail = &commit_list_insert(commit, tail)->next;
>       ++	total = commit_list_count(commits);
>       ++
>       ++	for (c = commits; c; c = c->next) {
>        +		const char *message, *body;
>       -+		struct strbuf one = STRBUF_INIT;
>       ++		size_t commented_len;
>       ++		int skip;
>        +
>       -+		message = repo_logmsg_reencode(repo, commit, NULL, NULL);
>       ++		message = repo_logmsg_reencode(repo, c->item, NULL, NULL);
>        +		find_commit_subject(message, &body);
>       -+		strbuf_addstr(&one, body);
>       -+		strbuf_trim_trailing_newline(&one);
>        +
>       -+		if (n++)
>       -+			strbuf_addch(out, '\n');
>       -+		strbuf_addbuf(out, &one);
>       ++		skip = starts_with(body, "fixup! ");
>       ++		commented_len = skip ? strlen(body) :
>       ++			squash_subject_comment_len(body, 1);
>       ++
>       ++		if (!n)
>       ++			add_squash_combination_header(out, total);
>        +		strbuf_addch(out, '\n');
>       ++		add_squash_message_header(out, ++n, skip);
>       ++		strbuf_addstr(out, "\n\n");
>       ++		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
>       ++		strbuf_addstr(out, body + commented_len);
>       ++		strbuf_complete_line(out);
>        +
>       -+		strbuf_release(&one);
>       -+		repo_unuse_commit_buffer(repo, commit, message);
>       ++		repo_unuse_commit_buffer(repo, c->item, message);
>        +	}
>        +
>        +	ret = 0;
>        +
>        +out:
>       ++	commit_list_free(commits);
>        +	reset_revision_walk();
>        +	release_revisions(&revs);
>        +	strvec_clear(&args);
>       @@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the olde
>        +	test_commit re-three file d &&
>        +
>        +	write_script editor <<-\EOF &&
>       -+	cp "$1" buffer &&
>       ++	cat "$1" >edited &&
>        +	echo combined >"$1"
>        +	EOF
>        +	test_set_editor "$(pwd)/editor" &&
>        +	git history squash --reedit-message start.. &&
>        +
>       -+	test_grep "re-one subject" buffer &&
>       -+	test_grep "re-one body line" buffer &&
>       -+	test_grep re-two buffer &&
>       -+	test_grep re-three buffer &&
>       -+	git log --format="%s" -1 >actual &&
>       ++	cat >expect <<-EOF &&
>       ++	# This is a combination of 3 commits.
>       ++	# This is the 1st commit message:
>       ++
>       ++	re-one subject
>       ++
>       ++	re-one body line
>       ++
>       ++	# This is the commit message #2:
>       ++
>       ++	re-two
>       ++
>       ++	# This is the commit message #3:
>       ++
>       ++	re-three
>       ++
>       ++	# Please enter the commit message for the squash changes. Lines starting
>       ++	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
>       ++	# Changes to be committed:
>       ++	#	modified:   file
>       ++	#
>       ++	EOF
>       ++	test_cmp expect edited &&
>        +	echo combined >expect &&
>       ++	git log --format="%s" -1 >actual &&
>        +	test_cmp expect actual
>        +'
>        +
>       ++test_expect_success '--reedit-message handles fixup!, squash! and amend! like rebase' '
>       ++	git reset --hard start &&
>       ++	test_commit --no-tag mark-base file b &&
>       ++	printf "fixup! mark-base\n\nfixup body\n" >msg &&
>       ++	echo c >file &&
>       ++	git add file &&
>       ++	git commit -qF msg &&
>       ++	printf "squash! mark-base\n\nsquash remark\n" >msg &&
>       ++	echo d >file &&
>       ++	git add file &&
>       ++	git commit -qF msg &&
>       ++	printf "amend! mark-base\n\namended message\n" >msg &&
>       ++	echo e >file &&
>       ++	git add file &&
>       ++	git commit -qF msg &&
>       ++
>       ++	write_script editor <<-\EOF &&
>       ++	cat "$1" >edited
>       ++	EOF
>       ++	test_set_editor "$(pwd)/editor" &&
>       ++	git history squash --reedit-message start.. &&
>       ++
>       ++	cat >expect <<-EOF &&
>       ++	# This is a combination of 4 commits.
>       ++	# This is the 1st commit message:
>       ++
>       ++	mark-base
>       ++
>       ++	# The commit message #2 will be skipped:
>       ++
>       ++	# fixup! mark-base
>       ++	#
>       ++	# fixup body
>       ++
>       ++	# This is the commit message #3:
>       ++
>       ++	# squash! mark-base
>       ++
>       ++	squash remark
>       ++
>       ++	# This is the commit message #4:
>       ++
>       ++	# amend! mark-base
>       ++
>       ++	amended message
>       ++
>       ++	# Please enter the commit message for the squash changes. Lines starting
>       ++	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
>       ++	# Changes to be committed:
>       ++	#	modified:   file
>       ++	#
>       ++	EOF
>       ++	test_cmp expect edited &&
>       ++	git log -1 --format="%B" >final &&
>       ++	test_grep ! "fixup body" final &&
>       ++	test_grep "squash remark" final &&
>       ++	test_grep "amended message" final
>       ++'
>       ++
>        +test_expect_success '--reedit-message aborts on an empty message' '
>        +	git reset --hard three &&
>        +	head_before=$(git rev-parse HEAD) &&
>       @@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the olde
>        +	test_cmp_rev "$head_before" HEAD
>        +'
>        +
>       - test_expect_success '--dry-run predicts the rewrite without performing it' '
>       + test_expect_success '--update-refs=head only moves HEAD' '
>         	git reset --hard three &&
>       - 	head_before=$(git rev-parse HEAD) &&
>       + 	git branch -f other HEAD &&
> 

Re: [PATCH v7 0/5] history: add squash subcommand to fold a range

[Harald Nordgren]

> There was some discussion [1] about making that the default and renaming
> it - was that overlooked? If not it would be helpful to comment on those
> discussions to explain why you don't think it is a good idea.

Not overlooked, but I side-stepped it because the discussion died
down, and yes I don't agree that it needs to be the default. I could
have mentioned my thinking in the cover letter.

> >     now builds the same editor template git rebase -i shows
> >     for a squash (a combination of N commits banner with each folded message
> >     under its own header) and follows autosquash for markers: a fixup!
> >     message falls out (commented under a will be skipped header), while a
> >     squash! or amend! keeps its body with only the marker subject commented
> >     so its remark can be reworded in. Only the message text is affected,
> >     every commit's changes are always folded in.
>
> Rebase re-orders commits so that fixups immediately follow their target
> - do you do that here? I think that is very relevant because here we may
> be dealing with several different commits each being targeted by a set
> of fixups and presenting them mixed together will be confusing.

No, I'm not doing that now, but I can take a look at that.

> I think it should allow squashing a bunch of fixups together though. I
> thought there was a plan [3] to refuse to squash a fixup unless the
> range included its target.

I attempted this with reject_fixupish_oldest(), assuming only the
first commit needs to be checked as not being a fixup/squash/amend.

But now I realize that maybe we need to check all of the commits, and
also check if the target is in the range or not. It just makes the
logic a lot bigger.

> The range-diff does not show any input sanitization - what happens when
> the user passes "--reverse" for example? As I said in [4] we should copy
> what "git replay" does to sanity check the rev-list options, otherwise
> we've got no idea whether the parent of the first commit returned by
> get_revision() is the commit we want to use as the parent of the
> squashed commit.

Yeah, good point.


Harald

Re: [PATCH v7 0/5] history: add squash subcommand to fold a range

[Harald Nordgren]

> > The range-diff does not show any input sanitization - what happens when
> > the user passes "--reverse" for example? As I said in [4] we should copy
> > what "git replay" does to sanity check the rev-list options, otherwise
> > we've got no idea whether the parent of the first commit returned by
> > get_revision() is the commit we want to use as the parent of the
> > squashed commit.
>
> Yeah, good point.

Well, the code already blocks "--reverse" and other unknown options,
but I can clarify that better in the commit message.


Harald

Re: [PATCH v7 0/5] history: add squash subcommand to fold a range

[Phillip Wood]

Hi Harald

On 07/07/2026 09:55, Harald Nordgren wrote:
>>> The range-diff does not show any input sanitization - what happens when
>>> the user passes "--reverse" for example? As I said in [4] we should copy
>>> what "git replay" does to sanity check the rev-list options, otherwise
>>> we've got no idea whether the parent of the first commit returned by
>>> get_revision() is the commit we want to use as the parent of the
>>> squashed commit.
>>
>> Yeah, good point.
> 
> Well, the code already blocks "--reverse" and other unknown options,
> but I can clarify that better in the commit message.
Well it accepts

	git history squash -- --reverse ...

because after calling parse_options() everything after the "--" is 
passed to setup_revisions(). There was some discussion about accepting 
rev-list options [2] so it would have been helpful to reference that in 
the cover letter. The cover letter should explain both the changes you 
have made and the suggestions that were discussed that have not been 
implemented so readers can get an overview of how this version relates 
to the previous discussion. Without that it is impossible to know if you 
disagree with a suggestion or have just forgotten it.

"git replay" supports arbitrary rev-list options by passing

      PARSE_OPT_KEEP_ARGV0 | PARSE_OPT_KEEP_UNKNOWN_OPT

to parse_options(), then passing the remaining options to 
setup_revisions(). After that it checks the various members of `struct 
rev_info` that it cares about are still set appropriately.

Thanks

Phillip

[1] https://lore.kernel.org/git/xmqqzf0dwalx.fsf@gitster.g

Re: [PATCH v7 0/5] history: add squash subcommand to fold a range

[Phillip Wood]

Hi Harald

On 07/07/2026 08:51, Harald Nordgren wrote:
>> There was some discussion [1] about making that the default and renaming
>> it - was that overlooked? If not it would be helpful to comment on those
>> discussions to explain why you don't think it is a good idea.
> 
> Not overlooked, but I side-stepped it because the discussion died
> down, and yes I don't agree that it needs to be the default. I could
> have mentioned my thinking in the cover letter.
> 
>>>      now builds the same editor template git rebase -i shows
>>>      for a squash (a combination of N commits banner with each folded message
>>>      under its own header) and follows autosquash for markers: a fixup!
>>>      message falls out (commented under a will be skipped header), while a
>>>      squash! or amend! keeps its body with only the marker subject commented
>>>      so its remark can be reworded in. Only the message text is affected,
>>>      every commit's changes are always folded in.
>>
>> Rebase re-orders commits so that fixups immediately follow their target
>> - do you do that here? I think that is very relevant because here we may
>> be dealing with several different commits each being targeted by a set
>> of fixups and presenting them mixed together will be confusing.
> 
> No, I'm not doing that now, but I can take a look at that.

That's great, it is fine to punt things like this which require quite a 
bit of work to implement to a later re-roll but please be clear in the 
cover letter so reviewers know what to expect.

>> I think it should allow squashing a bunch of fixups together though. I
>> thought there was a plan [3] to refuse to squash a fixup unless the
>> range included its target.
> 
> I attempted this with reject_fixupish_oldest(), assuming only the
> first commit needs to be checked as not being a fixup/squash/amend.
> 
> But now I realize that maybe we need to check all of the commits, and
> also check if the target is in the range or not. It just makes the
> logic a lot bigger.

Yes it is a bit more involved. If the first commit is a fixup! then we 
should allow the user to squash other fixups with the same target and 
take the message from the last "amend!" commit if we see one. If there 
are other commits it the range then we should refuse to squash as you do 
here.

If the first target is not a fixup then we should refuse fixup commits 
whose target we have not seen. As well as exact subject matches "git 
rebase" accepts prefix matches and "fixup! $objectid". I think it is 
fine to skip the prefix matches to start with here. The $objectid 
matches shouldn't be too much extra work and I think they are worth 
supporting because if I remember correctly git-gui creates them. Another 
gotcha is that fixuping up a fixup prepends a "fixup!" to the subject 
line so you need to be able to handle things like

	fixup! fixup! the real target
	fixup! amend! the real target
	squash! fixup! the real target

etc. Hopefully looking at the code that handles fixups in the sequencer 
will help

Thanks

Phillip

Re: [PATCH v7 0/5] history: add squash subcommand to fold a range

[Junio C Hamano]

"Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:

> Adds git history squash <revision-range> to fold a range of commits.

What I saw in the range-diff looked all reasonable.

>  3:  811e393ab4 ! 3:  cf3346a1cd history: add squash subcommand to fold a range
>      @@ Commit message
>           Add "git history squash <revision-range>" to do this directly. It folds
>           every commit in the range into the oldest one, keeping that commit's
>           message and authorship and taking the tree of the newest commit, then
>      -    replays the commits above the range on top. fixup!, squash! and amend!
>      -    commits are folded like any other and are not interpreted, so the
>      -    squashed message comes from the oldest commit, or from an editor with
>      -    --reedit-message.
>      +    replays the commits above the range on top. The squashed message comes
>      +    from the oldest commit, or from an editor with --reedit-message. As that
>      +    message is reused, a range whose oldest commit is a fixup!, squash! or
>      +    amend! is refused, since the marker's target cannot be in the range.
> ...
>      -+git history squash <revision-range> [--dry-run] [--update-refs=(branches|head)] [--reedit-message]
>      ++git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>

>      ++static int reject_fixupish_oldest(struct repository *repo,
>      ++				  struct commit *oldest)
>      ++{
>      ++	const char *message, *subject;
>      ++	int ret = 0;
>      ++
>      ++	message = repo_logmsg_reencode(repo, oldest, NULL, NULL);
>      ++	find_commit_subject(message, &subject);
>      ++	if (starts_with(subject, "fixup! ") ||
>      ++	    starts_with(subject, "squash! ") ||
>      ++	    starts_with(subject, "amend! "))
>      ++		ret = error(_("the range begins with a fixup!, squash! or amend! "
>      ++			      "commit whose target is not in the range"));
>      ++	repo_unuse_commit_buffer(repo, oldest, message);
>      ++	return ret;
>      ++}

Nice. I often see myself getting rescued by the corresponding sanity
checks in the sequencer.

Will replace.  Thanks.

[PATCH v8 0/5] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v8:

 * --reedit-message now builds the same editor template as git rebase -i
   --autosquash: fixup!, squash! and amend! commits are grouped under the
   commit they target instead of shown in commit order, and an amend!
   replaces its target's message.
 * A fixup!, squash! or amend! is refused only when its target is outside
   the range, so several fixups for an in-range commit fold together. A
   range that is entirely markers for one below-range target is combined
   into a single commit, keeping the last amend! message.
 * Merges inside the range are folded when the range has a single base, with
   no dedicated opt-in flag, --ancestry-path ensures only commits descended
   from the base are folded, and a range reaching more than one base is
   rejected.
 * Rev-list options are accepted and sanitized the way git replay does,
   forcing the walk order back with a warning, which also fixes git history
   squash -- --reverse slipping past the previous option check.
 * Kept this as an explicit squash subcommand rather than making
   --reedit-message the default or renaming the command.

Changes in v7:

 * --reedit-message now builds the same editor template git rebase -i shows
   for a squash (a combination of N commits banner with each folded message
   under its own header) and follows autosquash for markers: a fixup!
   message falls out (commented under a will be skipped header), while a
   squash! or amend! keeps its body with only the marker subject commented
   so its remark can be reworded in. Only the message text is affected,
   every commit's changes are always folded in.
 * Reuse git rebase -i's squash-message code: a preparatory sequencer:
   commit extracts the banner, header and marker-comment helpers so both
   rebase and git history squash build the identical template from one
   source.
 * Refuse a range whose oldest commit is a fixup!, squash! or amend!, since
   the marker's target cannot be inside the range.
 * Reorder the squash usage so dashed options come before <revision-range>,
   and spell out HEAD instead of @ in the documentation and examples.
 * Expand the squash commit message and documentation with this overview,
   and scope the merge limitation so it no longer contradicts squash folding
   a single-base interior merge.

Changes in v6:

 * git history squash now accepts multiple revision arguments, read like the
   arguments to git-rev-list, so a compound range such as @~3.. ^topic
   works.
 * The base to reparent onto is now the oldest in-range commit's parent; a
   boundary other than that base means the range has more than one base and
   is rejected. This also fixes the earlier overly-restrictive handling of
   merges and side branches.
 * A single-commit range (e.g. @^!) is rejected with "nothing to squash"
   (this also covers the @^!-style example that previously succeeded
   silently).
 * Commit messages reworded: the squash commit now gives an overview of
   fixup!/squash!/amend! handling, rewording, merge-parent and ref behavior.

Changes in v5:

 * The range walk now uses --ancestry-path, so only commits descended from
   the base are folded; a single revision such as HEAD or HEAD~1 is now
   rejected as "not a <base>..<tip> range" rather than treated as a squash
   down to the root.
 * This adopts the --ancestry-path suggestion; the multi-base rejection is
   unchanged, so a side branch that forked before the base and merged in is
   still refused.
 * Added tests covering more merge topologies: two interior merges, a nested
   merge, an octopus merge, an octopus arm forked before the base, a merge
   among the descendants replayed above the range, and a ref pointing at an
   interior merge commit.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (5):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  history: add squash subcommand to fold a range
  sequencer: share the squash message marker helpers and flags
  history: re-edit a squash with every message

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  54 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 522 +++++++++++++++++++--
 sequencer.c                      |  70 +--
 sequencer.h                      |  30 ++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 776 +++++++++++++++++++++++++++++++
 9 files changed, 1387 insertions(+), 72 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: f85a7e662054a7b0d9070e432508831afa214b47
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v8
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v8
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v7:

 1:  56ed8fadbb = 1:  ba77752282 history: extract helper for a commit's parent tree
 2:  212e9c228f = 2:  50f3572887 history: give commit_tree_ext a message template
 3:  cf3346a1cd ! 3:  2d81a40a05 history: add squash subcommand to fold a range
     @@ Commit message
          every commit in the range into the oldest one, keeping that commit's
          message and authorship and taking the tree of the newest commit, then
          replays the commits above the range on top. The squashed message comes
     -    from the oldest commit, or from an editor with --reedit-message. As that
     -    message is reused, a range whose oldest commit is a fixup!, squash! or
     -    amend! is refused, since the marker's target cannot be in the range.
     +    from the oldest commit, or from an editor with --reedit-message. A
     +    fixup!, squash! or amend! commit is refused unless the commit it targets
     +    is also in the range, so the fold does not silently absorb a marker meant
     +    for a commit outside it. The check runs the range through
     +    todo_list_rearrange_squash(), which leaves such a marker as a plain pick.
     +    Markers whose target is in the range fold in as usual. As an exception, a
     +    range made up entirely of markers for one target is combined anyway,
     +    taking its message from the last amend! if there is one, so a batch of
     +    fixups for the same commit can be collapsed.
      
          The range is read like the arguments to "git rev-list", so several
     -    arguments such as "HEAD~3..HEAD ^topic" are allowed. A merge inside the
     -    range is folded when its other parent is reachable from the base,
     -    otherwise the range has more than one base and is rejected. By default
     -    the command also refuses when a ref points at a commit that the fold
     -    would discard. Use --update-refs=head to rewrite only the current branch
     -    instead.
     +    revisions such as "HEAD~3..HEAD ^topic" may be given, and rev-list
     +    options are accepted too. As "git replay" does, the walk options the fold
     +    relies on are forced after setup_revisions() and a warning is printed if
     +    an option changed them, so the first commit returned is the range's
     +    oldest and its parent is the base regardless of what the user passed
     +    (including after a "--"). A merge inside the range is folded when its
     +    other parent is reachable from the base, otherwise the range has more
     +    than one base and is rejected. By default the command also refuses when a
     +    ref points at a commit that the fold would discard. Use --update-refs=head
     +    to rewrite only the current branch instead.
      
          Inspired-by: Sergey Chernov <serega.morph@gmail.com>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      +the commit just below the oldest commit to squash. For example, `git
      +history squash HEAD~3..HEAD` folds the three most recent commits into
      +one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
     -+while leaving the two newest commits in place. _<revision-range>_ is read
     -+like the arguments to linkgit:git-rev-list[1], so several arguments may be
     ++while leaving the two newest commits in place. Several revisions may be
      +given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
     -+already on `topic`.
     ++already on `topic`. Rev-list options may also be given, but any that would
     ++change how the range is walked are overridden with a warning.
      ++
      +The oldest commit's message and authorship are preserved by default,
      +unless you specify `--reedit-message`. A merge commit inside the range is
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      +that reaches more than one entry point (for example a side branch that
      +forked before the range and was later merged into it) is rejected.
      ++
     -+Because the oldest commit's message is reused, the range may not begin
     -+with a `fixup!`, `squash!`, or `amend!` commit, whose target is
     -+necessarily outside the range.
     ++A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
     ++targets is also in the range, so the fold does not silently absorb a
     ++marker meant for a commit outside it. As an exception, a range made up
     ++entirely of markers for one target is combined into a single commit,
     ++keeping the last `amend!` message if there is one.
      ++
      +A branch or tag that points at a commit inside the range would be left
      +dangling once those commits are folded away, so with the default
     @@ builtin/history.c: out:
      +	int ret;
      +
      +	repo_init_revisions(repo, &revs, NULL);
     ++	revs.reverse = 1;
     ++	revs.topo_order = 1;
     ++	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
     ++	revs.simplify_history = 0;
     ++	revs.boundary = 1;
     ++
      +	strvec_push(&args, "ignored");
     -+	strvec_push(&args, "--reverse");
     -+	strvec_push(&args, "--topo-order");
     -+	strvec_push(&args, "--boundary");
      +	strvec_push(&args, "--ancestry-path");
      +	strvec_pushv(&args, argv);
      +	setup_revisions_from_strvec(&args, &revs, NULL);
     @@ builtin/history.c: out:
      +		goto out;
      +	}
      +
     ++	if (revs.reverse != 1 || revs.topo_order != 1 ||
     ++	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
     ++	    revs.simplify_history != 0) {
     ++		warning(_("ignoring rev-list options that would change how the "
     ++			  "range is walked"));
     ++		revs.reverse = 1;
     ++		revs.topo_order = 1;
     ++		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
     ++		revs.simplify_history = 0;
     ++	}
     ++
      +	/*
      +	 * A squash needs a base to reparent onto, so the range has to exclude
      +	 * something, as in "<base>..<tip>". A revision range with no such
     @@ builtin/history.c: out:
      +		goto out;
      +	}
      +
     ++	/*
     ++	 * Set boundary commits aside for the base check below, and put every
     ++	 * in-range commit but the tip into the interior set. A ref pointing
     ++	 * at an interior commit would dangle once the range is folded away.
     ++	 */
      +	while ((commit = get_revision(&revs))) {
      +		if (commit->object.flags & BOUNDARY) {
      +			commit_list_insert(commit, &boundaries);
     @@ builtin/history.c: out:
      +	if (!oldest) {
      +		ret = error(_("the revision range is empty"));
      +		goto out;
     -+	}
     -+
     -+	if (oldest == tip) {
     ++	} else if (oldest == tip) {
      +		ret = error(_("the revision range holds a single commit; "
      +			      "nothing to squash"));
      +		goto out;
     -+	}
     -+
     -+	if (!oldest->parents)
     ++	} else if (!oldest->parents) {
      +		BUG("an in-range commit must have a parent");
     ++	}
      +	base = oldest->parents->item;
      +
      +	/*
     @@ builtin/history.c: out:
      +	return ret;
      +}
      +
     -+static int reject_fixupish_oldest(struct repository *repo,
     -+				  struct commit *oldest)
     ++static const char *autosquash_target(const char *subject)
     ++{
     ++	const char *rest;
     ++
     ++	while (skip_prefix(subject, "fixup! ", &rest) ||
     ++	       skip_prefix(subject, "squash! ", &rest) ||
     ++	       skip_prefix(subject, "amend! ", &rest))
     ++		subject = rest;
     ++	return subject;
     ++}
     ++
     ++static int reject_dangling_fixups(struct repository *repo,
     ++				  struct commit *base,
     ++				  struct commit *tip,
     ++				  struct commit *oldest,
     ++				  struct commit **msg_source)
      +{
     -+	const char *message, *subject;
     -+	int ret = 0;
     -+
     -+	message = repo_logmsg_reencode(repo, oldest, NULL, NULL);
     -+	find_commit_subject(message, &subject);
     -+	if (starts_with(subject, "fixup! ") ||
     -+	    starts_with(subject, "squash! ") ||
     -+	    starts_with(subject, "amend! "))
     -+		ret = error(_("the range begins with a fixup!, squash! or amend! "
     -+			      "commit whose target is not in the range"));
     -+	repo_unuse_commit_buffer(repo, oldest, message);
     ++	struct todo_list todo = TODO_LIST_INIT;
     ++	struct replay_opts opts = REPLAY_OPTS_INIT;
     ++	struct rev_info revs;
     ++	struct commit *commit, *last_amend = NULL;
     ++	struct strvec args = STRVEC_INIT;
     ++	char *dangling_subject = NULL, *dangling_target = NULL;
     ++	bool mixed_target = false, all_fixups_one_target;
     ++	int i, ret, nr_dangling = 0;
     ++
     ++	*msg_source = oldest;
     ++
     ++	repo_init_revisions(repo, &revs, NULL);
     ++	strvec_push(&args, "ignored");
     ++	strvec_push(&args, "--reverse");
     ++	strvec_push(&args, "--topo-order");
     ++	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
     ++		     oid_to_hex(&tip->object.oid));
     ++	setup_revisions_from_strvec(&args, &revs, NULL);
     ++
     ++	if (prepare_revision_walk(&revs) < 0) {
     ++		ret = error(_("error preparing revisions"));
     ++		goto out;
     ++	}
     ++	while ((commit = get_revision(&revs)))
     ++		strbuf_addf(&todo.buf, "pick %s\n",
     ++			    oid_to_hex(&commit->object.oid));
     ++
     ++	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
     ++	    todo_list_rearrange_squash(&todo) < 0) {
     ++		ret = error(_("could not check the range for fixups"));
     ++		goto out;
     ++	}
     ++
     ++	for (i = 0; i < todo.nr; i++) {
     ++		const char *message, *subject_start, *target;
     ++		char *subject;
     ++		size_t sublen;
     ++
     ++		if (todo.items[i].command != TODO_PICK)
     ++			continue;
     ++		message = repo_logmsg_reencode(repo, todo.items[i].commit,
     ++					       NULL, NULL);
     ++		sublen = find_commit_subject(message, &subject_start);
     ++		subject = xmemdupz(subject_start, sublen);
     ++		target = autosquash_target(subject);
     ++		if (target != subject) {
     ++			nr_dangling++;
     ++			if (!dangling_target) {
     ++				dangling_target = xstrdup(target);
     ++				dangling_subject = xstrdup(subject);
     ++			} else if (strcmp(dangling_target, target)) {
     ++				mixed_target = true;
     ++			}
     ++			if (starts_with(subject, "amend! "))
     ++				last_amend = todo.items[i].commit;
     ++		}
     ++		free(subject);
     ++		repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
     ++	}
     ++
     ++	all_fixups_one_target = nr_dangling == todo.nr && !mixed_target;
     ++	if (nr_dangling && !all_fixups_one_target) {
     ++		ret = error(_("cannot squash '%s': its target is not in the "
     ++			      "range"), dangling_subject);
     ++	} else {
     ++		if (last_amend)
     ++			*msg_source = last_amend;
     ++		ret = 0;
     ++	}
     ++
     ++out:
     ++	free(dangling_subject);
     ++	free(dangling_target);
     ++	todo_list_release(&todo);
     ++	replay_opts_release(&opts);
     ++	reset_revision_walk();
     ++	release_revisions(&revs);
     ++	strvec_clear(&args);
      +	return ret;
      +}
      +
     @@ builtin/history.c: out:
      +	};
      +	struct strbuf reflog_msg = STRBUF_INIT;
      +	struct oidset interior = OIDSET_INIT;
     -+	struct commit *base, *oldest, *tip, *rewritten;
     ++	struct commit *base, *oldest, *tip, *rewritten, *msg_source;
      +	const struct object_id *base_tree_oid, *tip_tree_oid;
      +	struct commit_list *parents = NULL;
      +	struct rev_info revs = { 0 };
      +	int ret;
      +
     -+	argc = parse_options(argc, argv, prefix, options, usage, 0);
     ++	argc = parse_options(argc, argv, prefix, options, usage,
     ++			     PARSE_OPT_KEEP_UNKNOWN_OPT);
      +	if (!argc) {
      +		ret = error(_("command expects a revision range"));
      +		goto out;
     @@ builtin/history.c: out:
      +	if (ret < 0)
      +		goto out;
      +
     -+	ret = reject_fixupish_oldest(repo, oldest);
     ++	ret = reject_dangling_fixups(repo, base, tip, oldest, &msg_source);
      +	if (ret < 0)
      +		goto out;
      +
     @@ builtin/history.c: out:
      +	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
      +	commit_list_append(base, &parents);
      +
     -+	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
     ++	ret = commit_tree_ext(repo, "squash", msg_source, NULL, parents,
      +			      base_tree_oid, tip_tree_oid, &rewritten, flags);
      +	if (ret < 0) {
      +		ret = error(_("failed writing squashed commit"));
     @@ t/t3455-history-squash.sh (new)
      +	test_grep "squash: updating" reflog
      +'
      +
     ++test_expect_success 'sanitizes rev-list walk options, before and after --' '
     ++	git reset --hard three &&
     ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
     ++
     ++	git history squash --date-order start.. 2>err &&
     ++	test_grep "ignoring rev-list options" err &&
     ++	test_cmp_rev start HEAD^ &&
     ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     ++
     ++	git reset --hard three &&
     ++	git history squash -- --reverse start.. 2>err &&
     ++	test_grep "ignoring rev-list options" err &&
     ++	test_cmp_rev start HEAD^ &&
     ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
     ++'
     ++
      +test_expect_success 'squashes an interior range and replays descendants verbatim' '
      +	git reset --hard three &&
      +	final_tree=$(git rev-parse HEAD^{tree}) &&
     @@ t/t3455-history-squash.sh (new)
      +'
      +
      +
     -+test_expect_success 'reuses the message of a fixup! commit in the range' '
     ++test_expect_success 'folds fixups whose target is in the range' '
      +	git reset --hard start &&
     -+	test_commit --no-tag reg1 file b &&
     -+	git commit --allow-empty -m "fixup! reg1" &&
     -+	test_commit reg2 file c &&
     ++	test_commit --no-tag target file b &&
     ++	git commit --allow-empty -m "fixup! target" &&
     ++	git commit --allow-empty -m "fixup! target" &&
     ++	test_commit --no-tag later file c &&
      +
      +	git history squash start.. &&
      +
     ++	git rev-list --count start..HEAD >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
      +	git log --format="%s" -1 >actual &&
     -+	echo reg1 >expect &&
     ++	echo target >expect &&
      +	test_cmp expect actual
      +'
      +
     -+test_expect_success 'refuses a range whose oldest commit is a fixup!' '
     ++test_expect_success 'refuses a below-range fixup! after an in-range commit' '
      +	git reset --hard start &&
     -+	test_commit --no-tag "fixup! something" file b &&
     -+	test_commit --no-tag tail file c &&
     ++	test_commit --no-tag inside file b &&
     ++	test_commit --no-tag "fixup! outside" file c &&
      +	head_before=$(git rev-parse HEAD) &&
      +
      +	test_must_fail git history squash start.. 2>err &&
     @@ t/t3455-history-squash.sh (new)
      +	test_cmp_rev "$head_before" HEAD
      +'
      +
     -+test_expect_success 'does not interpret squash! or amend! markers' '
     ++test_expect_success 'combines a run of fixups for one commit below the range' '
     ++	git reset --hard start &&
     ++	echo b >file && git add file && git commit -m "fixup! base" &&
     ++	echo c >file && git add file && git commit -m "fixup! base" &&
     ++
     ++	git history squash start.. &&
     ++
     ++	git rev-list --count start..HEAD >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
     ++	git log --format="%s" -1 >actual &&
     ++	echo "fixup! base" >expect &&
     ++	test_cmp expect actual
     ++'
     ++
     ++test_expect_success 'combining below-range fixups keeps the last amend! message' '
     ++	git reset --hard start &&
     ++	echo b >file && git add file && git commit -m "fixup! base" &&
     ++	printf "amend! base\n\namended body\n" >msg &&
     ++	echo c >file && git add file && git commit -qF msg &&
     ++
     ++	git history squash start.. &&
     ++
     ++	git rev-list --count start..HEAD >count &&
     ++	echo 1 >expect &&
     ++	test_cmp expect count &&
     ++	git log --format="%s" -1 >actual &&
     ++	echo "amend! base" >expect &&
     ++	test_cmp expect actual &&
     ++	git log --format="%b" -1 >body &&
     ++	test_grep "amended body" body
     ++'
     ++
     ++test_expect_success 'refuses fixups for two different commits below the range' '
     ++	git reset --hard start &&
     ++	echo b >file && git add file && git commit -m "fixup! aaa" &&
     ++	echo c >file && git add file && git commit -m "fixup! bbb" &&
     ++	head_before=$(git rev-parse HEAD) &&
     ++
     ++	test_must_fail git history squash start.. 2>err &&
     ++	test_grep "target is not in the range" err &&
     ++	test_cmp_rev "$head_before" HEAD
     ++'
     ++
     ++test_expect_success 'keeps the oldest message for in-range squash! and amend!' '
      +	git reset --hard start &&
      +	test_commit --no-tag marker-oldest file b &&
      +	git commit --allow-empty -m "squash! marker-oldest" &&
     @@ t/t3455-history-squash.sh (new)
      +test_expect_success 'advice.historyUpdateRefs silences the hint' '
      +	git reset --hard three &&
      +	git branch -f mid HEAD~1 &&
     ++	head_before=$(git rev-parse HEAD) &&
      +
      +	test_must_fail git -c advice.historyUpdateRefs=false \
      +		history squash start.. 2>err &&
      +	test_grep "points into the squashed range" err &&
      +	test_grep ! "hint:" err &&
     ++	test_cmp_rev "$head_before" HEAD &&
      +
      +	git branch -D mid
      +'
     @@ t/t3455-history-squash.sh (new)
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
      +'
      +
     -+test_expect_success 'refuses to squash a range with more than one base' '
     -+	git reset --hard start &&
     -+	main=$(git symbolic-ref --short HEAD) &&
     -+	git checkout -b forked-before &&
     -+	test_commit forked-side fside x &&
     -+	git checkout "$main" &&
     -+	test_commit forked-base file b &&
     -+	base=$(git rev-parse HEAD) &&
     -+	test_commit forked-main file c &&
     -+	git merge --no-ff -m merge forked-before &&
     -+	merged=$(git rev-parse HEAD) &&
     -+
     -+	test_must_fail git history squash "$base.." 2>err &&
     -+	test_grep "more than one base" err &&
     -+	test_cmp_rev "$merged" HEAD
     -+'
     -+
      +test_expect_success 'folds a range with two interior merges' '
      +	git reset --hard start &&
      +	main=$(git symbolic-ref --short HEAD) &&
 4:  001356db93 ! 4:  0a735117ad sequencer: extract helpers for the squash message markers
     @@ Metadata
      Author: Harald Nordgren <haraldnordgren@gmail.com>
      
       ## Commit message ##
     -    sequencer: extract helpers for the squash message markers
     +    sequencer: share the squash message marker helpers and flags
      
          When "git rebase -i" squashes commits it builds an editor template with a
          "This is a combination of N commits." banner, a "This is the 1st/Nth
     @@ Commit message
          Pull the three pieces out into add_squash_combination_header(),
          add_squash_message_header() (which takes a flag for the "will be skipped"
          variant) and squash_subject_comment_len(), and use them from
     -    update_squash_messages() and append_squash_message(). A later change
     -    reuses them to give "git history squash --reedit-message" the same
     -    template.
     +    update_squash_messages() and append_squash_message(). Also move the
     +    todo_item_flags enum to the header, so a caller reading the output of
     +    todo_list_rearrange_squash() can tell an amend! (TODO_REPLACE_FIXUP_MSG)
     +    from a plain fixup!. A later change reuses all of this to give "git
     +    history squash --reedit-message" the same template.
      
          No change in behavior.
      
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
       ## sequencer.c ##
     -@@ sequencer.c: static const char skip_first_commit_msg_str[] = N_("The 1st commit message will
     +@@ sequencer.c: static int is_pick_or_similar(enum todo_command command)
     + 	}
     + }
     + 
     +-enum todo_item_flags {
     +-	TODO_EDIT_MERGE_MSG    = (1 << 0),
     +-	TODO_REPLACE_FIXUP_MSG = (1 << 1),
     +-	TODO_EDIT_FIXUP_MSG    = (1 << 2),
     +-};
     +-
     + static const char first_commit_msg_str[] = N_("This is the 1st commit message:");
     + static const char nth_commit_msg_fmt[] = N_("This is the commit message #%d:");
     + static const char skip_first_commit_msg_str[] = N_("The 1st commit message will be skipped:");
       static const char skip_nth_commit_msg_fmt[] = N_("The commit message #%d will be skipped:");
       static const char combined_commit_msg_fmt[] = N_("This is a combination of %d commits.");
       
     @@ sequencer.c: static int update_squash_messages(struct repository *r,
       					   comment_line_str);
      
       ## sequencer.h ##
     +@@ sequencer.h: enum todo_command {
     + 	TODO_COMMENT
     + };
     + 
     ++/* Bits for the "flags" member of struct todo_item */
     ++enum todo_item_flags {
     ++	TODO_EDIT_MERGE_MSG    = (1 << 0),
     ++	TODO_REPLACE_FIXUP_MSG = (1 << 1),
     ++	TODO_EDIT_FIXUP_MSG    = (1 << 2),
     ++};
     ++
     + struct todo_item {
     + 	enum todo_command command;
     + 	struct commit *commit;
      @@ sequencer.h: int todo_list_rearrange_squash(struct todo_list *todo_list);
        */
       void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
 5:  615fe4dd3f ! 5:  baf7e6f0a6 history: re-edit a squash with every message
     @@ Commit message
      
          By default "git history squash" reuses the oldest commit's message.
          When --reedit-message is given it only reopened that one message, so the
     -    messages of the folded-in commits were lost.
     +    messages of the other commits in the range were lost.
      
     -    Gather the messages of every commit in the range, oldest first, and build
     -    the same editor template that "git rebase -i" shows for a squash, using
     +    Gather the message of every commit in the range and build the same editor
     +    template that "git rebase -i --autosquash" shows for a squash, reusing
          add_squash_combination_header(), add_squash_message_header() and
     -    squash_subject_comment_len(). Only the message text differs, the changes
     -    are always folded in. Following autosquash, a fixup!'s message is
     -    commented out in full under a "will be skipped" header, while a squash! or
     -    amend! keeps its body with only the marker subject commented.
     +    squash_subject_comment_len(). Feed the range through
     +    todo_list_rearrange_squash() so that each fixup!, squash! or amend! is
     +    grouped under the commit it targets rather than shown in commit order,
     +    exactly as autosquash would arrange them.
     +
     +    Only the message text differs, the changes are always folded in. A fixup!
     +    message is commented out in full under a "will be skipped" header, a
     +    squash! keeps its body with only the marker subject commented, and an
     +    amend! replaces its target's message unless a squash! already folded into
     +    that target, in which case it behaves like a squash!.
      
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
       ## Documentation/git-history.adoc ##
     -@@ Documentation/git-history.adoc: like the arguments to linkgit:git-rev-list[1], so several arguments may be
     - given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
     - already on `topic`.
     +@@ Documentation/git-history.adoc: given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
     + already on `topic`. Rev-list options may also be given, but any that would
     + change how the range is walked are overridden with a warning.
       +
      -The oldest commit's message and authorship are preserved by default,
      -unless you specify `--reedit-message`. A merge commit inside the range is
     @@ Documentation/git-history.adoc: like the arguments to linkgit:git-rev-list[1], s
       folded like any other, but the range must have a single base, so a range
       that reaches more than one entry point (for example a side branch that
       forked before the range and was later merged into it) is rejected.
     - +
     - Because the oldest commit's message is reused, the range may not begin
     - with a `fixup!`, `squash!`, or `amend!` commit, whose target is
     --necessarily outside the range.
     -+necessarily outside the range. The changes from every commit in the range
     -+are always folded in. Only the message text differs. With
     -+`--reedit-message` the template mirrors `git rebase -i`: the message of a
     -+`fixup!` elsewhere in the range is commented out in full, while a
     -+`squash!` or `amend!` keeps its message body with only the marker subject
     -+commented, so you can fold the remark into the result.
     +@@ Documentation/git-history.adoc: A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
     + targets is also in the range, so the fold does not silently absorb a
     + marker meant for a commit outside it. As an exception, a range made up
     + entirely of markers for one target is combined into a single commit,
     +-keeping the last `amend!` message if there is one.
     ++keeping the last `amend!` message if there is one. The changes from every
     ++commit in the range are always folded in. Only the message text differs.
     ++With `--reedit-message` the template mirrors `git rebase -i --autosquash`:
     ++each `fixup!`, `squash!`, or `amend!` is grouped under the commit it
     ++targets rather than shown in commit order. A `fixup!` message is dropped
     ++(commented out in full), a `squash!` keeps its body with only the marker
     ++subject commented, and an `amend!` replaces its target's message, unless
     ++a `squash!` folded into that target first, in which case it keeps its
     ++body like a `squash!`.
       +
       A branch or tag that points at a commit inside the range would be left
       dangling once those commits are folded away, so with the default
     @@ builtin/history.c: static int find_interior_ref(const struct reference *ref, voi
       	return 0;
       }
       
     ++static bool amend_replaces_target(struct todo_list *todo, int target)
     ++{
     ++	int i;
     ++
     ++	for (i = target + 1; i < todo->nr &&
     ++			     todo->items[i].command != TODO_PICK; i++) {
     ++		if (todo->items[i].command == TODO_SQUASH)
     ++			return false;
     ++		if (todo->items[i].flags & TODO_REPLACE_FIXUP_MSG)
     ++			return true;
     ++	}
     ++	return false;
     ++}
     ++
      +static int build_squash_message(struct repository *repo,
      +				struct commit *base,
      +				struct commit *tip,
      +				struct strbuf *out)
      +{
     -+	struct commit_list *commits = NULL, **tail = &commits, *c;
      +	struct rev_info revs;
      +	struct commit *commit;
      +	struct strvec args = STRVEC_INIT;
     -+	int n = 0, total, ret;
     ++	struct todo_list todo = TODO_LIST_INIT;
     ++	struct replay_opts opts = REPLAY_OPTS_INIT;
     ++	int i, nr_commits, ret;
      +
      +	repo_init_revisions(repo, &revs, NULL);
      +	strvec_push(&args, "ignored");
     @@ builtin/history.c: static int find_interior_ref(const struct reference *ref, voi
      +	}
      +
      +	while ((commit = get_revision(&revs)))
     -+		tail = &commit_list_insert(commit, tail)->next;
     -+	total = commit_list_count(commits);
     ++		strbuf_addf(&todo.buf, "pick %s\n",
     ++			    oid_to_hex(&commit->object.oid));
      +
     -+	for (c = commits; c; c = c->next) {
     ++	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
     ++	    todo_list_rearrange_squash(&todo) < 0) {
     ++		ret = error(_("could not prepare the squash message"));
     ++		goto out;
     ++	}
     ++
     ++	nr_commits = todo.nr;
     ++	for (i = 0; i < nr_commits; i++) {
     ++		struct todo_item *item = &todo.items[i];
      +		const char *message, *body;
      +		size_t commented_len;
     -+		int skip;
     ++		bool skip, squashing;
      +
     -+		message = repo_logmsg_reencode(repo, c->item, NULL, NULL);
     ++		squashing = item->command == TODO_SQUASH ||
     ++			    (item->flags & TODO_REPLACE_FIXUP_MSG);
     ++		if (item->command == TODO_PICK)
     ++			skip = amend_replaces_target(&todo, i);
     ++		else
     ++			skip = !squashing;
     ++
     ++		message = repo_logmsg_reencode(repo, item->commit, NULL, NULL);
      +		find_commit_subject(message, &body);
      +
     -+		skip = starts_with(body, "fixup! ");
     -+		commented_len = skip ? strlen(body) :
     -+			squash_subject_comment_len(body, 1);
     ++		if (skip)
     ++			commented_len = strlen(body);
     ++		else if (squashing)
     ++			commented_len = squash_subject_comment_len(body, 1);
     ++		else
     ++			commented_len = 0;
      +
     -+		if (!n)
     -+			add_squash_combination_header(out, total);
     ++		if (!i)
     ++			add_squash_combination_header(out, nr_commits);
      +		strbuf_addch(out, '\n');
     -+		add_squash_message_header(out, ++n, skip);
     ++		add_squash_message_header(out, i + 1, skip);
      +		strbuf_addstr(out, "\n\n");
      +		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
      +		strbuf_addstr(out, body + commented_len);
      +		strbuf_complete_line(out);
      +
     -+		repo_unuse_commit_buffer(repo, c->item, message);
     ++		repo_unuse_commit_buffer(repo, item->commit, message);
      +	}
      +
      +	ret = 0;
      +
      +out:
     -+	commit_list_free(commits);
     ++	todo_list_release(&todo);
     ++	replay_opts_release(&opts);
      +	reset_revision_walk();
      +	release_revisions(&revs);
      +	strvec_clear(&args);
     @@ builtin/history.c: static int cmd_history_squash(int argc,
       	struct strbuf reflog_msg = STRBUF_INIT;
      +	struct strbuf message = STRBUF_INIT;
       	struct oidset interior = OIDSET_INIT;
     - 	struct commit *base, *oldest, *tip, *rewritten;
     + 	struct commit *base, *oldest, *tip, *rewritten, *msg_source;
       	const struct object_id *base_tree_oid, *tip_tree_oid;
      @@ builtin/history.c: static int cmd_history_squash(int argc,
       		}
     @@ builtin/history.c: static int cmd_history_squash(int argc,
       	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
       	commit_list_append(base, &parents);
       
     --	ret = commit_tree_ext(repo, "squash", oldest, NULL, parents,
     -+	ret = commit_tree_ext(repo, "squash", oldest,
     +-	ret = commit_tree_ext(repo, "squash", msg_source, NULL, parents,
     ++	ret = commit_tree_ext(repo, "squash", msg_source,
      +			      message.len ? message.buf : NULL, parents,
       			      base_tree_oid, tip_tree_oid, &rewritten, flags);
       	if (ret < 0) {
     @@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the olde
      +	test_grep "amended message" final
      +'
      +
     ++test_expect_success '--reedit-message groups fixups under their targets' '
     ++	git reset --hard start &&
     ++	test_commit --no-tag alpha file a1 &&
     ++	test_commit --no-tag beta file b1 &&
     ++	printf "fixup! alpha\n" >msg &&
     ++	echo a2 >file &&
     ++	git add file &&
     ++	git commit -qF msg &&
     ++	printf "fixup! beta\n" >msg &&
     ++	echo b2 >file &&
     ++	git add file &&
     ++	git commit -qF msg &&
     ++
     ++	write_script editor <<-\EOF &&
     ++	cat "$1" >edited
     ++	EOF
     ++	test_set_editor "$(pwd)/editor" &&
     ++	git history squash --reedit-message start.. &&
     ++
     ++	cat >expect <<-EOF &&
     ++	# This is a combination of 4 commits.
     ++	# This is the 1st commit message:
     ++
     ++	alpha
     ++
     ++	# The commit message #2 will be skipped:
     ++
     ++	# fixup! alpha
     ++
     ++	# This is the commit message #3:
     ++
     ++	beta
     ++
     ++	# The commit message #4 will be skipped:
     ++
     ++	# fixup! beta
     ++
     ++	# Please enter the commit message for the squash changes. Lines starting
     ++	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     ++	# Changes to be committed:
     ++	#	modified:   file
     ++	#
     ++	EOF
     ++	test_cmp expect edited
     ++'
     ++
     ++test_expect_success '--reedit-message lets amend! replace its target message' '
     ++	git reset --hard start &&
     ++	test_commit --no-tag mark-base file b &&
     ++	printf "amend! mark-base\n\namended message\n" >msg &&
     ++	echo c >file &&
     ++	git add file &&
     ++	git commit -qF msg &&
     ++	printf "squash! mark-base\n\nsquash remark\n" >msg &&
     ++	echo d >file &&
     ++	git add file &&
     ++	git commit -qF msg &&
     ++
     ++	write_script editor <<-\EOF &&
     ++	cat "$1" >edited
     ++	EOF
     ++	test_set_editor "$(pwd)/editor" &&
     ++	git history squash --reedit-message start.. &&
     ++
     ++	cat >expect <<-EOF &&
     ++	# This is a combination of 3 commits.
     ++	# The 1st commit message will be skipped:
     ++
     ++	# mark-base
     ++
     ++	# This is the commit message #2:
     ++
     ++	# amend! mark-base
     ++
     ++	amended message
     ++
     ++	# This is the commit message #3:
     ++
     ++	# squash! mark-base
     ++
     ++	squash remark
     ++
     ++	# Please enter the commit message for the squash changes. Lines starting
     ++	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     ++	# Changes to be committed:
     ++	#	modified:   file
     ++	#
     ++	EOF
     ++	test_cmp expect edited &&
     ++	git log -1 --format="%B" >final &&
     ++	test_grep ! "mark-base" final &&
     ++	test_grep "amended message" final &&
     ++	test_grep "squash remark" final
     ++'
     ++
      +test_expect_success '--reedit-message aborts on an empty message' '
      +	git reset --hard three &&
      +	head_before=$(git rev-parse HEAD) &&

-- 
gitgitgadget

[PATCH v8 1/5] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index fd83de8265..9f516687fe 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -157,6 +157,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -164,21 +183,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -444,18 +453,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -799,16 +800,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v8 2/5] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 9f516687fe..cbba25096f 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -101,6 +101,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -130,13 +131,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -189,7 +193,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -644,7 +648,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -855,7 +859,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -872,7 +876,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v8 3/5] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git history squash <revision-range>" to do this directly. It folds
every commit in the range into the oldest one, keeping that commit's
message and authorship and taking the tree of the newest commit, then
replays the commits above the range on top. The squashed message comes
from the oldest commit, or from an editor with --reedit-message. A
fixup!, squash! or amend! commit is refused unless the commit it targets
is also in the range, so the fold does not silently absorb a marker meant
for a commit outside it. The check runs the range through
todo_list_rearrange_squash(), which leaves such a marker as a plain pick.
Markers whose target is in the range fold in as usual. As an exception, a
range made up entirely of markers for one target is combined anyway,
taking its message from the last amend! if there is one, so a batch of
fixups for the same commit can be collapsed.

The range is read like the arguments to "git rev-list", so several
revisions such as "HEAD~3..HEAD ^topic" may be given, and rev-list
options are accepted too. As "git replay" does, the walk options the fold
relies on are forced after setup_revisions() and a warning is printed if
an option changed them, so the first commit returned is the range's
oldest and its parent is the base regardless of what the user passed
(including after a "--"). A merge inside the range is folded when its
other parent is reachable from the base, otherwise the range has more
than one base and is rejected. By default the command also refuses when a
ref points at a commit that the fold would discard. Use --update-refs=head
to rewrite only the current branch instead.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  45 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 343 +++++++++++++++++++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 566 +++++++++++++++++++++++++++++++
 7 files changed, 958 insertions(+), 3 deletions(-)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index c3c190ba6a..cd27f7e795 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -59,6 +59,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a ref points
+		into the range being folded, to tell the user about
+		`--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 2ba8121795..ad921ac2be 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -11,6 +11,7 @@ SYNOPSIS
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>
 
 DESCRIPTION
 -----------
@@ -42,8 +43,11 @@ at once.
 LIMITATIONS
 -----------
 
-This command does not (yet) work with histories that contain merges. You
-should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
+This command does not (yet) replay merge commits onto the rewritten
+history: if a commit that would be replayed is a merge, the operation is
+rejected, and you should use linkgit:git-rebase[1] with the
+`--rebase-merges` flag instead. The `squash` subcommand can still fold a
+merge that lies inside the range, as long as the range has a single base.
 
 Furthermore, the command does not support operations that can result in merge
 conflicts. This limitation is by design as history rewrites are not intended to
@@ -97,6 +101,40 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's message and
+	authorship and takes the tree of the range's newest commit, so the
+	whole range collapses into a single commit. Commits above the range
+	are replayed on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash HEAD~3..HEAD` folds the three most recent commits into
+one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
+while leaving the two newest commits in place. Several revisions may be
+given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
+already on `topic`. Rev-list options may also be given, but any that would
+change how the range is walked are overridden with a warning.
++
+The oldest commit's message and authorship are preserved by default,
+unless you specify `--reedit-message`. A merge commit inside the range is
+folded like any other, but the range must have a single base, so a range
+that reaches more than one entry point (for example a side branch that
+forked before the range and was later merged into it) is rejected.
++
+A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
+targets is also in the range, so the fold does not silently absorb a
+marker meant for a commit outside it. As an exception, a range made up
+entirely of markers for one target is combined into a single commit,
+keeping the last `amend!` message if there is one.
++
+A branch or tag that points at a commit inside the range would be left
+dangling once those commits are folded away, so with the default
+`--update-refs=branches` the command refuses. Rerun with
+`--update-refs=head` to rewrite only the current branch and leave such
+refs pointing at the old commits.
+
 OPTIONS
 -------
 
@@ -107,7 +145,8 @@ OPTIONS
 	ref updates is generally safe.
 
 `--reedit-message`::
-	Open an editor to modify the target commit's message.
+	Open an editor to modify the rewritten commit's message. For `squash`
+	the editor is pre-filled with the messages of all the folded commits.
 
 `--empty=(drop|keep|abort)`::
 	Control what happens when a commit becomes empty as a result of the
diff --git a/advice.c b/advice.c
index 0018501b7b..5c6ff95e31 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 8def280688..911b4e4643 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index cbba25096f..d3f535ded9 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -30,6 +31,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -973,6 +976,344 @@ out:
 	return ret;
 }
 
+/*
+ * Resolve a "<base>..<tip>" revision range into the base commit just outside
+ * the range (which becomes the parent of the squashed commit), the oldest
+ * commit contained in the range (whose message the squash reuses), and the
+ * range tip (whose tree becomes the result). A merge inside the range is fine,
+ * but the range must have a single base and must not reach a root commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				const char **argv,
+				struct commit **base_out,
+				struct commit **oldest_out,
+				struct commit **tip_out,
+				struct oidset *interior_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
+	struct commit_list *boundaries = NULL, *b;
+	struct strvec args = STRVEC_INIT;
+	size_t i;
+	int ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	revs.reverse = 1;
+	revs.topo_order = 1;
+	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+	revs.simplify_history = 0;
+	revs.boundary = 1;
+
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--ancestry-path");
+	strvec_pushv(&args, argv);
+	setup_revisions_from_strvec(&args, &revs, NULL);
+	if (args.nr != 1) {
+		ret = error(_("unrecognized argument: %s"), args.v[1]);
+		goto out;
+	}
+
+	if (revs.reverse != 1 || revs.topo_order != 1 ||
+	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
+	    revs.simplify_history != 0) {
+		warning(_("ignoring rev-list options that would change how the "
+			  "range is walked"));
+		revs.reverse = 1;
+		revs.topo_order = 1;
+		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+		revs.simplify_history = 0;
+	}
+
+	/*
+	 * A squash needs a base to reparent onto, so the range has to exclude
+	 * something, as in "<base>..<tip>". A revision range with no such
+	 * bottom commit cannot be squashed.
+	 */
+	for (i = 0; i < revs.cmdline.nr; i++)
+		if (revs.cmdline.rev[i].flags & UNINTERESTING)
+			break;
+	if (i == revs.cmdline.nr) {
+		ret = error(_("not a '<base>..<tip>' revision range"));
+		goto out;
+	}
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	/*
+	 * Set boundary commits aside for the base check below, and put every
+	 * in-range commit but the tip into the interior set. A ref pointing
+	 * at an interior commit would dangle once the range is folded away.
+	 */
+	while ((commit = get_revision(&revs))) {
+		if (commit->object.flags & BOUNDARY) {
+			commit_list_insert(commit, &boundaries);
+			continue;
+		}
+		if (!oldest)
+			oldest = commit;
+		if (tip)
+			oidset_insert(interior_out, &tip->object.oid);
+		tip = commit;
+	}
+
+	if (!oldest) {
+		ret = error(_("the revision range is empty"));
+		goto out;
+	} else if (oldest == tip) {
+		ret = error(_("the revision range holds a single commit; "
+			      "nothing to squash"));
+		goto out;
+	} else if (!oldest->parents) {
+		BUG("an in-range commit must have a parent");
+	}
+	base = oldest->parents->item;
+
+	/*
+	 * A boundary other than the base is an in-range commit reaching a
+	 * commit outside the range, so the range has more than one base.
+	 */
+	for (b = boundaries; b; b = b->next) {
+		if (b->item != base) {
+			ret = error(_("the revision range has more than one base; "
+				      "cannot squash"));
+			goto out;
+		}
+	}
+
+	*base_out = base;
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	commit_list_free(boundaries);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+static const char *autosquash_target(const char *subject)
+{
+	const char *rest;
+
+	while (skip_prefix(subject, "fixup! ", &rest) ||
+	       skip_prefix(subject, "squash! ", &rest) ||
+	       skip_prefix(subject, "amend! ", &rest))
+		subject = rest;
+	return subject;
+}
+
+static int reject_dangling_fixups(struct repository *repo,
+				  struct commit *base,
+				  struct commit *tip,
+				  struct commit *oldest,
+				  struct commit **msg_source)
+{
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	struct rev_info revs;
+	struct commit *commit, *last_amend = NULL;
+	struct strvec args = STRVEC_INIT;
+	char *dangling_subject = NULL, *dangling_target = NULL;
+	bool mixed_target = false, all_fixups_one_target;
+	int i, ret, nr_dangling = 0;
+
+	*msg_source = oldest;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+	while ((commit = get_revision(&revs)))
+		strbuf_addf(&todo.buf, "pick %s\n",
+			    oid_to_hex(&commit->object.oid));
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not check the range for fixups"));
+		goto out;
+	}
+
+	for (i = 0; i < todo.nr; i++) {
+		const char *message, *subject_start, *target;
+		char *subject;
+		size_t sublen;
+
+		if (todo.items[i].command != TODO_PICK)
+			continue;
+		message = repo_logmsg_reencode(repo, todo.items[i].commit,
+					       NULL, NULL);
+		sublen = find_commit_subject(message, &subject_start);
+		subject = xmemdupz(subject_start, sublen);
+		target = autosquash_target(subject);
+		if (target != subject) {
+			nr_dangling++;
+			if (!dangling_target) {
+				dangling_target = xstrdup(target);
+				dangling_subject = xstrdup(subject);
+			} else if (strcmp(dangling_target, target)) {
+				mixed_target = true;
+			}
+			if (starts_with(subject, "amend! "))
+				last_amend = todo.items[i].commit;
+		}
+		free(subject);
+		repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
+	}
+
+	all_fixups_one_target = nr_dangling == todo.nr && !mixed_target;
+	if (nr_dangling && !all_fixups_one_target) {
+		ret = error(_("cannot squash '%s': its target is not in the "
+			      "range"), dangling_subject);
+	} else {
+		if (last_amend)
+			*msg_source = last_amend;
+		ret = 0;
+	}
+
+out:
+	free(dangling_subject);
+	free(dangling_target);
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+struct interior_ref_cb {
+	const struct oidset *interior;
+	const char *name;
+};
+
+static int find_interior_ref(const struct reference *ref, void *cb_data)
+{
+	struct interior_ref_cb *data = cb_data;
+
+	if (oidset_contains(data->interior, ref->oid)) {
+		data->name = xstrdup(ref->name);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	enum commit_tree_flags flags = 0;
+	int dry_run = 0;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BIT(0, "reedit-message", &flags,
+			N_("open an editor to modify the commit message"),
+			COMMIT_TREE_EDIT_MESSAGE),
+		OPT_END(),
+	};
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct oidset interior = OIDSET_INIT;
+	struct commit *base, *oldest, *tip, *rewritten, *msg_source;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	struct commit_list *parents = NULL;
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage,
+			     PARSE_OPT_KEEP_UNKNOWN_OPT);
+	if (!argc) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
+
+	ret = resolve_squash_range(repo, argv, &base, &oldest, &tip,
+				   &interior);
+	if (ret < 0)
+		goto out;
+
+	ret = reject_dangling_fixups(repo, base, tip, oldest, &msg_source);
+	if (ret < 0)
+		goto out;
+
+	if (action == REF_ACTION_BRANCHES) {
+		struct interior_ref_cb cb = { .interior = &interior };
+
+		refs_for_each_ref(get_main_ref_store(repo),
+				  find_interior_ref, &cb);
+		if (cb.name) {
+			ret = error(_("'%s' points into the squashed range"),
+				    cb.name);
+			advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+					  _("Use --update-refs=head to rewrite only "
+					    "the current branch and leave such refs "
+					    "untouched."));
+			free((char *)cb.name);
+			goto out;
+		}
+	}
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+	commit_list_append(base, &parents);
+
+	ret = commit_tree_ext(repo, "squash", msg_source, NULL, parents,
+			      base_tree_oid, tip_tree_oid, &rewritten, flags);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	strbuf_addf(&reflog_msg, "squash: updating %s", argv[0]);
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	oidset_clear(&interior);
+	commit_list_free(parents);
+	release_revisions(&revs);
+	return ret;
+}
+
 int cmd_history(int argc,
 		const char **argv,
 		const char *prefix,
@@ -982,6 +1323,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -989,6 +1331,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
diff --git a/t/meson.build b/t/meson.build
index 7c3c070426..459e251623 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -400,6 +400,7 @@ integration_tests = [
   't3451-history-reword.sh',
   't3452-history-split.sh',
   't3453-history-fixup.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..6bc0a89ebc
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,566 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+test_expect_success 'setup linear history touching two files' '
+	test_commit base file a &&
+	git tag start &&
+	test_commit --no-tag one other x &&
+	test_commit --no-tag two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "expects a revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the revision range is empty" err
+'
+
+test_expect_success 'errors on a single revision that is not a range' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "not a .*range" err &&
+	test_must_fail git history squash HEAD~1 2>err &&
+	test_grep "not a .*range" err
+'
+
+test_expect_success 'errors on a range holding a single commit' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "HEAD^!" 2>err &&
+	test_grep "single commit; nothing to squash" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'accepts multiple revision arguments with an exclusion' '
+	git reset --hard three &&
+	git branch -f keep HEAD~2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..HEAD ^keep &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	two
+	one
+	EOF
+	test_cmp expect actual &&
+	test_cmp_rev keep HEAD~1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git branch -D keep
+'
+
+test_expect_success 'squashes a branch the current branch is not on' '
+	git reset --hard three &&
+	main=$(git symbolic-ref --short HEAD) &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b off-history start &&
+	test_commit --no-tag off-one off a &&
+	test_commit --no-tag off-two off b &&
+	git checkout "$main" &&
+
+	git history squash start..off-history &&
+
+	git rev-list --count start..off-history >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D off-history
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash start.. &&
+
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	git log --format="%s" -1 >subject &&
+	echo one >expect &&
+	test_cmp expect subject &&
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'sanitizes rev-list walk options, before and after --' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --date-order start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git reset --hard three &&
+	git history squash -- --reverse start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..@~1 &&
+
+	git log --format="%s" start..HEAD >actual &&
+	cat >expect <<-\EOF &&
+	three
+	one
+	EOF
+	test_cmp expect actual &&
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$root.." &&
+
+	git rev-list --count "$root..HEAD" >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+
+test_expect_success 'folds fixups whose target is in the range' '
+	git reset --hard start &&
+	test_commit --no-tag target file b &&
+	git commit --allow-empty -m "fixup! target" &&
+	git commit --allow-empty -m "fixup! target" &&
+	test_commit --no-tag later file c &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	git log --format="%s" -1 >actual &&
+	echo target >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'refuses a below-range fixup! after an in-range commit' '
+	git reset --hard start &&
+	test_commit --no-tag inside file b &&
+	test_commit --no-tag "fixup! outside" file c &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "target is not in the range" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'combines a run of fixups for one commit below the range' '
+	git reset --hard start &&
+	echo b >file && git add file && git commit -m "fixup! base" &&
+	echo c >file && git add file && git commit -m "fixup! base" &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	git log --format="%s" -1 >actual &&
+	echo "fixup! base" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'combining below-range fixups keeps the last amend! message' '
+	git reset --hard start &&
+	echo b >file && git add file && git commit -m "fixup! base" &&
+	printf "amend! base\n\namended body\n" >msg &&
+	echo c >file && git add file && git commit -qF msg &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	git log --format="%s" -1 >actual &&
+	echo "amend! base" >expect &&
+	test_cmp expect actual &&
+	git log --format="%b" -1 >body &&
+	test_grep "amended body" body
+'
+
+test_expect_success 'refuses fixups for two different commits below the range' '
+	git reset --hard start &&
+	echo b >file && git add file && git commit -m "fixup! aaa" &&
+	echo c >file && git add file && git commit -m "fixup! bbb" &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "target is not in the range" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'keeps the oldest message for in-range squash! and amend!' '
+	git reset --hard start &&
+	test_commit --no-tag marker-oldest file b &&
+	git commit --allow-empty -m "squash! marker-oldest" &&
+	git commit --allow-empty -m "amend! marker-oldest" &&
+	test_commit --no-tag marker-newest file c &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	git log --format="%s" -1 >actual &&
+	echo marker-oldest >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'preserves authorship of the oldest commit' '
+	git reset --hard start &&
+	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
+		test_commit --no-tag oldest file b &&
+	test_commit newest file c &&
+
+	git history squash start.. &&
+
+	git log -1 --format="%an <%ae>" >actual &&
+	echo "Squasher <squash@example.com>" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --update-refs=head start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success 'refuses to fold a range a ref points into' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "error: .* points into the squashed range" err &&
+	test_grep "hint: .*--update-refs=head" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D mid
+'
+
+test_expect_success 'advice.historyUpdateRefs silences the hint' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "points into the squashed range" err &&
+	test_grep ! "hint:" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D mid
+'
+
+test_expect_success '--update-refs=head folds past a ref pointing into the range' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	mid_before=$(git rev-parse mid) &&
+
+	git history squash --update-refs=head start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$mid_before" mid &&
+
+	git branch -D mid
+'
+
+test_expect_success 'refuses to fold a range a tag points into' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "refs/tags/mark" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git tag -d mark
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout "$main" &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	test_commit --no-tag after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	git log --format="%s" -1 >subject &&
+	echo before-side >expect &&
+	test_cmp expect subject &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a merge of a branch that forked at the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b base-fork-side &&
+	test_commit --no-tag base-fork-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag base-fork-main file b &&
+	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
+	git branch -D base-fork-side &&
+	test_commit --no-tag base-fork-tail file c &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'refuses a merge whose other parent is outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$base.." &&
+
+	git rev-list --count "$base..HEAD" >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'folds a range with two interior merges' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag two-merge-a file a1 &&
+	git checkout -b two-merge-s1 &&
+	test_commit --no-tag two-merge-s1 s1 x &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s1" two-merge-s1 &&
+	test_commit --no-tag two-merge-b file b1 &&
+	git checkout -b two-merge-s2 &&
+	test_commit --no-tag two-merge-s2 s2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s2" two-merge-s2 &&
+	git branch -D two-merge-s1 two-merge-s2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file s1 &&
+	test_path_is_file s2
+'
+
+test_expect_success 'folds a range with a nested merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b nested-outer &&
+	test_commit --no-tag nested-outer outer x &&
+	git checkout -b nested-inner &&
+	test_commit --no-tag nested-inner inner y &&
+	git checkout nested-outer &&
+	git merge --no-ff -m "merge inner" nested-inner &&
+	git checkout "$main" &&
+	test_commit --no-tag nested-main file b1 &&
+	git merge --no-ff -m "merge outer" nested-outer &&
+	git branch -D nested-outer nested-inner &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file outer &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range with an octopus merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag octo-base file a1 &&
+	git checkout -b octo-1 &&
+	test_commit --no-tag octo-1 o1 x &&
+	git checkout "$main" &&
+	git checkout -b octo-2 &&
+	test_commit --no-tag octo-2 o2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-1 octo-2 &&
+	git branch -D octo-1 octo-2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	git rev-list --count start..HEAD >count &&
+	echo 1 >expect &&
+	test_cmp expect count &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file o1 &&
+	test_path_is_file o2
+'
+
+test_expect_success 'refuses an octopus merge with an arm forked before the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b octo-pre &&
+	test_commit octo-pre-side pside x &&
+	git checkout "$main" &&
+	test_commit octo-pre-main file b1 &&
+	octo_base=$(git rev-parse HEAD) &&
+	git checkout -b octo-within &&
+	test_commit --no-tag octo-within wside y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-pre octo-within &&
+	merged=$(git rev-parse HEAD) &&
+	git branch -D octo-pre octo-within &&
+
+	test_must_fail git history squash "$octo_base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'refuses when a descendant above the range is a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag desc-one file b &&
+	test_commit --no-tag desc-two file c &&
+	git tag desc-tip &&
+	git checkout -b desc-above &&
+	test_commit --no-tag desc-above above x &&
+	git checkout "$main" &&
+	test_commit --no-tag desc-main file d &&
+	git merge --no-ff -m "merge desc-above" desc-above &&
+	git branch -D desc-above &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start..desc-tip 2>err &&
+	test_grep "merge commits is not supported" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'refuses to fold a range a ref points into at a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag refmerge-base file b &&
+	git checkout -b refmerge-side &&
+	test_commit --no-tag refmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag refmerge-main file c &&
+	git merge --no-ff -m "interior merge" refmerge-side &&
+	git branch -D refmerge-side &&
+	git branch at-merge HEAD &&
+	test_commit --no-tag refmerge-tail file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "at-merge" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D at-merge
+'
+
+test_done
-- 
gitgitgadget

[PATCH v8 4/5] sequencer: share the squash message marker helpers and flags

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

When "git rebase -i" squashes commits it builds an editor template with a
"This is a combination of N commits." banner, a "This is the 1st/Nth
commit message:" header above each kept message (or a "will be skipped"
header for a dropped one), and a commented-out subject for any fixup!,
squash! or amend! commit. The banner, the headers and the
subject-commenting all live in static helpers in sequencer.c wired to the
rebase state, so no other command can present a squash the same way.

Pull the three pieces out into add_squash_combination_header(),
add_squash_message_header() (which takes a flag for the "will be skipped"
variant) and squash_subject_comment_len(), and use them from
update_squash_messages() and append_squash_message(). Also move the
todo_item_flags enum to the header, so a caller reading the output of
todo_list_rearrange_squash() can tell an amend! (TODO_REPLACE_FIXUP_MSG)
from a plain fixup!. A later change reuses all of this to give "git
history squash --reedit-message" the same template.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 sequencer.c | 70 +++++++++++++++++++++++++++++------------------------
 sequencer.h | 30 +++++++++++++++++++++++
 2 files changed, 69 insertions(+), 31 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 0fe8fed6c3..2387afd9b5 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1880,18 +1880,38 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
-enum todo_item_flags {
-	TODO_EDIT_MERGE_MSG    = (1 << 0),
-	TODO_REPLACE_FIXUP_MSG = (1 << 1),
-	TODO_EDIT_FIXUP_MSG    = (1 << 2),
-};
-
 static const char first_commit_msg_str[] = N_("This is the 1st commit message:");
 static const char nth_commit_msg_fmt[] = N_("This is the commit message #%d:");
 static const char skip_first_commit_msg_str[] = N_("The 1st commit message will be skipped:");
 static const char skip_nth_commit_msg_fmt[] = N_("The commit message #%d will be skipped:");
 static const char combined_commit_msg_fmt[] = N_("This is a combination of %d commits.");
 
+void add_squash_combination_header(struct strbuf *buf, int n)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	strbuf_addf(buf, _(combined_commit_msg_fmt), n);
+}
+
+void add_squash_message_header(struct strbuf *buf, int n, int skip)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	if (n == 1)
+		strbuf_addstr(buf, skip ? _(skip_first_commit_msg_str) :
+				   _(first_commit_msg_str));
+	else
+		strbuf_addf(buf, skip ? _(skip_nth_commit_msg_fmt) :
+			    _(nth_commit_msg_fmt), n);
+}
+
+size_t squash_subject_comment_len(const char *body, int squashing)
+{
+	if (starts_with(body, "amend!") ||
+	    (squashing && (starts_with(body, "squash!") ||
+			   starts_with(body, "fixup!"))))
+		return commit_subject_length(body);
+	return 0;
+}
+
 static int is_fixup_flag(enum todo_command command, unsigned flag)
 {
 	return command == TODO_FIXUP && ((flag & TODO_REPLACE_FIXUP_MSG) ||
@@ -2005,20 +2025,13 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 {
 	struct replay_ctx *ctx = opts->ctx;
 	const char *fixup_msg;
-	size_t commented_len = 0, fixup_off;
-	/*
-	 * amend is non-interactive and not normally used with fixup!
-	 * or squash! commits, so only comment out those subjects when
-	 * squashing commit messages.
-	 */
-	if (starts_with(body, "amend!") ||
-	    ((command == TODO_SQUASH || seen_squash(ctx)) &&
-	     (starts_with(body, "squash!") || starts_with(body, "fixup!"))))
-		commented_len = commit_subject_length(body);
+	size_t commented_len, fixup_off;
+
+	commented_len = squash_subject_comment_len(body,
+				command == TODO_SQUASH || seen_squash(ctx));
 
-	strbuf_addf(buf, "\n%s ", comment_line_str);
-	strbuf_addf(buf, _(nth_commit_msg_fmt),
-		    ++ctx->current_fixup_count + 1);
+	strbuf_addch(buf, '\n');
+	add_squash_message_header(buf, ++ctx->current_fixup_count + 1, 0);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len, comment_line_str);
 	/* buf->buf may be reallocated so store an offset into the buffer */
@@ -2083,9 +2096,8 @@ static int update_squash_messages(struct repository *r,
 		eol = !starts_with(buf.buf, comment_line_str) ?
 			buf.buf : strchrnul(buf.buf, '\n');
 
-		strbuf_addf(&header, "%s ", comment_line_str);
-		strbuf_addf(&header, _(combined_commit_msg_fmt),
-			    ctx->current_fixup_count + 2);
+		add_squash_combination_header(&header,
+					      ctx->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);
 		if (is_fixup_flag(command, flag) && !seen_squash(ctx))
@@ -2109,12 +2121,9 @@ static int update_squash_messages(struct repository *r,
 			repo_unuse_commit_buffer(r, head_commit, head_message);
 			return error(_("cannot write '%s'"), rebase_path_fixup_msg());
 		}
-		strbuf_addf(&buf, "%s ", comment_line_str);
-		strbuf_addf(&buf, _(combined_commit_msg_fmt), 2);
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addstr(&buf, is_fixup_flag(command, flag) ?
-			      _(skip_first_commit_msg_str) :
-			      _(first_commit_msg_str));
+		add_squash_combination_header(&buf, 2);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, 1, is_fixup_flag(command, flag));
 		strbuf_addstr(&buf, "\n\n");
 		if (is_fixup_flag(command, flag))
 			strbuf_add_commented_lines(&buf, body, strlen(body),
@@ -2133,9 +2142,8 @@ static int update_squash_messages(struct repository *r,
 	if (command == TODO_SQUASH || is_fixup_flag(command, flag)) {
 		res = append_squash_message(&buf, body, command, opts, flag);
 	} else if (command == TODO_FIXUP) {
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),
-			    ++ctx->current_fixup_count + 1);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, ++ctx->current_fixup_count + 1, 1);
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body),
 					   comment_line_str);
diff --git a/sequencer.h b/sequencer.h
index 64a9c7fb1b..b01f897020 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,6 +119,13 @@ enum todo_command {
 	TODO_COMMENT
 };
 
+/* Bits for the "flags" member of struct todo_item */
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG    = (1 << 0),
+	TODO_REPLACE_FIXUP_MSG = (1 << 1),
+	TODO_EDIT_FIXUP_MSG    = (1 << 2),
+};
+
 struct todo_item {
 	enum todo_command command;
 	struct commit *commit;
@@ -208,6 +215,29 @@ int todo_list_rearrange_squash(struct todo_list *todo_list);
  */
 void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
 
+/*
+ * Append the "This is a combination of N commits." banner that "git rebase
+ * -i" writes at the top of a squashed commit's message, commented out with
+ * the comment character.
+ */
+void add_squash_combination_header(struct strbuf *buf, int n);
+
+/*
+ * Append the header (1-based N) that "git rebase -i" writes above each message
+ * when squashing, commented out with the comment character. With SKIP it reads
+ * "The ... commit message will be skipped" for a message that is dropped (a
+ * fixup), otherwise "This is the ... commit message".
+ */
+void add_squash_message_header(struct strbuf *buf, int n, int skip);
+
+/*
+ * Return the length of the leading subject of BODY when it should be commented
+ * out in a squash message, or 0 otherwise. An "amend!" subject always
+ * qualifies; "squash!" and "fixup!" subjects only when SQUASHING, since a
+ * plain fixup chain keeps them.
+ */
+size_t squash_subject_comment_len(const char *body, int squashing);
+
 void append_conflicts_hint(struct index_state *istate,
 		struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
 enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,
-- 
gitgitgadget

[PATCH v8 5/5] history: re-edit a squash with every message

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

By default "git history squash" reuses the oldest commit's message.
When --reedit-message is given it only reopened that one message, so the
messages of the other commits in the range were lost.

Gather the message of every commit in the range and build the same editor
template that "git rebase -i --autosquash" shows for a squash, reusing
add_squash_combination_header(), add_squash_message_header() and
squash_subject_comment_len(). Feed the range through
todo_list_rearrange_squash() so that each fixup!, squash! or amend! is
grouped under the commit it targets rather than shown in commit order,
exactly as autosquash would arrange them.

Only the message text differs, the changes are always folded in. A fixup!
message is commented out in full under a "will be skipped" header, a
squash! keeps its body with only the marker subject commented, and an
amend! replaces its target's message unless a squash! already folded into
that target, in which case it behaves like a squash!.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  15 ++-
 builtin/history.c              | 107 ++++++++++++++++-
 t/t3455-history-squash.sh      | 210 +++++++++++++++++++++++++++++++++
 3 files changed, 328 insertions(+), 4 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index ad921ac2be..697155f5d8 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -117,8 +117,9 @@ given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
 already on `topic`. Rev-list options may also be given, but any that would
 change how the range is walked are overridden with a warning.
 +
-The oldest commit's message and authorship are preserved by default,
-unless you specify `--reedit-message`. A merge commit inside the range is
+The oldest commit's message and authorship are preserved by default. With
+`--reedit-message`, an editor opens pre-filled with the messages of all the
+folded commits so you can combine them. A merge commit inside the range is
 folded like any other, but the range must have a single base, so a range
 that reaches more than one entry point (for example a side branch that
 forked before the range and was later merged into it) is rejected.
@@ -127,7 +128,15 @@ A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
 targets is also in the range, so the fold does not silently absorb a
 marker meant for a commit outside it. As an exception, a range made up
 entirely of markers for one target is combined into a single commit,
-keeping the last `amend!` message if there is one.
+keeping the last `amend!` message if there is one. The changes from every
+commit in the range are always folded in. Only the message text differs.
+With `--reedit-message` the template mirrors `git rebase -i --autosquash`:
+each `fixup!`, `squash!`, or `amend!` is grouped under the commit it
+targets rather than shown in commit order. A `fixup!` message is dropped
+(commented out in full), a `squash!` keeps its body with only the marker
+subject commented, and an `amend!` replaces its target's message, unless
+a `squash!` folded into that target first, in which case it keeps its
+body like a `squash!`.
 +
 A branch or tag that points at a commit inside the range would be left
 dangling once those commits are folded away, so with the default
diff --git a/builtin/history.c b/builtin/history.c
index d3f535ded9..f82001508d 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1211,6 +1211,102 @@ static int find_interior_ref(const struct reference *ref, void *cb_data)
 	return 0;
 }
 
+static bool amend_replaces_target(struct todo_list *todo, int target)
+{
+	int i;
+
+	for (i = target + 1; i < todo->nr &&
+			     todo->items[i].command != TODO_PICK; i++) {
+		if (todo->items[i].command == TODO_SQUASH)
+			return false;
+		if (todo->items[i].flags & TODO_REPLACE_FIXUP_MSG)
+			return true;
+	}
+	return false;
+}
+
+static int build_squash_message(struct repository *repo,
+				struct commit *base,
+				struct commit *tip,
+				struct strbuf *out)
+{
+	struct rev_info revs;
+	struct commit *commit;
+	struct strvec args = STRVEC_INIT;
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	int i, nr_commits, ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs)))
+		strbuf_addf(&todo.buf, "pick %s\n",
+			    oid_to_hex(&commit->object.oid));
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not prepare the squash message"));
+		goto out;
+	}
+
+	nr_commits = todo.nr;
+	for (i = 0; i < nr_commits; i++) {
+		struct todo_item *item = &todo.items[i];
+		const char *message, *body;
+		size_t commented_len;
+		bool skip, squashing;
+
+		squashing = item->command == TODO_SQUASH ||
+			    (item->flags & TODO_REPLACE_FIXUP_MSG);
+		if (item->command == TODO_PICK)
+			skip = amend_replaces_target(&todo, i);
+		else
+			skip = !squashing;
+
+		message = repo_logmsg_reencode(repo, item->commit, NULL, NULL);
+		find_commit_subject(message, &body);
+
+		if (skip)
+			commented_len = strlen(body);
+		else if (squashing)
+			commented_len = squash_subject_comment_len(body, 1);
+		else
+			commented_len = 0;
+
+		if (!i)
+			add_squash_combination_header(out, nr_commits);
+		strbuf_addch(out, '\n');
+		add_squash_message_header(out, i + 1, skip);
+		strbuf_addstr(out, "\n\n");
+		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
+		strbuf_addstr(out, body + commented_len);
+		strbuf_complete_line(out);
+
+		repo_unuse_commit_buffer(repo, item->commit, message);
+	}
+
+	ret = 0;
+
+out:
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1235,6 +1331,7 @@ static int cmd_history_squash(int argc,
 		OPT_END(),
 	};
 	struct strbuf reflog_msg = STRBUF_INIT;
+	struct strbuf message = STRBUF_INIT;
 	struct oidset interior = OIDSET_INIT;
 	struct commit *base, *oldest, *tip, *rewritten, *msg_source;
 	const struct object_id *base_tree_oid, *tip_tree_oid;
@@ -1279,6 +1376,12 @@ static int cmd_history_squash(int argc,
 		}
 	}
 
+	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
+		ret = build_squash_message(repo, base, tip, &message);
+		if (ret < 0)
+			goto out;
+	}
+
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
 		goto out;
@@ -1287,7 +1390,8 @@ static int cmd_history_squash(int argc,
 	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
 	commit_list_append(base, &parents);
 
-	ret = commit_tree_ext(repo, "squash", msg_source, NULL, parents,
+	ret = commit_tree_ext(repo, "squash", msg_source,
+			      message.len ? message.buf : NULL, parents,
 			      base_tree_oid, tip_tree_oid, &rewritten, flags);
 	if (ret < 0) {
 		ret = error(_("failed writing squashed commit"));
@@ -1308,6 +1412,7 @@ static int cmd_history_squash(int argc,
 
 out:
 	strbuf_release(&reflog_msg);
+	strbuf_release(&message);
 	oidset_clear(&interior);
 	commit_list_free(parents);
 	release_revisions(&revs);
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index 6bc0a89ebc..9b24f546e0 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -250,6 +250,216 @@ test_expect_success 'preserves authorship of the oldest commit' '
 	test_cmp expect actual
 '
 
+test_expect_success '--reedit-message offers every folded-in message' '
+	git reset --hard start &&
+	echo b >file &&
+	git add file &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# This is the 1st commit message:
+
+	re-one subject
+
+	re-one body line
+
+	# This is the commit message #2:
+
+	re-two
+
+	# This is the commit message #3:
+
+	re-three
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	echo combined >expect &&
+	git log --format="%s" -1 >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--reedit-message handles fixup!, squash! and amend! like rebase' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	printf "fixup! mark-base\n\nfixup body\n" >msg &&
+	echo c >file &&
+	git add file &&
+	git commit -qF msg &&
+	printf "squash! mark-base\n\nsquash remark\n" >msg &&
+	echo d >file &&
+	git add file &&
+	git commit -qF msg &&
+	printf "amend! mark-base\n\namended message\n" >msg &&
+	echo e >file &&
+	git add file &&
+	git commit -qF msg &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	mark-base
+
+	# The commit message #2 will be skipped:
+
+	# fixup! mark-base
+	#
+	# fixup body
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# This is the commit message #4:
+
+	# amend! mark-base
+
+	amended message
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	git log -1 --format="%B" >final &&
+	test_grep ! "fixup body" final &&
+	test_grep "squash remark" final &&
+	test_grep "amended message" final
+'
+
+test_expect_success '--reedit-message groups fixups under their targets' '
+	git reset --hard start &&
+	test_commit --no-tag alpha file a1 &&
+	test_commit --no-tag beta file b1 &&
+	printf "fixup! alpha\n" >msg &&
+	echo a2 >file &&
+	git add file &&
+	git commit -qF msg &&
+	printf "fixup! beta\n" >msg &&
+	echo b2 >file &&
+	git add file &&
+	git commit -qF msg &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	alpha
+
+	# The commit message #2 will be skipped:
+
+	# fixup! alpha
+
+	# This is the commit message #3:
+
+	beta
+
+	# The commit message #4 will be skipped:
+
+	# fixup! beta
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited
+'
+
+test_expect_success '--reedit-message lets amend! replace its target message' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	printf "amend! mark-base\n\namended message\n" >msg &&
+	echo c >file &&
+	git add file &&
+	git commit -qF msg &&
+	printf "squash! mark-base\n\nsquash remark\n" >msg &&
+	echo d >file &&
+	git add file &&
+	git commit -qF msg &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# The 1st commit message will be skipped:
+
+	# mark-base
+
+	# This is the commit message #2:
+
+	# amend! mark-base
+
+	amended message
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	git log -1 --format="%B" >final &&
+	test_grep ! "mark-base" final &&
+	test_grep "amended message" final &&
+	test_grep "squash remark" final
+'
+
+test_expect_success '--reedit-message aborts on an empty message' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	test_must_fail git history squash --reedit-message start.. &&
+
+	test_cmp_rev "$head_before" HEAD
+'
+
 test_expect_success '--update-refs=head only moves HEAD' '
 	git reset --hard three &&
 	git branch -f other HEAD &&
-- 
gitgitgadget

Re: [PATCH v8 0/5] history: add squash subcommand to fold a range

[Matt Hunter]

On Fri Jul 10, 2026 at 5:06 AM EDT, Harald Nordgren via GitGitGadget wrote:
> Adds git history squash <revision-range> to fold a range of commits.
>
> Changes in v8:
>
>  * --reedit-message now builds the same editor template as git rebase -i
>    --autosquash: fixup!, squash! and amend! commits are grouped under the
>    commit they target instead of shown in commit order, and an amend!
>    replaces its target's message.
>  * A fixup!, squash! or amend! is refused only when its target is outside
>    the range, so several fixups for an in-range commit fold together. A
>    range that is entirely markers for one below-range target is combined
>    into a single commit, keeping the last amend! message.
>  * Merges inside the range are folded when the range has a single base, with
>    no dedicated opt-in flag, --ancestry-path ensures only commits descended
>    from the base are folded, and a range reaching more than one base is
>    rejected.
>  * Rev-list options are accepted and sanitized the way git replay does,
>    forcing the walk order back with a warning, which also fixes git history
>    squash -- --reverse slipping past the previous option check.
>  * Kept this as an explicit squash subcommand rather than making
>    --reedit-message the default or renaming the command.

This feature looks like it's coming together pretty well imo.  I just have
one observation I want to comment on:

I noticed that 'git history squash <range>', when --reedit-message is
omitted, will ignore any amend! message in the range that targets the
first folded commit.

On the surface, this makes sense.  The feature is pretty explicit that
it will faithfully stick with the first commit's message, unless
modified by use of --reedit-message.

However, this edge case is a little surprising, given that
'git history squash' seems to be aware of the semantics of fixup!, amend!,
and squash! messages whether --reedit-message was given or not.  For instance,
the default command notices when the range contains a squash! commit whose
target is elsewhere (a useful feature).  It seems consistent then, that the
default command would incorporate an amend! it is aware of when placing the
"first commit's" message in the resulting squash.  This seems useful to me
as well.

At the same time, I can understand why the current implementation does
what it does.  So I'm not entirely sure what the correct answer is here.

I'll mention as well that I really like the decisions made for how this
command handles squashing a bunch of related fixups.  This "fixup
consolidation" is a use-case that this command may steal away from rebase
for me.  And the way a final amend! is handled in this case is what got me
thinking about it in the general case.

Thanks for the work on this topic!

Re: [PATCH v8 0/5] history: add squash subcommand to fold a range

[Harald Nordgren]

> This feature looks like it's coming together pretty well imo.  I just have
> one observation I want to comment on:
>
> I noticed that 'git history squash <range>', when --reedit-message is
> omitted, will ignore any amend! message in the range that targets the
> first folded commit.
>
> On the surface, this makes sense.  The feature is pretty explicit that
> it will faithfully stick with the first commit's message, unless
> modified by use of --reedit-message.
>
> However, this edge case is a little surprising, given that
> 'git history squash' seems to be aware of the semantics of fixup!, amend!,
> and squash! messages whether --reedit-message was given or not.  For instance,
> the default command notices when the range contains a squash! commit whose
> target is elsewhere (a useful feature).  It seems consistent then, that the
> default command would incorporate an amend! it is aware of when placing the
> "first commit's" message in the resulting squash.  This seems useful to me
> as well.
>
> At the same time, I can understand why the current implementation does
> what it does.  So I'm not entirely sure what the correct answer is here.
>
> I'll mention as well that I really like the decisions made for how this
> command handles squashing a bunch of related fixups.  This "fixup
> consolidation" is a use-case that this command may steal away from rebase
> for me.  And the way a final amend! is handled in this case is what got me
> thinking about it in the general case.
>
> Thanks for the work on this topic!

Thanks!

That's an interesting observation, I'll see what I can do about it.


Harald

Re: [PATCH v8 0/5] history: add squash subcommand to fold a range

[Harald Nordgren]

I made a fix for this and also took the opportunity to create test
helpers to clarify the tests.

Same pattern as the ones @Phillip Wood helped me with on my
'delete-merged' topic. I would like to push out a new version before
anyone needs to review the current tests -- the new version would be a
lot easier to look at. Should I?


Harald

Re: [PATCH v8 0/5] history: add squash subcommand to fold a range

[Ben Knoble]

> Le 14 juil. 2026 à 00:45, Matt Hunter <m@lfurio.us> a écrit :
> 
> On Fri Jul 10, 2026 at 5:06 AM EDT, Harald Nordgren via GitGitGadget wrote:
>> Adds git history squash <revision-range> to fold a range of commits.

[snip]

> I'll mention as well that I really like the decisions made for how this
> command handles squashing a bunch of related fixups.  This "fixup
> consolidation" is a use-case that this command may steal away from rebase
> for me.  And the way a final amend! is handled in this case is what got me
> thinking about it in the general case.
> 
> Thanks for the work on this topic!

Ditto! I suspect that using a combination of « git history squash » and « git replay » to emulate « git rebase » in non-interactive autosquash mode will be much faster, too, due to the differences in implementation. If that proves to be the case and we can safely do so with feature compatibility, I wonder if it will be worth making the non-interactive autosquash rebase actually delegate through a history squash + replay.

I’m sure there’s a few instances that couldn’t be done (for example when the special! commits cross the current range and upstream; that is, a fixup! for an upstream commit or some such oddity;; there are also conflicts to consider), but in the cases it can be it ought to be a performance win.

Re: [PATCH v8 0/5] history: add squash subcommand to fold a range

[Junio C Hamano]

Ben Knoble <ben.knoble@gmail.com> writes:

>> Thanks for the work on this topic!
>
> Ditto! I suspect that using a combination of « git history squash
> » and « git replay » to emulate « git rebase » in non-interactive
> autosquash mode will be much faster, too, due to the differences
> in implementation. If that proves to be the case and we can safely
> do so with feature compatibility, I wonder if it will be worth
> making the non-interactive autosquash rebase actually delegate
> through a history squash + replay.

Yes, that would be an ideal future, and these efforts move us in
that direction.

> I’m sure there’s a few instances that couldn’t be done (for
> example when the special! commits cross the current range and
> upstream; that is, a fixup! for an upstream commit or some such
> oddity;; there are also conflicts to consider), but in the cases
> it can be it ought to be a performance win.

Since you assume "we can safely do so with feature compatibility"
above, once we are finished, there will, by definition, be no
such "special" commits that the combination cannot handle.  By
the time that happens, we will have replaced the internals of
"rebase [-i]" with a new implementation that does not need to
touch the working tree.

That would indeed be an exciting future.

[PATCH v9 0/5] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v9:

 * Use the last amend! targeting the oldest folded commit as the default
   squashed message. Ignore amend! markers targeting later commits while
   selecting that replacement message.
 * Improve tests.

Changes in v8:

 * --reedit-message now builds the same editor template as git rebase -i
   --autosquash: fixup!, squash! and amend! commits are grouped under the
   commit they target instead of shown in commit order, and an amend!
   replaces its target's message.
 * A fixup!, squash! or amend! is refused only when its target is outside
   the range, so several fixups for an in-range commit fold together. A
   range that is entirely markers for one below-range target is combined
   into a single commit, keeping the last amend! message.
 * Merges inside the range are folded when the range has a single base, with
   no dedicated opt-in flag, --ancestry-path ensures only commits descended
   from the base are folded, and a range reaching more than one base is
   rejected.
 * Rev-list options are accepted and sanitized the way git replay does,
   forcing the walk order back with a warning, which also fixes git history
   squash -- --reverse slipping past the previous option check.
 * Kept this as an explicit squash subcommand rather than making
   --reedit-message the default or renaming the command.

Changes in v7:

 * --reedit-message now builds the same editor template git rebase -i shows
   for a squash (a combination of N commits banner with each folded message
   under its own header) and follows autosquash for markers: a fixup!
   message falls out (commented under a will be skipped header), while a
   squash! or amend! keeps its body with only the marker subject commented
   so its remark can be reworded in. Only the message text is affected,
   every commit's changes are always folded in.
 * Reuse git rebase -i's squash-message code: a preparatory sequencer:
   commit extracts the banner, header and marker-comment helpers so both
   rebase and git history squash build the identical template from one
   source.
 * Refuse a range whose oldest commit is a fixup!, squash! or amend!, since
   the marker's target cannot be inside the range.
 * Reorder the squash usage so dashed options come before <revision-range>,
   and spell out HEAD instead of @ in the documentation and examples.
 * Expand the squash commit message and documentation with this overview,
   and scope the merge limitation so it no longer contradicts squash folding
   a single-base interior merge.

Changes in v6:

 * git history squash now accepts multiple revision arguments, read like the
   arguments to git-rev-list, so a compound range such as @~3.. ^topic
   works.
 * The base to reparent onto is now the oldest in-range commit's parent; a
   boundary other than that base means the range has more than one base and
   is rejected. This also fixes the earlier overly-restrictive handling of
   merges and side branches.
 * A single-commit range (e.g. @^!) is rejected with "nothing to squash"
   (this also covers the @^!-style example that previously succeeded
   silently).
 * Commit messages reworded: the squash commit now gives an overview of
   fixup!/squash!/amend! handling, rewording, merge-parent and ref behavior.

Changes in v5:

 * The range walk now uses --ancestry-path, so only commits descended from
   the base are folded; a single revision such as HEAD or HEAD~1 is now
   rejected as "not a <base>..<tip> range" rather than treated as a squash
   down to the root.
 * This adopts the --ancestry-path suggestion; the multi-base rejection is
   unchanged, so a side branch that forked before the base and merged in is
   still refused.
 * Added tests covering more merge topologies: two interior merges, a nested
   merge, an octopus merge, an octopus arm forked before the base, a merge
   among the descendants replayed above the range, and a ref pointing at an
   interior merge commit.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (5):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  history: add squash subcommand to fold a range
  sequencer: share the squash message marker helpers and flags
  history: re-edit a squash with every message

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  57 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 550 ++++++++++++++++++++--
 sequencer.c                      |  70 +--
 sequencer.h                      |  30 ++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 766 +++++++++++++++++++++++++++++++
 9 files changed, 1408 insertions(+), 72 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: 55526a18268bbc1ddaf8a6b7850c33d984eac9e9
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v9
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v9
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v8:

 1:  ba77752282 = 1:  352c818c29 history: extract helper for a commit's parent tree
 2:  50f3572887 = 2:  e06e49095b history: give commit_tree_ext a message template
 3:  2d81a40a05 ! 3:  ead974c317 history: add squash subcommand to fold a range
     @@ Commit message
      
          Add "git history squash <revision-range>" to do this directly. It folds
          every commit in the range into the oldest one, keeping that commit's
     -    message and authorship and taking the tree of the newest commit, then
     -    replays the commits above the range on top. The squashed message comes
     -    from the oldest commit, or from an editor with --reedit-message. A
     -    fixup!, squash! or amend! commit is refused unless the commit it targets
     -    is also in the range, so the fold does not silently absorb a marker meant
     -    for a commit outside it. The check runs the range through
     -    todo_list_rearrange_squash(), which leaves such a marker as a plain pick.
     -    Markers whose target is in the range fold in as usual. As an exception, a
     -    range made up entirely of markers for one target is combined anyway,
     -    taking its message from the last amend! if there is one, so a batch of
     -    fixups for the same commit can be collapsed.
     +    authorship and taking the tree of the newest commit, then replays the
     +    commits above the range on top. The squashed message comes from the
     +    oldest commit by default, or from the body of the last amend! commit
     +    targeting it. An editor opens with the selected message when
     +    --reedit-message is given. A fixup!, squash! or amend! commit is refused
     +    unless the commit it targets is also in the range, so the fold does not
     +    silently absorb a marker meant for a commit outside it. The check runs
     +    the range through todo_list_rearrange_squash(), which leaves such a
     +    marker as a plain pick. Markers whose target is in the range fold in as
     +    usual. As an exception, a range made up entirely of markers for one
     +    target is combined anyway, taking its message from the last amend! if
     +    there is one, so a batch of fixups for the same commit can be collapsed.
      
          The range is read like the arguments to "git rev-list", so several
          revisions such as "HEAD~3..HEAD ^topic" may be given, and rev-list
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
       
      +`squash <revision-range>`::
      +	Fold all commits in _<revision-range>_ into the oldest commit of that
     -+	range. The resulting commit keeps the oldest commit's message and
     -+	authorship and takes the tree of the range's newest commit, so the
     -+	whole range collapses into a single commit. Commits above the range
     -+	are replayed on top of the result.
     ++	range. The resulting commit keeps the oldest commit's authorship and
     ++	takes the tree of the range's newest commit, so the whole range
     ++	collapses into a single commit. Commits above the range are replayed
     ++	on top of the result.
      ++
      +The range is given in the usual `<base>..<tip>` form, where _<base>_ is
      +the commit just below the oldest commit to squash. For example, `git
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      +already on `topic`. Rev-list options may also be given, but any that would
      +change how the range is walked are overridden with a warning.
      ++
     -+The oldest commit's message and authorship are preserved by default,
     -+unless you specify `--reedit-message`. A merge commit inside the range is
     -+folded like any other, but the range must have a single base, so a range
     -+that reaches more than one entry point (for example a side branch that
     -+forked before the range and was later merged into it) is rejected.
     ++The oldest commit's message is preserved by default, except that an `amend!`
     ++commit targeting it replaces its message. Specify `--reedit-message` to edit
     ++the resulting message. A merge commit inside the range is folded like any
     ++other, but the range must have a single base, so a range that reaches more
     ++than one entry point (for example a side branch that forked before the range
     ++and was later merged into it) is rejected.
      ++
      +A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
      +targets is also in the range, so the fold does not silently absorb a
     -+marker meant for a commit outside it. As an exception, a range made up
     -+entirely of markers for one target is combined into a single commit,
     -+keeping the last `amend!` message if there is one.
     ++marker meant for a commit outside it. The body after an `amend!` subject
     ++replaces the oldest commit's message when the marker targets that commit. As
     ++an exception, a range made up entirely of markers for one target is combined
     ++into a single commit, keeping the last `amend!` message if there is one.
      ++
      +A branch or tag that points at a commit inside the range would be left
      +dangling once those commits are folded away, so with the default
     @@ builtin/history.c: out:
      +				  struct commit *base,
      +				  struct commit *tip,
      +				  struct commit *oldest,
     -+				  struct commit **msg_source)
     ++				  struct commit **msg_source,
     ++				  struct commit **amend_source)
      +{
      +	struct todo_list todo = TODO_LIST_INIT;
      +	struct replay_opts opts = REPLAY_OPTS_INIT;
     @@ builtin/history.c: out:
      +	struct strvec args = STRVEC_INIT;
      +	char *dangling_subject = NULL, *dangling_target = NULL;
      +	bool mixed_target = false, all_fixups_one_target;
     ++	bool past_oldest_group = false;
      +	int i, ret, nr_dangling = 0;
      +
      +	*msg_source = oldest;
     ++	*amend_source = NULL;
      +
      +	repo_init_revisions(repo, &revs, NULL);
      +	strvec_push(&args, "ignored");
     @@ builtin/history.c: out:
      +		char *subject;
      +		size_t sublen;
      +
     -+		if (todo.items[i].command != TODO_PICK)
     -+			continue;
      +		message = repo_logmsg_reencode(repo, todo.items[i].commit,
      +					       NULL, NULL);
      +		sublen = find_commit_subject(message, &subject_start);
     ++
     ++		if (todo.items[i].command != TODO_PICK) {
     ++			if (!past_oldest_group &&
     ++			    starts_with(subject_start, "amend! "))
     ++				*amend_source = todo.items[i].commit;
     ++			repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
     ++			continue;
     ++		}
     ++		if (i)
     ++			past_oldest_group = true;
     ++
      +		subject = xmemdupz(subject_start, sublen);
      +		target = autosquash_target(subject);
      +		if (target != subject) {
     @@ builtin/history.c: out:
      +		OPT_END(),
      +	};
      +	struct strbuf reflog_msg = STRBUF_INIT;
     ++	struct strbuf message = STRBUF_INIT;
      +	struct oidset interior = OIDSET_INIT;
     -+	struct commit *base, *oldest, *tip, *rewritten, *msg_source;
     ++	struct commit *base, *oldest, *tip, *rewritten, *msg_source,
     ++		*amend_source;
      +	const struct object_id *base_tree_oid, *tip_tree_oid;
     ++	const char *message_template = NULL;
      +	struct commit_list *parents = NULL;
      +	struct rev_info revs = { 0 };
      +	int ret;
     @@ builtin/history.c: out:
      +	if (ret < 0)
      +		goto out;
      +
     -+	ret = reject_dangling_fixups(repo, base, tip, oldest, &msg_source);
     ++	ret = reject_dangling_fixups(repo, base, tip, oldest, &msg_source,
     ++				     &amend_source);
      +	if (ret < 0)
      +		goto out;
     ++	if (amend_source) {
     ++		const char *amend_message, *body;
     ++
     ++		amend_message = repo_logmsg_reencode(repo, amend_source,
     ++						     NULL, NULL);
     ++		find_commit_subject(amend_message, &body);
     ++		body = skip_blank_lines(body + commit_subject_length(body));
     ++		strbuf_addstr(&message, body);
     ++		message_template = message.buf;
     ++		repo_unuse_commit_buffer(repo, amend_source, amend_message);
     ++	}
      +
      +	if (action == REF_ACTION_BRANCHES) {
      +		struct interior_ref_cb cb = { .interior = &interior };
     @@ builtin/history.c: out:
      +	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
      +	commit_list_append(base, &parents);
      +
     -+	ret = commit_tree_ext(repo, "squash", msg_source, NULL, parents,
     ++	ret = commit_tree_ext(repo, "squash", msg_source, message_template,
     ++			      parents,
      +			      base_tree_oid, tip_tree_oid, &rewritten, flags);
      +	if (ret < 0) {
      +		ret = error(_("failed writing squashed commit"));
     @@ builtin/history.c: out:
      +
      +out:
      +	strbuf_release(&reflog_msg);
     ++	strbuf_release(&message);
      +	oidset_clear(&interior);
      +	commit_list_free(parents);
      +	release_revisions(&revs);
     @@ t/t3455-history-squash.sh (new)
      +
      +. ./test-lib.sh
      +
     ++stage_file () {
     ++	printf "%s\n" "$1" >file &&
     ++	git add file
     ++}
     ++
     ++commit_with_message () {
     ++	printf "%b" "$1" >msg &&
     ++	git commit --allow-empty -qF msg
     ++}
     ++
     ++check_commit_count () {
     ++	git rev-list --count "$1" >actual &&
     ++	echo "$2" >expect &&
     ++	test_cmp expect actual
     ++}
     ++
     ++check_log_subjects () {
     ++	git log --format="%s" "$1" >actual &&
     ++	cat >expect &&
     ++	test_cmp expect actual
     ++}
     ++
     ++check_log_messages () {
     ++	git log --format="%B" "$1" >actual &&
     ++	cat >expect &&
     ++	test_cmp expect actual
     ++}
     ++
      +test_expect_success 'setup linear history touching two files' '
      +	test_commit base file a &&
      +	git tag start &&
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash start..HEAD ^keep &&
      +
     -+	git log --format="%s" start..HEAD >actual &&
     -+	cat >expect <<-\EOF &&
     ++	check_log_subjects start..HEAD <<-\EOF &&
      +	two
      +	one
      +	EOF
     -+	test_cmp expect actual &&
      +	test_cmp_rev keep HEAD~1 &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
      +
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash start..off-history &&
      +
     -+	git rev-list --count start..off-history >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     ++	check_commit_count start..off-history 1 &&
      +	test_cmp_rev "$head_before" HEAD &&
      +
      +	git branch -D off-history
     @@ t/t3455-history-squash.sh (new)
      +	git history squash start.. &&
      +
      +	test "$predicted" = "$(git rev-parse HEAD)" &&
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     ++	check_commit_count start..HEAD 1 &&
      +	test_cmp_rev start HEAD^ &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     -+	git log --format="%s" -1 >subject &&
     -+	echo one >expect &&
     -+	test_cmp expect subject &&
     ++	check_log_subjects -1 <<-\EOF &&
     ++	one
     ++	EOF
      +	git reflog >reflog &&
      +	test_grep "squash: updating" reflog
      +'
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash start..@~1 &&
      +
     -+	git log --format="%s" start..HEAD >actual &&
     -+	cat >expect <<-\EOF &&
     ++	check_log_subjects start..HEAD <<-\EOF &&
      +	three
      +	one
      +	EOF
     -+	test_cmp expect actual &&
      +
      +	test_cmp_rev start HEAD~2 &&
      +	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash "$root.." &&
      +
     -+	git rev-list --count "$root..HEAD" >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     ++	check_commit_count "$root..HEAD" 1 &&
      +	test_cmp_rev "$root" HEAD^ &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
      +'
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     -+	git log --format="%s" -1 >actual &&
     -+	echo target >expect &&
     -+	test_cmp expect actual
     ++	check_commit_count start..HEAD 1 &&
     ++	check_log_subjects -1 <<-\EOF
     ++	target
     ++	EOF
      +'
      +
      +test_expect_success 'refuses a below-range fixup! after an in-range commit' '
     @@ t/t3455-history-squash.sh (new)
      +
      +test_expect_success 'combines a run of fixups for one commit below the range' '
      +	git reset --hard start &&
     -+	echo b >file && git add file && git commit -m "fixup! base" &&
     -+	echo c >file && git add file && git commit -m "fixup! base" &&
     ++	stage_file b && git commit -m "fixup! base" &&
     ++	stage_file c && git commit -m "fixup! base" &&
      +
      +	git history squash start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     -+	git log --format="%s" -1 >actual &&
     -+	echo "fixup! base" >expect &&
     -+	test_cmp expect actual
     ++	check_commit_count start..HEAD 1 &&
     ++	check_log_subjects -1 <<-\EOF
     ++	fixup! base
     ++	EOF
      +'
      +
      +test_expect_success 'combining below-range fixups keeps the last amend! message' '
      +	git reset --hard start &&
     -+	echo b >file && git add file && git commit -m "fixup! base" &&
     -+	printf "amend! base\n\namended body\n" >msg &&
     -+	echo c >file && git add file && git commit -qF msg &&
     ++	stage_file b && git commit -m "fixup! base" &&
     ++	stage_file c &&
     ++	commit_with_message "amend! base\n\namended body\n" &&
      +
      +	git history squash start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     -+	git log --format="%s" -1 >actual &&
     -+	echo "amend! base" >expect &&
     -+	test_cmp expect actual &&
     -+	git log --format="%b" -1 >body &&
     -+	test_grep "amended body" body
     ++	check_commit_count start..HEAD 1 &&
     ++	check_log_messages -1 <<-\EOF
     ++	amend! base
     ++
     ++	amended body
     ++
     ++	EOF
      +'
      +
      +test_expect_success 'refuses fixups for two different commits below the range' '
      +	git reset --hard start &&
     -+	echo b >file && git add file && git commit -m "fixup! aaa" &&
     -+	echo c >file && git add file && git commit -m "fixup! bbb" &&
     ++	stage_file b && git commit -m "fixup! aaa" &&
     ++	stage_file c && git commit -m "fixup! bbb" &&
      +	head_before=$(git rev-parse HEAD) &&
      +
      +	test_must_fail git history squash start.. 2>err &&
     @@ t/t3455-history-squash.sh (new)
      +	test_cmp_rev "$head_before" HEAD
      +'
      +
     -+test_expect_success 'keeps the oldest message for in-range squash! and amend!' '
     ++test_expect_success 'the last amend! for the oldest commit replaces its message' '
      +	git reset --hard start &&
      +	test_commit --no-tag marker-oldest file b &&
      +	git commit --allow-empty -m "squash! marker-oldest" &&
     -+	git commit --allow-empty -m "amend! marker-oldest" &&
     -+	test_commit --no-tag marker-newest file c &&
     ++	commit_with_message "amend! marker-oldest\n\nearlier message\n" &&
     ++	commit_with_message \
     ++		"amend! marker-oldest\n\namended subject\n\namended body\n" &&
     ++	test_commit --no-tag marker-later file c &&
     ++	commit_with_message "amend! marker-later\n\nwrong message\n" &&
      +
      +	git history squash start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     -+	git log --format="%s" -1 >actual &&
     -+	echo marker-oldest >expect &&
     -+	test_cmp expect actual
     ++	check_commit_count start..HEAD 1 &&
     ++	check_log_messages -1 <<-\EOF
     ++	amended subject
     ++
     ++	amended body
     ++
     ++	EOF
      +'
      +
      +test_expect_success 'preserves authorship of the oldest commit' '
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash --update-refs=head start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     ++	check_commit_count start..HEAD 1 &&
      +	test_cmp_rev "$other_before" other
      +'
      +
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash --update-refs=head start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     ++	check_commit_count start..HEAD 1 &&
      +	test_cmp_rev "$mid_before" mid &&
      +
      +	git branch -D mid
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     -+	git log --format="%s" -1 >subject &&
     -+	echo before-side >expect &&
     -+	test_cmp expect subject &&
     ++	check_commit_count start..HEAD 1 &&
     ++	check_log_subjects -1 <<-\EOF &&
     ++	before-side
     ++	EOF
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
      +	test_path_is_file inner
      +'
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     ++	check_commit_count start..HEAD 1 &&
      +	test_cmp_rev start HEAD^ &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
      +	test_path_is_file side
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     ++	check_commit_count start..HEAD 1 &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
      +	test_path_is_file side
      +'
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash "$base.." &&
      +
     -+	git rev-list --count "$base..HEAD" >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     ++	check_commit_count "$base..HEAD" 1 &&
      +	test_cmp_rev "$base" HEAD^ &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
      +'
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     ++	check_commit_count start..HEAD 1 &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
      +	test_path_is_file s1 &&
      +	test_path_is_file s2
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     ++	check_commit_count start..HEAD 1 &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
      +	test_path_is_file outer &&
      +	test_path_is_file inner
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash start.. &&
      +
     -+	git rev-list --count start..HEAD >count &&
     -+	echo 1 >expect &&
     -+	test_cmp expect count &&
     ++	check_commit_count start..HEAD 1 &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
      +	test_path_is_file o1 &&
      +	test_path_is_file o2
 4:  0a735117ad = 4:  08915cee51 sequencer: share the squash message marker helpers and flags
 5:  baf7e6f0a6 ! 5:  fb76afe31c history: re-edit a squash with every message
     @@ Metadata
       ## Commit message ##
          history: re-edit a squash with every message
      
     -    By default "git history squash" reuses the oldest commit's message.
     -    When --reedit-message is given it only reopened that one message, so the
     +    By default "git history squash" reuses the oldest commit's message, or
     +    the replacement body from an amend! commit targeting it. When
     +    --reedit-message is given it only reopened that selected message, so the
          messages of the other commits in the range were lost.
      
          Gather the message of every commit in the range and build the same editor
     @@ Commit message
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
       ## Documentation/git-history.adoc ##
     -@@ Documentation/git-history.adoc: given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
     - already on `topic`. Rev-list options may also be given, but any that would
     +@@ Documentation/git-history.adoc: already on `topic`. Rev-list options may also be given, but any that would
       change how the range is walked are overridden with a warning.
       +
     --The oldest commit's message and authorship are preserved by default,
     --unless you specify `--reedit-message`. A merge commit inside the range is
     -+The oldest commit's message and authorship are preserved by default. With
     -+`--reedit-message`, an editor opens pre-filled with the messages of all the
     -+folded commits so you can combine them. A merge commit inside the range is
     - folded like any other, but the range must have a single base, so a range
     - that reaches more than one entry point (for example a side branch that
     - forked before the range and was later merged into it) is rejected.
     -@@ Documentation/git-history.adoc: A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
     + The oldest commit's message is preserved by default, except that an `amend!`
     +-commit targeting it replaces its message. Specify `--reedit-message` to edit
     +-the resulting message. A merge commit inside the range is folded like any
     +-other, but the range must have a single base, so a range that reaches more
     +-than one entry point (for example a side branch that forked before the range
     +-and was later merged into it) is rejected.
     ++commit targeting it replaces its message. With `--reedit-message`, an editor
     ++opens pre-filled with the messages of all the folded commits so you can
     ++combine them. A merge commit inside the range is folded like any other, but
     ++the range must have a single base, so a range that reaches more than one entry
     ++point (for example a side branch that forked before the range and was later
     ++merged into it) is rejected.
     + +
     + A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
       targets is also in the range, so the fold does not silently absorb a
     - marker meant for a commit outside it. As an exception, a range made up
     - entirely of markers for one target is combined into a single commit,
     --keeping the last `amend!` message if there is one.
     -+keeping the last `amend!` message if there is one. The changes from every
     -+commit in the range are always folded in. Only the message text differs.
     +@@ Documentation/git-history.adoc: marker meant for a commit outside it. The body after an `amend!` subject
     + replaces the oldest commit's message when the marker targets that commit. As
     + an exception, a range made up entirely of markers for one target is combined
     + into a single commit, keeping the last `amend!` message if there is one.
     ++The changes from every commit in the range are always folded in. Only the
     ++message text differs.
      +With `--reedit-message` the template mirrors `git rebase -i --autosquash`:
      +each `fixup!`, `squash!`, or `amend!` is grouped under the commit it
      +targets rather than shown in commit order. A `fixup!` message is dropped
     @@ builtin/history.c: static int find_interior_ref(const struct reference *ref, voi
       static int cmd_history_squash(int argc,
       			      const char **argv,
       			      const char *prefix,
     -@@ builtin/history.c: static int cmd_history_squash(int argc,
     - 		OPT_END(),
     - 	};
     - 	struct strbuf reflog_msg = STRBUF_INIT;
     -+	struct strbuf message = STRBUF_INIT;
     - 	struct oidset interior = OIDSET_INIT;
     - 	struct commit *base, *oldest, *tip, *rewritten, *msg_source;
     - 	const struct object_id *base_tree_oid, *tip_tree_oid;
      @@ builtin/history.c: static int cmd_history_squash(int argc,
       		}
       	}
       
      +	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
     ++		strbuf_reset(&message);
      +		ret = build_squash_message(repo, base, tip, &message);
      +		if (ret < 0)
      +			goto out;
     ++		message_template = message.buf;
      +	}
      +
       	ret = setup_revwalk(repo, action, tip, &revs);
       	if (ret < 0)
       		goto out;
     -@@ builtin/history.c: static int cmd_history_squash(int argc,
     - 	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
     - 	commit_list_append(base, &parents);
     - 
     --	ret = commit_tree_ext(repo, "squash", msg_source, NULL, parents,
     -+	ret = commit_tree_ext(repo, "squash", msg_source,
     -+			      message.len ? message.buf : NULL, parents,
     - 			      base_tree_oid, tip_tree_oid, &rewritten, flags);
     - 	if (ret < 0) {
     - 		ret = error(_("failed writing squashed commit"));
     -@@ builtin/history.c: static int cmd_history_squash(int argc,
     - 
     - out:
     - 	strbuf_release(&reflog_msg);
     -+	strbuf_release(&message);
     - 	oidset_clear(&interior);
     - 	commit_list_free(parents);
     - 	release_revisions(&revs);
      
       ## t/t3455-history-squash.sh ##
      @@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the oldest commit' '
     @@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the olde
       
      +test_expect_success '--reedit-message offers every folded-in message' '
      +	git reset --hard start &&
     -+	echo b >file &&
     -+	git add file &&
     ++	stage_file b &&
      +	git commit -m "re-one subject" -m "re-one body line" &&
      +	test_commit --no-tag re-two file c &&
      +	test_commit re-three file d &&
     @@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the olde
      +	#
      +	EOF
      +	test_cmp expect edited &&
     -+	echo combined >expect &&
     -+	git log --format="%s" -1 >actual &&
     -+	test_cmp expect actual
     ++	check_log_subjects -1 <<-\EOF
     ++	combined
     ++	EOF
      +'
      +
      +test_expect_success '--reedit-message handles fixup!, squash! and amend! like rebase' '
      +	git reset --hard start &&
      +	test_commit --no-tag mark-base file b &&
     -+	printf "fixup! mark-base\n\nfixup body\n" >msg &&
     -+	echo c >file &&
     -+	git add file &&
     -+	git commit -qF msg &&
     -+	printf "squash! mark-base\n\nsquash remark\n" >msg &&
     -+	echo d >file &&
     -+	git add file &&
     -+	git commit -qF msg &&
     -+	printf "amend! mark-base\n\namended message\n" >msg &&
     -+	echo e >file &&
     -+	git add file &&
     -+	git commit -qF msg &&
     ++	stage_file c &&
     ++	commit_with_message "fixup! mark-base\n\nfixup body\n" &&
     ++	stage_file d &&
     ++	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
     ++	stage_file e &&
     ++	commit_with_message "amend! mark-base\n\namended message\n" &&
      +
      +	write_script editor <<-\EOF &&
      +	cat "$1" >edited
     @@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the olde
      +	#
      +	EOF
      +	test_cmp expect edited &&
     -+	git log -1 --format="%B" >final &&
     -+	test_grep ! "fixup body" final &&
     -+	test_grep "squash remark" final &&
     -+	test_grep "amended message" final
     ++	check_log_messages -1 <<-\EOF
     ++	mark-base
     ++
     ++	squash remark
     ++
     ++	amended message
     ++
     ++	EOF
      +'
      +
      +test_expect_success '--reedit-message groups fixups under their targets' '
      +	git reset --hard start &&
      +	test_commit --no-tag alpha file a1 &&
      +	test_commit --no-tag beta file b1 &&
     -+	printf "fixup! alpha\n" >msg &&
     -+	echo a2 >file &&
     -+	git add file &&
     -+	git commit -qF msg &&
     -+	printf "fixup! beta\n" >msg &&
     -+	echo b2 >file &&
     -+	git add file &&
     -+	git commit -qF msg &&
     ++	stage_file a2 &&
     ++	commit_with_message "fixup! alpha\n" &&
     ++	stage_file b2 &&
     ++	commit_with_message "fixup! beta\n" &&
      +
      +	write_script editor <<-\EOF &&
      +	cat "$1" >edited
     @@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the olde
      +test_expect_success '--reedit-message lets amend! replace its target message' '
      +	git reset --hard start &&
      +	test_commit --no-tag mark-base file b &&
     -+	printf "amend! mark-base\n\namended message\n" >msg &&
     -+	echo c >file &&
     -+	git add file &&
     -+	git commit -qF msg &&
     -+	printf "squash! mark-base\n\nsquash remark\n" >msg &&
     -+	echo d >file &&
     -+	git add file &&
     -+	git commit -qF msg &&
     ++	stage_file c &&
     ++	commit_with_message "amend! mark-base\n\namended message\n" &&
     ++	stage_file d &&
     ++	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
      +
      +	write_script editor <<-\EOF &&
      +	cat "$1" >edited
     @@ t/t3455-history-squash.sh: test_expect_success 'preserves authorship of the olde
      +	#
      +	EOF
      +	test_cmp expect edited &&
     -+	git log -1 --format="%B" >final &&
     -+	test_grep ! "mark-base" final &&
     -+	test_grep "amended message" final &&
     -+	test_grep "squash remark" final
     ++	check_log_messages -1 <<-\EOF
     ++	amended message
     ++
     ++	squash remark
     ++
     ++	EOF
      +'
      +
      +test_expect_success '--reedit-message aborts on an empty message' '

-- 
gitgitgadget

[PATCH v9 1/5] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index fd83de8265..9f516687fe 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -157,6 +157,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -164,21 +183,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -444,18 +453,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -799,16 +800,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v9 2/5] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 9f516687fe..cbba25096f 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -101,6 +101,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -130,13 +131,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -189,7 +193,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -644,7 +648,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -855,7 +859,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -872,7 +876,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v9 3/5] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git history squash <revision-range>" to do this directly. It folds
every commit in the range into the oldest one, keeping that commit's
authorship and taking the tree of the newest commit, then replays the
commits above the range on top. The squashed message comes from the
oldest commit by default, or from the body of the last amend! commit
targeting it. An editor opens with the selected message when
--reedit-message is given. A fixup!, squash! or amend! commit is refused
unless the commit it targets is also in the range, so the fold does not
silently absorb a marker meant for a commit outside it. The check runs
the range through todo_list_rearrange_squash(), which leaves such a
marker as a plain pick. Markers whose target is in the range fold in as
usual. As an exception, a range made up entirely of markers for one
target is combined anyway, taking its message from the last amend! if
there is one, so a batch of fixups for the same commit can be collapsed.

The range is read like the arguments to "git rev-list", so several
revisions such as "HEAD~3..HEAD ^topic" may be given, and rev-list
options are accepted too. As "git replay" does, the walk options the fold
relies on are forced after setup_revisions() and a warning is printed if
an option changed them, so the first commit returned is the range's
oldest and its parent is the base regardless of what the user passed
(including after a "--"). A merge inside the range is folded when its
other parent is reachable from the base, otherwise the range has more
than one base and is rejected. By default the command also refuses when a
ref points at a commit that the fold would discard. Use --update-refs=head
to rewrite only the current branch instead.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  47 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 372 ++++++++++++++++++++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 565 +++++++++++++++++++++++++++++++
 7 files changed, 988 insertions(+), 3 deletions(-)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 81f80a9274..e2a3487778 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -59,6 +59,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a ref points
+		into the range being folded, to tell the user about
+		`--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 2ba8121795..2c0d861303 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -11,6 +11,7 @@ SYNOPSIS
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>
 
 DESCRIPTION
 -----------
@@ -42,8 +43,11 @@ at once.
 LIMITATIONS
 -----------
 
-This command does not (yet) work with histories that contain merges. You
-should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
+This command does not (yet) replay merge commits onto the rewritten
+history: if a commit that would be replayed is a merge, the operation is
+rejected, and you should use linkgit:git-rebase[1] with the
+`--rebase-merges` flag instead. The `squash` subcommand can still fold a
+merge that lies inside the range, as long as the range has a single base.
 
 Furthermore, the command does not support operations that can result in merge
 conflicts. This limitation is by design as history rewrites are not intended to
@@ -97,6 +101,42 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's authorship and
+	takes the tree of the range's newest commit, so the whole range
+	collapses into a single commit. Commits above the range are replayed
+	on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash HEAD~3..HEAD` folds the three most recent commits into
+one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
+while leaving the two newest commits in place. Several revisions may be
+given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
+already on `topic`. Rev-list options may also be given, but any that would
+change how the range is walked are overridden with a warning.
++
+The oldest commit's message is preserved by default, except that an `amend!`
+commit targeting it replaces its message. Specify `--reedit-message` to edit
+the resulting message. A merge commit inside the range is folded like any
+other, but the range must have a single base, so a range that reaches more
+than one entry point (for example a side branch that forked before the range
+and was later merged into it) is rejected.
++
+A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
+targets is also in the range, so the fold does not silently absorb a
+marker meant for a commit outside it. The body after an `amend!` subject
+replaces the oldest commit's message when the marker targets that commit. As
+an exception, a range made up entirely of markers for one target is combined
+into a single commit, keeping the last `amend!` message if there is one.
++
+A branch or tag that points at a commit inside the range would be left
+dangling once those commits are folded away, so with the default
+`--update-refs=branches` the command refuses. Rerun with
+`--update-refs=head` to rewrite only the current branch and leave such
+refs pointing at the old commits.
+
 OPTIONS
 -------
 
@@ -107,7 +147,8 @@ OPTIONS
 	ref updates is generally safe.
 
 `--reedit-message`::
-	Open an editor to modify the target commit's message.
+	Open an editor to modify the rewritten commit's message. For `squash`
+	the editor is pre-filled with the messages of all the folded commits.
 
 `--empty=(drop|keep|abort)`::
 	Control what happens when a commit becomes empty as a result of the
diff --git a/advice.c b/advice.c
index 63bf8b0c5f..401d047391 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 66f6cd6a77..3f0b4f0485 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index cbba25096f..edf98a21d3 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -30,6 +31,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -973,6 +976,373 @@ out:
 	return ret;
 }
 
+/*
+ * Resolve a "<base>..<tip>" revision range into the base commit just outside
+ * the range (which becomes the parent of the squashed commit), the oldest
+ * commit contained in the range (whose message the squash reuses), and the
+ * range tip (whose tree becomes the result). A merge inside the range is fine,
+ * but the range must have a single base and must not reach a root commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				const char **argv,
+				struct commit **base_out,
+				struct commit **oldest_out,
+				struct commit **tip_out,
+				struct oidset *interior_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
+	struct commit_list *boundaries = NULL, *b;
+	struct strvec args = STRVEC_INIT;
+	size_t i;
+	int ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	revs.reverse = 1;
+	revs.topo_order = 1;
+	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+	revs.simplify_history = 0;
+	revs.boundary = 1;
+
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--ancestry-path");
+	strvec_pushv(&args, argv);
+	setup_revisions_from_strvec(&args, &revs, NULL);
+	if (args.nr != 1) {
+		ret = error(_("unrecognized argument: %s"), args.v[1]);
+		goto out;
+	}
+
+	if (revs.reverse != 1 || revs.topo_order != 1 ||
+	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
+	    revs.simplify_history != 0) {
+		warning(_("ignoring rev-list options that would change how the "
+			  "range is walked"));
+		revs.reverse = 1;
+		revs.topo_order = 1;
+		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+		revs.simplify_history = 0;
+	}
+
+	/*
+	 * A squash needs a base to reparent onto, so the range has to exclude
+	 * something, as in "<base>..<tip>". A revision range with no such
+	 * bottom commit cannot be squashed.
+	 */
+	for (i = 0; i < revs.cmdline.nr; i++)
+		if (revs.cmdline.rev[i].flags & UNINTERESTING)
+			break;
+	if (i == revs.cmdline.nr) {
+		ret = error(_("not a '<base>..<tip>' revision range"));
+		goto out;
+	}
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	/*
+	 * Set boundary commits aside for the base check below, and put every
+	 * in-range commit but the tip into the interior set. A ref pointing
+	 * at an interior commit would dangle once the range is folded away.
+	 */
+	while ((commit = get_revision(&revs))) {
+		if (commit->object.flags & BOUNDARY) {
+			commit_list_insert(commit, &boundaries);
+			continue;
+		}
+		if (!oldest)
+			oldest = commit;
+		if (tip)
+			oidset_insert(interior_out, &tip->object.oid);
+		tip = commit;
+	}
+
+	if (!oldest) {
+		ret = error(_("the revision range is empty"));
+		goto out;
+	} else if (oldest == tip) {
+		ret = error(_("the revision range holds a single commit; "
+			      "nothing to squash"));
+		goto out;
+	} else if (!oldest->parents) {
+		BUG("an in-range commit must have a parent");
+	}
+	base = oldest->parents->item;
+
+	/*
+	 * A boundary other than the base is an in-range commit reaching a
+	 * commit outside the range, so the range has more than one base.
+	 */
+	for (b = boundaries; b; b = b->next) {
+		if (b->item != base) {
+			ret = error(_("the revision range has more than one base; "
+				      "cannot squash"));
+			goto out;
+		}
+	}
+
+	*base_out = base;
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	commit_list_free(boundaries);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+static const char *autosquash_target(const char *subject)
+{
+	const char *rest;
+
+	while (skip_prefix(subject, "fixup! ", &rest) ||
+	       skip_prefix(subject, "squash! ", &rest) ||
+	       skip_prefix(subject, "amend! ", &rest))
+		subject = rest;
+	return subject;
+}
+
+static int reject_dangling_fixups(struct repository *repo,
+				  struct commit *base,
+				  struct commit *tip,
+				  struct commit *oldest,
+				  struct commit **msg_source,
+				  struct commit **amend_source)
+{
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	struct rev_info revs;
+	struct commit *commit, *last_amend = NULL;
+	struct strvec args = STRVEC_INIT;
+	char *dangling_subject = NULL, *dangling_target = NULL;
+	bool mixed_target = false, all_fixups_one_target;
+	bool past_oldest_group = false;
+	int i, ret, nr_dangling = 0;
+
+	*msg_source = oldest;
+	*amend_source = NULL;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+	while ((commit = get_revision(&revs)))
+		strbuf_addf(&todo.buf, "pick %s\n",
+			    oid_to_hex(&commit->object.oid));
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not check the range for fixups"));
+		goto out;
+	}
+
+	for (i = 0; i < todo.nr; i++) {
+		const char *message, *subject_start, *target;
+		char *subject;
+		size_t sublen;
+
+		message = repo_logmsg_reencode(repo, todo.items[i].commit,
+					       NULL, NULL);
+		sublen = find_commit_subject(message, &subject_start);
+
+		if (todo.items[i].command != TODO_PICK) {
+			if (!past_oldest_group &&
+			    starts_with(subject_start, "amend! "))
+				*amend_source = todo.items[i].commit;
+			repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
+			continue;
+		}
+		if (i)
+			past_oldest_group = true;
+
+		subject = xmemdupz(subject_start, sublen);
+		target = autosquash_target(subject);
+		if (target != subject) {
+			nr_dangling++;
+			if (!dangling_target) {
+				dangling_target = xstrdup(target);
+				dangling_subject = xstrdup(subject);
+			} else if (strcmp(dangling_target, target)) {
+				mixed_target = true;
+			}
+			if (starts_with(subject, "amend! "))
+				last_amend = todo.items[i].commit;
+		}
+		free(subject);
+		repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
+	}
+
+	all_fixups_one_target = nr_dangling == todo.nr && !mixed_target;
+	if (nr_dangling && !all_fixups_one_target) {
+		ret = error(_("cannot squash '%s': its target is not in the "
+			      "range"), dangling_subject);
+	} else {
+		if (last_amend)
+			*msg_source = last_amend;
+		ret = 0;
+	}
+
+out:
+	free(dangling_subject);
+	free(dangling_target);
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+struct interior_ref_cb {
+	const struct oidset *interior;
+	const char *name;
+};
+
+static int find_interior_ref(const struct reference *ref, void *cb_data)
+{
+	struct interior_ref_cb *data = cb_data;
+
+	if (oidset_contains(data->interior, ref->oid)) {
+		data->name = xstrdup(ref->name);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	enum commit_tree_flags flags = 0;
+	int dry_run = 0;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BIT(0, "reedit-message", &flags,
+			N_("open an editor to modify the commit message"),
+			COMMIT_TREE_EDIT_MESSAGE),
+		OPT_END(),
+	};
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct strbuf message = STRBUF_INIT;
+	struct oidset interior = OIDSET_INIT;
+	struct commit *base, *oldest, *tip, *rewritten, *msg_source,
+		*amend_source;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	const char *message_template = NULL;
+	struct commit_list *parents = NULL;
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage,
+			     PARSE_OPT_KEEP_UNKNOWN_OPT);
+	if (!argc) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
+
+	ret = resolve_squash_range(repo, argv, &base, &oldest, &tip,
+				   &interior);
+	if (ret < 0)
+		goto out;
+
+	ret = reject_dangling_fixups(repo, base, tip, oldest, &msg_source,
+				     &amend_source);
+	if (ret < 0)
+		goto out;
+	if (amend_source) {
+		const char *amend_message, *body;
+
+		amend_message = repo_logmsg_reencode(repo, amend_source,
+						     NULL, NULL);
+		find_commit_subject(amend_message, &body);
+		body = skip_blank_lines(body + commit_subject_length(body));
+		strbuf_addstr(&message, body);
+		message_template = message.buf;
+		repo_unuse_commit_buffer(repo, amend_source, amend_message);
+	}
+
+	if (action == REF_ACTION_BRANCHES) {
+		struct interior_ref_cb cb = { .interior = &interior };
+
+		refs_for_each_ref(get_main_ref_store(repo),
+				  find_interior_ref, &cb);
+		if (cb.name) {
+			ret = error(_("'%s' points into the squashed range"),
+				    cb.name);
+			advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+					  _("Use --update-refs=head to rewrite only "
+					    "the current branch and leave such refs "
+					    "untouched."));
+			free((char *)cb.name);
+			goto out;
+		}
+	}
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+	commit_list_append(base, &parents);
+
+	ret = commit_tree_ext(repo, "squash", msg_source, message_template,
+			      parents,
+			      base_tree_oid, tip_tree_oid, &rewritten, flags);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	strbuf_addf(&reflog_msg, "squash: updating %s", argv[0]);
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	strbuf_release(&message);
+	oidset_clear(&interior);
+	commit_list_free(parents);
+	release_revisions(&revs);
+	return ret;
+}
+
 int cmd_history(int argc,
 		const char **argv,
 		const char *prefix,
@@ -982,6 +1352,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -989,6 +1360,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
diff --git a/t/meson.build b/t/meson.build
index 7c3c070426..459e251623 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -400,6 +400,7 @@ integration_tests = [
   't3451-history-reword.sh',
   't3452-history-split.sh',
   't3453-history-fixup.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..d6199b9644
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,565 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+stage_file () {
+	printf "%s\n" "$1" >file &&
+	git add file
+}
+
+commit_with_message () {
+	printf "%b" "$1" >msg &&
+	git commit --allow-empty -qF msg
+}
+
+check_commit_count () {
+	git rev-list --count "$1" >actual &&
+	echo "$2" >expect &&
+	test_cmp expect actual
+}
+
+check_log_subjects () {
+	git log --format="%s" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+check_log_messages () {
+	git log --format="%B" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+test_expect_success 'setup linear history touching two files' '
+	test_commit base file a &&
+	git tag start &&
+	test_commit --no-tag one other x &&
+	test_commit --no-tag two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "expects a revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the revision range is empty" err
+'
+
+test_expect_success 'errors on a single revision that is not a range' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "not a .*range" err &&
+	test_must_fail git history squash HEAD~1 2>err &&
+	test_grep "not a .*range" err
+'
+
+test_expect_success 'errors on a range holding a single commit' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "HEAD^!" 2>err &&
+	test_grep "single commit; nothing to squash" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'accepts multiple revision arguments with an exclusion' '
+	git reset --hard three &&
+	git branch -f keep HEAD~2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..HEAD ^keep &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	two
+	one
+	EOF
+	test_cmp_rev keep HEAD~1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git branch -D keep
+'
+
+test_expect_success 'squashes a branch the current branch is not on' '
+	git reset --hard three &&
+	main=$(git symbolic-ref --short HEAD) &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b off-history start &&
+	test_commit --no-tag off-one off a &&
+	test_commit --no-tag off-two off b &&
+	git checkout "$main" &&
+
+	git history squash start..off-history &&
+
+	check_commit_count start..off-history 1 &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D off-history
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash start.. &&
+
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	check_log_subjects -1 <<-\EOF &&
+	one
+	EOF
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'sanitizes rev-list walk options, before and after --' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --date-order start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git reset --hard three &&
+	git history squash -- --reverse start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..@~1 &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	three
+	one
+	EOF
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$root.." &&
+
+	check_commit_count "$root..HEAD" 1 &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+
+test_expect_success 'folds fixups whose target is in the range' '
+	git reset --hard start &&
+	test_commit --no-tag target file b &&
+	git commit --allow-empty -m "fixup! target" &&
+	git commit --allow-empty -m "fixup! target" &&
+	test_commit --no-tag later file c &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF
+	target
+	EOF
+'
+
+test_expect_success 'refuses a below-range fixup! after an in-range commit' '
+	git reset --hard start &&
+	test_commit --no-tag inside file b &&
+	test_commit --no-tag "fixup! outside" file c &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "target is not in the range" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'combines a run of fixups for one commit below the range' '
+	git reset --hard start &&
+	stage_file b && git commit -m "fixup! base" &&
+	stage_file c && git commit -m "fixup! base" &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF
+	fixup! base
+	EOF
+'
+
+test_expect_success 'combining below-range fixups keeps the last amend! message' '
+	git reset --hard start &&
+	stage_file b && git commit -m "fixup! base" &&
+	stage_file c &&
+	commit_with_message "amend! base\n\namended body\n" &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_messages -1 <<-\EOF
+	amend! base
+
+	amended body
+
+	EOF
+'
+
+test_expect_success 'refuses fixups for two different commits below the range' '
+	git reset --hard start &&
+	stage_file b && git commit -m "fixup! aaa" &&
+	stage_file c && git commit -m "fixup! bbb" &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "target is not in the range" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'the last amend! for the oldest commit replaces its message' '
+	git reset --hard start &&
+	test_commit --no-tag marker-oldest file b &&
+	git commit --allow-empty -m "squash! marker-oldest" &&
+	commit_with_message "amend! marker-oldest\n\nearlier message\n" &&
+	commit_with_message \
+		"amend! marker-oldest\n\namended subject\n\namended body\n" &&
+	test_commit --no-tag marker-later file c &&
+	commit_with_message "amend! marker-later\n\nwrong message\n" &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_messages -1 <<-\EOF
+	amended subject
+
+	amended body
+
+	EOF
+'
+
+test_expect_success 'preserves authorship of the oldest commit' '
+	git reset --hard start &&
+	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
+		test_commit --no-tag oldest file b &&
+	test_commit newest file c &&
+
+	git history squash start.. &&
+
+	git log -1 --format="%an <%ae>" >actual &&
+	echo "Squasher <squash@example.com>" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --update-refs=head start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success 'refuses to fold a range a ref points into' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "error: .* points into the squashed range" err &&
+	test_grep "hint: .*--update-refs=head" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D mid
+'
+
+test_expect_success 'advice.historyUpdateRefs silences the hint' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "points into the squashed range" err &&
+	test_grep ! "hint:" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D mid
+'
+
+test_expect_success '--update-refs=head folds past a ref pointing into the range' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	mid_before=$(git rev-parse mid) &&
+
+	git history squash --update-refs=head start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev "$mid_before" mid &&
+
+	git branch -D mid
+'
+
+test_expect_success 'refuses to fold a range a tag points into' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "refs/tags/mark" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git tag -d mark
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout "$main" &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	test_commit --no-tag after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF &&
+	before-side
+	EOF
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a merge of a branch that forked at the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b base-fork-side &&
+	test_commit --no-tag base-fork-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag base-fork-main file b &&
+	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
+	git branch -D base-fork-side &&
+	test_commit --no-tag base-fork-tail file c &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'refuses a merge whose other parent is outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$base.." &&
+
+	check_commit_count "$base..HEAD" 1 &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'folds a range with two interior merges' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag two-merge-a file a1 &&
+	git checkout -b two-merge-s1 &&
+	test_commit --no-tag two-merge-s1 s1 x &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s1" two-merge-s1 &&
+	test_commit --no-tag two-merge-b file b1 &&
+	git checkout -b two-merge-s2 &&
+	test_commit --no-tag two-merge-s2 s2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s2" two-merge-s2 &&
+	git branch -D two-merge-s1 two-merge-s2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file s1 &&
+	test_path_is_file s2
+'
+
+test_expect_success 'folds a range with a nested merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b nested-outer &&
+	test_commit --no-tag nested-outer outer x &&
+	git checkout -b nested-inner &&
+	test_commit --no-tag nested-inner inner y &&
+	git checkout nested-outer &&
+	git merge --no-ff -m "merge inner" nested-inner &&
+	git checkout "$main" &&
+	test_commit --no-tag nested-main file b1 &&
+	git merge --no-ff -m "merge outer" nested-outer &&
+	git branch -D nested-outer nested-inner &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file outer &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range with an octopus merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag octo-base file a1 &&
+	git checkout -b octo-1 &&
+	test_commit --no-tag octo-1 o1 x &&
+	git checkout "$main" &&
+	git checkout -b octo-2 &&
+	test_commit --no-tag octo-2 o2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-1 octo-2 &&
+	git branch -D octo-1 octo-2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file o1 &&
+	test_path_is_file o2
+'
+
+test_expect_success 'refuses an octopus merge with an arm forked before the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b octo-pre &&
+	test_commit octo-pre-side pside x &&
+	git checkout "$main" &&
+	test_commit octo-pre-main file b1 &&
+	octo_base=$(git rev-parse HEAD) &&
+	git checkout -b octo-within &&
+	test_commit --no-tag octo-within wside y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-pre octo-within &&
+	merged=$(git rev-parse HEAD) &&
+	git branch -D octo-pre octo-within &&
+
+	test_must_fail git history squash "$octo_base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'refuses when a descendant above the range is a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag desc-one file b &&
+	test_commit --no-tag desc-two file c &&
+	git tag desc-tip &&
+	git checkout -b desc-above &&
+	test_commit --no-tag desc-above above x &&
+	git checkout "$main" &&
+	test_commit --no-tag desc-main file d &&
+	git merge --no-ff -m "merge desc-above" desc-above &&
+	git branch -D desc-above &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start..desc-tip 2>err &&
+	test_grep "merge commits is not supported" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'refuses to fold a range a ref points into at a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag refmerge-base file b &&
+	git checkout -b refmerge-side &&
+	test_commit --no-tag refmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag refmerge-main file c &&
+	git merge --no-ff -m "interior merge" refmerge-side &&
+	git branch -D refmerge-side &&
+	git branch at-merge HEAD &&
+	test_commit --no-tag refmerge-tail file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "at-merge" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D at-merge
+'
+
+test_done
-- 
gitgitgadget

Re: [PATCH v9 3/5] history: add squash subcommand to fold a range

[Matt Hunter]

Hi Harald,

The new functionality for amend! messages seems to be working well, so I
dug a little deeper and found the following...

On Wed Jul 15, 2026 at 11:16 AM EDT, Harald Nordgren via GitGitGadget wrote:
> ++
> +The range is given in the usual `<base>..<tip>` form, where _<base>_ is
> +the commit just below the oldest commit to squash. For example, `git
> +history squash HEAD~3..HEAD` folds the three most recent commits into
> +one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
> +while leaving the two newest commits in place. Several revisions may be
> +given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
> +already on `topic`. Rev-list options may also be given, but any that would
> +change how the range is walked are overridden with a warning.
> ++
> +The oldest commit's message is preserved by default, except that an `amend!`
> +commit targeting it replaces its message.

The new behavior from v9 is documented here, but...

>                                            Specify `--reedit-message` to edit
> +the resulting message. A merge commit inside the range is folded like any
> +other, but the range must have a single base, so a range that reaches more
> +than one entry point (for example a side branch that forked before the range
> +and was later merged into it) is rejected.
> ++
> +A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
> +targets is also in the range, so the fold does not silently absorb a
> +marker meant for a commit outside it. The body after an `amend!` subject
> +replaces the oldest commit's message when the marker targets that commit.

...a redundant explanation appears here too.  Personally, I think this
paragraph flows better if the 'The body after an `amend!`...targets that
commit.' sentence were removed.

> +As an exception, a range made up entirely of markers for one target is combined
> +into a single commit, keeping the last `amend!` message if there is one.
> ++
> +A branch or tag that points at a commit inside the range would be left
> +dangling once those commits are folded away, so with the default
> +`--update-refs=branches` the command refuses. Rerun with
> +`--update-refs=head` to rewrite only the current branch and leave such
> +refs pointing at the old commits.
> +
>  OPTIONS
>  -------
>  
> @@ -107,7 +147,8 @@ OPTIONS
>  	ref updates is generally safe.
>  
>  `--reedit-message`::
> -	Open an editor to modify the target commit's message.
> +	Open an editor to modify the rewritten commit's message. For `squash`
> +	the editor is pre-filled with the messages of all the folded commits.

At the moment of this patch, this is a false statement, though it is
made true by patch 5/5 pre-filling all messages.

> diff --git a/builtin/history.c b/builtin/history.c
> index cbba25096f..edf98a21d3 100644
> --- a/builtin/history.c
> +++ b/builtin/history.c
> +
> +	repo_init_revisions(repo, &revs, NULL);
> +	revs.reverse = 1;
> +	revs.topo_order = 1;
> +	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
> +	revs.simplify_history = 0;
> +	revs.boundary = 1;
> +
> +	strvec_push(&args, "ignored");
> +	strvec_push(&args, "--ancestry-path");
> +	strvec_pushv(&args, argv);
> +	setup_revisions_from_strvec(&args, &revs, NULL);
> +	if (args.nr != 1) {
> +		ret = error(_("unrecognized argument: %s"), args.v[1]);
> +		goto out;
> +	}
> +
> +	if (revs.reverse != 1 || revs.topo_order != 1 ||
> +	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
> +	    revs.simplify_history != 0) {
> +		warning(_("ignoring rev-list options that would change how the "
> +			  "range is walked"));
> +		revs.reverse = 1;
> +		revs.topo_order = 1;
> +		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
> +		revs.simplify_history = 0;
> +	}

Should revs.boundary still == 1 be asserted here too?

> +
> +	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
> +	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
> +	commit_list_append(base, &parents);
> +
> +	ret = commit_tree_ext(repo, "squash", msg_source, message_template,
> +			      parents,
> +			      base_tree_oid, tip_tree_oid, &rewritten, flags);
> +	if (ret < 0) {
> +		ret = error(_("failed writing squashed commit"));
> +		goto out;
> +	}
> +
> +	strbuf_addf(&reflog_msg, "squash: updating %s", argv[0]);

With this format string, the reflog will miss cases like:

    git history squash HEAD~5..HEAD ^origin/master

Only "squash: updating HEAD~5..HEAD" will be recorded in the log.

Re: [PATCH v9 3/5] history: add squash subcommand to fold a range

[Harald Nordgren]

Thanks, good points!


Harald

[PATCH v9 4/5] sequencer: share the squash message marker helpers and flags

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

When "git rebase -i" squashes commits it builds an editor template with a
"This is a combination of N commits." banner, a "This is the 1st/Nth
commit message:" header above each kept message (or a "will be skipped"
header for a dropped one), and a commented-out subject for any fixup!,
squash! or amend! commit. The banner, the headers and the
subject-commenting all live in static helpers in sequencer.c wired to the
rebase state, so no other command can present a squash the same way.

Pull the three pieces out into add_squash_combination_header(),
add_squash_message_header() (which takes a flag for the "will be skipped"
variant) and squash_subject_comment_len(), and use them from
update_squash_messages() and append_squash_message(). Also move the
todo_item_flags enum to the header, so a caller reading the output of
todo_list_rearrange_squash() can tell an amend! (TODO_REPLACE_FIXUP_MSG)
from a plain fixup!. A later change reuses all of this to give "git
history squash --reedit-message" the same template.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 sequencer.c | 70 +++++++++++++++++++++++++++++------------------------
 sequencer.h | 30 +++++++++++++++++++++++
 2 files changed, 69 insertions(+), 31 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 0fe8fed6c3..2387afd9b5 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1880,18 +1880,38 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
-enum todo_item_flags {
-	TODO_EDIT_MERGE_MSG    = (1 << 0),
-	TODO_REPLACE_FIXUP_MSG = (1 << 1),
-	TODO_EDIT_FIXUP_MSG    = (1 << 2),
-};
-
 static const char first_commit_msg_str[] = N_("This is the 1st commit message:");
 static const char nth_commit_msg_fmt[] = N_("This is the commit message #%d:");
 static const char skip_first_commit_msg_str[] = N_("The 1st commit message will be skipped:");
 static const char skip_nth_commit_msg_fmt[] = N_("The commit message #%d will be skipped:");
 static const char combined_commit_msg_fmt[] = N_("This is a combination of %d commits.");
 
+void add_squash_combination_header(struct strbuf *buf, int n)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	strbuf_addf(buf, _(combined_commit_msg_fmt), n);
+}
+
+void add_squash_message_header(struct strbuf *buf, int n, int skip)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	if (n == 1)
+		strbuf_addstr(buf, skip ? _(skip_first_commit_msg_str) :
+				   _(first_commit_msg_str));
+	else
+		strbuf_addf(buf, skip ? _(skip_nth_commit_msg_fmt) :
+			    _(nth_commit_msg_fmt), n);
+}
+
+size_t squash_subject_comment_len(const char *body, int squashing)
+{
+	if (starts_with(body, "amend!") ||
+	    (squashing && (starts_with(body, "squash!") ||
+			   starts_with(body, "fixup!"))))
+		return commit_subject_length(body);
+	return 0;
+}
+
 static int is_fixup_flag(enum todo_command command, unsigned flag)
 {
 	return command == TODO_FIXUP && ((flag & TODO_REPLACE_FIXUP_MSG) ||
@@ -2005,20 +2025,13 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 {
 	struct replay_ctx *ctx = opts->ctx;
 	const char *fixup_msg;
-	size_t commented_len = 0, fixup_off;
-	/*
-	 * amend is non-interactive and not normally used with fixup!
-	 * or squash! commits, so only comment out those subjects when
-	 * squashing commit messages.
-	 */
-	if (starts_with(body, "amend!") ||
-	    ((command == TODO_SQUASH || seen_squash(ctx)) &&
-	     (starts_with(body, "squash!") || starts_with(body, "fixup!"))))
-		commented_len = commit_subject_length(body);
+	size_t commented_len, fixup_off;
+
+	commented_len = squash_subject_comment_len(body,
+				command == TODO_SQUASH || seen_squash(ctx));
 
-	strbuf_addf(buf, "\n%s ", comment_line_str);
-	strbuf_addf(buf, _(nth_commit_msg_fmt),
-		    ++ctx->current_fixup_count + 1);
+	strbuf_addch(buf, '\n');
+	add_squash_message_header(buf, ++ctx->current_fixup_count + 1, 0);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len, comment_line_str);
 	/* buf->buf may be reallocated so store an offset into the buffer */
@@ -2083,9 +2096,8 @@ static int update_squash_messages(struct repository *r,
 		eol = !starts_with(buf.buf, comment_line_str) ?
 			buf.buf : strchrnul(buf.buf, '\n');
 
-		strbuf_addf(&header, "%s ", comment_line_str);
-		strbuf_addf(&header, _(combined_commit_msg_fmt),
-			    ctx->current_fixup_count + 2);
+		add_squash_combination_header(&header,
+					      ctx->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);
 		if (is_fixup_flag(command, flag) && !seen_squash(ctx))
@@ -2109,12 +2121,9 @@ static int update_squash_messages(struct repository *r,
 			repo_unuse_commit_buffer(r, head_commit, head_message);
 			return error(_("cannot write '%s'"), rebase_path_fixup_msg());
 		}
-		strbuf_addf(&buf, "%s ", comment_line_str);
-		strbuf_addf(&buf, _(combined_commit_msg_fmt), 2);
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addstr(&buf, is_fixup_flag(command, flag) ?
-			      _(skip_first_commit_msg_str) :
-			      _(first_commit_msg_str));
+		add_squash_combination_header(&buf, 2);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, 1, is_fixup_flag(command, flag));
 		strbuf_addstr(&buf, "\n\n");
 		if (is_fixup_flag(command, flag))
 			strbuf_add_commented_lines(&buf, body, strlen(body),
@@ -2133,9 +2142,8 @@ static int update_squash_messages(struct repository *r,
 	if (command == TODO_SQUASH || is_fixup_flag(command, flag)) {
 		res = append_squash_message(&buf, body, command, opts, flag);
 	} else if (command == TODO_FIXUP) {
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),
-			    ++ctx->current_fixup_count + 1);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, ++ctx->current_fixup_count + 1, 1);
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body),
 					   comment_line_str);
diff --git a/sequencer.h b/sequencer.h
index 64a9c7fb1b..b01f897020 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,6 +119,13 @@ enum todo_command {
 	TODO_COMMENT
 };
 
+/* Bits for the "flags" member of struct todo_item */
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG    = (1 << 0),
+	TODO_REPLACE_FIXUP_MSG = (1 << 1),
+	TODO_EDIT_FIXUP_MSG    = (1 << 2),
+};
+
 struct todo_item {
 	enum todo_command command;
 	struct commit *commit;
@@ -208,6 +215,29 @@ int todo_list_rearrange_squash(struct todo_list *todo_list);
  */
 void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
 
+/*
+ * Append the "This is a combination of N commits." banner that "git rebase
+ * -i" writes at the top of a squashed commit's message, commented out with
+ * the comment character.
+ */
+void add_squash_combination_header(struct strbuf *buf, int n);
+
+/*
+ * Append the header (1-based N) that "git rebase -i" writes above each message
+ * when squashing, commented out with the comment character. With SKIP it reads
+ * "The ... commit message will be skipped" for a message that is dropped (a
+ * fixup), otherwise "This is the ... commit message".
+ */
+void add_squash_message_header(struct strbuf *buf, int n, int skip);
+
+/*
+ * Return the length of the leading subject of BODY when it should be commented
+ * out in a squash message, or 0 otherwise. An "amend!" subject always
+ * qualifies; "squash!" and "fixup!" subjects only when SQUASHING, since a
+ * plain fixup chain keeps them.
+ */
+size_t squash_subject_comment_len(const char *body, int squashing);
+
 void append_conflicts_hint(struct index_state *istate,
 		struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
 enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,
-- 
gitgitgadget

[PATCH v9 5/5] history: re-edit a squash with every message

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

By default "git history squash" reuses the oldest commit's message, or
the replacement body from an amend! commit targeting it. When
--reedit-message is given it only reopened that selected message, so the
messages of the other commits in the range were lost.

Gather the message of every commit in the range and build the same editor
template that "git rebase -i --autosquash" shows for a squash, reusing
add_squash_combination_header(), add_squash_message_header() and
squash_subject_comment_len(). Feed the range through
todo_list_rearrange_squash() so that each fixup!, squash! or amend! is
grouped under the commit it targets rather than shown in commit order,
exactly as autosquash would arrange them.

Only the message text differs, the changes are always folded in. A fixup!
message is commented out in full under a "will be skipped" header, a
squash! keeps its body with only the marker subject commented, and an
amend! replaces its target's message unless a squash! already folded into
that target, in which case it behaves like a squash!.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  20 +++-
 builtin/history.c              | 104 +++++++++++++++++
 t/t3455-history-squash.sh      | 201 +++++++++++++++++++++++++++++++++
 3 files changed, 320 insertions(+), 5 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 2c0d861303..dc5580531f 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -118,11 +118,12 @@ already on `topic`. Rev-list options may also be given, but any that would
 change how the range is walked are overridden with a warning.
 +
 The oldest commit's message is preserved by default, except that an `amend!`
-commit targeting it replaces its message. Specify `--reedit-message` to edit
-the resulting message. A merge commit inside the range is folded like any
-other, but the range must have a single base, so a range that reaches more
-than one entry point (for example a side branch that forked before the range
-and was later merged into it) is rejected.
+commit targeting it replaces its message. With `--reedit-message`, an editor
+opens pre-filled with the messages of all the folded commits so you can
+combine them. A merge commit inside the range is folded like any other, but
+the range must have a single base, so a range that reaches more than one entry
+point (for example a side branch that forked before the range and was later
+merged into it) is rejected.
 +
 A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
 targets is also in the range, so the fold does not silently absorb a
@@ -130,6 +131,15 @@ marker meant for a commit outside it. The body after an `amend!` subject
 replaces the oldest commit's message when the marker targets that commit. As
 an exception, a range made up entirely of markers for one target is combined
 into a single commit, keeping the last `amend!` message if there is one.
+The changes from every commit in the range are always folded in. Only the
+message text differs.
+With `--reedit-message` the template mirrors `git rebase -i --autosquash`:
+each `fixup!`, `squash!`, or `amend!` is grouped under the commit it
+targets rather than shown in commit order. A `fixup!` message is dropped
+(commented out in full), a `squash!` keeps its body with only the marker
+subject commented, and an `amend!` replaces its target's message, unless
+a `squash!` folded into that target first, in which case it keeps its
+body like a `squash!`.
 +
 A branch or tag that points at a commit inside the range would be left
 dangling once those commits are folded away, so with the default
diff --git a/builtin/history.c b/builtin/history.c
index edf98a21d3..b1f84e8297 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1223,6 +1223,102 @@ static int find_interior_ref(const struct reference *ref, void *cb_data)
 	return 0;
 }
 
+static bool amend_replaces_target(struct todo_list *todo, int target)
+{
+	int i;
+
+	for (i = target + 1; i < todo->nr &&
+			     todo->items[i].command != TODO_PICK; i++) {
+		if (todo->items[i].command == TODO_SQUASH)
+			return false;
+		if (todo->items[i].flags & TODO_REPLACE_FIXUP_MSG)
+			return true;
+	}
+	return false;
+}
+
+static int build_squash_message(struct repository *repo,
+				struct commit *base,
+				struct commit *tip,
+				struct strbuf *out)
+{
+	struct rev_info revs;
+	struct commit *commit;
+	struct strvec args = STRVEC_INIT;
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	int i, nr_commits, ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs)))
+		strbuf_addf(&todo.buf, "pick %s\n",
+			    oid_to_hex(&commit->object.oid));
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not prepare the squash message"));
+		goto out;
+	}
+
+	nr_commits = todo.nr;
+	for (i = 0; i < nr_commits; i++) {
+		struct todo_item *item = &todo.items[i];
+		const char *message, *body;
+		size_t commented_len;
+		bool skip, squashing;
+
+		squashing = item->command == TODO_SQUASH ||
+			    (item->flags & TODO_REPLACE_FIXUP_MSG);
+		if (item->command == TODO_PICK)
+			skip = amend_replaces_target(&todo, i);
+		else
+			skip = !squashing;
+
+		message = repo_logmsg_reencode(repo, item->commit, NULL, NULL);
+		find_commit_subject(message, &body);
+
+		if (skip)
+			commented_len = strlen(body);
+		else if (squashing)
+			commented_len = squash_subject_comment_len(body, 1);
+		else
+			commented_len = 0;
+
+		if (!i)
+			add_squash_combination_header(out, nr_commits);
+		strbuf_addch(out, '\n');
+		add_squash_message_header(out, i + 1, skip);
+		strbuf_addstr(out, "\n\n");
+		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
+		strbuf_addstr(out, body + commented_len);
+		strbuf_complete_line(out);
+
+		repo_unuse_commit_buffer(repo, item->commit, message);
+	}
+
+	ret = 0;
+
+out:
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1306,6 +1402,14 @@ static int cmd_history_squash(int argc,
 		}
 	}
 
+	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
+		strbuf_reset(&message);
+		ret = build_squash_message(repo, base, tip, &message);
+		if (ret < 0)
+			goto out;
+		message_template = message.buf;
+	}
+
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
 		goto out;
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index d6199b9644..f2835f5379 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -267,6 +267,207 @@ test_expect_success 'preserves authorship of the oldest commit' '
 	test_cmp expect actual
 '
 
+test_expect_success '--reedit-message offers every folded-in message' '
+	git reset --hard start &&
+	stage_file b &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# This is the 1st commit message:
+
+	re-one subject
+
+	re-one body line
+
+	# This is the commit message #2:
+
+	re-two
+
+	# This is the commit message #3:
+
+	re-three
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_subjects -1 <<-\EOF
+	combined
+	EOF
+'
+
+test_expect_success '--reedit-message handles fixup!, squash! and amend! like rebase' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "fixup! mark-base\n\nfixup body\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+	stage_file e &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	mark-base
+
+	# The commit message #2 will be skipped:
+
+	# fixup! mark-base
+	#
+	# fixup body
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# This is the commit message #4:
+
+	# amend! mark-base
+
+	amended message
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	mark-base
+
+	squash remark
+
+	amended message
+
+	EOF
+'
+
+test_expect_success '--reedit-message groups fixups under their targets' '
+	git reset --hard start &&
+	test_commit --no-tag alpha file a1 &&
+	test_commit --no-tag beta file b1 &&
+	stage_file a2 &&
+	commit_with_message "fixup! alpha\n" &&
+	stage_file b2 &&
+	commit_with_message "fixup! beta\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	alpha
+
+	# The commit message #2 will be skipped:
+
+	# fixup! alpha
+
+	# This is the commit message #3:
+
+	beta
+
+	# The commit message #4 will be skipped:
+
+	# fixup! beta
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited
+'
+
+test_expect_success '--reedit-message lets amend! replace its target message' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# The 1st commit message will be skipped:
+
+	# mark-base
+
+	# This is the commit message #2:
+
+	# amend! mark-base
+
+	amended message
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	amended message
+
+	squash remark
+
+	EOF
+'
+
+test_expect_success '--reedit-message aborts on an empty message' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	test_must_fail git history squash --reedit-message start.. &&
+
+	test_cmp_rev "$head_before" HEAD
+'
+
 test_expect_success '--update-refs=head only moves HEAD' '
 	git reset --hard three &&
 	git branch -f other HEAD &&
-- 
gitgitgadget

Re: [PATCH v9 5/5] history: re-edit a squash with every message

[Matt Hunter]

On Wed Jul 15, 2026 at 11:16 AM EDT, Harald Nordgren via GitGitGadget wrote:
> @@ -130,6 +131,15 @@ marker meant for a commit outside it. The body after an `amend!` subject
>  replaces the oldest commit's message when the marker targets that commit. As
>  an exception, a range made up entirely of markers for one target is combined
>  into a single commit, keeping the last `amend!` message if there is one.

> +The changes from every commit in the range are always folded in. Only the
> +message text differs.

This sentence kept puzzling me when I re-read this part.  That isn't to
say that it doesn't make sense on its own, or isn't correct.  But in
this context, I wasn't sure why it was included.

For whatever reason, the diff from your v8 made it click, and I believe
you're trying to explain the previous sentence about the last `amend!`,
stating that all the other _effects_ of the other fixup!s are also kept
even though the message changes.  Is that right?

If so, I might suggest removing this sentence too.  At least to my
brain, it doesn't contribute to my understanding of the command, and
makes the paragraph feel like it changes subject in the middle.

> +With `--reedit-message` the template mirrors `git rebase -i --autosquash`:
> +each `fixup!`, `squash!`, or `amend!` is grouped under the commit it
> +targets rather than shown in commit order. A `fixup!` message is dropped
> +(commented out in full), a `squash!` keeps its body with only the marker
> +subject commented, and an `amend!` replaces its target's message, unless
> +a `squash!` folded into that target first, in which case it keeps its
> +body like a `squash!`.

This bit that comes right after would possibly do better as its own
paragraph imo.

Thanks!

Re: [PATCH v9 5/5] history: re-edit a squash with every message

[Harald Nordgren]

Good points!


Harald

[PATCH v10 0/5] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v10:

 * Record the full revision expression in squash reflog.
 * Preserve the boundary-walk invariant when sanitizing rev-list options.
 * Clarify amend! and --reedit-message documentation.

Changes in v9:

 * Use the last amend! targeting the oldest folded commit as the default
   squashed message. Ignore amend! markers targeting later commits while
   selecting that replacement message.
 * Improve tests.

Changes in v8:

 * --reedit-message now builds the same editor template as git rebase -i
   --autosquash: fixup!, squash! and amend! commits are grouped under the
   commit they target instead of shown in commit order, and an amend!
   replaces its target's message.
 * A fixup!, squash! or amend! is refused only when its target is outside
   the range, so several fixups for an in-range commit fold together. A
   range that is entirely markers for one below-range target is combined
   into a single commit, keeping the last amend! message.
 * Merges inside the range are folded when the range has a single base, with
   no dedicated opt-in flag, --ancestry-path ensures only commits descended
   from the base are folded, and a range reaching more than one base is
   rejected.
 * Rev-list options are accepted and sanitized the way git replay does,
   forcing the walk order back with a warning, which also fixes git history
   squash -- --reverse slipping past the previous option check.
 * Kept this as an explicit squash subcommand rather than making
   --reedit-message the default or renaming the command.

Changes in v7:

 * --reedit-message now builds the same editor template git rebase -i shows
   for a squash (a combination of N commits banner with each folded message
   under its own header) and follows autosquash for markers: a fixup!
   message falls out (commented under a will be skipped header), while a
   squash! or amend! keeps its body with only the marker subject commented
   so its remark can be reworded in. Only the message text is affected,
   every commit's changes are always folded in.
 * Reuse git rebase -i's squash-message code: a preparatory sequencer:
   commit extracts the banner, header and marker-comment helpers so both
   rebase and git history squash build the identical template from one
   source.
 * Refuse a range whose oldest commit is a fixup!, squash! or amend!, since
   the marker's target cannot be inside the range.
 * Reorder the squash usage so dashed options come before <revision-range>,
   and spell out HEAD instead of @ in the documentation and examples.
 * Expand the squash commit message and documentation with this overview,
   and scope the merge limitation so it no longer contradicts squash folding
   a single-base interior merge.

Changes in v6:

 * git history squash now accepts multiple revision arguments, read like the
   arguments to git-rev-list, so a compound range such as @~3.. ^topic
   works.
 * The base to reparent onto is now the oldest in-range commit's parent; a
   boundary other than that base means the range has more than one base and
   is rejected. This also fixes the earlier overly-restrictive handling of
   merges and side branches.
 * A single-commit range (e.g. @^!) is rejected with "nothing to squash"
   (this also covers the @^!-style example that previously succeeded
   silently).
 * Commit messages reworded: the squash commit now gives an overview of
   fixup!/squash!/amend! handling, rewording, merge-parent and ref behavior.

Changes in v5:

 * The range walk now uses --ancestry-path, so only commits descended from
   the base are folded; a single revision such as HEAD or HEAD~1 is now
   rejected as "not a <base>..<tip> range" rather than treated as a squash
   down to the root.
 * This adopts the --ancestry-path suggestion; the multi-base rejection is
   unchanged, so a side branch that forked before the base and merged in is
   still refused.
 * Added tests covering more merge topologies: two interior merges, a nested
   merge, an octopus merge, an octopus arm forked before the base, a merge
   among the descendants replayed above the range, and a ref pointing at an
   interior merge commit.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (5):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  history: add squash subcommand to fold a range
  sequencer: share the squash message marker helpers and flags
  history: re-edit a squash with every message

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  55 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 552 ++++++++++++++++++++--
 sequencer.c                      |  70 +--
 sequencer.h                      |  30 ++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 770 +++++++++++++++++++++++++++++++
 9 files changed, 1412 insertions(+), 72 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: 41365c2a9ba347870b80881c0d67454edd22fd49
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v10
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v10
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v9:

 1:  352c818c29 = 1:  f848103497 history: extract helper for a commit's parent tree
 2:  e06e49095b = 2:  49dadc3410 history: give commit_tree_ext a message template
 3:  ead974c317 ! 3:  6b5b2c93f2 history: add squash subcommand to fold a range
     @@ Documentation/config/advice.adoc: all advice messages.
       		set as executable.
      
       ## Documentation/git-history.adoc ##
     -@@ Documentation/git-history.adoc: SYNOPSIS
     +@@ Documentation/git-history.adoc: git history drop <commit> [--dry-run] [--update-refs=(branches|head)] [--empty=(
       git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
       git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
       git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      ++
      +A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
      +targets is also in the range, so the fold does not silently absorb a
     -+marker meant for a commit outside it. The body after an `amend!` subject
     -+replaces the oldest commit's message when the marker targets that commit. As
     -+an exception, a range made up entirely of markers for one target is combined
     -+into a single commit, keeping the last `amend!` message if there is one.
     ++marker meant for a commit outside it. As an exception, a range made up entirely
     ++of markers for one target is combined into a single commit, keeping the last
     ++`amend!` message if there is one.
      ++
      +A branch or tag that points at a commit inside the range would be left
      +dangling once those commits are folded away, so with the default
     @@ Documentation/git-history.adoc: OPTIONS
       
       `--reedit-message`::
      -	Open an editor to modify the target commit's message.
     -+	Open an editor to modify the rewritten commit's message. For `squash`
     -+	the editor is pre-filled with the messages of all the folded commits.
     ++	Open an editor to modify the rewritten commit's message.
       
       `--empty=(drop|keep|abort)`::
       	Control what happens when a commit becomes empty as a result of the
     @@ builtin/history.c: out:
      +
      +	if (revs.reverse != 1 || revs.topo_order != 1 ||
      +	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
     -+	    revs.simplify_history != 0) {
     ++	    revs.simplify_history != 0 || revs.boundary != 1) {
      +		warning(_("ignoring rev-list options that would change how the "
      +			  "range is walked"));
      +		revs.reverse = 1;
      +		revs.topo_order = 1;
      +		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
      +		revs.simplify_history = 0;
     ++		revs.boundary = 1;
      +	}
      +
      +	/*
     @@ builtin/history.c: out:
      +		goto out;
      +	}
      +
     -+	strbuf_addf(&reflog_msg, "squash: updating %s", argv[0]);
     ++	strbuf_addstr(&reflog_msg, "squash: updating ");
     ++	strbuf_join_argv(&reflog_msg, argc, argv, ' ');
      +
      +	ret = handle_reference_updates(&revs, action, tip, rewritten,
      +				       reflog_msg.buf, dry_run,
     @@ builtin/history.c: out:
      +	return ret;
      +}
      +
     - int cmd_history(int argc,
     - 		const char **argv,
     - 		const char *prefix,
     + static int update_worktree(struct repository *repo,
     + 			   const struct commit *old_head,
     + 			   const struct commit *new_head,
      @@ builtin/history.c: int cmd_history(int argc,
       		GIT_HISTORY_FIXUP_USAGE,
       		GIT_HISTORY_REWORD_USAGE,
     @@ builtin/history.c: int cmd_history(int argc,
      
       ## t/meson.build ##
      @@ t/meson.build: integration_tests = [
     -   't3451-history-reword.sh',
         't3452-history-split.sh',
         't3453-history-fixup.sh',
     +   't3454-history-drop.sh',
      +  't3455-history-squash.sh',
         't3500-cherry.sh',
         't3501-revert-cherry-pick.sh',
     @@ t/t3455-history-squash.sh (new)
      +
      +	git history squash start..HEAD ^keep &&
      +
     ++	git reflog -1 --format=%gs >actual &&
     ++	echo "squash: updating start..HEAD ^keep" >expect &&
     ++	test_cmp expect actual &&
     ++
      +	check_log_subjects start..HEAD <<-\EOF &&
      +	two
      +	one
 4:  08915cee51 = 4:  41156c9afb sequencer: share the squash message marker helpers and flags
 5:  fb76afe31c ! 5:  cdbc183428 history: re-edit a squash with every message
     @@ Documentation/git-history.adoc: already on `topic`. Rev-list options may also be
       +
       A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
       targets is also in the range, so the fold does not silently absorb a
     -@@ Documentation/git-history.adoc: marker meant for a commit outside it. The body after an `amend!` subject
     - replaces the oldest commit's message when the marker targets that commit. As
     - an exception, a range made up entirely of markers for one target is combined
     - into a single commit, keeping the last `amend!` message if there is one.
     -+The changes from every commit in the range are always folded in. Only the
     -+message text differs.
     +@@ Documentation/git-history.adoc: marker meant for a commit outside it. As an exception, a range made up entirely
     + of markers for one target is combined into a single commit, keeping the last
     + `amend!` message if there is one.
     + +
      +With `--reedit-message` the template mirrors `git rebase -i --autosquash`:
      +each `fixup!`, `squash!`, or `amend!` is grouped under the commit it
      +targets rather than shown in commit order. A `fixup!` message is dropped
     @@ Documentation/git-history.adoc: marker meant for a commit outside it. The body a
      +subject commented, and an `amend!` replaces its target's message, unless
      +a `squash!` folded into that target first, in which case it keeps its
      +body like a `squash!`.
     - +
     +++
       A branch or tag that points at a commit inside the range would be left
       dangling once those commits are folded away, so with the default
     + `--update-refs=branches` the command refuses. Rerun with
     +@@ Documentation/git-history.adoc: OPTIONS
     + 	ref updates is generally safe.
     + 
     + `--reedit-message`::
     +-	Open an editor to modify the rewritten commit's message.
     ++	Open an editor to modify the rewritten commit's message. For `squash`
     ++	the editor is pre-filled with the messages of all the folded commits.
     + 
     + `--empty=(drop|keep|abort)`::
     + 	Control what happens when a commit becomes empty as a result of the
      
       ## builtin/history.c ##
      @@ builtin/history.c: static int find_interior_ref(const struct reference *ref, void *cb_data)

-- 
gitgitgadget

[PATCH v10 1/5] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index d28c1f08bb..673744a55a 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -164,6 +164,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -171,21 +190,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -475,18 +484,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -830,16 +831,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v10 2/5] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 673744a55a..b592b98393 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -108,6 +108,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -137,13 +138,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -196,7 +200,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -675,7 +679,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -886,7 +890,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -903,7 +907,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v10 3/5] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git history squash <revision-range>" to do this directly. It folds
every commit in the range into the oldest one, keeping that commit's
authorship and taking the tree of the newest commit, then replays the
commits above the range on top. The squashed message comes from the
oldest commit by default, or from the body of the last amend! commit
targeting it. An editor opens with the selected message when
--reedit-message is given. A fixup!, squash! or amend! commit is refused
unless the commit it targets is also in the range, so the fold does not
silently absorb a marker meant for a commit outside it. The check runs
the range through todo_list_rearrange_squash(), which leaves such a
marker as a plain pick. Markers whose target is in the range fold in as
usual. As an exception, a range made up entirely of markers for one
target is combined anyway, taking its message from the last amend! if
there is one, so a batch of fixups for the same commit can be collapsed.

The range is read like the arguments to "git rev-list", so several
revisions such as "HEAD~3..HEAD ^topic" may be given, and rev-list
options are accepted too. As "git replay" does, the walk options the fold
relies on are forced after setup_revisions() and a warning is printed if
an option changed them, so the first commit returned is the range's
oldest and its parent is the base regardless of what the user passed
(including after a "--"). A merge inside the range is folded when its
other parent is reachable from the base, otherwise the range has more
than one base and is rejected. By default the command also refuses when a
ref points at a commit that the fold would discard. Use --update-refs=head
to rewrite only the current branch instead.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  45 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 374 ++++++++++++++++++++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 569 +++++++++++++++++++++++++++++++
 7 files changed, 992 insertions(+), 3 deletions(-)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 81f80a9274..e2a3487778 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -59,6 +59,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a ref points
+		into the range being folded, to tell the user about
+		`--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 28b477cd37..e1e930f355 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -12,6 +12,7 @@ git history drop <commit> [--dry-run] [--update-refs=(branches|head)] [--empty=(
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>
 
 DESCRIPTION
 -----------
@@ -43,8 +44,11 @@ at once.
 LIMITATIONS
 -----------
 
-This command does not (yet) work with histories that contain merges. You
-should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
+This command does not (yet) replay merge commits onto the rewritten
+history: if a commit that would be replayed is a merge, the operation is
+rejected, and you should use linkgit:git-rebase[1] with the
+`--rebase-merges` flag instead. The `squash` subcommand can still fold a
+merge that lies inside the range, as long as the range has a single base.
 
 Furthermore, the command does not support operations that can result in merge
 conflicts. This limitation is by design as history rewrites are not intended to
@@ -113,6 +117,41 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's authorship and
+	takes the tree of the range's newest commit, so the whole range
+	collapses into a single commit. Commits above the range are replayed
+	on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash HEAD~3..HEAD` folds the three most recent commits into
+one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
+while leaving the two newest commits in place. Several revisions may be
+given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
+already on `topic`. Rev-list options may also be given, but any that would
+change how the range is walked are overridden with a warning.
++
+The oldest commit's message is preserved by default, except that an `amend!`
+commit targeting it replaces its message. Specify `--reedit-message` to edit
+the resulting message. A merge commit inside the range is folded like any
+other, but the range must have a single base, so a range that reaches more
+than one entry point (for example a side branch that forked before the range
+and was later merged into it) is rejected.
++
+A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
+targets is also in the range, so the fold does not silently absorb a
+marker meant for a commit outside it. As an exception, a range made up entirely
+of markers for one target is combined into a single commit, keeping the last
+`amend!` message if there is one.
++
+A branch or tag that points at a commit inside the range would be left
+dangling once those commits are folded away, so with the default
+`--update-refs=branches` the command refuses. Rerun with
+`--update-refs=head` to rewrite only the current branch and leave such
+refs pointing at the old commits.
+
 OPTIONS
 -------
 
@@ -123,7 +162,7 @@ OPTIONS
 	ref updates is generally safe.
 
 `--reedit-message`::
-	Open an editor to modify the target commit's message.
+	Open an editor to modify the rewritten commit's message.
 
 `--empty=(drop|keep|abort)`::
 	Control what happens when a commit becomes empty as a result of the
diff --git a/advice.c b/advice.c
index 63bf8b0c5f..401d047391 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 66f6cd6a77..3f0b4f0485 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index b592b98393..423c8beaaf 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -34,6 +35,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -1004,6 +1007,375 @@ out:
 	return ret;
 }
 
+/*
+ * Resolve a "<base>..<tip>" revision range into the base commit just outside
+ * the range (which becomes the parent of the squashed commit), the oldest
+ * commit contained in the range (whose message the squash reuses), and the
+ * range tip (whose tree becomes the result). A merge inside the range is fine,
+ * but the range must have a single base and must not reach a root commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				const char **argv,
+				struct commit **base_out,
+				struct commit **oldest_out,
+				struct commit **tip_out,
+				struct oidset *interior_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
+	struct commit_list *boundaries = NULL, *b;
+	struct strvec args = STRVEC_INIT;
+	size_t i;
+	int ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	revs.reverse = 1;
+	revs.topo_order = 1;
+	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+	revs.simplify_history = 0;
+	revs.boundary = 1;
+
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--ancestry-path");
+	strvec_pushv(&args, argv);
+	setup_revisions_from_strvec(&args, &revs, NULL);
+	if (args.nr != 1) {
+		ret = error(_("unrecognized argument: %s"), args.v[1]);
+		goto out;
+	}
+
+	if (revs.reverse != 1 || revs.topo_order != 1 ||
+	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
+	    revs.simplify_history != 0 || revs.boundary != 1) {
+		warning(_("ignoring rev-list options that would change how the "
+			  "range is walked"));
+		revs.reverse = 1;
+		revs.topo_order = 1;
+		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+		revs.simplify_history = 0;
+		revs.boundary = 1;
+	}
+
+	/*
+	 * A squash needs a base to reparent onto, so the range has to exclude
+	 * something, as in "<base>..<tip>". A revision range with no such
+	 * bottom commit cannot be squashed.
+	 */
+	for (i = 0; i < revs.cmdline.nr; i++)
+		if (revs.cmdline.rev[i].flags & UNINTERESTING)
+			break;
+	if (i == revs.cmdline.nr) {
+		ret = error(_("not a '<base>..<tip>' revision range"));
+		goto out;
+	}
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	/*
+	 * Set boundary commits aside for the base check below, and put every
+	 * in-range commit but the tip into the interior set. A ref pointing
+	 * at an interior commit would dangle once the range is folded away.
+	 */
+	while ((commit = get_revision(&revs))) {
+		if (commit->object.flags & BOUNDARY) {
+			commit_list_insert(commit, &boundaries);
+			continue;
+		}
+		if (!oldest)
+			oldest = commit;
+		if (tip)
+			oidset_insert(interior_out, &tip->object.oid);
+		tip = commit;
+	}
+
+	if (!oldest) {
+		ret = error(_("the revision range is empty"));
+		goto out;
+	} else if (oldest == tip) {
+		ret = error(_("the revision range holds a single commit; "
+			      "nothing to squash"));
+		goto out;
+	} else if (!oldest->parents) {
+		BUG("an in-range commit must have a parent");
+	}
+	base = oldest->parents->item;
+
+	/*
+	 * A boundary other than the base is an in-range commit reaching a
+	 * commit outside the range, so the range has more than one base.
+	 */
+	for (b = boundaries; b; b = b->next) {
+		if (b->item != base) {
+			ret = error(_("the revision range has more than one base; "
+				      "cannot squash"));
+			goto out;
+		}
+	}
+
+	*base_out = base;
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	commit_list_free(boundaries);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+static const char *autosquash_target(const char *subject)
+{
+	const char *rest;
+
+	while (skip_prefix(subject, "fixup! ", &rest) ||
+	       skip_prefix(subject, "squash! ", &rest) ||
+	       skip_prefix(subject, "amend! ", &rest))
+		subject = rest;
+	return subject;
+}
+
+static int reject_dangling_fixups(struct repository *repo,
+				  struct commit *base,
+				  struct commit *tip,
+				  struct commit *oldest,
+				  struct commit **msg_source,
+				  struct commit **amend_source)
+{
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	struct rev_info revs;
+	struct commit *commit, *last_amend = NULL;
+	struct strvec args = STRVEC_INIT;
+	char *dangling_subject = NULL, *dangling_target = NULL;
+	bool mixed_target = false, all_fixups_one_target;
+	bool past_oldest_group = false;
+	int i, ret, nr_dangling = 0;
+
+	*msg_source = oldest;
+	*amend_source = NULL;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+	while ((commit = get_revision(&revs)))
+		strbuf_addf(&todo.buf, "pick %s\n",
+			    oid_to_hex(&commit->object.oid));
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not check the range for fixups"));
+		goto out;
+	}
+
+	for (i = 0; i < todo.nr; i++) {
+		const char *message, *subject_start, *target;
+		char *subject;
+		size_t sublen;
+
+		message = repo_logmsg_reencode(repo, todo.items[i].commit,
+					       NULL, NULL);
+		sublen = find_commit_subject(message, &subject_start);
+
+		if (todo.items[i].command != TODO_PICK) {
+			if (!past_oldest_group &&
+			    starts_with(subject_start, "amend! "))
+				*amend_source = todo.items[i].commit;
+			repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
+			continue;
+		}
+		if (i)
+			past_oldest_group = true;
+
+		subject = xmemdupz(subject_start, sublen);
+		target = autosquash_target(subject);
+		if (target != subject) {
+			nr_dangling++;
+			if (!dangling_target) {
+				dangling_target = xstrdup(target);
+				dangling_subject = xstrdup(subject);
+			} else if (strcmp(dangling_target, target)) {
+				mixed_target = true;
+			}
+			if (starts_with(subject, "amend! "))
+				last_amend = todo.items[i].commit;
+		}
+		free(subject);
+		repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
+	}
+
+	all_fixups_one_target = nr_dangling == todo.nr && !mixed_target;
+	if (nr_dangling && !all_fixups_one_target) {
+		ret = error(_("cannot squash '%s': its target is not in the "
+			      "range"), dangling_subject);
+	} else {
+		if (last_amend)
+			*msg_source = last_amend;
+		ret = 0;
+	}
+
+out:
+	free(dangling_subject);
+	free(dangling_target);
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+struct interior_ref_cb {
+	const struct oidset *interior;
+	const char *name;
+};
+
+static int find_interior_ref(const struct reference *ref, void *cb_data)
+{
+	struct interior_ref_cb *data = cb_data;
+
+	if (oidset_contains(data->interior, ref->oid)) {
+		data->name = xstrdup(ref->name);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	enum commit_tree_flags flags = 0;
+	int dry_run = 0;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BIT(0, "reedit-message", &flags,
+			N_("open an editor to modify the commit message"),
+			COMMIT_TREE_EDIT_MESSAGE),
+		OPT_END(),
+	};
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct strbuf message = STRBUF_INIT;
+	struct oidset interior = OIDSET_INIT;
+	struct commit *base, *oldest, *tip, *rewritten, *msg_source,
+		*amend_source;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	const char *message_template = NULL;
+	struct commit_list *parents = NULL;
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage,
+			     PARSE_OPT_KEEP_UNKNOWN_OPT);
+	if (!argc) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
+
+	ret = resolve_squash_range(repo, argv, &base, &oldest, &tip,
+				   &interior);
+	if (ret < 0)
+		goto out;
+
+	ret = reject_dangling_fixups(repo, base, tip, oldest, &msg_source,
+				     &amend_source);
+	if (ret < 0)
+		goto out;
+	if (amend_source) {
+		const char *amend_message, *body;
+
+		amend_message = repo_logmsg_reencode(repo, amend_source,
+						     NULL, NULL);
+		find_commit_subject(amend_message, &body);
+		body = skip_blank_lines(body + commit_subject_length(body));
+		strbuf_addstr(&message, body);
+		message_template = message.buf;
+		repo_unuse_commit_buffer(repo, amend_source, amend_message);
+	}
+
+	if (action == REF_ACTION_BRANCHES) {
+		struct interior_ref_cb cb = { .interior = &interior };
+
+		refs_for_each_ref(get_main_ref_store(repo),
+				  find_interior_ref, &cb);
+		if (cb.name) {
+			ret = error(_("'%s' points into the squashed range"),
+				    cb.name);
+			advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+					  _("Use --update-refs=head to rewrite only "
+					    "the current branch and leave such refs "
+					    "untouched."));
+			free((char *)cb.name);
+			goto out;
+		}
+	}
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+	commit_list_append(base, &parents);
+
+	ret = commit_tree_ext(repo, "squash", msg_source, message_template,
+			      parents,
+			      base_tree_oid, tip_tree_oid, &rewritten, flags);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	strbuf_addstr(&reflog_msg, "squash: updating ");
+	strbuf_join_argv(&reflog_msg, argc, argv, ' ');
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	strbuf_release(&message);
+	oidset_clear(&interior);
+	commit_list_free(parents);
+	release_revisions(&revs);
+	return ret;
+}
+
 static int update_worktree(struct repository *repo,
 			   const struct commit *old_head,
 			   const struct commit *new_head,
@@ -1192,6 +1564,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -1200,6 +1573,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
diff --git a/t/meson.build b/t/meson.build
index 8ae6ab6c5f..89cff16405 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -405,6 +405,7 @@ integration_tests = [
   't3452-history-split.sh',
   't3453-history-fixup.sh',
   't3454-history-drop.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..9c362f3094
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,569 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+stage_file () {
+	printf "%s\n" "$1" >file &&
+	git add file
+}
+
+commit_with_message () {
+	printf "%b" "$1" >msg &&
+	git commit --allow-empty -qF msg
+}
+
+check_commit_count () {
+	git rev-list --count "$1" >actual &&
+	echo "$2" >expect &&
+	test_cmp expect actual
+}
+
+check_log_subjects () {
+	git log --format="%s" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+check_log_messages () {
+	git log --format="%B" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+test_expect_success 'setup linear history touching two files' '
+	test_commit base file a &&
+	git tag start &&
+	test_commit --no-tag one other x &&
+	test_commit --no-tag two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "expects a revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the revision range is empty" err
+'
+
+test_expect_success 'errors on a single revision that is not a range' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "not a .*range" err &&
+	test_must_fail git history squash HEAD~1 2>err &&
+	test_grep "not a .*range" err
+'
+
+test_expect_success 'errors on a range holding a single commit' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "HEAD^!" 2>err &&
+	test_grep "single commit; nothing to squash" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'accepts multiple revision arguments with an exclusion' '
+	git reset --hard three &&
+	git branch -f keep HEAD~2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..HEAD ^keep &&
+
+	git reflog -1 --format=%gs >actual &&
+	echo "squash: updating start..HEAD ^keep" >expect &&
+	test_cmp expect actual &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	two
+	one
+	EOF
+	test_cmp_rev keep HEAD~1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git branch -D keep
+'
+
+test_expect_success 'squashes a branch the current branch is not on' '
+	git reset --hard three &&
+	main=$(git symbolic-ref --short HEAD) &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b off-history start &&
+	test_commit --no-tag off-one off a &&
+	test_commit --no-tag off-two off b &&
+	git checkout "$main" &&
+
+	git history squash start..off-history &&
+
+	check_commit_count start..off-history 1 &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D off-history
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash start.. &&
+
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	check_log_subjects -1 <<-\EOF &&
+	one
+	EOF
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'sanitizes rev-list walk options, before and after --' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --date-order start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git reset --hard three &&
+	git history squash -- --reverse start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start..@~1 &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	three
+	one
+	EOF
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$root.." &&
+
+	check_commit_count "$root..HEAD" 1 &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+
+test_expect_success 'folds fixups whose target is in the range' '
+	git reset --hard start &&
+	test_commit --no-tag target file b &&
+	git commit --allow-empty -m "fixup! target" &&
+	git commit --allow-empty -m "fixup! target" &&
+	test_commit --no-tag later file c &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF
+	target
+	EOF
+'
+
+test_expect_success 'refuses a below-range fixup! after an in-range commit' '
+	git reset --hard start &&
+	test_commit --no-tag inside file b &&
+	test_commit --no-tag "fixup! outside" file c &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "target is not in the range" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'combines a run of fixups for one commit below the range' '
+	git reset --hard start &&
+	stage_file b && git commit -m "fixup! base" &&
+	stage_file c && git commit -m "fixup! base" &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF
+	fixup! base
+	EOF
+'
+
+test_expect_success 'combining below-range fixups keeps the last amend! message' '
+	git reset --hard start &&
+	stage_file b && git commit -m "fixup! base" &&
+	stage_file c &&
+	commit_with_message "amend! base\n\namended body\n" &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_messages -1 <<-\EOF
+	amend! base
+
+	amended body
+
+	EOF
+'
+
+test_expect_success 'refuses fixups for two different commits below the range' '
+	git reset --hard start &&
+	stage_file b && git commit -m "fixup! aaa" &&
+	stage_file c && git commit -m "fixup! bbb" &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "target is not in the range" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'the last amend! for the oldest commit replaces its message' '
+	git reset --hard start &&
+	test_commit --no-tag marker-oldest file b &&
+	git commit --allow-empty -m "squash! marker-oldest" &&
+	commit_with_message "amend! marker-oldest\n\nearlier message\n" &&
+	commit_with_message \
+		"amend! marker-oldest\n\namended subject\n\namended body\n" &&
+	test_commit --no-tag marker-later file c &&
+	commit_with_message "amend! marker-later\n\nwrong message\n" &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_messages -1 <<-\EOF
+	amended subject
+
+	amended body
+
+	EOF
+'
+
+test_expect_success 'preserves authorship of the oldest commit' '
+	git reset --hard start &&
+	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
+		test_commit --no-tag oldest file b &&
+	test_commit newest file c &&
+
+	git history squash start.. &&
+
+	git log -1 --format="%an <%ae>" >actual &&
+	echo "Squasher <squash@example.com>" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --update-refs=head start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success 'refuses to fold a range a ref points into' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "error: .* points into the squashed range" err &&
+	test_grep "hint: .*--update-refs=head" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D mid
+'
+
+test_expect_success 'advice.historyUpdateRefs silences the hint' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "points into the squashed range" err &&
+	test_grep ! "hint:" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D mid
+'
+
+test_expect_success '--update-refs=head folds past a ref pointing into the range' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	mid_before=$(git rev-parse mid) &&
+
+	git history squash --update-refs=head start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev "$mid_before" mid &&
+
+	git branch -D mid
+'
+
+test_expect_success 'refuses to fold a range a tag points into' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "refs/tags/mark" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git tag -d mark
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout "$main" &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	test_commit --no-tag after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF &&
+	before-side
+	EOF
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a merge of a branch that forked at the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b base-fork-side &&
+	test_commit --no-tag base-fork-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag base-fork-main file b &&
+	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
+	git branch -D base-fork-side &&
+	test_commit --no-tag base-fork-tail file c &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'refuses a merge whose other parent is outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash "$base.." &&
+
+	check_commit_count "$base..HEAD" 1 &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'folds a range with two interior merges' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag two-merge-a file a1 &&
+	git checkout -b two-merge-s1 &&
+	test_commit --no-tag two-merge-s1 s1 x &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s1" two-merge-s1 &&
+	test_commit --no-tag two-merge-b file b1 &&
+	git checkout -b two-merge-s2 &&
+	test_commit --no-tag two-merge-s2 s2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s2" two-merge-s2 &&
+	git branch -D two-merge-s1 two-merge-s2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file s1 &&
+	test_path_is_file s2
+'
+
+test_expect_success 'folds a range with a nested merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b nested-outer &&
+	test_commit --no-tag nested-outer outer x &&
+	git checkout -b nested-inner &&
+	test_commit --no-tag nested-inner inner y &&
+	git checkout nested-outer &&
+	git merge --no-ff -m "merge inner" nested-inner &&
+	git checkout "$main" &&
+	test_commit --no-tag nested-main file b1 &&
+	git merge --no-ff -m "merge outer" nested-outer &&
+	git branch -D nested-outer nested-inner &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file outer &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range with an octopus merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag octo-base file a1 &&
+	git checkout -b octo-1 &&
+	test_commit --no-tag octo-1 o1 x &&
+	git checkout "$main" &&
+	git checkout -b octo-2 &&
+	test_commit --no-tag octo-2 o2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-1 octo-2 &&
+	git branch -D octo-1 octo-2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file o1 &&
+	test_path_is_file o2
+'
+
+test_expect_success 'refuses an octopus merge with an arm forked before the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b octo-pre &&
+	test_commit octo-pre-side pside x &&
+	git checkout "$main" &&
+	test_commit octo-pre-main file b1 &&
+	octo_base=$(git rev-parse HEAD) &&
+	git checkout -b octo-within &&
+	test_commit --no-tag octo-within wside y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-pre octo-within &&
+	merged=$(git rev-parse HEAD) &&
+	git branch -D octo-pre octo-within &&
+
+	test_must_fail git history squash "$octo_base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'refuses when a descendant above the range is a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag desc-one file b &&
+	test_commit --no-tag desc-two file c &&
+	git tag desc-tip &&
+	git checkout -b desc-above &&
+	test_commit --no-tag desc-above above x &&
+	git checkout "$main" &&
+	test_commit --no-tag desc-main file d &&
+	git merge --no-ff -m "merge desc-above" desc-above &&
+	git branch -D desc-above &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start..desc-tip 2>err &&
+	test_grep "merge commits is not supported" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'refuses to fold a range a ref points into at a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag refmerge-base file b &&
+	git checkout -b refmerge-side &&
+	test_commit --no-tag refmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag refmerge-main file c &&
+	git merge --no-ff -m "interior merge" refmerge-side &&
+	git branch -D refmerge-side &&
+	git branch at-merge HEAD &&
+	test_commit --no-tag refmerge-tail file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "at-merge" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D at-merge
+'
+
+test_done
-- 
gitgitgadget

Re: [PATCH v10 3/5] history: add squash subcommand to fold a range

[Phillip Wood]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

On 20/07/2026 09:27, Harald Nordgren via GitGitGadget wrote:
> From: Harald Nordgren <haraldnordgren@gmail.com>
> 
> Folding a series of commits into one required either an interactive
> rebase where each commit after the first was hand-edited to "fixup", or
> a "git reset --soft" to the merge base followed by "git commit --amend".
> 
> Add "git history squash <revision-range>" to do this directly. 

As promised, here are a few suggestions in the form of fixup
commits. I've reworked the message generation when it's not being
edited, but have not had time to improve the template message when
it is being editing.  As v11 has come out (despite a suggestion to
hold off for a few days[1]) I don't think it worth my while spending
more time working off a stale base.

Patch 1: clean up the option parsing.
Patch 2: checks for BOTTOM rather than UNINTERESTING commits.
Patch 3: reject root commits.
Patch 4: reject ranges with more than one tip.
Patch 5: refuse to squash if there are any branches descended from
    commits in the squashed range other than the tip of the range.
Patch 6: never discard the message from an "amend!" or "squash!" 
    commits.
Patch 7: fix squashing a merge. 

Some of these issues are addressed in v11. The last four patches
are the most interesting in terms of improving the behavior and
implementation. Besides the difference in the way fixups are handled,
the main change is in the way the code is structured to perform a
single pass over the commits being squashed, rather than multiple
passes for checking the connectivity and generating the commit message.

These patches can be fetched with

  git fetch https://github.com/phillipwood/git wip/hn/history-squash/v10-early-part

note that they do not support editing the commit message of the
squashed commit.

Thanks

Phillip

[1] https://lore.kernel.org/git/414ebe62-c7f6-4d44-bde2-b689e35accfc@gmail.com

Phillip Wood (7):
  fixup! history: add squash subcommand to fold a range
  fixup! history: add squash subcommand to fold a range
  fixup! history: add squash subcommand to fold a range
  fixup! history: add squash subcommand to fold a range
  fixup! history: add squash subcommand to fold a range
  fixup! history: add squash subcommand to fold a range
  fixup! history: add squash subcommand to fold a range

 builtin/history.c         | 617 +++++++++++++++++++++++---------------
 object.h                  |   1 +
 t/t3455-history-squash.sh | 385 +++++++++++++++---------
 3 files changed, 623 insertions(+), 380 deletions(-)

-- 
2.54.0.200.gfd8d68259e3

[PATCH v10 3.1/3.7] fixup! history: add squash subcommand to fold a range

[Phillip Wood]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

Rework the parsing of rev-list options

The code for setting up the options for setup_revisions() is a strange
mix of passing options and directly setting members of struct rev_info.
Consistently set the required options in the struct so that we don't
have to duplicate argv. This matches what we do in "git replay".

While I don't think it is possible for the user to override
--ancestry-path currently, add checks incase that becomes possible
in the future.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 builtin/history.c | 35 +++++++++++++++++++----------------
 1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 423c8beaaf..1d6d934bbe 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1015,7 +1015,7 @@ static int cmd_history_split(int argc,
  * but the range must have a single base and must not reach a root commit.
  */
 static int resolve_squash_range(struct repository *repo,
-				const char **argv,
+				int argc, const char **argv,
 				struct commit **base_out,
 				struct commit **oldest_out,
 				struct commit **tip_out,
@@ -1024,7 +1024,6 @@ static int resolve_squash_range(struct repository *repo,
 	struct rev_info revs;
 	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
 	struct commit_list *boundaries = NULL, *b;
-	struct strvec args = STRVEC_INIT;
 	size_t i;
 	int ret;
 
@@ -1034,26 +1033,31 @@ static int resolve_squash_range(struct repository *repo,
 	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
 	revs.simplify_history = 0;
 	revs.boundary = 1;
+	revs.ancestry_path = 1;
+	revs.limited = 1;
+	revs.ancestry_path_implicit_bottoms = 1;
 
-	strvec_push(&args, "ignored");
-	strvec_push(&args, "--ancestry-path");
-	strvec_pushv(&args, argv);
-	setup_revisions_from_strvec(&args, &revs, NULL);
-	if (args.nr != 1) {
-		ret = error(_("unrecognized argument: %s"), args.v[1]);
+	argc = setup_revisions(argc, argv, &revs, NULL);
+	if (argc > 1) {
+		ret = error(_("unrecognized argument: %s"), argv[1]);
 		goto out;
 	}
 
 	if (revs.reverse != 1 || revs.topo_order != 1 ||
 	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
-	    revs.simplify_history != 0 || revs.boundary != 1) {
+	    revs.simplify_history != 0 || revs.boundary != 1 ||
+	    revs.ancestry_path != 1 || revs.limited != 1 ||
+	    revs.ancestry_path_implicit_bottoms != 1) {
 		warning(_("ignoring rev-list options that would change how the "
 			  "range is walked"));
 		revs.reverse = 1;
 		revs.topo_order = 1;
 		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
 		revs.simplify_history = 0;
 		revs.boundary = 1;
+		revs.ancestry_path = 1;
+		revs.limited = 1;
+		revs.ancestry_path_implicit_bottoms = 1;
 	}
 
 	/*
@@ -1124,7 +1128,6 @@ static int resolve_squash_range(struct repository *repo,
 	commit_list_free(boundaries);
 	reset_revision_walk();
 	release_revisions(&revs);
-	strvec_clear(&args);
 	return ret;
 }
 
@@ -1290,8 +1293,8 @@ static int cmd_history_squash(int argc,
 	int ret;
 
 	argc = parse_options(argc, argv, prefix, options, usage,
-			     PARSE_OPT_KEEP_UNKNOWN_OPT);
-	if (!argc) {
+			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
+	if (argc < 2) {
 		ret = error(_("command expects a revision range"));
 		goto out;
 	}
@@ -1300,7 +1303,10 @@ static int cmd_history_squash(int argc,
 	if (action == REF_ACTION_DEFAULT)
 		action = REF_ACTION_BRANCHES;
 
-	ret = resolve_squash_range(repo, argv, &base, &oldest, &tip,
+	strbuf_addstr(&reflog_msg, "squash: updating ");
+	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
+
+	ret = resolve_squash_range(repo, argc, argv, &base, &oldest, &tip,
 				   &interior);
 	if (ret < 0)
 		goto out;
@@ -1353,9 +1359,6 @@ static int cmd_history_squash(int argc,
 		ret = error(_("failed writing squashed commit"));
 		goto out;
 	}
-
-	strbuf_addstr(&reflog_msg, "squash: updating ");
-	strbuf_join_argv(&reflog_msg, argc, argv, ' ');
 
 	ret = handle_reference_updates(&revs, action, tip, rewritten,
 				       reflog_msg.buf, dry_run,
-- 
2.54.0.200.gfd8d68259e3

[PATCH v10 3.2/3.7] fixup! history: add squash subcommand to fold a range

[Phillip Wood]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

Look for BOTTOM commit instead of an UNINTERESTING commit

There are a number of reasons why a commit may be marked as
UNINTERESTING, we are specifically interested in finding a BOTTOM commit
that marks the bottom of the commit range that is being squashed.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 builtin/history.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/builtin/history.c b/builtin/history.c
index 1d6d934bbe..64c9914c2f 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1066,7 +1066,7 @@ static int resolve_squash_range(struct repository *repo,
 	 * bottom commit cannot be squashed.
 	 */
 	for (i = 0; i < revs.cmdline.nr; i++)
-		if (revs.cmdline.rev[i].flags & UNINTERESTING)
+		if (revs.cmdline.rev[i].flags & BOTTOM)
 			break;
 	if (i == revs.cmdline.nr) {
 		ret = error(_("not a '<base>..<tip>' revision range"));
-- 
2.54.0.200.gfd8d68259e3

[PATCH v10 3.3/3.7] fixup! history: add squash subcommand to fold a range

[Phillip Wood]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

reject root commits

We do not support squashing down to the root commit yet (we should
probably require explicit confirmation if we ever do support it to avoid
nasty surprises) so error out if we see a commit with no parents. As
explained in the test, because we use --ancestry-path it is not
straight forward to trick it into walking back to the root commit.
---
 builtin/history.c         |  4 ++++
 t/t3455-history-squash.sh | 12 ++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/builtin/history.c b/builtin/history.c
index 64c9914c2f..4dcfdb109d 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1087,6 +1087,10 @@ static int resolve_squash_range(struct repository *repo,
 		if (commit->object.flags & BOUNDARY) {
 			commit_list_insert(commit, &boundaries);
 			continue;
+		}
+		if (!commit->parents) {
+			ret = error(_("cannot squash down to root commit"));
+			goto out;
 		}
 		if (!oldest)
 			oldest = commit;
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index 9c362f3094..b181f93892 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -64,6 +64,18 @@ test_expect_success 'errors on a range holding a single commit' '
 	test_must_fail git history squash "HEAD^!" 2>err &&
 	test_grep "single commit; nothing to squash" err &&
 	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'rejects root commit' '
+	# create a disconnected root commit
+	oid=$(git commit-tree -m root three^{tree}) &&
+	# because we pass --ancestry-path when calling setup_revs() it the
+	# revision walk will only include commits decended from $oid so
+	# we need to give it another --ancestry-path commit to actually walk
+	# any commits.
+	test_must_fail git history squash --ancestry-path=start $oid..three 2>err &&
+	echo "error: cannot squash down to root commit" >expect &&
+	test_cmp expect err
 '
 
 test_expect_success 'accepts multiple revision arguments with an exclusion' '
-- 
2.54.0.200.gfd8d68259e3

[PATCH v10 3.4/3.7] fixup! history: add squash subcommand to fold a range

[Phillip Wood]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

Reject ranges with more than one tip

Given

          C
         /
    A - B - D

then

   git history squash ^A C D

should fail because the way we squash commits assumes the range has
a single tip. While we might want to support multiple tips in the
future lets not complicate things now.

To check for multiple tips mark each commit we see as a tip and
increment a tip counter, then, iterate over the parents of each commit,
removing the mark and decrementing the counter if the mark was set. As
we have to iterate over the parents anyway, stop using "--boundary"
and check that we've seen each parent before which allows us to
produce a better error message.

Note: I'm not sure what our policy is with respect to adding new
users of object flags. If that's a problem, we could use a commit
slab instead.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 builtin/history.c         | 80 ++++++++++++++++++++++++---------------
 object.h                  |  1 +
 t/t3455-history-squash.sh | 19 ++++++++--
 3 files changed, 65 insertions(+), 35 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 4dcfdb109d..bb4a74ec1a 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1006,6 +1006,10 @@ static int cmd_history_split(int argc,
 	release_revisions(&revs);
 	return ret;
 }
+
+/*Remember to update object flag allocation in object.h */
+#define SQUASH_SEEN (1u << 11)
+#define SQUASH_TIP (1u << 12)
 
 /*
  * Resolve a "<base>..<tip>" revision range into the base commit just outside
@@ -1023,16 +1027,14 @@ static int resolve_squash_range(struct repository *repo,
 {
 	struct rev_info revs;
 	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
-	struct commit_list *boundaries = NULL, *b;
 	size_t i;
-	int ret;
+	int ret, tip_count = 0;
 
 	repo_init_revisions(repo, &revs, NULL);
 	revs.reverse = 1;
 	revs.topo_order = 1;
 	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
 	revs.simplify_history = 0;
-	revs.boundary = 1;
 	revs.ancestry_path = 1;
 	revs.limited = 1;
 	revs.ancestry_path_implicit_bottoms = 1;
@@ -1045,7 +1047,7 @@ static int resolve_squash_range(struct repository *repo,
 
 	if (revs.reverse != 1 || revs.topo_order != 1 ||
 	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
-	    revs.simplify_history != 0 || revs.boundary != 1 ||
+	    revs.simplify_history != 0 || revs.boundary == 1 ||
 	    revs.ancestry_path != 1 || revs.limited != 1 ||
 	    revs.ancestry_path_implicit_bottoms != 1) {
 		warning(_("ignoring rev-list options that would change how the "
@@ -1054,7 +1056,7 @@ static int resolve_squash_range(struct repository *repo,
 		revs.topo_order = 1;
 		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
 		revs.simplify_history = 0;
-		revs.boundary = 1;
+		revs.boundary = 0;
 		revs.ancestry_path = 1;
 		revs.limited = 1;
 		revs.ancestry_path_implicit_bottoms = 1;
@@ -1077,59 +1079,75 @@ static int resolve_squash_range(struct repository *repo,
 		ret = error(_("error preparing revisions"));
 		goto out;
 	}
-
-	/*
-	 * Set boundary commits aside for the base check below, and put every
-	 * in-range commit but the tip into the interior set. A ref pointing
-	 * at an interior commit would dangle once the range is folded away.
-	 */
 	while ((commit = get_revision(&revs))) {
-		if (commit->object.flags & BOUNDARY) {
-			commit_list_insert(commit, &boundaries);
-			continue;
-		}
+		struct commit_list *p;
+
 		if (!commit->parents) {
 			ret = error(_("cannot squash down to root commit"));
 			goto out;
+		}
+		for (p = commit->parents; oldest && p; p = p->next) {
+			struct commit_list *q;
+			struct object *o;
+			bool seen;
+
+			if (repo_parse_commit(repo, p->item)) {
+				ret = error(_("cannot parse commit"));
+				goto out;
+			}
+			o = &p->item->object;
+			seen = o->flags & SQUASH_SEEN;
+			/*
+			 * Allow parents that match the parents of the
+			 * squashed commit.
+			 */
+			for (q = oldest->parents; !seen && q; q = q->next)
+				seen = p->item == q->item;
+			if (!seen) {
+				ret = error(_("parent %s of commit %s is "
+					      "outside the revision range"),
+					    repo_find_unique_abbrev(repo, &o->oid,
+								    DEFAULT_ABBREV),
+					    repo_find_unique_abbrev(repo, &commit->object.oid,
+								    DEFAULT_ABBREV));
+				goto out;
+			}
+			if (o->flags & SQUASH_TIP) {
+				tip_count--;
+				o->flags &= ~SQUASH_TIP;
+			}
 		}
 		if (!oldest)
 			oldest = commit;
 		if (tip)
 			oidset_insert(interior_out, &tip->object.oid);
 		tip = commit;
+		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
+		tip_count++;
 	}
-
-	if (!oldest) {
+	if (!tip_count) {
 		ret = error(_("the revision range is empty"));
 		goto out;
-	} else if (oldest == tip) {
+	} else if (tip_count != 1) {
+		  ret = error(_("the revision range contains more than one tip "
+				"commit"));
+		  goto out;
+	  } else if (oldest == tip) {
 		ret = error(_("the revision range holds a single commit; "
 			      "nothing to squash"));
 		goto out;
 	} else if (!oldest->parents) {
 		BUG("an in-range commit must have a parent");
 	}
 	base = oldest->parents->item;
-
-	/*
-	 * A boundary other than the base is an in-range commit reaching a
-	 * commit outside the range, so the range has more than one base.
-	 */
-	for (b = boundaries; b; b = b->next) {
-		if (b->item != base) {
-			ret = error(_("the revision range has more than one base; "
-				      "cannot squash"));
-			goto out;
-		}
-	}
 
 	*base_out = base;
 	*oldest_out = oldest;
 	*tip_out = tip;
 	ret = 0;
 
 out:
-	commit_list_free(boundaries);
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
 	reset_revision_walk();
 	release_revisions(&revs);
 	return ret;
diff --git a/object.h b/object.h
index 8fb03ff90a..ad18ffcc55 100644
--- a/object.h
+++ b/object.h
@@ -74,6 +74,7 @@ void object_array_init(struct object_array *array);
  * bisect.c:                                        16
  * bundle.c:                                        16
  * http-push.c:                          11-----14
+ * builtin/history.c:                    11-12
  * commit-graph.c:                                15
  * commit-reach.c:                                  16-------20
  * builtin/last-modified.c:                         1617
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index b181f93892..ba826df592 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -33,8 +33,7 @@ check_log_messages () {
 }
 
 test_expect_success 'setup linear history touching two files' '
-	test_commit base file a &&
-	git tag start &&
+	test_commit base file a start &&
 	test_commit --no-tag one other x &&
 	test_commit --no-tag two file c &&
 	test_commit three file d
@@ -76,6 +75,18 @@ test_expect_success 'rejects root commit' '
 	test_must_fail git history squash --ancestry-path=start $oid..three 2>err &&
 	echo "error: cannot squash down to root commit" >expect &&
 	test_cmp expect err
+'
+
+test_expect_success 'rejects multiple tips' '
+	oid=$(git commit-tree -m tip -p start^0 three^{tree}) &&
+	test_must_fail git history squash ^start $oid three~1 2>err &&
+	echo "error: the revision range contains more than one tip commit" >expect &&
+	test_cmp expect err &&
+
+	git reset --hard three &&
+	git history squash ^start three~1 three &&
+	test_cmp_rev HEAD~1 start^0 &&
+	test_cmp_rev HEAD^{tree} three^{tree}
 '
 
 test_expect_success 'accepts multiple revision arguments with an exclusion' '
@@ -404,7 +415,7 @@ test_expect_success 'refuses a merge whose other parent is outside the range' '
 	merged=$(git rev-parse HEAD) &&
 
 	test_must_fail git history squash "$base.." 2>err &&
-	test_grep "more than one base" err &&
+	test_grep "parent .* of commit .* is outside the revision range" err &&
 	test_cmp_rev "$merged" HEAD
 '
 
@@ -533,7 +544,7 @@ test_expect_success 'refuses an octopus merge with an arm forked before the base
 	git branch -D octo-pre octo-within &&
 
 	test_must_fail git history squash "$octo_base.." 2>err &&
-	test_grep "more than one base" err &&
+	test_grep "parent .* of commit .* is outside the revision range" err &&
 	test_cmp_rev "$merged" HEAD
 '
 
-- 
2.54.0.200.gfd8d68259e3

[PATCH v10 3.5/3.7] fixup! history: add squash subcommand to fold a range

[Phillip Wood]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

Refuse to squash if there are branches descended from squashed commits

Rework the detection of branches descended from squashed commits
to protect branches that are not updated (i.e. any branch that is
descended from the squashed range but not the tip of the range). The
current behavior of protecting only those branches that point directly
at a squashed commit but not those descended from the same commit
is inconsistent and confusing. Note that this change means we now
complain when a branch points to the start of the squashed range.

When walking the commits we only need to add those with a parent
outside the squashed range to the ref filter as all the other commits
are descended from those. This patch needs some polishing to print the
branches that are causing us to error out. I've updated the existing
tests to reflect that, though I'm unclear what extra coverage the last
test (squashes a range whose internal merge has a single base) adds.

We do not protect detached HEADs that point to a commit in the
squashed range. I think that's reasonable - if HEAD is detached,
the user is likely experimenting so does not necessarily care that
the commits are being squashed in a different worktree. Protecting
them would require a separate revision walk including the detached
HEADs from all worktrees and excluding the base of the squashed range.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 builtin/history.c         | 85 +++++++++++++++++----------------------
 t/t3455-history-squash.sh | 67 ++++++++++++++----------------
 2 files changed, 68 insertions(+), 84 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index bb4a74ec1a..84e13fd75a 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -17,6 +17,7 @@
 #include "path.h"
 #include "read-cache.h"
 #include "refs.h"
+#include "ref-filter.h"
 #include "replay.h"
 #include "reset.h"
 #include "revision.h"
@@ -1019,16 +1020,18 @@ static int cmd_history_split(int argc,
  * but the range must have a single base and must not reach a root commit.
  */
 static int resolve_squash_range(struct repository *repo,
+				bool update_branches,
 				int argc, const char **argv,
 				struct commit **base_out,
 				struct commit **oldest_out,
-				struct commit **tip_out,
-				struct oidset *interior_out)
+				struct commit **tip_out)
 {
 	struct rev_info revs;
 	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
 	size_t i;
 	int ret, tip_count = 0;
+	struct ref_filter filter = REF_FILTER_INIT;
+	struct ref_array refs = { 0 };
 
 	repo_init_revisions(repo, &revs, NULL);
 	revs.reverse = 1;
@@ -1101,8 +1104,12 @@ static int resolve_squash_range(struct repository *repo,
 			 * Allow parents that match the parents of the
 			 * squashed commit.
 			 */
-			for (q = oldest->parents; !seen && q; q = q->next)
-				seen = p->item == q->item;
+			for (q = oldest->parents; !seen && q; q = q->next) {
+				if (p->item == q->item) {
+					seen = true;
+					commit_list_insert(commit, &filter.with_commit);
+				}
+			}
 			if (!seen) {
 				ret = error(_("parent %s of commit %s is "
 					      "outside the revision range"),
@@ -1117,14 +1124,16 @@ static int resolve_squash_range(struct repository *repo,
 				o->flags &= ~SQUASH_TIP;
 			}
 		}
-		if (!oldest)
+		if (!oldest) {
+			commit_list_insert(commit, &filter.with_commit);
 			oldest = commit;
-		if (tip)
-			oidset_insert(interior_out, &tip->object.oid);
+		}
 		tip = commit;
 		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
 		tip_count++;
 	}
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
+	reset_revision_walk();
 	if (!tip_count) {
 		ret = error(_("the revision range is empty"));
 		goto out;
@@ -1138,6 +1147,24 @@ static int resolve_squash_range(struct repository *repo,
 		goto out;
 	} else if (!oldest->parents) {
 		BUG("an in-range commit must have a parent");
+	}
+	commit_list_insert(tip, &filter.no_commit);
+	filter.kind = FILTER_REFS_BRANCHES;
+	if (update_branches &&
+	    filter_refs(&refs, &filter, filter.kind)) {
+		ret = error(_("could not filter refs"));
+		goto out;
+	}
+	if (refs.nr) {
+		/*
+		 * TODO: list the branches and also check HEADS from other worktrees
+		 */
+		ret = error(_("a branch points to a commit that is being squashed"));
+		advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+				  _("Use --update-refs=head to rewrite only "
+				    "the current branch and leave such refs "
+				    "untouched."));
+		goto out;
 	}
 	base = oldest->parents->item;
 
@@ -1147,9 +1174,9 @@ static int resolve_squash_range(struct repository *repo,
 	ret = 0;
 
 out:
-	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
-	reset_revision_walk();
 	release_revisions(&revs);
+	ref_filter_clear(&filter);
+	ref_array_clear(&refs);
 	return ret;
 }
 
@@ -1261,23 +1288,6 @@ static int reject_dangling_fixups(struct repository *repo,
 	release_revisions(&revs);
 	strvec_clear(&args);
 	return ret;
-}
-
-struct interior_ref_cb {
-	const struct oidset *interior;
-	const char *name;
-};
-
-static int find_interior_ref(const struct reference *ref, void *cb_data)
-{
-	struct interior_ref_cb *data = cb_data;
-
-	if (oidset_contains(data->interior, ref->oid)) {
-		data->name = xstrdup(ref->name);
-		return 1;
-	}
-
-	return 0;
 }
 
 static int cmd_history_squash(int argc,
@@ -1305,7 +1315,6 @@ static int cmd_history_squash(int argc,
 	};
 	struct strbuf reflog_msg = STRBUF_INIT;
 	struct strbuf message = STRBUF_INIT;
-	struct oidset interior = OIDSET_INIT;
 	struct commit *base, *oldest, *tip, *rewritten, *msg_source,
 		*amend_source;
 	const struct object_id *base_tree_oid, *tip_tree_oid;
@@ -1328,8 +1337,8 @@ static int cmd_history_squash(int argc,
 	strbuf_addstr(&reflog_msg, "squash: updating ");
 	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
 
-	ret = resolve_squash_range(repo, argc, argv, &base, &oldest, &tip,
-				   &interior);
+	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
+				   argc, argv, &base, &oldest, &tip);
 	if (ret < 0)
 		goto out;
 
@@ -1347,23 +1356,6 @@ static int cmd_history_squash(int argc,
 		strbuf_addstr(&message, body);
 		message_template = message.buf;
 		repo_unuse_commit_buffer(repo, amend_source, amend_message);
-	}
-
-	if (action == REF_ACTION_BRANCHES) {
-		struct interior_ref_cb cb = { .interior = &interior };
-
-		refs_for_each_ref(get_main_ref_store(repo),
-				  find_interior_ref, &cb);
-		if (cb.name) {
-			ret = error(_("'%s' points into the squashed range"),
-				    cb.name);
-			advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
-					  _("Use --update-refs=head to rewrite only "
-					    "the current branch and leave such refs "
-					    "untouched."));
-			free((char *)cb.name);
-			goto out;
-		}
 	}
 
 	ret = setup_revwalk(repo, action, tip, &revs);
@@ -1395,7 +1387,6 @@ static int cmd_history_squash(int argc,
 out:
 	strbuf_release(&reflog_msg);
 	strbuf_release(&message);
-	oidset_clear(&interior);
 	commit_list_free(parents);
 	release_revisions(&revs);
 	return ret;
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index ba826df592..d7697489a0 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -305,17 +305,36 @@ test_expect_success '--update-refs=head only moves HEAD' '
 	test_cmp_rev "$other_before" other
 '
 
-test_expect_success 'refuses to fold a range a ref points into' '
-	git reset --hard three &&
-	git branch -f mid HEAD~1 &&
-	head_before=$(git rev-parse HEAD) &&
+test_expect_success 'refuses to fold a range a branch points into' '
+	test_when_finished \
+		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
+		 git branch -D feature" &&
+	git checkout -f -b feature start &&
+	test_commit C1 &&
+	test_commit C2 &&
+	git checkout -b topic-1 start &&
+	test_commit C3 &&
+	test_commit C4 &&
+	git checkout C3 &&
+	test_commit C5 &&
+	git checkout feature &&
+	git merge C5 &&
+	test_commit C6 &&
+	git checkout -b topic-2 C2 &&
+	test_commit C7 &&
+	git checkout feature &&
 
 	test_must_fail git history squash start.. 2>err &&
-	test_grep "error: .* points into the squashed range" err &&
-	test_grep "hint: .*--update-refs=head" err &&
-	test_cmp_rev "$head_before" HEAD &&
+	# TODO: check the branch names when we print them (topic-1 & topic-2)
+	test_grep "^error: a branch points to" err &&
+	test_grep "^hint: .* --update-refs=head" err &&
+	test_cmp_rev C6 HEAD &&
 
-	git branch -D mid
+	# squash succeeds with --update-refs=head
+	git history squash --update-refs=head start.. &&
+	test_cmp_rev start HEAD^ &&
+	test_cmp_rev C6^{tree} HEAD^{tree} &&
+	test_cmp_rev C6 HEAD@{1}
 '
 
 test_expect_success 'advice.historyUpdateRefs silences the hint' '
@@ -325,37 +344,11 @@ test_expect_success 'advice.historyUpdateRefs silences the hint' '
 
 	test_must_fail git -c advice.historyUpdateRefs=false \
 		history squash start.. 2>err &&
-	test_grep "points into the squashed range" err &&
+	test_grep "^error: a branch points to" err &&
 	test_grep ! "hint:" err &&
 	test_cmp_rev "$head_before" HEAD &&
 
 	git branch -D mid
-'
-
-test_expect_success '--update-refs=head folds past a ref pointing into the range' '
-	git reset --hard three &&
-	git branch -f mid HEAD~1 &&
-	mid_before=$(git rev-parse mid) &&
-
-	git history squash --update-refs=head start.. &&
-
-	check_commit_count start..HEAD 1 &&
-	test_cmp_rev "$mid_before" mid &&
-
-	git branch -D mid
-'
-
-test_expect_success 'refuses to fold a range a tag points into' '
-	git reset --hard three &&
-	git tag -f mark HEAD~1 &&
-	head_before=$(git rev-parse HEAD) &&
-
-	test_must_fail git history squash start.. 2>err &&
-	test_grep "refs/tags/mark" err &&
-	test_grep "points into the squashed range" err &&
-	test_cmp_rev "$head_before" HEAD &&
-
-	git tag -d mark
 '
 
 test_expect_success 'squashes a range whose internal merge has a single base' '
@@ -582,8 +575,8 @@ test_expect_success 'refuses to fold a range a ref points into at a merge' '
 	head_before=$(git rev-parse HEAD) &&
 
 	test_must_fail git history squash start.. 2>err &&
-	test_grep "at-merge" err &&
-	test_grep "points into the squashed range" err &&
+	# TODO: test for branch nome "at-merge"
+	test_grep "a branch points to a commit" err &&
 	test_cmp_rev "$head_before" HEAD &&
 
 	git branch -D at-merge
-- 
2.54.0.200.gfd8d68259e3

[PATCH v10 3.6/3.7] fixup! history: add squash subcommand to fold a range

[Phillip Wood]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

Do not discard "squash!" or "amend!" messages

"squash!" and "amend!" commit messages are a strong indication that
the user intended to reword the target commit when squashing. To
that end only squash them if the message ends up being used. If an
"amend!" message targets a commit that's being squashed, but is not
the first commit that's being squashed, then refuse to squash it
unless the commit message is being edited. Also refuse to squash a
"squash!" message unless it is being squashed into a "fixup!" or
"squash!" message with the same target, or the message is being
edited. If an "amend!" or "squash!" message is being squashed into
a "fixup!" message, then we retain the original target text. This
means that we can safely squash 'def456 "amend! abc123"' into 'abc123
"fixup! add new feature"', and later squash the result into '098765
"add new feature"'.

The logic is implemented directly, rather than creating a rebase
todo list which is more efficient and hopefully clearer (I had a hard
time understanding what the existing code does). It also allows us to
tailor the rules to suit the new command. In particular we are much
more careful when handling "fixup! <object-name>" subjects, rejecting
subjects like "fixup! HEAD^" that do not have a fixed target. We also
support squashing "fixup! abc123" into "fixup! <subject of abc123>"
to make it easier to squash a group of fixups together.

The authorship of the squashed commit is always taken from the first
commit being squashed which matches what rebase does (if there is
an "amend!" commit the existing code takes the authorship from that
instead). While an "amend!" commit might contain substantial changes
that justify changing the authorship it could equally be correcting
a simple typo. There is no reason to assume that changes in "amend!"
commits are more significant that those in "fixup!" or "squash!"
commits.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 builtin/history.c         | 409 +++++++++++++++++++++++++-------------
 object.h                  |   2 +-
 t/t3455-history-squash.sh | 261 ++++++++++++++----------
 3 files changed, 431 insertions(+), 241 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 84e13fd75a..894da69f31 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1011,6 +1011,260 @@ static int cmd_history_split(int argc,
 /*Remember to update object flag allocation in object.h */
 #define SQUASH_SEEN (1u << 11)
 #define SQUASH_TIP (1u << 12)
+#define SQUASH_AMEND_TARGET (1u << 13)
+
+static bool is_autosquash_subject(const char *s)
+{
+	return starts_with(s, "amend!") || starts_with(s, "fixup!") ||
+		starts_with(s, "squash!");
+}
+
+static bool skip_one_autosquash_prefix(const char *s, const char **out)
+{
+	if (skip_prefix(s, "amend!", out) || skip_prefix(s, "fixup!", out) ||
+	    skip_prefix(s, "squash!", out)) {
+		while (**out == ' ')
+			(*out)++;
+		return true;
+	}
+	return false;
+}
+
+static void truncate_message_to_subject(struct strbuf *msg)
+{
+	const char *eos = strstr(msg->buf, "\n\n");
+
+	if (eos)
+		strbuf_setlen(msg, eos - msg->buf + 1);
+}
+
+struct subject_data {
+	struct strintmap subjects;
+	struct strbuf subject;
+	struct strbuf squash_message;
+	const char *message;
+	bool edit_message;
+};
+
+#define SUBJECT_DATA_INIT {		\
+	.subjects = STRINTMAP_INIT,	\
+	.subject = STRBUF_INIT,		\
+	.squash_message = STRBUF_INIT,	\
+}
+
+static void subject_data_clear(struct subject_data *data)
+{
+	strintmap_clear(&data->subjects);
+	strbuf_release(&data->subject);
+	strbuf_release(&data->squash_message);
+}
+
+static int squash_amend_message(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data,
+				unsigned flags)
+{
+	const char *body = data->message + data->subject.len;
+
+	while (isspace(*body))
+		body++;
+
+	if (!*body) {
+		warning(_("ignoring %s (%s): message body is empty"),
+			repo_find_unique_abbrev(repo, &commit->object.oid,
+						DEFAULT_ABBREV),
+			data->subject.buf);
+		return 0;
+	}
+
+	if (data->edit_message) {
+		BUG("Editing is not implemented yet");
+	} else if (flags & SQUASH_AMEND_TARGET) {
+		if (starts_with(data->squash_message.buf, "squash!"))
+			return error(_("squashing %s (%s) would overwrite "
+				       "'squash!' message, please combine them "
+				       "using '--reedit-message'"),
+				     repo_find_unique_abbrev(repo,
+							     &commit->object.oid,
+							     DEFAULT_ABBREV),
+				     data->subject.buf);
+		if (starts_with(data->squash_message.buf, "fixup!"))
+			strbuf_splice(&data->squash_message, 0, 5, "amend!", 5);
+		if (starts_with(data->squash_message.buf, "amend!")) {
+			truncate_message_to_subject(&data->squash_message);
+			strbuf_addch(&data->squash_message, '\n');
+		} else {
+			strbuf_reset(&data->squash_message);
+		}
+		strbuf_addstr(&data->squash_message, body);
+		strbuf_complete_line(&data->squash_message);
+	} else {
+		return error(_("cannot squash %s (%s) that does not target "
+			       "base commit without '--reedit-message'"),
+			     repo_find_unique_abbrev(repo, &commit->object.oid,
+						     DEFAULT_ABBREV),
+			     data->subject.buf);
+	}
+	return 0;
+}
+
+static int squash_squash_message(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data,
+				unsigned flags)
+{
+	const char *body = data->message + data->subject.len;
+
+	while (isspace(*body))
+		body++;
+
+	if (data->edit_message) {
+		BUG("Editing is not implemented yet");
+	} else if (flags & SQUASH_AMEND_TARGET) {
+		if (starts_with(data->squash_message.buf, "fixup!")) {
+			truncate_message_to_subject(&data->squash_message);
+			strbuf_splice(&data->squash_message, 0, 5, "squash", 6);
+		}
+		if (starts_with(data->squash_message.buf, "squash!")) {
+			strbuf_addch(&data->squash_message, '\n');
+			strbuf_addstr(&data->squash_message, body);
+			strbuf_complete_line(&data->squash_message);
+		} else {
+			return error(_("squashing %s (%s) would discard its "
+				       "message, please combine them using "
+				       "'--reedit-message'"),
+				     repo_find_unique_abbrev(repo,
+							     &commit->object.oid,
+							     DEFAULT_ABBREV),
+				     data->subject.buf);
+		}
+	} else {
+		return error(_("cannot squash %s (%s) that does not target "
+			       "base commit without '--reedit-message'"),
+			      repo_find_unique_abbrev(repo, &commit->object.oid,
+						      DEFAULT_ABBREV),
+			      data->subject.buf);
+	}
+	return 0;
+}
+
+static int squash_check_can_autosquash(struct repository *repo,
+				       struct commit *commit,
+				       struct subject_data *data,
+				       unsigned flags)
+{
+	commit->object.flags |= flags & SQUASH_AMEND_TARGET;
+	if (starts_with(data->subject.buf, "amend!"))
+		return squash_amend_message(repo, commit, data, flags);
+	else if (starts_with(data->subject.buf, "squash!"))
+		return squash_squash_message(repo, commit, data, flags);
+
+	return 0;
+}
+
+static int squash_check_autosquash_subject(struct repository *repo,
+					   struct commit *commit,
+					   struct subject_data *data)
+{
+	const char* s = data->subject.buf;
+	struct commit *target;
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+	/* Try skipping autosquash prefixes one at a time to allow
+	 * squashing
+	 *     a commit
+	 *     fixup! fixup! a commit
+	 *
+	 * where we may have started with
+	 *     a commit
+	 *     fixup! a commit
+	 *     fixup! fixup! a commit
+	 *
+	 * and squashed the first fixup separately from the second
+	 */
+	while (skip_one_autosquash_prefix(s, &s)) {
+		unsigned flags = strintmap_get(&data->subjects, s);
+		if (flags)
+			return squash_check_can_autosquash(repo, commit, data, flags);
+	}
+	/*
+	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
+	 * "fixup! main". If the target is not being squshed check the subject
+	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
+	 * squashed together.
+	 */
+	target = lookup_commit_reference_by_name(s);
+	if (target && istarts_with(oid_to_hex(&target->object.oid), s)) {
+		unsigned flags =
+			target->object.flags & (SQUASH_SEEN | SQUASH_AMEND_TARGET);
+		if (!flags) {
+			const char *subject_start;
+			const char *buffer = repo_logmsg_reencode(repo, target,
+								  NULL, NULL);
+			size_t subject_len = find_commit_subject(buffer,
+								 &subject_start);
+			char *subject = xmemdupz(subject_start, subject_len);
+
+			flags = strintmap_get(&data->subjects, subject);
+			free(subject);
+			repo_unuse_commit_buffer(repo, target, buffer);
+		}
+		if (flags)
+			return squash_check_can_autosquash(repo, commit,
+							   data, flags);
+	}
+	/* Try subject prefix matches */
+	strintmap_for_each_entry(&data->subjects, &iter, entry) {
+		s = data->subject.buf;
+		while(skip_one_autosquash_prefix(s, &s)) {
+			if (starts_with(entry->key, s)) {
+				unsigned value = (intptr_t)entry->value;
+
+				return squash_check_can_autosquash(repo, commit,
+								   data, value);
+			}
+		}
+	}
+	return error(_("cannot squash %s (%s): its target is not being "
+		       "squashed"),
+		       repo_find_unique_abbrev(repo, &commit->object.oid,
+					       DEFAULT_ABBREV),
+		       data->subject.buf);
+}
+
+static int squash_check_subject(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data)
+{
+	int ret = 0;
+	const char *buf = repo_logmsg_reencode(repo, commit, NULL, NULL);
+	size_t subject_len = find_commit_subject(buf, &data->message);
+
+	strbuf_reset(&data->subject);
+	strbuf_add(&data->subject, data->message, subject_len);
+
+	if (!strintmap_get_size(&data->subjects)) {
+		const char *s;
+
+		strbuf_addstr(&data->squash_message, data->message);
+		strbuf_complete_line(&data->squash_message);
+		/*
+		 * Strip a single autosquash prefix to allow squashing
+		 *     fixup! base
+		 *     amend! base
+		 */
+		s = data->subject.buf;
+		skip_one_autosquash_prefix(s, &s);
+		strintmap_set(&data->subjects, s, SQUASH_AMEND_TARGET | SQUASH_SEEN);
+		commit->object.flags |= SQUASH_AMEND_TARGET;
+	} else if (is_autosquash_subject(data->subject.buf)) {
+		ret = squash_check_autosquash_subject(repo, commit, data);
+	} else {
+		strintmap_set(&data->subjects, data->subject.buf, SQUASH_SEEN);
+	}
+	repo_unuse_commit_buffer(repo, commit, buf);
+	return ret;
+}
 
 /*
  * Resolve a "<base>..<tip>" revision range into the base commit just outside
@@ -1024,9 +1278,11 @@ static int resolve_squash_range(struct repository *repo,
 				int argc, const char **argv,
 				struct commit **base_out,
 				struct commit **oldest_out,
-				struct commit **tip_out)
+				struct commit **tip_out,
+				char **message_out)
 {
 	struct rev_info revs;
+	struct subject_data subject_data = SUBJECT_DATA_INIT;
 	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
 	size_t i;
 	int ret, tip_count = 0;
@@ -1127,12 +1383,16 @@ static int resolve_squash_range(struct repository *repo,
 		if (!oldest) {
 			commit_list_insert(commit, &filter.with_commit);
 			oldest = commit;
+		}
+		if (squash_check_subject(repo, commit, &subject_data)) {
+			ret = -1;
+			goto out;
 		}
 		tip = commit;
 		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
 		tip_count++;
 	}
-	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP | SQUASH_AMEND_TARGET);
 	reset_revision_walk();
 	if (!tip_count) {
 		ret = error(_("the revision range is empty"));
@@ -1171,122 +1431,14 @@ static int resolve_squash_range(struct repository *repo,
 	*base_out = base;
 	*oldest_out = oldest;
 	*tip_out = tip;
+	*message_out = strbuf_detach(&subject_data.squash_message, NULL);
 	ret = 0;
 
 out:
+	subject_data_clear(&subject_data);
 	release_revisions(&revs);
 	ref_filter_clear(&filter);
 	ref_array_clear(&refs);
-	return ret;
-}
-
-static const char *autosquash_target(const char *subject)
-{
-	const char *rest;
-
-	while (skip_prefix(subject, "fixup! ", &rest) ||
-	       skip_prefix(subject, "squash! ", &rest) ||
-	       skip_prefix(subject, "amend! ", &rest))
-		subject = rest;
-	return subject;
-}
-
-static int reject_dangling_fixups(struct repository *repo,
-				  struct commit *base,
-				  struct commit *tip,
-				  struct commit *oldest,
-				  struct commit **msg_source,
-				  struct commit **amend_source)
-{
-	struct todo_list todo = TODO_LIST_INIT;
-	struct replay_opts opts = REPLAY_OPTS_INIT;
-	struct rev_info revs;
-	struct commit *commit, *last_amend = NULL;
-	struct strvec args = STRVEC_INIT;
-	char *dangling_subject = NULL, *dangling_target = NULL;
-	bool mixed_target = false, all_fixups_one_target;
-	bool past_oldest_group = false;
-	int i, ret, nr_dangling = 0;
-
-	*msg_source = oldest;
-	*amend_source = NULL;
-
-	repo_init_revisions(repo, &revs, NULL);
-	strvec_push(&args, "ignored");
-	strvec_push(&args, "--reverse");
-	strvec_push(&args, "--topo-order");
-	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
-		     oid_to_hex(&tip->object.oid));
-	setup_revisions_from_strvec(&args, &revs, NULL);
-
-	if (prepare_revision_walk(&revs) < 0) {
-		ret = error(_("error preparing revisions"));
-		goto out;
-	}
-	while ((commit = get_revision(&revs)))
-		strbuf_addf(&todo.buf, "pick %s\n",
-			    oid_to_hex(&commit->object.oid));
-
-	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
-	    todo_list_rearrange_squash(&todo) < 0) {
-		ret = error(_("could not check the range for fixups"));
-		goto out;
-	}
-
-	for (i = 0; i < todo.nr; i++) {
-		const char *message, *subject_start, *target;
-		char *subject;
-		size_t sublen;
-
-		message = repo_logmsg_reencode(repo, todo.items[i].commit,
-					       NULL, NULL);
-		sublen = find_commit_subject(message, &subject_start);
-
-		if (todo.items[i].command != TODO_PICK) {
-			if (!past_oldest_group &&
-			    starts_with(subject_start, "amend! "))
-				*amend_source = todo.items[i].commit;
-			repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
-			continue;
-		}
-		if (i)
-			past_oldest_group = true;
-
-		subject = xmemdupz(subject_start, sublen);
-		target = autosquash_target(subject);
-		if (target != subject) {
-			nr_dangling++;
-			if (!dangling_target) {
-				dangling_target = xstrdup(target);
-				dangling_subject = xstrdup(subject);
-			} else if (strcmp(dangling_target, target)) {
-				mixed_target = true;
-			}
-			if (starts_with(subject, "amend! "))
-				last_amend = todo.items[i].commit;
-		}
-		free(subject);
-		repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
-	}
-
-	all_fixups_one_target = nr_dangling == todo.nr && !mixed_target;
-	if (nr_dangling && !all_fixups_one_target) {
-		ret = error(_("cannot squash '%s': its target is not in the "
-			      "range"), dangling_subject);
-	} else {
-		if (last_amend)
-			*msg_source = last_amend;
-		ret = 0;
-	}
-
-out:
-	free(dangling_subject);
-	free(dangling_target);
-	todo_list_release(&todo);
-	replay_opts_release(&opts);
-	reset_revision_walk();
-	release_revisions(&revs);
-	strvec_clear(&args);
 	return ret;
 }
 
@@ -1314,11 +1466,9 @@ static int cmd_history_squash(int argc,
 		OPT_END(),
 	};
 	struct strbuf reflog_msg = STRBUF_INIT;
-	struct strbuf message = STRBUF_INIT;
-	struct commit *base, *oldest, *tip, *rewritten, *msg_source,
-		*amend_source;
+	struct commit *base, *oldest, *tip, *rewritten;
 	const struct object_id *base_tree_oid, *tip_tree_oid;
-	const char *message_template = NULL;
+	char *message_template = NULL;
 	struct commit_list *parents = NULL;
 	struct rev_info revs = { 0 };
 	int ret;
@@ -1338,25 +1488,10 @@ static int cmd_history_squash(int argc,
 	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
 
 	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
-				   argc, argv, &base, &oldest, &tip);
-	if (ret < 0)
-		goto out;
-
-	ret = reject_dangling_fixups(repo, base, tip, oldest, &msg_source,
-				     &amend_source);
-	if (ret < 0)
-		goto out;
-	if (amend_source) {
-		const char *amend_message, *body;
-
-		amend_message = repo_logmsg_reencode(repo, amend_source,
-						     NULL, NULL);
-		find_commit_subject(amend_message, &body);
-		body = skip_blank_lines(body + commit_subject_length(body));
-		strbuf_addstr(&message, body);
-		message_template = message.buf;
-		repo_unuse_commit_buffer(repo, amend_source, amend_message);
-	}
+				   argc, argv, &base, &oldest, &tip,
+				   &message_template);
+	if (ret < 0)
+		goto out;
 
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
@@ -1366,7 +1501,7 @@ static int cmd_history_squash(int argc,
 	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
 	commit_list_append(base, &parents);
 
-	ret = commit_tree_ext(repo, "squash", msg_source, message_template,
+	ret = commit_tree_ext(repo, "squash", oldest, message_template,
 			      parents,
 			      base_tree_oid, tip_tree_oid, &rewritten, flags);
 	if (ret < 0) {
@@ -1386,9 +1521,9 @@ static int cmd_history_squash(int argc,
 
 out:
 	strbuf_release(&reflog_msg);
-	strbuf_release(&message);
 	commit_list_free(parents);
 	release_revisions(&revs);
+	free(message_template);
 	return ret;
 }
 
diff --git a/object.h b/object.h
index ad18ffcc55..46cade33fb 100644
--- a/object.h
+++ b/object.h
@@ -74,7 +74,7 @@ void object_array_init(struct object_array *array);
  * bisect.c:                                        16
  * bundle.c:                                        16
  * http-push.c:                          11-----14
- * builtin/history.c:                    11-12
+ * builtin/history.c:                    11---13
  * commit-graph.c:                                15
  * commit-reach.c:                                  16-------20
  * builtin/last-modified.c:                         1617
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index d7697489a0..26c4b4e29e 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -29,14 +29,25 @@ check_log_subjects () {
 check_log_messages () {
 	git log --format="%B" "$1" >actual &&
 	cat >expect &&
+	test_cmp expect actual
+}
+
+# Checks that the author data of two commits matches
+# Usage: check_commit_author <rev1> <rev2>
+check_commit_author () {
+	git show -s --format="%an <%ae> %ad" "$1" >expect &&
+	git show -s --format="%an <%ae> %ad" "$1" >actual &&
 	test_cmp expect actual
 }
 
 test_expect_success 'setup linear history touching two files' '
 	test_commit base file a start &&
-	test_commit --no-tag one other x &&
-	test_commit --no-tag two file c &&
-	test_commit three file d
+	GIT_AUTHOR_NAME=One GIT_AUTHOR_EMAIL=one@example.com \
+		test_commit one other x &&
+	GIT_AUTHOR_NAME=Two GIT_AUTHOR_EMAIL=two@example.com \
+		test_commit two file c &&
+	GIT_AUTHOR_NAME=Three GIT_AUTHOR_EMAIL=three@example.com \
+		test_commit three file d
 '
 
 test_expect_success 'errors on missing range argument' '
@@ -192,106 +203,150 @@ test_expect_success 'squashes when the base is the root commit' '
 	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
 '
 
-
-test_expect_success 'folds fixups whose target is in the range' '
-	git reset --hard start &&
-	test_commit --no-tag target file b &&
-	git commit --allow-empty -m "fixup! target" &&
-	git commit --allow-empty -m "fixup! target" &&
-	test_commit --no-tag later file c &&
-
-	git history squash start.. &&
-
-	check_commit_count start..HEAD 1 &&
-	check_log_subjects -1 <<-\EOF
-	target
-	EOF
-'
-
-test_expect_success 'refuses a below-range fixup! after an in-range commit' '
-	git reset --hard start &&
-	test_commit --no-tag inside file b &&
-	test_commit --no-tag "fixup! outside" file c &&
-	head_before=$(git rev-parse HEAD) &&
-
-	test_must_fail git history squash start.. 2>err &&
-	test_grep "target is not in the range" err &&
-	test_cmp_rev "$head_before" HEAD
-'
-
-test_expect_success 'combines a run of fixups for one commit below the range' '
-	git reset --hard start &&
-	stage_file b && git commit -m "fixup! base" &&
-	stage_file c && git commit -m "fixup! base" &&
-
-	git history squash start.. &&
-
-	check_commit_count start..HEAD 1 &&
-	check_log_subjects -1 <<-\EOF
-	fixup! base
-	EOF
-'
-
-test_expect_success 'combining below-range fixups keeps the last amend! message' '
-	git reset --hard start &&
-	stage_file b && git commit -m "fixup! base" &&
-	stage_file c &&
-	commit_with_message "amend! base\n\namended body\n" &&
-
-	git history squash start.. &&
-
-	check_commit_count start..HEAD 1 &&
-	check_log_messages -1 <<-\EOF
-	amend! base
-
-	amended body
-
-	EOF
-'
-
-test_expect_success 'refuses fixups for two different commits below the range' '
-	git reset --hard start &&
-	stage_file b && git commit -m "fixup! aaa" &&
-	stage_file c && git commit -m "fixup! bbb" &&
-	head_before=$(git rev-parse HEAD) &&
-
-	test_must_fail git history squash start.. 2>err &&
-	test_grep "target is not in the range" err &&
-	test_cmp_rev "$head_before" HEAD
-'
-
-test_expect_success 'the last amend! for the oldest commit replaces its message' '
-	git reset --hard start &&
-	test_commit --no-tag marker-oldest file b &&
-	git commit --allow-empty -m "squash! marker-oldest" &&
-	commit_with_message "amend! marker-oldest\n\nearlier message\n" &&
-	commit_with_message \
-		"amend! marker-oldest\n\namended subject\n\namended body\n" &&
-	test_commit --no-tag marker-later file c &&
-	commit_with_message "amend! marker-later\n\nwrong message\n" &&
-
-	git history squash start.. &&
-
-	check_commit_count start..HEAD 1 &&
-	check_log_messages -1 <<-\EOF
-	amended subject
-
-	amended body
-
-	EOF
-'
-
-test_expect_success 'preserves authorship of the oldest commit' '
-	git reset --hard start &&
-	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
-		test_commit --no-tag oldest file b &&
-	test_commit newest file c &&
-
-	git history squash start.. &&
-
-	git log -1 --format="%an <%ae>" >actual &&
-	echo "Squasher <squash@example.com>" >expect &&
-	test_cmp expect actual
+test_expect_success 'squashing a mix of fixups' '
+	git reset --hard three &&
+	echo fix >file &&
+	git commit --fixup=two -a &&
+	echo really fix >file &&
+	git commit --fixup=one -a &&
+	echo really really fix >file &&
+	git commit --fixup=HEAD~1 -a && # fixup! two
+	echo really really really fix >file &&
+	git commit --fixup=HEAD~1 -a && # fixup! one
+
+	# squashing fixup! with a target that is not being squashed fails
+	test_must_fail git history squash one.. 2>err &&
+	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
+
+	# squashing fixup! into fixup! with a different target fails
+	test_must_fail git history squash HEAD~4.. 2>err && # HEAD~4 is fixup! two
+	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
+
+	# squashing a sequence of fixup! commits into their targets
+	git history squash start..HEAD~1 &&
+	test_cmp_rev start HEAD~2 &&
+	check_commit_author one HEAD~1 &&
+	test_commit_message HEAD~1 -m one &&
+
+	# squashing "fixup! fixup! <target>" into "<target>"
+	git history squash start.. &&
+	test_cmp_rev start HEAD~1 &&
+	check_commit_author one HEAD &&
+	test_commit_message HEAD -m one
+'
+
+test_expect_success 'squashing "squash!" messages' '
+	git reset --hard two &&
+	echo fix >file &&
+	git commit --fixup=HEAD -a &&
+	echo better fix >file &&
+	git commit -a -F - <<-EOF &&
+	squash! $(git rev-parse two)
+
+	Append this
+	EOF
+
+	echo an even better fix >file &&
+	git commit -a -F - <<-EOF &&
+	squash! squash! two
+
+	Append this as well
+	EOF
+
+	# must edit when squashing "squash!" into its target
+	test_must_fail git history squash two^.. 2>err &&
+	test_grep "^error: squashing .* (squash! [a-f0-9]*) would discard its message" err &&
+
+	# squashing "squash!" into "fixup!" appends messages and changes
+	# subject prefix
+	git history squash two.. &&
+	test_cmp_rev HEAD^ two &&
+	test_commit_message HEAD <<-\EOF &&
+	squash! two
+
+	Append this
+
+	Append this as well
+	EOF
+	check_commit_author two HEAD &&
+
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! two
+
+	A new message
+	EOF
+
+	# "amend!" does not replace "squash!"
+	test_must_fail git history squash HEAD~2.. 2>err &&
+	test_grep "^error: squashing .* (amend! two) would overwrite .squash!. message" err
+'
+
+test_expect_success 'squash commit uses last "amend!" message' '
+	git reset --hard three &&
+	echo fix >file &&
+	git commit --author="Fix Me <fix.me@example.com>" --fixup=HEAD -a &&
+	git commit --allow-empty -F - <<-EOF &&
+	amend! $(git rev-parse --short HEAD)
+
+	The first reword
+
+	More detail
+	EOF
+
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! three
+
+	The second reword
+
+	Extra detail
+	EOF
+
+	test_commit WIP &&
+
+	cat >msg <<-EOF &&
+	amend! $(git rev-parse HEAD^ | tr a-f A-F)
+
+	The third reword
+
+	Excruciating detail
+	EOF
+
+	git commit --author="Someone Else <s.else@example.com>" --allow-empty \
+		-F msg &&
+
+	# squashing amend! updates the commit message
+	git history squash three^.. &&
+	sed -e 1,2d msg | test_commit_message HEAD &&
+	check_commit_author three HEAD &&
+	test_cmp_rev HEAD^ three^ &&
+
+	# squashing amend! into fixup! updates subject prefix
+	git reset --hard HEAD@{1} &&
+	git history squash three.. &&
+	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
+	check_commit_author HEAD@{1}~4 HEAD &&
+	test_cmp_rev HEAD^ three &&
+
+	# squashing amend! into amend! keeps original subject line
+	git reset --hard HEAD@{1} &&
+	git history squash HEAD~3.. &&
+	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
+	test_cmp_rev HEAD~3 three &&
+
+	# all amend! messages must target the first commit
+	git reset --hard HEAD@{1} &&
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! WIP
+
+	The real message
+	EOF
+
+	test_must_fail git history squash HEAD~4.. 2>err &&
+	test_grep "^error: cannot squash .* that does not target" err &&
+
+	# amend! message that targets commit that is not in range is rejected
+	test_must_fail git history squash HEAD~3.. 2>err &&
+	test_grep "^error: cannot squash .* target is not being squashed" err
 '
 
 test_expect_success '--update-refs=head only moves HEAD' '
-- 
2.54.0.200.gfd8d68259e3

[PATCH v10 3.7/3.7] fixup! history: add squash subcommand to fold a range

[Phillip Wood]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

Fix squashing into a merge

If the first commit of the range is a merge then the squashed commit
should also be a merge. Unfortunately, we assume that the first
commit in the range only has a single parent, but do not error out
if that's not the case. This means that fixing up a merge drops the
second and later parents. Correct this by using the list of parents
from the first commit in the range when creating the squashed commit.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 builtin/history.c         | 20 +++++++-------------
 t/t3455-history-squash.sh | 26 ++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 13 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 894da69f31..e21ef31e7e 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1276,14 +1276,13 @@ static int squash_check_subject(struct repository *repo,
 static int resolve_squash_range(struct repository *repo,
 				bool update_branches,
 				int argc, const char **argv,
-				struct commit **base_out,
 				struct commit **oldest_out,
 				struct commit **tip_out,
 				char **message_out)
 {
 	struct rev_info revs;
 	struct subject_data subject_data = SUBJECT_DATA_INIT;
-	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
+	struct commit *commit, *oldest = NULL, *tip = NULL;
 	size_t i;
 	int ret, tip_count = 0;
 	struct ref_filter filter = REF_FILTER_INIT;
@@ -1426,9 +1425,6 @@ static int resolve_squash_range(struct repository *repo,
 				    "untouched."));
 		goto out;
 	}
-	base = oldest->parents->item;
-
-	*base_out = base;
 	*oldest_out = oldest;
 	*tip_out = tip;
 	*message_out = strbuf_detach(&subject_data.squash_message, NULL);
@@ -1466,10 +1462,9 @@ static int cmd_history_squash(int argc,
 		OPT_END(),
 	};
 	struct strbuf reflog_msg = STRBUF_INIT;
-	struct commit *base, *oldest, *tip, *rewritten;
+	struct commit *oldest, *tip, *rewritten;
 	const struct object_id *base_tree_oid, *tip_tree_oid;
 	char *message_template = NULL;
-	struct commit_list *parents = NULL;
 	struct rev_info revs = { 0 };
 	int ret;
 
@@ -1488,7 +1483,7 @@ static int cmd_history_squash(int argc,
 	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
 
 	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
-				   argc, argv, &base, &oldest, &tip,
+				   argc, argv, &oldest, &tip,
 				   &message_template);
 	if (ret < 0)
 		goto out;
@@ -1497,13 +1492,13 @@ static int cmd_history_squash(int argc,
 	if (ret < 0)
 		goto out;
 
-	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
+	base_tree_oid = &repo_get_commit_tree(repo,
+					oldest->parents->item)->object.oid;
 	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
-	commit_list_append(base, &parents);
 
 	ret = commit_tree_ext(repo, "squash", oldest, message_template,
-			      parents,
-			      base_tree_oid, tip_tree_oid, &rewritten, flags);
+			      oldest->parents, base_tree_oid, tip_tree_oid,
+			      &rewritten, flags);
 	if (ret < 0) {
 		ret = error(_("failed writing squashed commit"));
 		goto out;
@@ -1521,7 +1516,6 @@ static int cmd_history_squash(int argc,
 
 out:
 	strbuf_release(&reflog_msg);
-	commit_list_free(parents);
 	release_revisions(&revs);
 	free(message_template);
 	return ret;
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index 26c4b4e29e..1713d6dcc3 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -347,6 +347,32 @@ test_expect_success 'squash commit uses last "amend!" message' '
 	# amend! message that targets commit that is not in range is rejected
 	test_must_fail git history squash HEAD~3.. 2>err &&
 	test_grep "^error: cannot squash .* target is not being squashed" err
+'
+
+test_expect_success 'squashing fixups into a merge' '
+	test_when_finished \
+		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
+		 git branch -D feature" &&
+	git checkout -f start &&
+	test_commit F1 &&
+	git checkout -b feature start &&
+	test_commit F2 &&
+	git merge F1 &&
+	echo fixed >F1.t &&
+	cat >msg <<-EOF &&
+	amend! $(git rev-parse HEAD)
+
+	merge F1 and F2
+
+	reworded
+	EOF
+
+	git commit -a -F msg &&
+	git history squash HEAD^^! HEAD &&
+	test_cmp_rev HEAD^1 F2 &&
+	test_cmp_rev HEAD^2 F1 &&
+	test_cmp_rev HEAD@{1}^{tree} HEAD^{tree} &&
+	sed 1,2d msg | test_commit_message HEAD
 '
 
 test_expect_success '--update-refs=head only moves HEAD' '
-- 
2.54.0.200.gfd8d68259e3

Re: [PATCH v10 3/5] history: add squash subcommand to fold a range

[Harald Nordgren]

> These patches can be fetched with
>
>   git fetch https://github.com/phillipwood/git wip/hn/history-squash/v10-early-part
>
> note that they do not support editing the commit message of the
> squashed commit.

Thanks, what should I do with it?

Is it a replacement for my branch, or should it apply them as fixups
(if so how do we handle the lack of re-edit support)?


Harald

Re: [PATCH v10 3/5] history: add squash subcommand to fold a range

[Phillip Wood]

Hi Harald

On 03/08/2026 17:35, Harald Nordgren wrote:
>> These patches can be fetched with
>>
>>    git fetch https://github.com/phillipwood/git wip/hn/history-squash/v10-early-part
>>
>> note that they do not support editing the commit message of the
>> squashed commit.
> 
> Thanks, what should I do with it?
> 
> Is it a replacement for my branch, or should it apply them as fixups
> (if so how do we handle the lack of re-edit support)?

I'd start by reading through them and asking any questions you have 
about the implementation or the reasoning behind it. Before you send a 
new version patch 3.5 needs some work to print the branch names (that 
shouldn't be difficult the ref-filter has functions to handle sorting 
and printing the contents of the ref_array) and patch 3.6 needs tweaking 
to work with editing the commit message (I'm afraid I haven't given that 
any thought yet). We should also think about how to split the series up 
to make it easier to review: the last patch in v12 is over 1500 lines of 
new code and tests. It would be better if we could split it into a few steps

1 - add the skeleton command with option parsing and the checks for
     rev-list arguments and BOTTOM commits.
2 - walk the revs and add all the error checks for multiple tips, merges
     outside the range, root commits etc.
3 - add the check for branches that point into the range.
4 - add the code that creates the new commit and its message when it is
     not being edited.
5 - add support for editing the commit message.

That makes each logical step easier to review and gives you the 
opportunity to explain the rationale for the design and implementation 
of each step in the commit messages.

I see you've sent another version already - it would have been helpful 
to wait for a response to this message first. The mailing list is 
asynchronous so you wont always receive an immediate response to your 
messages. Each time you send a new version you should think what it is 
you want to achieve from that iteration. Simply sending a series of what 
are in effect works-in-progress without any indication of what feedback 
you are looking for just clutters the list and makes it hard for 
reviewers to keep up.

Thanks

Phillip

Re: [PATCH v10 3/5] history: add squash subcommand to fold a range

[Junio C Hamano]

Harald Nordgren <haraldnordgren@gmail.com> writes:

>> These patches can be fetched with
>>
>>   git fetch https://github.com/phillipwood/git wip/hn/history-squash/v10-early-part
>>
>> note that they do not support editing the commit message of the
>> squashed commit.
>
> Thanks, what should I do with it?
>
> Is it a replacement for my branch, or should it apply them as fixups
> (if so how do we handle the lack of re-edit support)?

I am not Phillip, but in light of what I said elsewhere, I would
expect you to review them as if they were patch submissions to your
tree.  You may agree with some parts while disagreeing with others.

Respond to them.

Respond even to the ones you agree with, just as you would when
giving a positive review.  Demonstrate that you read them,
understood how they work, and then state that you agree.  If you
disagree, explain why you think it is better without such
changes.  

Just do not send a new iteration without a thorough explanation of
how you addressed each of the review comments, including those
review messages disguised as patches.  Be inviting to even those who
have not been involved in this topic so far to join the discussion,
which requires you to be transparent.  Engage in dialogue.  Explain
what you are doing.  Do not let patches alone explain themselves.

First and foremost, this development community is built on humans
collaborating with other humans.  An author posts a patch, a
reviewer responds with suggestions or critiques, and the author
replies to that e-mail.  In their own words, the author might:

 - build on the suggestion, rephrasing it and proposing further
   improvements;

 - disagree and offer a counter-proposal;

 - concede the patch's shortcomings and outline how they plan to fix
   them; or

 - defend their original design to give the reviewer a chance to
   reconsider.

Doing this in your own words helps reviewers see how close we are to
an agreement.  This kind of discussion often needs a few rounds of
back-and-forth.  It should also welcome folks watching from the
sidelines, which means letting the globe spin at least once so
developers in other timezones can chime in before we declare a rough
consensus.

Firing off a new iteration before there is a rough consensus on what
the final shape of the patches should look like makes it appear as
though the only thing you care about is producing the next
iteration, and that you care much less about collaborating with
others.

Thanks, Phillip, for these patches-as-reviews.

Re: [PATCH v10 3/5] history: add squash subcommand to fold a range

[Harald Nordgren]

Hi Phillip and Junio!

I admit I’m trying to expedite the process. Especially given what
feels like endless review cycles, and some frustration that this topic
was queued for ’master’ and now it feels like we’re miles away again.
I recognize that this mindset is not a good collaborative attitude, so
I’ll try to step back and re-adjust my mindset.

I am used to a work process where moving fast is paramount, and good
enough is good enough in terms of code quality. I’m not seeing a
healthy code review process here — any feedback halts the process
completely. Should it really take months to merge a topic?

I realize I'm too impatient for asynchronous communication, I get very
stressed about the idea of getting out-of-sync. When Phillip
graciously wrote a lot of code for me, I wanted to bring us up to
speed as soon as possible so his changes were not wasted if someone
else also started reviewing v11 in parallel. (In this particular case
I went back to v10, applied the fixups and then fit my v11 work on top
of that.)

I have v13 already in the pipeline, but I won’t send it now.


Harald

Re: [PATCH v10 3/5] history: add squash subcommand to fold a range

[Harald Nordgren]

Btw, I have now twice seen this message from Google when using Reply
All, which sends to Phillip's reply-to email, whereas mails are
actually sent from phillip.wood123@gmail.com:

"Your message wasn't delivered to phillip.wood@dunlem.org.uk because
the domain dunlem.org.uk couldn't be found

DNS Error: DNS type 'mx' lookup of dunlem.org.uk responded with code
NXDOMAIN Domain name not found: dunlem.org.uk For more information, go
to https://support.google.com/mail/?p=BadRcptDomain"


Harald

Re: [PATCH v10 3/5] history: add squash subcommand to fold a range

[Tuomas Ahola]

Harald Nordgren <haraldnordgren@gmail.com> wrote:

> Btw, I have now twice seen this message from Google when using Reply
> All, which sends to Phillip's reply-to email, whereas mails are
> actually sent from phillip.wood123@gmail.com:
> 
> "Your message wasn't delivered to phillip.wood@dunlem.org.uk because
> the domain dunlem.org.uk couldn't be found
> 
> DNS Error: DNS type 'mx' lookup of dunlem.org.uk responded with code
> NXDOMAIN Domain name not found: dunlem.org.uk For more information, go
> to https://support.google.com/mail/?p=BadRcptDomain"
> 
> 
> Harald
> 

There is a typo in the domain---should be dunelm, not dunlem.

--Tuomas

Re: [PATCH v10 3/5] history: add squash subcommand to fold a range

[Junio C Hamano]

Harald Nordgren <haraldnordgren@gmail.com> writes:

> Hi Phillip and Junio!
>
> I admit I’m trying to expedite the process. Especially given what
> feels like endless review cycles, and some frustration that this topic
> was queued for ’master’ and now it feels like we’re miles away again.
> I recognize that this mindset is not a good collaborative attitude, so
> I’ll try to step back and re-adjust my mindset.
>
> I am used to a work process where moving fast is paramount, and good
> enough is good enough in terms of code quality. I’m not seeing a
> healthy code review process here — any feedback halts the process
> completely. Should it really take months to merge a topic?

When you reroll too fast without waiting for reviewers, it
invalidates almost-done-but-yet-unpublished reviews.  If you
repeatedly do so, it exacerbates the problem by discouraging
reviewers from even looking at your topic, as they wonder if a
rapid reroll will invalidate their reviews yet again.

If it is taking months, I suspect that half of that is due to your
rapid rerolls, which have discouraged people from engaging, as they
cannot make a time commitment to a bottomless time sink.  The summer
being a relatively slow season certainly has played a role, too.

Thanks.

Re: [PATCH v10 3/5] history: add squash subcommand to fold a range

[Phillip Wood]

On 04/08/2026 22:12, Junio C Hamano wrote:
> Harald Nordgren <haraldnordgren@gmail.com> writes:
> 
>> Hi Phillip and Junio!
>>
>> I admit I’m trying to expedite the process. Especially given what
>> feels like endless review cycles, and some frustration that this topic
>> was queued for ’master’ and now it feels like we’re miles away again.
>> I recognize that this mindset is not a good collaborative attitude, so
>> I’ll try to step back and re-adjust my mindset.
>>
>> I am used to a work process where moving fast is paramount, and good
>> enough is good enough in terms of code quality.

We don't have the luxury of being able to easily roll-back features that 
have been merged and are being used in the wider world so need to have a 
considered approach to designing new features.

Hardly anyone who is employed to work on git is given work time to 
review random patches that are not of direct interest to their employer, 
   the reviews are mostly from people volunteering their own time. 
Therefore comparing it to what happens inside a company where it is part 
of the job to review others code is not a realistic comparison.

>> I’m not seeing a
>> healthy code review process here — any feedback halts the process
>> completely. Should it really take months to merge a topic?

I'm not sure what you mean by "any feedback halts the process 
completely". If you spot something you want to improve, you can flag 
that on the list and still work on your patches while you're waiting for 
a review. Though, if you're frequently doing that, then it is an 
indication that you're posting patches that are not ready for review.

The communication around the code is just as important as the code 
itself and, especially in the early stages of a topic, when the design 
is being thrashed out, it is more important than the code. Sending out a 
re-roll immediately in response to every comment is not productive, as 
it leads to a multitude of different versions with small changes between 
them. It's far better to reply to any questions and comments, and allow 
others time to comment as well, so that we reach a consensus before the 
next set of patches are posted. If you're not following other topics on 
the list then it might be a good idea to start - you'll see others are 
not posting 20 revisions before their work is merged.

> When you reroll too fast without waiting for reviewers, it
> invalidates almost-done-but-yet-unpublished reviews.  If you
> repeatedly do so, it exacerbates the problem by discouraging
> reviewers from even looking at your topic, as they wonder if a
> rapid reroll will invalidate their reviews yet again.

Yes, I've definitely waited a couple of days to see if another iteration 
is going to appear before starting a review.

> If it is taking months, I suspect that half of that is due to your
> rapid rerolls, which have discouraged people from engaging, as they
> cannot make a time commitment to a bottomless time sink.  The summer
> being a relatively slow season certainly has played a role, too.

I've found these series taking more time than I'd like to review. Part 
of that is the rapid re-rolls, the other part is the very brief cover 
letters that are not very detailed or explicit with regard to what 
exactly has changed in the implementation and behavior [1] since the 
last version.

I'm going to be off the list next week, so it be a while before I look 
at these patches again. I'm hoping to see a reply to [2] when I'm back.

Thanks

Phillip

[1] For example in <pull.2285.v20.git.git.1784704238.gitgitgadget@gmail.com>

     * Protect branches transitively required by a surviving local
       upstream stack. Traverse upstream chains once and defer delete-set
       mutation until traversal completes.

That was actually a change in behavior from the previous version but it 
was not clear to me at all. It would have been much more helpful to 
explicitly call that out as a change in behavior and explain why the 
behavior had changed.

[2] 
https://lore.kernel.org/git/ddd0160c-7f4c-41c7-855f-58288db00050@gmail.com

Re: [PATCH v10 3/5] history: add squash subcommand to fold a range

[Harald Nordgren]

> We don't have the luxury of being able to easily roll-back features that
> have been merged and are being used in the wider world so need to have a
> considered approach to designing new features.

This is fair and an important point since Git is distributed as a
binary. However, I still think there is a balance to be struck.

> Hardly anyone who is employed to work on git is given work time to
> review random patches that are not of direct interest to their employer,
>    the reviews are mostly from people volunteering their own time.
> Therefore comparing it to what happens inside a company where it is part
> of the job to review others code is not a realistic comparison.

This is very fair and of course makes a lot of sense!

> > When you reroll too fast without waiting for reviewers, it
> > invalidates almost-done-but-yet-unpublished reviews.  If you
> > repeatedly do so, it exacerbates the problem by discouraging
> > reviewers from even looking at your topic, as they wonder if a
> > rapid reroll will invalidate their reviews yet again.
>
> Yes, I've definitely waited a couple of days to see if another iteration
> is going to appear before starting a review.

This puts us on a "resonant frequency" since I often finish the work
and then wait a day before sending out. I think there are definitely
cases where rerolling quicker would also be beneficial.

> [2]
> https://lore.kernel.org/git/ddd0160c-7f4c-41c7-855f-58288db00050@gmail.com

My main opposition to this is two-fold:

1. I don't see the value that the new format would bring; I don't
understand that the proposed format is better than the current one (I
am not sure if I actually understand the new format at all), and Junio
expressed a similar sentiment earlier so I have been counting on this
discussion dying down organically.

2. It's consistent to keep them the same, which is in itself valuable.
And it requires work to implement a new format, so there should be a
good reason to do that, which goes back to my point 1.


Harald

Re: [PATCH v10 3/5] history: add squash subcommand to fold a range

[Kristoffer Haugsbakk]

On Tue, Aug 4, 2026, at 22:41, Harald Nordgren wrote:
> I admit I’m trying to expedite the process. Especially given what
> feels like endless review cycles, and some frustration that this topic
> was queued for ’master’ and now it feels like we’re miles away again.
> I recognize that this mindset is not a good collaborative attitude, so
> I’ll try to step back and re-adjust my mindset.

Collaboration is at the heart of wanting to integrate your changes with
the main Git tree.

You already know that you can have this extension for yourself right
now, in fact immediately after you were happy with it. But you want to
get it into the main Git tree as well. Maybe because you don’t want to
deal with updates to the surrounding context as you have to update your
tree according to the main Git tree. Maybe because you, for example,
know that someone else is working on another subcommand. And all of that
is about collaboration, just one level higher (or one step further?).

>[snip]

[PATCH v10 4/5] sequencer: share the squash message marker helpers and flags

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

When "git rebase -i" squashes commits it builds an editor template with a
"This is a combination of N commits." banner, a "This is the 1st/Nth
commit message:" header above each kept message (or a "will be skipped"
header for a dropped one), and a commented-out subject for any fixup!,
squash! or amend! commit. The banner, the headers and the
subject-commenting all live in static helpers in sequencer.c wired to the
rebase state, so no other command can present a squash the same way.

Pull the three pieces out into add_squash_combination_header(),
add_squash_message_header() (which takes a flag for the "will be skipped"
variant) and squash_subject_comment_len(), and use them from
update_squash_messages() and append_squash_message(). Also move the
todo_item_flags enum to the header, so a caller reading the output of
todo_list_rearrange_squash() can tell an amend! (TODO_REPLACE_FIXUP_MSG)
from a plain fixup!. A later change reuses all of this to give "git
history squash --reedit-message" the same template.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 sequencer.c | 70 +++++++++++++++++++++++++++++------------------------
 sequencer.h | 30 +++++++++++++++++++++++
 2 files changed, 69 insertions(+), 31 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 1355a99a09..3c704fd5ab 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1880,18 +1880,38 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
-enum todo_item_flags {
-	TODO_EDIT_MERGE_MSG    = (1 << 0),
-	TODO_REPLACE_FIXUP_MSG = (1 << 1),
-	TODO_EDIT_FIXUP_MSG    = (1 << 2),
-};
-
 static const char first_commit_msg_str[] = N_("This is the 1st commit message:");
 static const char nth_commit_msg_fmt[] = N_("This is the commit message #%d:");
 static const char skip_first_commit_msg_str[] = N_("The 1st commit message will be skipped:");
 static const char skip_nth_commit_msg_fmt[] = N_("The commit message #%d will be skipped:");
 static const char combined_commit_msg_fmt[] = N_("This is a combination of %d commits.");
 
+void add_squash_combination_header(struct strbuf *buf, int n)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	strbuf_addf(buf, _(combined_commit_msg_fmt), n);
+}
+
+void add_squash_message_header(struct strbuf *buf, int n, int skip)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	if (n == 1)
+		strbuf_addstr(buf, skip ? _(skip_first_commit_msg_str) :
+				   _(first_commit_msg_str));
+	else
+		strbuf_addf(buf, skip ? _(skip_nth_commit_msg_fmt) :
+			    _(nth_commit_msg_fmt), n);
+}
+
+size_t squash_subject_comment_len(const char *body, int squashing)
+{
+	if (starts_with(body, "amend!") ||
+	    (squashing && (starts_with(body, "squash!") ||
+			   starts_with(body, "fixup!"))))
+		return commit_subject_length(body);
+	return 0;
+}
+
 static int is_fixup_flag(enum todo_command command, unsigned flag)
 {
 	return command == TODO_FIXUP && ((flag & TODO_REPLACE_FIXUP_MSG) ||
@@ -2005,20 +2025,13 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 {
 	struct replay_ctx *ctx = opts->ctx;
 	const char *fixup_msg;
-	size_t commented_len = 0, fixup_off;
-	/*
-	 * amend is non-interactive and not normally used with fixup!
-	 * or squash! commits, so only comment out those subjects when
-	 * squashing commit messages.
-	 */
-	if (starts_with(body, "amend!") ||
-	    ((command == TODO_SQUASH || seen_squash(ctx)) &&
-	     (starts_with(body, "squash!") || starts_with(body, "fixup!"))))
-		commented_len = commit_subject_length(body);
+	size_t commented_len, fixup_off;
+
+	commented_len = squash_subject_comment_len(body,
+				command == TODO_SQUASH || seen_squash(ctx));
 
-	strbuf_addf(buf, "\n%s ", comment_line_str);
-	strbuf_addf(buf, _(nth_commit_msg_fmt),
-		    ++ctx->current_fixup_count + 1);
+	strbuf_addch(buf, '\n');
+	add_squash_message_header(buf, ++ctx->current_fixup_count + 1, 0);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len, comment_line_str);
 	/* buf->buf may be reallocated so store an offset into the buffer */
@@ -2083,9 +2096,8 @@ static int update_squash_messages(struct repository *r,
 		eol = !starts_with(buf.buf, comment_line_str) ?
 			buf.buf : strchrnul(buf.buf, '\n');
 
-		strbuf_addf(&header, "%s ", comment_line_str);
-		strbuf_addf(&header, _(combined_commit_msg_fmt),
-			    ctx->current_fixup_count + 2);
+		add_squash_combination_header(&header,
+					      ctx->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);
 		if (is_fixup_flag(command, flag) && !seen_squash(ctx))
@@ -2109,12 +2121,9 @@ static int update_squash_messages(struct repository *r,
 			repo_unuse_commit_buffer(r, head_commit, head_message);
 			return error(_("cannot write '%s'"), rebase_path_fixup_msg());
 		}
-		strbuf_addf(&buf, "%s ", comment_line_str);
-		strbuf_addf(&buf, _(combined_commit_msg_fmt), 2);
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addstr(&buf, is_fixup_flag(command, flag) ?
-			      _(skip_first_commit_msg_str) :
-			      _(first_commit_msg_str));
+		add_squash_combination_header(&buf, 2);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, 1, is_fixup_flag(command, flag));
 		strbuf_addstr(&buf, "\n\n");
 		if (is_fixup_flag(command, flag))
 			strbuf_add_commented_lines(&buf, body, strlen(body),
@@ -2133,9 +2142,8 @@ static int update_squash_messages(struct repository *r,
 	if (command == TODO_SQUASH || is_fixup_flag(command, flag)) {
 		res = append_squash_message(&buf, body, command, opts, flag);
 	} else if (command == TODO_FIXUP) {
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),
-			    ++ctx->current_fixup_count + 1);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, ++ctx->current_fixup_count + 1, 1);
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body),
 					   comment_line_str);
diff --git a/sequencer.h b/sequencer.h
index 64a9c7fb1b..b01f897020 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,6 +119,13 @@ enum todo_command {
 	TODO_COMMENT
 };
 
+/* Bits for the "flags" member of struct todo_item */
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG    = (1 << 0),
+	TODO_REPLACE_FIXUP_MSG = (1 << 1),
+	TODO_EDIT_FIXUP_MSG    = (1 << 2),
+};
+
 struct todo_item {
 	enum todo_command command;
 	struct commit *commit;
@@ -208,6 +215,29 @@ int todo_list_rearrange_squash(struct todo_list *todo_list);
  */
 void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
 
+/*
+ * Append the "This is a combination of N commits." banner that "git rebase
+ * -i" writes at the top of a squashed commit's message, commented out with
+ * the comment character.
+ */
+void add_squash_combination_header(struct strbuf *buf, int n);
+
+/*
+ * Append the header (1-based N) that "git rebase -i" writes above each message
+ * when squashing, commented out with the comment character. With SKIP it reads
+ * "The ... commit message will be skipped" for a message that is dropped (a
+ * fixup), otherwise "This is the ... commit message".
+ */
+void add_squash_message_header(struct strbuf *buf, int n, int skip);
+
+/*
+ * Return the length of the leading subject of BODY when it should be commented
+ * out in a squash message, or 0 otherwise. An "amend!" subject always
+ * qualifies; "squash!" and "fixup!" subjects only when SQUASHING, since a
+ * plain fixup chain keeps them.
+ */
+size_t squash_subject_comment_len(const char *body, int squashing);
+
 void append_conflicts_hint(struct index_state *istate,
 		struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
 enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,
-- 
gitgitgadget

[PATCH v10 5/5] history: re-edit a squash with every message

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

By default "git history squash" reuses the oldest commit's message, or
the replacement body from an amend! commit targeting it. When
--reedit-message is given it only reopened that selected message, so the
messages of the other commits in the range were lost.

Gather the message of every commit in the range and build the same editor
template that "git rebase -i --autosquash" shows for a squash, reusing
add_squash_combination_header(), add_squash_message_header() and
squash_subject_comment_len(). Feed the range through
todo_list_rearrange_squash() so that each fixup!, squash! or amend! is
grouped under the commit it targets rather than shown in commit order,
exactly as autosquash would arrange them.

Only the message text differs, the changes are always folded in. A fixup!
message is commented out in full under a "will be skipped" header, a
squash! keeps its body with only the marker subject commented, and an
amend! replaces its target's message unless a squash! already folded into
that target, in which case it behaves like a squash!.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  22 +++-
 builtin/history.c              | 104 +++++++++++++++++
 t/t3455-history-squash.sh      | 201 +++++++++++++++++++++++++++++++++
 3 files changed, 321 insertions(+), 6 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index e1e930f355..6f3b031d2a 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -134,11 +134,12 @@ already on `topic`. Rev-list options may also be given, but any that would
 change how the range is walked are overridden with a warning.
 +
 The oldest commit's message is preserved by default, except that an `amend!`
-commit targeting it replaces its message. Specify `--reedit-message` to edit
-the resulting message. A merge commit inside the range is folded like any
-other, but the range must have a single base, so a range that reaches more
-than one entry point (for example a side branch that forked before the range
-and was later merged into it) is rejected.
+commit targeting it replaces its message. With `--reedit-message`, an editor
+opens pre-filled with the messages of all the folded commits so you can
+combine them. A merge commit inside the range is folded like any other, but
+the range must have a single base, so a range that reaches more than one entry
+point (for example a side branch that forked before the range and was later
+merged into it) is rejected.
 +
 A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
 targets is also in the range, so the fold does not silently absorb a
@@ -146,6 +147,14 @@ marker meant for a commit outside it. As an exception, a range made up entirely
 of markers for one target is combined into a single commit, keeping the last
 `amend!` message if there is one.
 +
+With `--reedit-message` the template mirrors `git rebase -i --autosquash`:
+each `fixup!`, `squash!`, or `amend!` is grouped under the commit it
+targets rather than shown in commit order. A `fixup!` message is dropped
+(commented out in full), a `squash!` keeps its body with only the marker
+subject commented, and an `amend!` replaces its target's message, unless
+a `squash!` folded into that target first, in which case it keeps its
+body like a `squash!`.
++
 A branch or tag that points at a commit inside the range would be left
 dangling once those commits are folded away, so with the default
 `--update-refs=branches` the command refuses. Rerun with
@@ -162,7 +171,8 @@ OPTIONS
 	ref updates is generally safe.
 
 `--reedit-message`::
-	Open an editor to modify the rewritten commit's message.
+	Open an editor to modify the rewritten commit's message. For `squash`
+	the editor is pre-filled with the messages of all the folded commits.
 
 `--empty=(drop|keep|abort)`::
 	Control what happens when a commit becomes empty as a result of the
diff --git a/builtin/history.c b/builtin/history.c
index 423c8beaaf..2542ea33a0 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1255,6 +1255,102 @@ static int find_interior_ref(const struct reference *ref, void *cb_data)
 	return 0;
 }
 
+static bool amend_replaces_target(struct todo_list *todo, int target)
+{
+	int i;
+
+	for (i = target + 1; i < todo->nr &&
+			     todo->items[i].command != TODO_PICK; i++) {
+		if (todo->items[i].command == TODO_SQUASH)
+			return false;
+		if (todo->items[i].flags & TODO_REPLACE_FIXUP_MSG)
+			return true;
+	}
+	return false;
+}
+
+static int build_squash_message(struct repository *repo,
+				struct commit *base,
+				struct commit *tip,
+				struct strbuf *out)
+{
+	struct rev_info revs;
+	struct commit *commit;
+	struct strvec args = STRVEC_INIT;
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	int i, nr_commits, ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs)))
+		strbuf_addf(&todo.buf, "pick %s\n",
+			    oid_to_hex(&commit->object.oid));
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not prepare the squash message"));
+		goto out;
+	}
+
+	nr_commits = todo.nr;
+	for (i = 0; i < nr_commits; i++) {
+		struct todo_item *item = &todo.items[i];
+		const char *message, *body;
+		size_t commented_len;
+		bool skip, squashing;
+
+		squashing = item->command == TODO_SQUASH ||
+			    (item->flags & TODO_REPLACE_FIXUP_MSG);
+		if (item->command == TODO_PICK)
+			skip = amend_replaces_target(&todo, i);
+		else
+			skip = !squashing;
+
+		message = repo_logmsg_reencode(repo, item->commit, NULL, NULL);
+		find_commit_subject(message, &body);
+
+		if (skip)
+			commented_len = strlen(body);
+		else if (squashing)
+			commented_len = squash_subject_comment_len(body, 1);
+		else
+			commented_len = 0;
+
+		if (!i)
+			add_squash_combination_header(out, nr_commits);
+		strbuf_addch(out, '\n');
+		add_squash_message_header(out, i + 1, skip);
+		strbuf_addstr(out, "\n\n");
+		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
+		strbuf_addstr(out, body + commented_len);
+		strbuf_complete_line(out);
+
+		repo_unuse_commit_buffer(repo, item->commit, message);
+	}
+
+	ret = 0;
+
+out:
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1338,6 +1434,14 @@ static int cmd_history_squash(int argc,
 		}
 	}
 
+	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
+		strbuf_reset(&message);
+		ret = build_squash_message(repo, base, tip, &message);
+		if (ret < 0)
+			goto out;
+		message_template = message.buf;
+	}
+
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
 		goto out;
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index 9c362f3094..6fce924327 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -271,6 +271,207 @@ test_expect_success 'preserves authorship of the oldest commit' '
 	test_cmp expect actual
 '
 
+test_expect_success '--reedit-message offers every folded-in message' '
+	git reset --hard start &&
+	stage_file b &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# This is the 1st commit message:
+
+	re-one subject
+
+	re-one body line
+
+	# This is the commit message #2:
+
+	re-two
+
+	# This is the commit message #3:
+
+	re-three
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_subjects -1 <<-\EOF
+	combined
+	EOF
+'
+
+test_expect_success '--reedit-message handles fixup!, squash! and amend! like rebase' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "fixup! mark-base\n\nfixup body\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+	stage_file e &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	mark-base
+
+	# The commit message #2 will be skipped:
+
+	# fixup! mark-base
+	#
+	# fixup body
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# This is the commit message #4:
+
+	# amend! mark-base
+
+	amended message
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	mark-base
+
+	squash remark
+
+	amended message
+
+	EOF
+'
+
+test_expect_success '--reedit-message groups fixups under their targets' '
+	git reset --hard start &&
+	test_commit --no-tag alpha file a1 &&
+	test_commit --no-tag beta file b1 &&
+	stage_file a2 &&
+	commit_with_message "fixup! alpha\n" &&
+	stage_file b2 &&
+	commit_with_message "fixup! beta\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	alpha
+
+	# The commit message #2 will be skipped:
+
+	# fixup! alpha
+
+	# This is the commit message #3:
+
+	beta
+
+	# The commit message #4 will be skipped:
+
+	# fixup! beta
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited
+'
+
+test_expect_success '--reedit-message lets amend! replace its target message' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --reedit-message start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# The 1st commit message will be skipped:
+
+	# mark-base
+
+	# This is the commit message #2:
+
+	# amend! mark-base
+
+	amended message
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	amended message
+
+	squash remark
+
+	EOF
+'
+
+test_expect_success '--reedit-message aborts on an empty message' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	test_must_fail git history squash --reedit-message start.. &&
+
+	test_cmp_rev "$head_before" HEAD
+'
+
 test_expect_success '--update-refs=head only moves HEAD' '
 	git reset --hard three &&
 	git branch -f other HEAD &&
-- 
gitgitgadget

Re: [PATCH v10 0/5] history: add squash subcommand to fold a range

[Matt Hunter]

On Mon Jul 20, 2026 at 4:26 AM EDT, Harald Nordgren via GitGitGadget wrote:
> Adds git history squash <revision-range> to fold a range of commits.
>
> Changes in v10:
>
>  * Record the full revision expression in squash reflog.
>  * Preserve the boundary-walk invariant when sanitizing rev-list options.
>  * Clarify amend! and --reedit-message documentation.
>

v10 looks good to me!
Thanks!

[PATCH v11 0/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v11:

 * Make message editing the default with the autosquash-style template, add
   --no-edit instead of squash-specific --reedit-message.
 * Validate one actual boundary and tip, rejecting root-reaching and
   multi-tip ranges.
 * Protect only interior local branches, leaving tags and remote-tracking
   refs unchanged.
 * Move sequencer preparation before squash and fold the later
   message-editing patch into the feature commit.

Changes in v10:

 * Record the full revision expression in squash reflog.
 * Preserve the boundary-walk invariant when sanitizing rev-list options.
 * Clarify amend! and --reedit-message documentation.

Changes in v9:

 * Use the last amend! targeting the oldest folded commit as the default
   squashed message. Ignore amend! markers targeting later commits while
   selecting that replacement message.
 * Improve tests.

Changes in v8:

 * --reedit-message now builds the same editor template as git rebase -i
   --autosquash: fixup!, squash! and amend! commits are grouped under the
   commit they target instead of shown in commit order, and an amend!
   replaces its target's message.
 * A fixup!, squash! or amend! is refused only when its target is outside
   the range, so several fixups for an in-range commit fold together. A
   range that is entirely markers for one below-range target is combined
   into a single commit, keeping the last amend! message.
 * Merges inside the range are folded when the range has a single base, with
   no dedicated opt-in flag, --ancestry-path ensures only commits descended
   from the base are folded, and a range reaching more than one base is
   rejected.
 * Rev-list options are accepted and sanitized the way git replay does,
   forcing the walk order back with a warning, which also fixes git history
   squash -- --reverse slipping past the previous option check.
 * Kept this as an explicit squash subcommand rather than making
   --reedit-message the default or renaming the command.

Changes in v7:

 * --reedit-message now builds the same editor template git rebase -i shows
   for a squash (a combination of N commits banner with each folded message
   under its own header) and follows autosquash for markers: a fixup!
   message falls out (commented under a will be skipped header), while a
   squash! or amend! keeps its body with only the marker subject commented
   so its remark can be reworded in. Only the message text is affected,
   every commit's changes are always folded in.
 * Reuse git rebase -i's squash-message code: a preparatory sequencer:
   commit extracts the banner, header and marker-comment helpers so both
   rebase and git history squash build the identical template from one
   source.
 * Refuse a range whose oldest commit is a fixup!, squash! or amend!, since
   the marker's target cannot be inside the range.
 * Reorder the squash usage so dashed options come before <revision-range>,
   and spell out HEAD instead of @ in the documentation and examples.
 * Expand the squash commit message and documentation with this overview,
   and scope the merge limitation so it no longer contradicts squash folding
   a single-base interior merge.

Changes in v6:

 * git history squash now accepts multiple revision arguments, read like the
   arguments to git-rev-list, so a compound range such as @~3.. ^topic
   works.
 * The base to reparent onto is now the oldest in-range commit's parent; a
   boundary other than that base means the range has more than one base and
   is rejected. This also fixes the earlier overly-restrictive handling of
   merges and side branches.
 * A single-commit range (e.g. @^!) is rejected with "nothing to squash"
   (this also covers the @^!-style example that previously succeeded
   silently).
 * Commit messages reworded: the squash commit now gives an overview of
   fixup!/squash!/amend! handling, rewording, merge-parent and ref behavior.

Changes in v5:

 * The range walk now uses --ancestry-path, so only commits descended from
   the base are folded; a single revision such as HEAD or HEAD~1 is now
   rejected as "not a <base>..<tip> range" rather than treated as a squash
   down to the root.
 * This adopts the --ancestry-path suggestion; the multi-base rejection is
   unchanged, so a side branch that forked before the base and merged in is
   still refused.
 * Added tests covering more merge topologies: two interior merges, a nested
   merge, an octopus merge, an octopus arm forked before the base, a merge
   among the descendants replayed above the range, and a ref pointing at an
   interior merge commit.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (4):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  sequencer: share the squash message marker helpers and flags
  history: add squash subcommand to fold a range

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  57 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 578 +++++++++++++++++++++--
 sequencer.c                      |  70 +--
 sequencer.h                      |  30 ++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 758 +++++++++++++++++++++++++++++++
 9 files changed, 1429 insertions(+), 71 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: 13c7afec212fc97ce257d15601659314c6673d6c
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v11
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v11
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v10:

 1:  f848103497 = 1:  dd1deb5e5b history: extract helper for a commit's parent tree
 2:  49dadc3410 = 2:  7309f64485 history: give commit_tree_ext a message template
 4:  41156c9afb ! 3:  0762589e22 sequencer: share the squash message marker helpers and flags
     @@ Commit message
          todo_item_flags enum to the header, so a caller reading the output of
          todo_list_rearrange_squash() can tell an amend! (TODO_REPLACE_FIXUP_MSG)
          from a plain fixup!. A later change reuses all of this to give "git
     -    history squash --reedit-message" the same template.
     +    history squash" the same template.
      
          No change in behavior.
      
 3:  6b5b2c93f2 ! 4:  7abda3643c history: add squash subcommand to fold a range
     @@ Commit message
          a "git reset --soft" to the merge base followed by "git commit --amend".
      
          Add "git history squash <revision-range>" to do this directly. It folds
     -    every commit in the range into the oldest one, keeping that commit's
     -    authorship and taking the tree of the newest commit, then replays the
     -    commits above the range on top. The squashed message comes from the
     -    oldest commit by default, or from the body of the last amend! commit
     -    targeting it. An editor opens with the selected message when
     -    --reedit-message is given. A fixup!, squash! or amend! commit is refused
     -    unless the commit it targets is also in the range, so the fold does not
     -    silently absorb a marker meant for a commit outside it. The check runs
     -    the range through todo_list_rearrange_squash(), which leaves such a
     -    marker as a plain pick. Markers whose target is in the range fold in as
     -    usual. As an exception, a range made up entirely of markers for one
     -    target is combined anyway, taking its message from the last amend! if
     -    there is one, so a batch of fixups for the same commit can be collapsed.
     +    every commit in the range into one commit, preserving the authorship of
     +    the oldest commit and taking the tree of the tip, then replays commits
     +    above the range. The editor opens with every folded message in the same
     +    template used by "git rebase -i --autosquash". With --no-edit, the
     +    oldest message is kept, or the last amend! replacement that targets it.
     +
     +    A fixup!, squash! or amend! commit is refused unless its target is also
     +    in the range, so the fold does not silently absorb a marker intended for
     +    another commit. As an exception, a range made up entirely of markers for
     +    one target is combined, allowing a batch of related fixups to be
     +    consolidated.
      
          The range is read like the arguments to "git rev-list", so several
          revisions such as "HEAD~3..HEAD ^topic" may be given, and rev-list
     -    options are accepted too. As "git replay" does, the walk options the fold
     -    relies on are forced after setup_revisions() and a warning is printed if
     -    an option changed them, so the first commit returned is the range's
     -    oldest and its parent is the base regardless of what the user passed
     -    (including after a "--"). A merge inside the range is folded when its
     -    other parent is reachable from the base, otherwise the range has more
     -    than one base and is rejected. By default the command also refuses when a
     -    ref points at a commit that the fold would discard. Use --update-refs=head
     -    to rewrite only the current branch instead.
     +    options are accepted too. Walk-order options needed by the fold are
     +    restored after setup_revisions(), with a warning when an option changed
     +    them. The selected graph must have one actual boundary and one actual
     +    tip and must not reach a root. A merge inside the range is folded when
     +    all selected history reaches the same boundary; otherwise the range has
     +    more than one base and is rejected.
     +
     +    By default the command refuses when a local branch points inside the
     +    range, because that branch cannot be replayed as a descendant of the
     +    result. Tags and remote-tracking refs are left unchanged. Use
     +    --update-refs=head to leave interior branches unchanged as well.
      
          Inspired-by: Sergey Chernov <serega.morph@gmail.com>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
     @@ Documentation/git-history.adoc: git history drop <commit> [--dry-run] [--update-
       git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
       git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
       git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
     -+git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>
     ++git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>
       
       DESCRIPTION
       -----------
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      +already on `topic`. Rev-list options may also be given, but any that would
      +change how the range is walked are overridden with a warning.
      ++
     -+The oldest commit's message is preserved by default, except that an `amend!`
     -+commit targeting it replaces its message. Specify `--reedit-message` to edit
     -+the resulting message. A merge commit inside the range is folded like any
     -+other, but the range must have a single base, so a range that reaches more
     ++An editor opens pre-filled with the messages of all the folded commits so
     ++you can combine them. With `--no-edit`, the oldest commit's message is
     ++preserved instead, except that an `amend!` commit targeting it replaces its
     ++message. A merge commit inside the range is folded like any other, but the
     ++range must have a single base and a single tip. A range that reaches more
      +than one entry point (for example a side branch that forked before the range
     -+and was later merged into it) is rejected.
     ++and was later merged into it), or that selects two unmerged tips, is rejected.
      ++
      +A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
      +targets is also in the range, so the fold does not silently absorb a
      +marker meant for a commit outside it. As an exception, a range made up entirely
     -+of markers for one target is combined into a single commit, keeping the last
     -+`amend!` message if there is one.
     ++of markers for one target is combined into a single commit. With `--no-edit`,
     ++the last `amend!` message is used if there is one.
      ++
     -+A branch or tag that points at a commit inside the range would be left
     -+dangling once those commits are folded away, so with the default
     -+`--update-refs=branches` the command refuses. Rerun with
     -+`--update-refs=head` to rewrite only the current branch and leave such
     -+refs pointing at the old commits.
     ++The template mirrors `git rebase -i --autosquash`: each `fixup!`, `squash!`,
     ++or `amend!` is grouped under the commit it targets rather than shown in
     ++commit order. A `fixup!` message is dropped (commented out in full), a
     ++`squash!` keeps its body with only the marker subject commented, and an
     ++`amend!` replaces its target's message, unless a `squash!` folded into that
     ++target first, in which case it keeps its body like a `squash!`.
     +++
     ++A local branch that points at a commit inside the range cannot be rewritten
     ++as a descendant of the result, so with the default `--update-refs=branches`
     ++the command refuses. Rerun with `--update-refs=head` to rewrite only the
     ++current branch and leave such branches pointing at the old commits. Tags and
     ++remote-tracking refs are always left unchanged.
      +
       OPTIONS
       -------
       
      @@ Documentation/git-history.adoc: OPTIONS
     + 	objects will be written into the repository, so applying these printed
       	ref updates is generally safe.
       
     ++`--edit`::
     ++`--no-edit`::
     ++	For `squash`, open an editor to combine the messages of the folded commits.
     ++	This is the default; use `--no-edit` to keep the selected message
     ++	without opening an editor.
     ++
       `--reedit-message`::
     --	Open an editor to modify the target commit's message.
     -+	Open an editor to modify the rewritten commit's message.
     + 	Open an editor to modify the target commit's message.
       
     - `--empty=(drop|keep|abort)`::
     - 	Control what happens when a commit becomes empty as a result of the
      
       ## advice.c ##
      @@ advice.c: static struct {
     @@ builtin/history.c
       #define GIT_HISTORY_SPLIT_USAGE \
       	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
      +#define GIT_HISTORY_SQUASH_USAGE \
     -+	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--reedit-message] <revision-range>")
     ++	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>")
       
       static void change_data_free(void *util, const char *str UNUSED)
       {
     @@ builtin/history.c: out:
      +{
      +	struct rev_info revs;
      +	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
     -+	struct commit_list *boundaries = NULL, *b;
     ++	struct commit_list *boundaries = NULL, *commits = NULL, *iter,
     ++		**commits_tail = &commits;
     ++	struct oidset selected = OIDSET_INIT, has_children = OIDSET_INIT;
      +	struct strvec args = STRVEC_INIT;
     ++	bool reaches_root = false;
      +	size_t i;
      +	int ret;
      +
     @@ builtin/history.c: out:
      +		revs.boundary = 1;
      +	}
      +
     -+	/*
     -+	 * A squash needs a base to reparent onto, so the range has to exclude
     -+	 * something, as in "<base>..<tip>". A revision range with no such
     -+	 * bottom commit cannot be squashed.
     -+	 */
     ++	/* A squash range must name a bottom revision to reparent onto. */
      +	for (i = 0; i < revs.cmdline.nr; i++)
     -+		if (revs.cmdline.rev[i].flags & UNINTERESTING)
     ++		if (revs.cmdline.rev[i].flags & BOTTOM)
      +			break;
      +	if (i == revs.cmdline.nr) {
      +		ret = error(_("not a '<base>..<tip>' revision range"));
     @@ builtin/history.c: out:
      +		goto out;
      +	}
      +
     -+	/*
     -+	 * Set boundary commits aside for the base check below, and put every
     -+	 * in-range commit but the tip into the interior set. A ref pointing
     -+	 * at an interior commit would dangle once the range is folded away.
     -+	 */
     ++	/* Set boundary commits aside for the base check below. */
      +	while ((commit = get_revision(&revs))) {
      +		if (commit->object.flags & BOUNDARY) {
      +			commit_list_insert(commit, &boundaries);
     @@ builtin/history.c: out:
      +		}
      +		if (!oldest)
      +			oldest = commit;
     -+		if (tip)
     -+			oidset_insert(interior_out, &tip->object.oid);
     -+		tip = commit;
     ++		oidset_insert(&selected, &commit->object.oid);
     ++		commits_tail = commit_list_append(commit, commits_tail);
      +	}
      +
      +	if (!oldest) {
      +		ret = error(_("the revision range is empty"));
      +		goto out;
     -+	} else if (oldest == tip) {
     ++	} else if (!commits->next) {
      +		ret = error(_("the revision range holds a single commit; "
      +			      "nothing to squash"));
      +		goto out;
     -+	} else if (!oldest->parents) {
     -+		BUG("an in-range commit must have a parent");
      +	}
     -+	base = oldest->parents->item;
      +
      +	/*
     -+	 * A boundary other than the base is an in-range commit reaching a
     -+	 * commit outside the range, so the range has more than one base.
     ++	 * Find the selected commits that have selected children. The only
     ++	 * remaining commit must be the tip whose tree becomes the result.
      +	 */
     -+	for (b = boundaries; b; b = b->next) {
     -+		if (b->item != base) {
     ++	for (iter = commits; iter; iter = iter->next) {
     ++		struct commit_list *p;
     ++
     ++		if (!iter->item->parents)
     ++			reaches_root = true;
     ++		for (p = iter->item->parents; p; p = p->next)
     ++			if (oidset_contains(&selected, &p->item->object.oid))
     ++				oidset_insert(&has_children,
     ++					      &p->item->object.oid);
     ++	}
     ++	if (reaches_root) {
     ++		ret = error(_("the revision range reaches a root commit; "
     ++			      "cannot squash"));
     ++		goto out;
     ++	}
     ++	for (iter = commits; iter; iter = iter->next) {
     ++		if (oidset_contains(&has_children, &iter->item->object.oid))
     ++			continue;
     ++		if (tip) {
     ++			ret = error(_("the revision range has more than one tip; "
     ++				      "cannot squash"));
     ++			goto out;
     ++		}
     ++		tip = iter->item;
     ++	}
     ++
     ++	/* The range must reach exactly one commit outside it. */
     ++	if (!boundaries) {
     ++		ret = error(_("the revision range has no base; cannot squash"));
     ++		goto out;
     ++	}
     ++	base = boundaries->item;
     ++	for (iter = boundaries; iter; iter = iter->next) {
     ++		if (iter->item != base) {
      +			ret = error(_("the revision range has more than one base; "
      +				      "cannot squash"));
      +			goto out;
      +		}
      +	}
      +
     ++	for (iter = commits; iter; iter = iter->next)
     ++		if (iter->item != tip)
     ++			oidset_insert(interior_out, &iter->item->object.oid);
     ++
      +	*base_out = base;
      +	*oldest_out = oldest;
      +	*tip_out = tip;
     @@ builtin/history.c: out:
      +
      +out:
      +	commit_list_free(boundaries);
     ++	commit_list_free(commits);
     ++	oidset_clear(&selected);
     ++	oidset_clear(&has_children);
      +	reset_revision_walk();
      +	release_revisions(&revs);
      +	strvec_clear(&args);
     @@ builtin/history.c: out:
      +static int reject_dangling_fixups(struct repository *repo,
      +				  struct commit *base,
      +				  struct commit *tip,
     -+				  struct commit *oldest,
     -+				  struct commit **msg_source,
      +				  struct commit **amend_source)
      +{
      +	struct todo_list todo = TODO_LIST_INIT;
     @@ builtin/history.c: out:
      +	bool past_oldest_group = false;
      +	int i, ret, nr_dangling = 0;
      +
     -+	*msg_source = oldest;
      +	*amend_source = NULL;
      +
      +	repo_init_revisions(repo, &revs, NULL);
     @@ builtin/history.c: out:
      +			      "range"), dangling_subject);
      +	} else {
      +		if (last_amend)
     -+			*msg_source = last_amend;
     ++			*amend_source = last_amend;
      +		ret = 0;
      +	}
      +
     @@ builtin/history.c: out:
      +	return 0;
      +}
      +
     ++static bool amend_replaces_target(struct todo_list *todo, int target)
     ++{
     ++	int i;
     ++
     ++	for (i = target + 1; i < todo->nr &&
     ++			     todo->items[i].command != TODO_PICK; i++) {
     ++		if (todo->items[i].command == TODO_SQUASH)
     ++			return false;
     ++		if (todo->items[i].flags & TODO_REPLACE_FIXUP_MSG)
     ++			return true;
     ++	}
     ++	return false;
     ++}
     ++
     ++static int build_squash_message(struct repository *repo,
     ++				struct commit *base,
     ++				struct commit *tip,
     ++				struct strbuf *out)
     ++{
     ++	struct rev_info revs;
     ++	struct commit *commit;
     ++	struct strvec args = STRVEC_INIT;
     ++	struct todo_list todo = TODO_LIST_INIT;
     ++	struct replay_opts opts = REPLAY_OPTS_INIT;
     ++	int i, nr_commits, ret;
     ++
     ++	repo_init_revisions(repo, &revs, NULL);
     ++	strvec_push(&args, "ignored");
     ++	strvec_push(&args, "--reverse");
     ++	strvec_push(&args, "--topo-order");
     ++	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
     ++		     oid_to_hex(&tip->object.oid));
     ++	setup_revisions_from_strvec(&args, &revs, NULL);
     ++
     ++	if (prepare_revision_walk(&revs) < 0) {
     ++		ret = error(_("error preparing revisions"));
     ++		goto out;
     ++	}
     ++
     ++	while ((commit = get_revision(&revs)))
     ++		strbuf_addf(&todo.buf, "pick %s\n",
     ++			    oid_to_hex(&commit->object.oid));
     ++
     ++	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
     ++	    todo_list_rearrange_squash(&todo) < 0) {
     ++		ret = error(_("could not prepare the squash message"));
     ++		goto out;
     ++	}
     ++
     ++	nr_commits = todo.nr;
     ++	for (i = 0; i < nr_commits; i++) {
     ++		struct todo_item *item = &todo.items[i];
     ++		const char *message, *body;
     ++		size_t commented_len;
     ++		bool skip, squashing;
     ++
     ++		squashing = item->command == TODO_SQUASH ||
     ++			    (item->flags & TODO_REPLACE_FIXUP_MSG);
     ++		if (item->command == TODO_PICK)
     ++			skip = amend_replaces_target(&todo, i);
     ++		else
     ++			skip = !squashing;
     ++
     ++		message = repo_logmsg_reencode(repo, item->commit, NULL, NULL);
     ++		find_commit_subject(message, &body);
     ++
     ++		if (skip)
     ++			commented_len = strlen(body);
     ++		else if (squashing)
     ++			commented_len = squash_subject_comment_len(body, 1);
     ++		else
     ++			commented_len = 0;
     ++
     ++		if (!i)
     ++			add_squash_combination_header(out, nr_commits);
     ++		strbuf_addch(out, '\n');
     ++		add_squash_message_header(out, i + 1, skip);
     ++		strbuf_addstr(out, "\n\n");
     ++		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
     ++		strbuf_addstr(out, body + commented_len);
     ++		strbuf_complete_line(out);
     ++
     ++		repo_unuse_commit_buffer(repo, item->commit, message);
     ++	}
     ++
     ++	ret = 0;
     ++
     ++out:
     ++	todo_list_release(&todo);
     ++	replay_opts_release(&opts);
     ++	reset_revision_walk();
     ++	release_revisions(&revs);
     ++	strvec_clear(&args);
     ++	return ret;
     ++}
     ++
      +static int cmd_history_squash(int argc,
      +			      const char **argv,
      +			      const char *prefix,
     @@ builtin/history.c: out:
      +	enum ref_action action = REF_ACTION_DEFAULT;
      +	enum commit_tree_flags flags = 0;
      +	int dry_run = 0;
     ++	int edit = 1;
      +	struct option options[] = {
      +		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
      +			       N_("control which refs should be updated"),
      +			       PARSE_OPT_NONEG, parse_ref_action),
      +		OPT_BOOL('n', "dry-run", &dry_run,
      +			 N_("perform a dry-run without updating any refs")),
     -+		OPT_BIT(0, "reedit-message", &flags,
     -+			N_("open an editor to modify the commit message"),
     -+			COMMIT_TREE_EDIT_MESSAGE),
     ++		OPT_BOOL('e', "edit", &edit,
     ++			 N_("edit the commit message")),
      +		OPT_END(),
      +	};
      +	struct strbuf reflog_msg = STRBUF_INIT;
      +	struct strbuf message = STRBUF_INIT;
      +	struct oidset interior = OIDSET_INIT;
     -+	struct commit *base, *oldest, *tip, *rewritten, *msg_source,
     -+		*amend_source;
     ++	struct commit *base = NULL, *oldest = NULL, *tip = NULL, *rewritten,
     ++		*amend_source = NULL;
      +	const struct object_id *base_tree_oid, *tip_tree_oid;
      +	const char *message_template = NULL;
      +	struct commit_list *parents = NULL;
     @@ builtin/history.c: out:
      +	if (ret < 0)
      +		goto out;
      +
     -+	ret = reject_dangling_fixups(repo, base, tip, oldest, &msg_source,
     -+				     &amend_source);
     ++	ret = reject_dangling_fixups(repo, base, tip, &amend_source);
      +	if (ret < 0)
      +		goto out;
     -+	if (amend_source) {
     ++	if (!edit && amend_source) {
      +		const char *amend_message, *body;
      +
      +		amend_message = repo_logmsg_reencode(repo, amend_source,
     @@ builtin/history.c: out:
      +	if (action == REF_ACTION_BRANCHES) {
      +		struct interior_ref_cb cb = { .interior = &interior };
      +
     -+		refs_for_each_ref(get_main_ref_store(repo),
     -+				  find_interior_ref, &cb);
     ++		refs_for_each_branch_ref(get_main_ref_store(repo),
     ++					 find_interior_ref, &cb);
      +		if (cb.name) {
      +			ret = error(_("'%s' points into the squashed range"),
      +				    cb.name);
     @@ builtin/history.c: out:
      +		}
      +	}
      +
     ++	if (edit) {
     ++		ret = build_squash_message(repo, base, tip, &message);
     ++		if (ret < 0)
     ++			goto out;
     ++		message_template = message.buf;
     ++		flags |= COMMIT_TREE_EDIT_MESSAGE;
     ++	}
     ++
      +	ret = setup_revwalk(repo, action, tip, &revs);
      +	if (ret < 0)
      +		goto out;
     @@ builtin/history.c: out:
      +	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
      +	commit_list_append(base, &parents);
      +
     -+	ret = commit_tree_ext(repo, "squash", msg_source, message_template,
     ++	ret = commit_tree_ext(repo, "squash", oldest, message_template,
      +			      parents,
      +			      base_tree_oid, tip_tree_oid, &rewritten, flags);
      +	if (ret < 0) {
     @@ t/t3455-history-squash.sh (new)
      +test_expect_success 'setup linear history touching two files' '
      +	test_commit base file a &&
      +	git tag start &&
     -+	test_commit --no-tag one other x &&
     ++	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
     ++		test_commit --no-tag one other x &&
      +	test_commit --no-tag two file c &&
      +	test_commit three file d
      +'
     @@ t/t3455-history-squash.sh (new)
      +	git branch -f keep HEAD~2 &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	git history squash start..HEAD ^keep &&
     ++	git history squash --no-edit start..HEAD ^keep &&
      +
      +	git reflog -1 --format=%gs >actual &&
      +	echo "squash: updating start..HEAD ^keep" >expect &&
     @@ t/t3455-history-squash.sh (new)
      +	git branch -D keep
      +'
      +
     ++test_expect_success 'refuses a range with more than one tip' '
     ++	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
     ++	test_commit --no-tag main-one file b &&
     ++	test_commit --no-tag main-two file c &&
     ++	git checkout -b other-tip start &&
     ++	test_commit --no-tag other-tip other d &&
     ++	git checkout "$main" &&
     ++	main_before=$(git rev-parse HEAD) &&
     ++	other_before=$(git rev-parse other-tip) &&
     ++
     ++	test_must_fail git history squash ^start HEAD other-tip 2>err &&
     ++	test_grep "more than one tip" err &&
     ++	test_cmp_rev "$main_before" HEAD &&
     ++	test_cmp_rev "$other_before" other-tip &&
     ++
     ++	git branch -D other-tip
     ++'
     ++
     ++test_expect_success 'refuses a range that reaches a root commit' '
     ++	git reset --hard three &&
     ++	root=$(printf "unrelated root\n" |
     ++		git commit-tree "$(git rev-parse HEAD^{tree})") &&
     ++	head_before=$(git rev-parse HEAD) &&
     ++
     ++	test_must_fail git history squash --ancestry-path="$root" \
     ++		^start HEAD "$root" 2>err &&
     ++	test_grep "reaches a root commit" err &&
     ++	test_cmp_rev "$head_before" HEAD
     ++'
     ++
      +test_expect_success 'squashes a branch the current branch is not on' '
      +	git reset --hard three &&
      +	main=$(git symbolic-ref --short HEAD) &&
     @@ t/t3455-history-squash.sh (new)
      +	test_commit --no-tag off-two off b &&
      +	git checkout "$main" &&
      +
     -+	git history squash start..off-history &&
     ++	git history squash --no-edit start..off-history &&
      +
      +	check_commit_count start..off-history 1 &&
      +	test_cmp_rev "$head_before" HEAD &&
     @@ t/t3455-history-squash.sh (new)
      +	git branch -D off-history
      +'
      +
     -+test_expect_success 'squashes a range into a single commit without changing the tree' '
     ++test_expect_success 'squashes a range preserving its tree and oldest authorship' '
      +	git reset --hard three &&
      +	head_before=$(git rev-parse HEAD) &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
     @@ t/t3455-history-squash.sh (new)
      +	check_log_subjects -1 <<-\EOF &&
      +	one
      +	EOF
     ++	git log -1 --format="%an <%ae>" >actual &&
     ++	echo "Squasher <squash@example.com>" >expect &&
     ++	test_cmp expect actual &&
      +	git reflog >reflog &&
      +	test_grep "squash: updating" reflog
      +'
     @@ t/t3455-history-squash.sh (new)
      +	git reset --hard three &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	git history squash --date-order start.. 2>err &&
     ++	git history squash --no-edit --date-order start.. 2>err &&
      +	test_grep "ignoring rev-list options" err &&
      +	test_cmp_rev start HEAD^ &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
      +
      +	git reset --hard three &&
     -+	git history squash -- --reverse start.. 2>err &&
     ++	git history squash --no-edit -- --reverse start.. 2>err &&
      +	test_grep "ignoring rev-list options" err &&
      +	test_cmp_rev start HEAD^ &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
     @@ t/t3455-history-squash.sh (new)
      +	git reset --hard three &&
      +	final_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	git history squash start..@~1 &&
     ++	git history squash --no-edit start..@~1 &&
      +
      +	check_log_subjects start..HEAD <<-\EOF &&
      +	three
     @@ t/t3455-history-squash.sh (new)
      +	root=$(git rev-list --max-parents=0 HEAD) &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	git history squash "$root.." &&
     ++	git history squash --no-edit "$root.." &&
      +
      +	check_commit_count "$root..HEAD" 1 &&
      +	test_cmp_rev "$root" HEAD^ &&
     @@ t/t3455-history-squash.sh (new)
      +	git commit --allow-empty -m "fixup! target" &&
      +	test_commit --no-tag later file c &&
      +
     -+	git history squash start.. &&
     ++	git history squash --no-edit start.. &&
      +
      +	check_commit_count start..HEAD 1 &&
      +	check_log_subjects -1 <<-\EOF
     @@ t/t3455-history-squash.sh (new)
      +	stage_file b && git commit -m "fixup! base" &&
      +	stage_file c && git commit -m "fixup! base" &&
      +
     -+	git history squash start.. &&
     ++	git history squash --no-edit start.. &&
      +
      +	check_commit_count start..HEAD 1 &&
      +	check_log_subjects -1 <<-\EOF
     @@ t/t3455-history-squash.sh (new)
      +	EOF
      +'
      +
     -+test_expect_success 'combining below-range fixups keeps the last amend! message' '
     ++test_expect_success 'combining below-range markers offers every message' '
      +	git reset --hard start &&
      +	stage_file b && git commit -m "fixup! base" &&
      +	stage_file c &&
     @@ t/t3455-history-squash.sh (new)
      +
      +	check_commit_count start..HEAD 1 &&
      +	check_log_messages -1 <<-\EOF
     ++	fixup! base
     ++
      +	amend! base
      +
      +	amended body
     @@ t/t3455-history-squash.sh (new)
      +	test_cmp_rev "$head_before" HEAD
      +'
      +
     -+test_expect_success 'the last amend! for the oldest commit replaces its message' '
     ++test_expect_success 'does not discard squash! or amend! message bodies' '
      +	git reset --hard start &&
      +	test_commit --no-tag marker-oldest file b &&
      +	git commit --allow-empty -m "squash! marker-oldest" &&
     @@ t/t3455-history-squash.sh (new)
      +
      +	check_commit_count start..HEAD 1 &&
      +	check_log_messages -1 <<-\EOF
     ++	marker-oldest
     ++
     ++	earlier message
     ++
      +	amended subject
      +
      +	amended body
      +
     ++	wrong message
     ++
      +	EOF
      +'
      +
     -+test_expect_success 'preserves authorship of the oldest commit' '
     ++test_expect_success '--no-edit keeps the selected message without an editor' '
      +	git reset --hard start &&
     -+	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
     -+		test_commit --no-tag oldest file b &&
     -+	test_commit newest file c &&
     ++	test_commit --no-tag no-edit-target file b &&
     ++	git commit --allow-empty -m "squash! no-edit-target" &&
     ++	commit_with_message "amend! no-edit-target\n\namended subject\n\namended body\n" &&
     ++
     ++	write_script editor <<-\EOF &&
     ++	exit 1
     ++	EOF
     ++	test_set_editor "$(pwd)/editor" &&
     ++	git history squash --no-edit start.. &&
     ++
     ++	check_log_messages -1 <<-\EOF &&
     ++	amended subject
     ++
     ++	amended body
     ++
     ++	EOF
     ++	test_set_editor :
     ++'
     ++
     ++test_expect_success 'edits every message and aborts on an empty result' '
     ++	git reset --hard start &&
     ++	stage_file b &&
     ++	git commit -m "re-one subject" -m "re-one body line" &&
     ++	test_commit --no-tag re-two file c &&
     ++	test_commit re-three file d &&
     ++	head_before=$(git rev-parse HEAD) &&
     ++
     ++	write_script empty-editor <<-\EOF &&
     ++	>"$1"
     ++	EOF
     ++	test_set_editor "$(pwd)/empty-editor" &&
     ++	test_must_fail git history squash start.. 2>err &&
     ++	test_grep "Aborting commit due to empty commit message" err &&
     ++	test_cmp_rev "$head_before" HEAD &&
      +
     ++	write_script editor <<-\EOF &&
     ++	cat "$1" >edited &&
     ++	echo combined >"$1"
     ++	EOF
     ++	test_set_editor "$(pwd)/editor" &&
      +	git history squash start.. &&
      +
     -+	git log -1 --format="%an <%ae>" >actual &&
     -+	echo "Squasher <squash@example.com>" >expect &&
     -+	test_cmp expect actual
     ++	cat >expect <<-EOF &&
     ++	# This is a combination of 3 commits.
     ++	# This is the 1st commit message:
     ++
     ++	re-one subject
     ++
     ++	re-one body line
     ++
     ++	# This is the commit message #2:
     ++
     ++	re-two
     ++
     ++	# This is the commit message #3:
     ++
     ++	re-three
     ++
     ++	# Please enter the commit message for the squash changes. Lines starting
     ++	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     ++	# Changes to be committed:
     ++	#	modified:   file
     ++	#
     ++	EOF
     ++	test_cmp expect edited &&
     ++	check_log_subjects -1 <<-\EOF
     ++	combined
     ++	EOF
      +'
      +
     -+test_expect_success '--update-refs=head only moves HEAD' '
     -+	git reset --hard three &&
     -+	git branch -f other HEAD &&
     -+	other_before=$(git rev-parse other) &&
     ++test_expect_success 'handles fixup!, squash! and amend! messages like rebase' '
     ++	git reset --hard start &&
     ++	test_commit --no-tag mark-base file b &&
     ++	stage_file c &&
     ++	commit_with_message "fixup! mark-base\n\nfixup body\n" &&
     ++	stage_file d &&
     ++	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
     ++	stage_file e &&
     ++	commit_with_message "amend! mark-base\n\namended message\n" &&
     ++
     ++	write_script editor <<-\EOF &&
     ++	cat "$1" >edited
     ++	EOF
     ++	test_set_editor "$(pwd)/editor" &&
     ++	git history squash start.. &&
      +
     -+	git history squash --update-refs=head start.. &&
     ++	cat >expect <<-EOF &&
     ++	# This is a combination of 4 commits.
     ++	# This is the 1st commit message:
      +
     -+	check_commit_count start..HEAD 1 &&
     -+	test_cmp_rev "$other_before" other
     ++	mark-base
     ++
     ++	# The commit message #2 will be skipped:
     ++
     ++	# fixup! mark-base
     ++	#
     ++	# fixup body
     ++
     ++	# This is the commit message #3:
     ++
     ++	# squash! mark-base
     ++
     ++	squash remark
     ++
     ++	# This is the commit message #4:
     ++
     ++	# amend! mark-base
     ++
     ++	amended message
     ++
     ++	# Please enter the commit message for the squash changes. Lines starting
     ++	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     ++	# Changes to be committed:
     ++	#	modified:   file
     ++	#
     ++	EOF
     ++	test_cmp expect edited &&
     ++	check_log_messages -1 <<-\EOF
     ++	mark-base
     ++
     ++	squash remark
     ++
     ++	amended message
     ++
     ++	EOF
     ++'
     ++
     ++test_expect_success 'groups fixups under their targets in the editor' '
     ++	git reset --hard start &&
     ++	test_commit --no-tag alpha file a1 &&
     ++	test_commit --no-tag beta file b1 &&
     ++	stage_file a2 &&
     ++	commit_with_message "fixup! alpha\n" &&
     ++	stage_file b2 &&
     ++	commit_with_message "fixup! beta\n" &&
     ++
     ++	write_script editor <<-\EOF &&
     ++	cat "$1" >edited
     ++	EOF
     ++	test_set_editor "$(pwd)/editor" &&
     ++	git history squash start.. &&
     ++
     ++	cat >expect <<-EOF &&
     ++	# This is a combination of 4 commits.
     ++	# This is the 1st commit message:
     ++
     ++	alpha
     ++
     ++	# The commit message #2 will be skipped:
     ++
     ++	# fixup! alpha
     ++
     ++	# This is the commit message #3:
     ++
     ++	beta
     ++
     ++	# The commit message #4 will be skipped:
     ++
     ++	# fixup! beta
     ++
     ++	# Please enter the commit message for the squash changes. Lines starting
     ++	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     ++	# Changes to be committed:
     ++	#	modified:   file
     ++	#
     ++	EOF
     ++	test_cmp expect edited
     ++'
     ++
     ++test_expect_success 'lets amend! replace its target message in the editor' '
     ++	git reset --hard start &&
     ++	test_commit --no-tag mark-base file b &&
     ++	stage_file c &&
     ++	commit_with_message "amend! mark-base\n\namended message\n" &&
     ++	stage_file d &&
     ++	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
     ++
     ++	write_script editor <<-\EOF &&
     ++	cat "$1" >edited
     ++	EOF
     ++	test_set_editor "$(pwd)/editor" &&
     ++	git history squash start.. &&
     ++
     ++	cat >expect <<-EOF &&
     ++	# This is a combination of 3 commits.
     ++	# The 1st commit message will be skipped:
     ++
     ++	# mark-base
     ++
     ++	# This is the commit message #2:
     ++
     ++	# amend! mark-base
     ++
     ++	amended message
     ++
     ++	# This is the commit message #3:
     ++
     ++	# squash! mark-base
     ++
     ++	squash remark
     ++
     ++	# Please enter the commit message for the squash changes. Lines starting
     ++	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     ++	# Changes to be committed:
     ++	#	modified:   file
     ++	#
     ++	EOF
     ++	test_cmp expect edited &&
     ++	check_log_messages -1 <<-\EOF
     ++	amended message
     ++
     ++	squash remark
     ++
     ++	EOF
      +'
      +
     -+test_expect_success 'refuses to fold a range a ref points into' '
     ++test_expect_success 'handles branches pointing at the squashed range' '
      +	git reset --hard three &&
     ++	git branch -f other HEAD &&
      +	git branch -f mid HEAD~1 &&
     ++	other_before=$(git rev-parse other) &&
     ++	mid_before=$(git rev-parse mid) &&
      +	head_before=$(git rev-parse HEAD) &&
      +
      +	test_must_fail git history squash start.. 2>err &&
     @@ t/t3455-history-squash.sh (new)
      +	test_grep "hint: .*--update-refs=head" err &&
      +	test_cmp_rev "$head_before" HEAD &&
      +
     -+	git branch -D mid
     -+'
     -+
     -+test_expect_success 'advice.historyUpdateRefs silences the hint' '
     -+	git reset --hard three &&
     -+	git branch -f mid HEAD~1 &&
     -+	head_before=$(git rev-parse HEAD) &&
     -+
      +	test_must_fail git -c advice.historyUpdateRefs=false \
      +		history squash start.. 2>err &&
      +	test_grep "points into the squashed range" err &&
      +	test_grep ! "hint:" err &&
      +	test_cmp_rev "$head_before" HEAD &&
      +
     -+	git branch -D mid
     -+'
     -+
     -+test_expect_success '--update-refs=head folds past a ref pointing into the range' '
     -+	git reset --hard three &&
     -+	git branch -f mid HEAD~1 &&
     -+	mid_before=$(git rev-parse mid) &&
     -+
     -+	git history squash --update-refs=head start.. &&
     ++	git history squash --no-edit --update-refs=head start.. &&
      +
      +	check_commit_count start..HEAD 1 &&
     ++	test_cmp_rev "$other_before" other &&
      +	test_cmp_rev "$mid_before" mid &&
      +
     -+	git branch -D mid
     ++	git branch -D other mid
      +'
      +
     -+test_expect_success 'refuses to fold a range a tag points into' '
     ++test_expect_success 'leaves tags and remote-tracking refs unchanged' '
      +	git reset --hard three &&
      +	git tag -f mark HEAD~1 &&
     -+	head_before=$(git rev-parse HEAD) &&
     ++	git update-ref refs/remotes/origin/mark HEAD~1 &&
     ++	mark_before=$(git rev-parse mark) &&
      +
     -+	test_must_fail git history squash start.. 2>err &&
     -+	test_grep "refs/tags/mark" err &&
     -+	test_grep "points into the squashed range" err &&
     -+	test_cmp_rev "$head_before" HEAD &&
     ++	git history squash --no-edit start.. &&
     ++
     ++	test_cmp_rev "$mark_before" mark &&
     ++	test_cmp_rev "$mark_before" refs/remotes/origin/mark &&
      +
     -+	git tag -d mark
     ++	git tag -d mark &&
     ++	git update-ref -d refs/remotes/origin/mark
      +'
      +
     -+test_expect_success 'squashes a range whose internal merge has a single base' '
     ++test_expect_success 'handles a branch pointing at an internal merge' '
      +	git reset --hard start &&
      +	main=$(git symbolic-ref --short HEAD) &&
      +	test_commit --no-tag before-side file b &&
     @@ t/t3455-history-squash.sh (new)
      +	test_commit --no-tag after-side file c &&
      +	git merge --no-ff -m merge inner-side &&
      +	git branch -D inner-side &&
     ++	git branch at-merge HEAD &&
      +	test_commit --no-tag after-merge file d &&
     ++	head_before=$(git rev-parse HEAD) &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	git history squash start.. &&
     ++	test_must_fail git history squash start.. 2>err &&
     ++	test_grep "at-merge" err &&
     ++	test_grep "points into the squashed range" err &&
     ++	test_cmp_rev "$head_before" HEAD &&
     ++	git branch -D at-merge &&
     ++
     ++	git history squash --no-edit start.. &&
      +
      +	check_commit_count start..HEAD 1 &&
      +	check_log_subjects -1 <<-\EOF &&
     @@ t/t3455-history-squash.sh (new)
      +	test_commit --no-tag base-fork-tail file c &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	git history squash start.. &&
     ++	git history squash --no-edit start.. &&
      +
      +	check_commit_count start..HEAD 1 &&
      +	test_cmp_rev start HEAD^ &&
     @@ t/t3455-history-squash.sh (new)
      +	git branch -D tipmerge-side &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	git history squash start.. &&
     ++	git history squash --no-edit start.. &&
      +
      +	check_commit_count start..HEAD 1 &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     @@ t/t3455-history-squash.sh (new)
      +	test_commit --no-tag basemerge-two file d &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	git history squash "$base.." &&
     ++	git history squash --no-edit "$base.." &&
      +
      +	check_commit_count "$base..HEAD" 1 &&
      +	test_cmp_rev "$base" HEAD^ &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
      +'
      +
     -+test_expect_success 'folds a range with two interior merges' '
     -+	git reset --hard start &&
     -+	main=$(git symbolic-ref --short HEAD) &&
     -+	test_commit --no-tag two-merge-a file a1 &&
     -+	git checkout -b two-merge-s1 &&
     -+	test_commit --no-tag two-merge-s1 s1 x &&
     -+	git checkout "$main" &&
     -+	git merge --no-ff -m "merge s1" two-merge-s1 &&
     -+	test_commit --no-tag two-merge-b file b1 &&
     -+	git checkout -b two-merge-s2 &&
     -+	test_commit --no-tag two-merge-s2 s2 y &&
     -+	git checkout "$main" &&
     -+	git merge --no-ff -m "merge s2" two-merge-s2 &&
     -+	git branch -D two-merge-s1 two-merge-s2 &&
     -+	tip_tree=$(git rev-parse HEAD^{tree}) &&
     -+
     -+	git history squash start.. &&
     -+
     -+	check_commit_count start..HEAD 1 &&
     -+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     -+	test_path_is_file s1 &&
     -+	test_path_is_file s2
     -+'
     -+
      +test_expect_success 'folds a range with a nested merge' '
      +	git reset --hard start &&
      +	main=$(git symbolic-ref --short HEAD) &&
     @@ t/t3455-history-squash.sh (new)
      +	git branch -D nested-outer nested-inner &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	git history squash start.. &&
     ++	git history squash --no-edit start.. &&
      +
      +	check_commit_count start..HEAD 1 &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     @@ t/t3455-history-squash.sh (new)
      +	git branch -D octo-1 octo-2 &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	git history squash start.. &&
     ++	git history squash --no-edit start.. &&
      +
      +	check_commit_count start..HEAD 1 &&
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     @@ t/t3455-history-squash.sh (new)
      +	git branch -D desc-above &&
      +	head_before=$(git rev-parse HEAD) &&
      +
     -+	test_must_fail git history squash start..desc-tip 2>err &&
     ++	test_must_fail git history squash --no-edit start..desc-tip 2>err &&
      +	test_grep "merge commits is not supported" err &&
      +	test_cmp_rev "$head_before" HEAD
      +'
      +
     -+test_expect_success 'refuses to fold a range a ref points into at a merge' '
     -+	git reset --hard start &&
     -+	main=$(git symbolic-ref --short HEAD) &&
     -+	test_commit --no-tag refmerge-base file b &&
     -+	git checkout -b refmerge-side &&
     -+	test_commit --no-tag refmerge-side side x &&
     -+	git checkout "$main" &&
     -+	test_commit --no-tag refmerge-main file c &&
     -+	git merge --no-ff -m "interior merge" refmerge-side &&
     -+	git branch -D refmerge-side &&
     -+	git branch at-merge HEAD &&
     -+	test_commit --no-tag refmerge-tail file d &&
     -+	head_before=$(git rev-parse HEAD) &&
     -+
     -+	test_must_fail git history squash start.. 2>err &&
     -+	test_grep "at-merge" err &&
     -+	test_grep "points into the squashed range" err &&
     -+	test_cmp_rev "$head_before" HEAD &&
     -+
     -+	git branch -D at-merge
     -+'
     -+
      +test_done
 5:  cdbc183428 < -:  ---------- history: re-edit a squash with every message

-- 
gitgitgadget

[PATCH v11 1/4] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index d28c1f08bb..673744a55a 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -164,6 +164,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -171,21 +190,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -475,18 +484,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -830,16 +831,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v11 2/4] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 673744a55a..b592b98393 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -108,6 +108,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -137,13 +138,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -196,7 +200,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -675,7 +679,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -886,7 +890,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -903,7 +907,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v11 3/4] sequencer: share the squash message marker helpers and flags

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

When "git rebase -i" squashes commits it builds an editor template with a
"This is a combination of N commits." banner, a "This is the 1st/Nth
commit message:" header above each kept message (or a "will be skipped"
header for a dropped one), and a commented-out subject for any fixup!,
squash! or amend! commit. The banner, the headers and the
subject-commenting all live in static helpers in sequencer.c wired to the
rebase state, so no other command can present a squash the same way.

Pull the three pieces out into add_squash_combination_header(),
add_squash_message_header() (which takes a flag for the "will be skipped"
variant) and squash_subject_comment_len(), and use them from
update_squash_messages() and append_squash_message(). Also move the
todo_item_flags enum to the header, so a caller reading the output of
todo_list_rearrange_squash() can tell an amend! (TODO_REPLACE_FIXUP_MSG)
from a plain fixup!. A later change reuses all of this to give "git
history squash" the same template.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 sequencer.c | 70 +++++++++++++++++++++++++++++------------------------
 sequencer.h | 30 +++++++++++++++++++++++
 2 files changed, 69 insertions(+), 31 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 82ab3c536f..642dfa9d91 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1880,18 +1880,38 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
-enum todo_item_flags {
-	TODO_EDIT_MERGE_MSG    = (1 << 0),
-	TODO_REPLACE_FIXUP_MSG = (1 << 1),
-	TODO_EDIT_FIXUP_MSG    = (1 << 2),
-};
-
 static const char first_commit_msg_str[] = N_("This is the 1st commit message:");
 static const char nth_commit_msg_fmt[] = N_("This is the commit message #%d:");
 static const char skip_first_commit_msg_str[] = N_("The 1st commit message will be skipped:");
 static const char skip_nth_commit_msg_fmt[] = N_("The commit message #%d will be skipped:");
 static const char combined_commit_msg_fmt[] = N_("This is a combination of %d commits.");
 
+void add_squash_combination_header(struct strbuf *buf, int n)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	strbuf_addf(buf, _(combined_commit_msg_fmt), n);
+}
+
+void add_squash_message_header(struct strbuf *buf, int n, int skip)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	if (n == 1)
+		strbuf_addstr(buf, skip ? _(skip_first_commit_msg_str) :
+				   _(first_commit_msg_str));
+	else
+		strbuf_addf(buf, skip ? _(skip_nth_commit_msg_fmt) :
+			    _(nth_commit_msg_fmt), n);
+}
+
+size_t squash_subject_comment_len(const char *body, int squashing)
+{
+	if (starts_with(body, "amend!") ||
+	    (squashing && (starts_with(body, "squash!") ||
+			   starts_with(body, "fixup!"))))
+		return commit_subject_length(body);
+	return 0;
+}
+
 static int is_fixup_flag(enum todo_command command, unsigned flag)
 {
 	return command == TODO_FIXUP && ((flag & TODO_REPLACE_FIXUP_MSG) ||
@@ -2005,20 +2025,13 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 {
 	struct replay_ctx *ctx = opts->ctx;
 	const char *fixup_msg;
-	size_t commented_len = 0, fixup_off;
-	/*
-	 * amend is non-interactive and not normally used with fixup!
-	 * or squash! commits, so only comment out those subjects when
-	 * squashing commit messages.
-	 */
-	if (starts_with(body, "amend!") ||
-	    ((command == TODO_SQUASH || seen_squash(ctx)) &&
-	     (starts_with(body, "squash!") || starts_with(body, "fixup!"))))
-		commented_len = commit_subject_length(body);
+	size_t commented_len, fixup_off;
+
+	commented_len = squash_subject_comment_len(body,
+				command == TODO_SQUASH || seen_squash(ctx));
 
-	strbuf_addf(buf, "\n%s ", comment_line_str);
-	strbuf_addf(buf, _(nth_commit_msg_fmt),
-		    ++ctx->current_fixup_count + 1);
+	strbuf_addch(buf, '\n');
+	add_squash_message_header(buf, ++ctx->current_fixup_count + 1, 0);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len, comment_line_str);
 	/* buf->buf may be reallocated so store an offset into the buffer */
@@ -2083,9 +2096,8 @@ static int update_squash_messages(struct repository *r,
 		eol = !starts_with(buf.buf, comment_line_str) ?
 			buf.buf : strchrnul(buf.buf, '\n');
 
-		strbuf_addf(&header, "%s ", comment_line_str);
-		strbuf_addf(&header, _(combined_commit_msg_fmt),
-			    ctx->current_fixup_count + 2);
+		add_squash_combination_header(&header,
+					      ctx->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);
 		if (is_fixup_flag(command, flag) && !seen_squash(ctx))
@@ -2109,12 +2121,9 @@ static int update_squash_messages(struct repository *r,
 			repo_unuse_commit_buffer(r, head_commit, head_message);
 			return error(_("cannot write '%s'"), rebase_path_fixup_msg());
 		}
-		strbuf_addf(&buf, "%s ", comment_line_str);
-		strbuf_addf(&buf, _(combined_commit_msg_fmt), 2);
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addstr(&buf, is_fixup_flag(command, flag) ?
-			      _(skip_first_commit_msg_str) :
-			      _(first_commit_msg_str));
+		add_squash_combination_header(&buf, 2);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, 1, is_fixup_flag(command, flag));
 		strbuf_addstr(&buf, "\n\n");
 		if (is_fixup_flag(command, flag))
 			strbuf_add_commented_lines(&buf, body, strlen(body),
@@ -2133,9 +2142,8 @@ static int update_squash_messages(struct repository *r,
 	if (command == TODO_SQUASH || is_fixup_flag(command, flag)) {
 		res = append_squash_message(&buf, body, command, opts, flag);
 	} else if (command == TODO_FIXUP) {
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),
-			    ++ctx->current_fixup_count + 1);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, ++ctx->current_fixup_count + 1, 1);
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body),
 					   comment_line_str);
diff --git a/sequencer.h b/sequencer.h
index 64a9c7fb1b..b01f897020 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,6 +119,13 @@ enum todo_command {
 	TODO_COMMENT
 };
 
+/* Bits for the "flags" member of struct todo_item */
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG    = (1 << 0),
+	TODO_REPLACE_FIXUP_MSG = (1 << 1),
+	TODO_EDIT_FIXUP_MSG    = (1 << 2),
+};
+
 struct todo_item {
 	enum todo_command command;
 	struct commit *commit;
@@ -208,6 +215,29 @@ int todo_list_rearrange_squash(struct todo_list *todo_list);
  */
 void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
 
+/*
+ * Append the "This is a combination of N commits." banner that "git rebase
+ * -i" writes at the top of a squashed commit's message, commented out with
+ * the comment character.
+ */
+void add_squash_combination_header(struct strbuf *buf, int n);
+
+/*
+ * Append the header (1-based N) that "git rebase -i" writes above each message
+ * when squashing, commented out with the comment character. With SKIP it reads
+ * "The ... commit message will be skipped" for a message that is dropped (a
+ * fixup), otherwise "This is the ... commit message".
+ */
+void add_squash_message_header(struct strbuf *buf, int n, int skip);
+
+/*
+ * Return the length of the leading subject of BODY when it should be commented
+ * out in a squash message, or 0 otherwise. An "amend!" subject always
+ * qualifies; "squash!" and "fixup!" subjects only when SQUASHING, since a
+ * plain fixup chain keeps them.
+ */
+size_t squash_subject_comment_len(const char *body, int squashing);
+
 void append_conflicts_hint(struct index_state *istate,
 		struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
 enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,
-- 
gitgitgadget

[PATCH v11 4/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git history squash <revision-range>" to do this directly. It folds
every commit in the range into one commit, preserving the authorship of
the oldest commit and taking the tree of the tip, then replays commits
above the range. The editor opens with every folded message in the same
template used by "git rebase -i --autosquash". With --no-edit, the
oldest message is kept, or the last amend! replacement that targets it.

A fixup!, squash! or amend! commit is refused unless its target is also
in the range, so the fold does not silently absorb a marker intended for
another commit. As an exception, a range made up entirely of markers for
one target is combined, allowing a batch of related fixups to be
consolidated.

The range is read like the arguments to "git rev-list", so several
revisions such as "HEAD~3..HEAD ^topic" may be given, and rev-list
options are accepted too. Walk-order options needed by the fold are
restored after setup_revisions(), with a warning when an option changed
them. The selected graph must have one actual boundary and one actual
tip and must not reach a root. A merge inside the range is folded when
all selected history reaches the same boundary; otherwise the range has
more than one base and is rejected.

By default the command refuses when a local branch points inside the
range, because that branch cannot be replayed as a descendant of the
result. Tags and remote-tracking refs are left unchanged. Use
--update-refs=head to leave interior branches unchanged as well.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  57 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 504 ++++++++++++++++++++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 758 +++++++++++++++++++++++++++++++
 7 files changed, 1324 insertions(+), 2 deletions(-)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 81f80a9274..e2a3487778 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -59,6 +59,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a ref points
+		into the range being folded, to tell the user about
+		`--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 28b477cd37..12cf06c2c5 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -12,6 +12,7 @@ git history drop <commit> [--dry-run] [--update-refs=(branches|head)] [--empty=(
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>
 
 DESCRIPTION
 -----------
@@ -43,8 +44,11 @@ at once.
 LIMITATIONS
 -----------
 
-This command does not (yet) work with histories that contain merges. You
-should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
+This command does not (yet) replay merge commits onto the rewritten
+history: if a commit that would be replayed is a merge, the operation is
+rejected, and you should use linkgit:git-rebase[1] with the
+`--rebase-merges` flag instead. The `squash` subcommand can still fold a
+merge that lies inside the range, as long as the range has a single base.
 
 Furthermore, the command does not support operations that can result in merge
 conflicts. This limitation is by design as history rewrites are not intended to
@@ -113,6 +117,49 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's authorship and
+	takes the tree of the range's newest commit, so the whole range
+	collapses into a single commit. Commits above the range are replayed
+	on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash HEAD~3..HEAD` folds the three most recent commits into
+one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
+while leaving the two newest commits in place. Several revisions may be
+given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
+already on `topic`. Rev-list options may also be given, but any that would
+change how the range is walked are overridden with a warning.
++
+An editor opens pre-filled with the messages of all the folded commits so
+you can combine them. With `--no-edit`, the oldest commit's message is
+preserved instead, except that an `amend!` commit targeting it replaces its
+message. A merge commit inside the range is folded like any other, but the
+range must have a single base and a single tip. A range that reaches more
+than one entry point (for example a side branch that forked before the range
+and was later merged into it), or that selects two unmerged tips, is rejected.
++
+A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
+targets is also in the range, so the fold does not silently absorb a
+marker meant for a commit outside it. As an exception, a range made up entirely
+of markers for one target is combined into a single commit. With `--no-edit`,
+the last `amend!` message is used if there is one.
++
+The template mirrors `git rebase -i --autosquash`: each `fixup!`, `squash!`,
+or `amend!` is grouped under the commit it targets rather than shown in
+commit order. A `fixup!` message is dropped (commented out in full), a
+`squash!` keeps its body with only the marker subject commented, and an
+`amend!` replaces its target's message, unless a `squash!` folded into that
+target first, in which case it keeps its body like a `squash!`.
++
+A local branch that points at a commit inside the range cannot be rewritten
+as a descendant of the result, so with the default `--update-refs=branches`
+the command refuses. Rerun with `--update-refs=head` to rewrite only the
+current branch and leave such branches pointing at the old commits. Tags and
+remote-tracking refs are always left unchanged.
+
 OPTIONS
 -------
 
@@ -122,6 +169,12 @@ OPTIONS
 	objects will be written into the repository, so applying these printed
 	ref updates is generally safe.
 
+`--edit`::
+`--no-edit`::
+	For `squash`, open an editor to combine the messages of the folded commits.
+	This is the default; use `--no-edit` to keep the selected message
+	without opening an editor.
+
 `--reedit-message`::
 	Open an editor to modify the target commit's message.
 
diff --git a/advice.c b/advice.c
index 63bf8b0c5f..401d047391 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 66f6cd6a77..3f0b4f0485 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index b592b98393..43714fcb56 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -34,6 +35,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -1004,6 +1007,505 @@ out:
 	return ret;
 }
 
+/*
+ * Resolve a "<base>..<tip>" revision range into the base commit just outside
+ * the range (which becomes the parent of the squashed commit), the oldest
+ * commit contained in the range (whose message the squash reuses), and the
+ * range tip (whose tree becomes the result). A merge inside the range is fine,
+ * but the range must have a single base and must not reach a root commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				const char **argv,
+				struct commit **base_out,
+				struct commit **oldest_out,
+				struct commit **tip_out,
+				struct oidset *interior_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
+	struct commit_list *boundaries = NULL, *commits = NULL, *iter,
+		**commits_tail = &commits;
+	struct oidset selected = OIDSET_INIT, has_children = OIDSET_INIT;
+	struct strvec args = STRVEC_INIT;
+	bool reaches_root = false;
+	size_t i;
+	int ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	revs.reverse = 1;
+	revs.topo_order = 1;
+	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+	revs.simplify_history = 0;
+	revs.boundary = 1;
+
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--ancestry-path");
+	strvec_pushv(&args, argv);
+	setup_revisions_from_strvec(&args, &revs, NULL);
+	if (args.nr != 1) {
+		ret = error(_("unrecognized argument: %s"), args.v[1]);
+		goto out;
+	}
+
+	if (revs.reverse != 1 || revs.topo_order != 1 ||
+	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
+	    revs.simplify_history != 0 || revs.boundary != 1) {
+		warning(_("ignoring rev-list options that would change how the "
+			  "range is walked"));
+		revs.reverse = 1;
+		revs.topo_order = 1;
+		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+		revs.simplify_history = 0;
+		revs.boundary = 1;
+	}
+
+	/* A squash range must name a bottom revision to reparent onto. */
+	for (i = 0; i < revs.cmdline.nr; i++)
+		if (revs.cmdline.rev[i].flags & BOTTOM)
+			break;
+	if (i == revs.cmdline.nr) {
+		ret = error(_("not a '<base>..<tip>' revision range"));
+		goto out;
+	}
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	/* Set boundary commits aside for the base check below. */
+	while ((commit = get_revision(&revs))) {
+		if (commit->object.flags & BOUNDARY) {
+			commit_list_insert(commit, &boundaries);
+			continue;
+		}
+		if (!oldest)
+			oldest = commit;
+		oidset_insert(&selected, &commit->object.oid);
+		commits_tail = commit_list_append(commit, commits_tail);
+	}
+
+	if (!oldest) {
+		ret = error(_("the revision range is empty"));
+		goto out;
+	} else if (!commits->next) {
+		ret = error(_("the revision range holds a single commit; "
+			      "nothing to squash"));
+		goto out;
+	}
+
+	/*
+	 * Find the selected commits that have selected children. The only
+	 * remaining commit must be the tip whose tree becomes the result.
+	 */
+	for (iter = commits; iter; iter = iter->next) {
+		struct commit_list *p;
+
+		if (!iter->item->parents)
+			reaches_root = true;
+		for (p = iter->item->parents; p; p = p->next)
+			if (oidset_contains(&selected, &p->item->object.oid))
+				oidset_insert(&has_children,
+					      &p->item->object.oid);
+	}
+	if (reaches_root) {
+		ret = error(_("the revision range reaches a root commit; "
+			      "cannot squash"));
+		goto out;
+	}
+	for (iter = commits; iter; iter = iter->next) {
+		if (oidset_contains(&has_children, &iter->item->object.oid))
+			continue;
+		if (tip) {
+			ret = error(_("the revision range has more than one tip; "
+				      "cannot squash"));
+			goto out;
+		}
+		tip = iter->item;
+	}
+
+	/* The range must reach exactly one commit outside it. */
+	if (!boundaries) {
+		ret = error(_("the revision range has no base; cannot squash"));
+		goto out;
+	}
+	base = boundaries->item;
+	for (iter = boundaries; iter; iter = iter->next) {
+		if (iter->item != base) {
+			ret = error(_("the revision range has more than one base; "
+				      "cannot squash"));
+			goto out;
+		}
+	}
+
+	for (iter = commits; iter; iter = iter->next)
+		if (iter->item != tip)
+			oidset_insert(interior_out, &iter->item->object.oid);
+
+	*base_out = base;
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	commit_list_free(boundaries);
+	commit_list_free(commits);
+	oidset_clear(&selected);
+	oidset_clear(&has_children);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+static const char *autosquash_target(const char *subject)
+{
+	const char *rest;
+
+	while (skip_prefix(subject, "fixup! ", &rest) ||
+	       skip_prefix(subject, "squash! ", &rest) ||
+	       skip_prefix(subject, "amend! ", &rest))
+		subject = rest;
+	return subject;
+}
+
+static int reject_dangling_fixups(struct repository *repo,
+				  struct commit *base,
+				  struct commit *tip,
+				  struct commit **amend_source)
+{
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	struct rev_info revs;
+	struct commit *commit, *last_amend = NULL;
+	struct strvec args = STRVEC_INIT;
+	char *dangling_subject = NULL, *dangling_target = NULL;
+	bool mixed_target = false, all_fixups_one_target;
+	bool past_oldest_group = false;
+	int i, ret, nr_dangling = 0;
+
+	*amend_source = NULL;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+	while ((commit = get_revision(&revs)))
+		strbuf_addf(&todo.buf, "pick %s\n",
+			    oid_to_hex(&commit->object.oid));
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not check the range for fixups"));
+		goto out;
+	}
+
+	for (i = 0; i < todo.nr; i++) {
+		const char *message, *subject_start, *target;
+		char *subject;
+		size_t sublen;
+
+		message = repo_logmsg_reencode(repo, todo.items[i].commit,
+					       NULL, NULL);
+		sublen = find_commit_subject(message, &subject_start);
+
+		if (todo.items[i].command != TODO_PICK) {
+			if (!past_oldest_group &&
+			    starts_with(subject_start, "amend! "))
+				*amend_source = todo.items[i].commit;
+			repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
+			continue;
+		}
+		if (i)
+			past_oldest_group = true;
+
+		subject = xmemdupz(subject_start, sublen);
+		target = autosquash_target(subject);
+		if (target != subject) {
+			nr_dangling++;
+			if (!dangling_target) {
+				dangling_target = xstrdup(target);
+				dangling_subject = xstrdup(subject);
+			} else if (strcmp(dangling_target, target)) {
+				mixed_target = true;
+			}
+			if (starts_with(subject, "amend! "))
+				last_amend = todo.items[i].commit;
+		}
+		free(subject);
+		repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
+	}
+
+	all_fixups_one_target = nr_dangling == todo.nr && !mixed_target;
+	if (nr_dangling && !all_fixups_one_target) {
+		ret = error(_("cannot squash '%s': its target is not in the "
+			      "range"), dangling_subject);
+	} else {
+		if (last_amend)
+			*amend_source = last_amend;
+		ret = 0;
+	}
+
+out:
+	free(dangling_subject);
+	free(dangling_target);
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+struct interior_ref_cb {
+	const struct oidset *interior;
+	const char *name;
+};
+
+static int find_interior_ref(const struct reference *ref, void *cb_data)
+{
+	struct interior_ref_cb *data = cb_data;
+
+	if (oidset_contains(data->interior, ref->oid)) {
+		data->name = xstrdup(ref->name);
+		return 1;
+	}
+
+	return 0;
+}
+
+static bool amend_replaces_target(struct todo_list *todo, int target)
+{
+	int i;
+
+	for (i = target + 1; i < todo->nr &&
+			     todo->items[i].command != TODO_PICK; i++) {
+		if (todo->items[i].command == TODO_SQUASH)
+			return false;
+		if (todo->items[i].flags & TODO_REPLACE_FIXUP_MSG)
+			return true;
+	}
+	return false;
+}
+
+static int build_squash_message(struct repository *repo,
+				struct commit *base,
+				struct commit *tip,
+				struct strbuf *out)
+{
+	struct rev_info revs;
+	struct commit *commit;
+	struct strvec args = STRVEC_INIT;
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	int i, nr_commits, ret;
+
+	repo_init_revisions(repo, &revs, NULL);
+	strvec_push(&args, "ignored");
+	strvec_push(&args, "--reverse");
+	strvec_push(&args, "--topo-order");
+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
+		     oid_to_hex(&tip->object.oid));
+	setup_revisions_from_strvec(&args, &revs, NULL);
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+
+	while ((commit = get_revision(&revs)))
+		strbuf_addf(&todo.buf, "pick %s\n",
+			    oid_to_hex(&commit->object.oid));
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not prepare the squash message"));
+		goto out;
+	}
+
+	nr_commits = todo.nr;
+	for (i = 0; i < nr_commits; i++) {
+		struct todo_item *item = &todo.items[i];
+		const char *message, *body;
+		size_t commented_len;
+		bool skip, squashing;
+
+		squashing = item->command == TODO_SQUASH ||
+			    (item->flags & TODO_REPLACE_FIXUP_MSG);
+		if (item->command == TODO_PICK)
+			skip = amend_replaces_target(&todo, i);
+		else
+			skip = !squashing;
+
+		message = repo_logmsg_reencode(repo, item->commit, NULL, NULL);
+		find_commit_subject(message, &body);
+
+		if (skip)
+			commented_len = strlen(body);
+		else if (squashing)
+			commented_len = squash_subject_comment_len(body, 1);
+		else
+			commented_len = 0;
+
+		if (!i)
+			add_squash_combination_header(out, nr_commits);
+		strbuf_addch(out, '\n');
+		add_squash_message_header(out, i + 1, skip);
+		strbuf_addstr(out, "\n\n");
+		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
+		strbuf_addstr(out, body + commented_len);
+		strbuf_complete_line(out);
+
+		repo_unuse_commit_buffer(repo, item->commit, message);
+	}
+
+	ret = 0;
+
+out:
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	reset_revision_walk();
+	release_revisions(&revs);
+	strvec_clear(&args);
+	return ret;
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	enum commit_tree_flags flags = 0;
+	int dry_run = 0;
+	int edit = 1;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BOOL('e', "edit", &edit,
+			 N_("edit the commit message")),
+		OPT_END(),
+	};
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct strbuf message = STRBUF_INIT;
+	struct oidset interior = OIDSET_INIT;
+	struct commit *base = NULL, *oldest = NULL, *tip = NULL, *rewritten,
+		*amend_source = NULL;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	const char *message_template = NULL;
+	struct commit_list *parents = NULL;
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage,
+			     PARSE_OPT_KEEP_UNKNOWN_OPT);
+	if (!argc) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
+
+	ret = resolve_squash_range(repo, argv, &base, &oldest, &tip,
+				   &interior);
+	if (ret < 0)
+		goto out;
+
+	ret = reject_dangling_fixups(repo, base, tip, &amend_source);
+	if (ret < 0)
+		goto out;
+	if (!edit && amend_source) {
+		const char *amend_message, *body;
+
+		amend_message = repo_logmsg_reencode(repo, amend_source,
+						     NULL, NULL);
+		find_commit_subject(amend_message, &body);
+		body = skip_blank_lines(body + commit_subject_length(body));
+		strbuf_addstr(&message, body);
+		message_template = message.buf;
+		repo_unuse_commit_buffer(repo, amend_source, amend_message);
+	}
+
+	if (action == REF_ACTION_BRANCHES) {
+		struct interior_ref_cb cb = { .interior = &interior };
+
+		refs_for_each_branch_ref(get_main_ref_store(repo),
+					 find_interior_ref, &cb);
+		if (cb.name) {
+			ret = error(_("'%s' points into the squashed range"),
+				    cb.name);
+			advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+					  _("Use --update-refs=head to rewrite only "
+					    "the current branch and leave such refs "
+					    "untouched."));
+			free((char *)cb.name);
+			goto out;
+		}
+	}
+
+	if (edit) {
+		ret = build_squash_message(repo, base, tip, &message);
+		if (ret < 0)
+			goto out;
+		message_template = message.buf;
+		flags |= COMMIT_TREE_EDIT_MESSAGE;
+	}
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+	commit_list_append(base, &parents);
+
+	ret = commit_tree_ext(repo, "squash", oldest, message_template,
+			      parents,
+			      base_tree_oid, tip_tree_oid, &rewritten, flags);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	strbuf_addstr(&reflog_msg, "squash: updating ");
+	strbuf_join_argv(&reflog_msg, argc, argv, ' ');
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	strbuf_release(&message);
+	oidset_clear(&interior);
+	commit_list_free(parents);
+	release_revisions(&revs);
+	return ret;
+}
+
 static int update_worktree(struct repository *repo,
 			   const struct commit *old_head,
 			   const struct commit *new_head,
@@ -1192,6 +1694,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -1200,6 +1703,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
diff --git a/t/meson.build b/t/meson.build
index d8161c368b..797c5a75d1 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -405,6 +405,7 @@ integration_tests = [
   't3452-history-split.sh',
   't3453-history-fixup.sh',
   't3454-history-drop.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..0461046d85
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,758 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+stage_file () {
+	printf "%s\n" "$1" >file &&
+	git add file
+}
+
+commit_with_message () {
+	printf "%b" "$1" >msg &&
+	git commit --allow-empty -qF msg
+}
+
+check_commit_count () {
+	git rev-list --count "$1" >actual &&
+	echo "$2" >expect &&
+	test_cmp expect actual
+}
+
+check_log_subjects () {
+	git log --format="%s" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+check_log_messages () {
+	git log --format="%B" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+test_expect_success 'setup linear history touching two files' '
+	test_commit base file a &&
+	git tag start &&
+	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
+		test_commit --no-tag one other x &&
+	test_commit --no-tag two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "expects a revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the revision range is empty" err
+'
+
+test_expect_success 'errors on a single revision that is not a range' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "not a .*range" err &&
+	test_must_fail git history squash HEAD~1 2>err &&
+	test_grep "not a .*range" err
+'
+
+test_expect_success 'errors on a range holding a single commit' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "HEAD^!" 2>err &&
+	test_grep "single commit; nothing to squash" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'accepts multiple revision arguments with an exclusion' '
+	git reset --hard three &&
+	git branch -f keep HEAD~2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start..HEAD ^keep &&
+
+	git reflog -1 --format=%gs >actual &&
+	echo "squash: updating start..HEAD ^keep" >expect &&
+	test_cmp expect actual &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	two
+	one
+	EOF
+	test_cmp_rev keep HEAD~1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git branch -D keep
+'
+
+test_expect_success 'refuses a range with more than one tip' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag main-one file b &&
+	test_commit --no-tag main-two file c &&
+	git checkout -b other-tip start &&
+	test_commit --no-tag other-tip other d &&
+	git checkout "$main" &&
+	main_before=$(git rev-parse HEAD) &&
+	other_before=$(git rev-parse other-tip) &&
+
+	test_must_fail git history squash ^start HEAD other-tip 2>err &&
+	test_grep "more than one tip" err &&
+	test_cmp_rev "$main_before" HEAD &&
+	test_cmp_rev "$other_before" other-tip &&
+
+	git branch -D other-tip
+'
+
+test_expect_success 'refuses a range that reaches a root commit' '
+	git reset --hard three &&
+	root=$(printf "unrelated root\n" |
+		git commit-tree "$(git rev-parse HEAD^{tree})") &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash --ancestry-path="$root" \
+		^start HEAD "$root" 2>err &&
+	test_grep "reaches a root commit" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'squashes a branch the current branch is not on' '
+	git reset --hard three &&
+	main=$(git symbolic-ref --short HEAD) &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b off-history start &&
+	test_commit --no-tag off-one off a &&
+	test_commit --no-tag off-two off b &&
+	git checkout "$main" &&
+
+	git history squash --no-edit start..off-history &&
+
+	check_commit_count start..off-history 1 &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D off-history
+'
+
+test_expect_success 'squashes a range preserving its tree and oldest authorship' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash start.. &&
+
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	check_log_subjects -1 <<-\EOF &&
+	one
+	EOF
+	git log -1 --format="%an <%ae>" >actual &&
+	echo "Squasher <squash@example.com>" >expect &&
+	test_cmp expect actual &&
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'sanitizes rev-list walk options, before and after --' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit --date-order start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git reset --hard three &&
+	git history squash --no-edit -- --reverse start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start..@~1 &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	three
+	one
+	EOF
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit "$root.." &&
+
+	check_commit_count "$root..HEAD" 1 &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+
+test_expect_success 'folds fixups whose target is in the range' '
+	git reset --hard start &&
+	test_commit --no-tag target file b &&
+	git commit --allow-empty -m "fixup! target" &&
+	git commit --allow-empty -m "fixup! target" &&
+	test_commit --no-tag later file c &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF
+	target
+	EOF
+'
+
+test_expect_success 'refuses a below-range fixup! after an in-range commit' '
+	git reset --hard start &&
+	test_commit --no-tag inside file b &&
+	test_commit --no-tag "fixup! outside" file c &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "target is not in the range" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'combines a run of fixups for one commit below the range' '
+	git reset --hard start &&
+	stage_file b && git commit -m "fixup! base" &&
+	stage_file c && git commit -m "fixup! base" &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF
+	fixup! base
+	EOF
+'
+
+test_expect_success 'combining below-range markers offers every message' '
+	git reset --hard start &&
+	stage_file b && git commit -m "fixup! base" &&
+	stage_file c &&
+	commit_with_message "amend! base\n\namended body\n" &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_messages -1 <<-\EOF
+	fixup! base
+
+	amend! base
+
+	amended body
+
+	EOF
+'
+
+test_expect_success 'refuses fixups for two different commits below the range' '
+	git reset --hard start &&
+	stage_file b && git commit -m "fixup! aaa" &&
+	stage_file c && git commit -m "fixup! bbb" &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "target is not in the range" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'does not discard squash! or amend! message bodies' '
+	git reset --hard start &&
+	test_commit --no-tag marker-oldest file b &&
+	git commit --allow-empty -m "squash! marker-oldest" &&
+	commit_with_message "amend! marker-oldest\n\nearlier message\n" &&
+	commit_with_message \
+		"amend! marker-oldest\n\namended subject\n\namended body\n" &&
+	test_commit --no-tag marker-later file c &&
+	commit_with_message "amend! marker-later\n\nwrong message\n" &&
+
+	git history squash start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_messages -1 <<-\EOF
+	marker-oldest
+
+	earlier message
+
+	amended subject
+
+	amended body
+
+	wrong message
+
+	EOF
+'
+
+test_expect_success '--no-edit keeps the selected message without an editor' '
+	git reset --hard start &&
+	test_commit --no-tag no-edit-target file b &&
+	git commit --allow-empty -m "squash! no-edit-target" &&
+	commit_with_message "amend! no-edit-target\n\namended subject\n\namended body\n" &&
+
+	write_script editor <<-\EOF &&
+	exit 1
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash --no-edit start.. &&
+
+	check_log_messages -1 <<-\EOF &&
+	amended subject
+
+	amended body
+
+	EOF
+	test_set_editor :
+'
+
+test_expect_success 'edits every message and aborts on an empty result' '
+	git reset --hard start &&
+	stage_file b &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script empty-editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/empty-editor" &&
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "Aborting commit due to empty commit message" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# This is the 1st commit message:
+
+	re-one subject
+
+	re-one body line
+
+	# This is the commit message #2:
+
+	re-two
+
+	# This is the commit message #3:
+
+	re-three
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_subjects -1 <<-\EOF
+	combined
+	EOF
+'
+
+test_expect_success 'handles fixup!, squash! and amend! messages like rebase' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "fixup! mark-base\n\nfixup body\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+	stage_file e &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	mark-base
+
+	# The commit message #2 will be skipped:
+
+	# fixup! mark-base
+	#
+	# fixup body
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# This is the commit message #4:
+
+	# amend! mark-base
+
+	amended message
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	mark-base
+
+	squash remark
+
+	amended message
+
+	EOF
+'
+
+test_expect_success 'groups fixups under their targets in the editor' '
+	git reset --hard start &&
+	test_commit --no-tag alpha file a1 &&
+	test_commit --no-tag beta file b1 &&
+	stage_file a2 &&
+	commit_with_message "fixup! alpha\n" &&
+	stage_file b2 &&
+	commit_with_message "fixup! beta\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	alpha
+
+	# The commit message #2 will be skipped:
+
+	# fixup! alpha
+
+	# This is the commit message #3:
+
+	beta
+
+	# The commit message #4 will be skipped:
+
+	# fixup! beta
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited
+'
+
+test_expect_success 'lets amend! replace its target message in the editor' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# The 1st commit message will be skipped:
+
+	# mark-base
+
+	# This is the commit message #2:
+
+	# amend! mark-base
+
+	amended message
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	amended message
+
+	squash remark
+
+	EOF
+'
+
+test_expect_success 'handles branches pointing at the squashed range' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	git branch -f mid HEAD~1 &&
+	other_before=$(git rev-parse other) &&
+	mid_before=$(git rev-parse mid) &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "error: .* points into the squashed range" err &&
+	test_grep "hint: .*--update-refs=head" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "points into the squashed range" err &&
+	test_grep ! "hint:" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash --no-edit --update-refs=head start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev "$other_before" other &&
+	test_cmp_rev "$mid_before" mid &&
+
+	git branch -D other mid
+'
+
+test_expect_success 'leaves tags and remote-tracking refs unchanged' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	git update-ref refs/remotes/origin/mark HEAD~1 &&
+	mark_before=$(git rev-parse mark) &&
+
+	git history squash --no-edit start.. &&
+
+	test_cmp_rev "$mark_before" mark &&
+	test_cmp_rev "$mark_before" refs/remotes/origin/mark &&
+
+	git tag -d mark &&
+	git update-ref -d refs/remotes/origin/mark
+'
+
+test_expect_success 'handles a branch pointing at an internal merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout "$main" &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	git branch at-merge HEAD &&
+	test_commit --no-tag after-merge file d &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "at-merge" err &&
+	test_grep "points into the squashed range" err &&
+	test_cmp_rev "$head_before" HEAD &&
+	git branch -D at-merge &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF &&
+	before-side
+	EOF
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a merge of a branch that forked at the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b base-fork-side &&
+	test_commit --no-tag base-fork-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag base-fork-main file b &&
+	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
+	git branch -D base-fork-side &&
+	test_commit --no-tag base-fork-tail file c &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'refuses a merge whose other parent is outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit "$base.." &&
+
+	check_commit_count "$base..HEAD" 1 &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'folds a range with a nested merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b nested-outer &&
+	test_commit --no-tag nested-outer outer x &&
+	git checkout -b nested-inner &&
+	test_commit --no-tag nested-inner inner y &&
+	git checkout nested-outer &&
+	git merge --no-ff -m "merge inner" nested-inner &&
+	git checkout "$main" &&
+	test_commit --no-tag nested-main file b1 &&
+	git merge --no-ff -m "merge outer" nested-outer &&
+	git branch -D nested-outer nested-inner &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file outer &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range with an octopus merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag octo-base file a1 &&
+	git checkout -b octo-1 &&
+	test_commit --no-tag octo-1 o1 x &&
+	git checkout "$main" &&
+	git checkout -b octo-2 &&
+	test_commit --no-tag octo-2 o2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-1 octo-2 &&
+	git branch -D octo-1 octo-2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file o1 &&
+	test_path_is_file o2
+'
+
+test_expect_success 'refuses an octopus merge with an arm forked before the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b octo-pre &&
+	test_commit octo-pre-side pside x &&
+	git checkout "$main" &&
+	test_commit octo-pre-main file b1 &&
+	octo_base=$(git rev-parse HEAD) &&
+	git checkout -b octo-within &&
+	test_commit --no-tag octo-within wside y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-pre octo-within &&
+	merged=$(git rev-parse HEAD) &&
+	git branch -D octo-pre octo-within &&
+
+	test_must_fail git history squash "$octo_base.." 2>err &&
+	test_grep "more than one base" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'refuses when a descendant above the range is a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag desc-one file b &&
+	test_commit --no-tag desc-two file c &&
+	git tag desc-tip &&
+	git checkout -b desc-above &&
+	test_commit --no-tag desc-above above x &&
+	git checkout "$main" &&
+	test_commit --no-tag desc-main file d &&
+	git merge --no-ff -m "merge desc-above" desc-above &&
+	git branch -D desc-above &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash --no-edit start..desc-tip 2>err &&
+	test_grep "merge commits is not supported" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_done
-- 
gitgitgadget

[PATCH v12 0/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v12:

 * Incorporated fixups from Phillip:
   * Reworks range validation into a single walk that rejects roots and
     multiple tips while preserving every parent when squashing into a
     merge.
   * Resolves fixup!, squash! and amend! targets directly, preserving
     message intent and safely consolidating related markers.
   * Builds the editor template from the exact selected revisions, including
     exclusions, while retaining --no-edit behavior.
   * Protects descendant local branches while leaving tags and
     remote-tracking refs unchanged.

Changes in v11:

 * Make message editing the default with the autosquash-style template, add
   --no-edit instead of squash-specific --reedit-message.
 * Validate one actual boundary and tip, rejecting root-reaching and
   multi-tip ranges.
 * Protect only interior local branches, leaving tags and remote-tracking
   refs unchanged.
 * Move sequencer preparation before squash and fold the later
   message-editing patch into the feature commit.

Changes in v10:

 * Record the full revision expression in squash reflog.
 * Preserve the boundary-walk invariant when sanitizing rev-list options.
 * Clarify amend! and --reedit-message documentation.

Changes in v9:

 * Use the last amend! targeting the oldest folded commit as the default
   squashed message. Ignore amend! markers targeting later commits while
   selecting that replacement message.
 * Improve tests.

Changes in v8:

 * --reedit-message now builds the same editor template as git rebase -i
   --autosquash: fixup!, squash! and amend! commits are grouped under the
   commit they target instead of shown in commit order, and an amend!
   replaces its target's message.
 * A fixup!, squash! or amend! is refused only when its target is outside
   the range, so several fixups for an in-range commit fold together. A
   range that is entirely markers for one below-range target is combined
   into a single commit, keeping the last amend! message.
 * Merges inside the range are folded when the range has a single base, with
   no dedicated opt-in flag, --ancestry-path ensures only commits descended
   from the base are folded, and a range reaching more than one base is
   rejected.
 * Rev-list options are accepted and sanitized the way git replay does,
   forcing the walk order back with a warning, which also fixes git history
   squash -- --reverse slipping past the previous option check.
 * Kept this as an explicit squash subcommand rather than making
   --reedit-message the default or renaming the command.

Changes in v7:

 * --reedit-message now builds the same editor template git rebase -i shows
   for a squash (a combination of N commits banner with each folded message
   under its own header) and follows autosquash for markers: a fixup!
   message falls out (commented under a will be skipped header), while a
   squash! or amend! keeps its body with only the marker subject commented
   so its remark can be reworded in. Only the message text is affected,
   every commit's changes are always folded in.
 * Reuse git rebase -i's squash-message code: a preparatory sequencer:
   commit extracts the banner, header and marker-comment helpers so both
   rebase and git history squash build the identical template from one
   source.
 * Refuse a range whose oldest commit is a fixup!, squash! or amend!, since
   the marker's target cannot be inside the range.
 * Reorder the squash usage so dashed options come before <revision-range>,
   and spell out HEAD instead of @ in the documentation and examples.
 * Expand the squash commit message and documentation with this overview,
   and scope the merge limitation so it no longer contradicts squash folding
   a single-base interior merge.

Changes in v6:

 * git history squash now accepts multiple revision arguments, read like the
   arguments to git-rev-list, so a compound range such as @~3.. ^topic
   works.
 * The base to reparent onto is now the oldest in-range commit's parent; a
   boundary other than that base means the range has more than one base and
   is rejected. This also fixes the earlier overly-restrictive handling of
   merges and side branches.
 * A single-commit range (e.g. @^!) is rejected with "nothing to squash"
   (this also covers the @^!-style example that previously succeeded
   silently).
 * Commit messages reworded: the squash commit now gives an overview of
   fixup!/squash!/amend! handling, rewording, merge-parent and ref behavior.

Changes in v5:

 * The range walk now uses --ancestry-path, so only commits descended from
   the base are folded; a single revision such as HEAD or HEAD~1 is now
   rejected as "not a <base>..<tip> range" rather than treated as a squash
   down to the root.
 * This adopts the --ancestry-path suggestion; the multi-base rejection is
   unchanged, so a side branch that forked before the base and merged in is
   still refused.
 * Added tests covering more merge topologies: two interior merges, a nested
   merge, an octopus merge, an octopus arm forked before the base, a merge
   among the descendants replayed above the range, and a ref pointing at an
   interior merge commit.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (4):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  sequencer: share the squash message marker helpers and flags
  history: add squash subcommand to fold a range

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  59 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 685 ++++++++++++++++++++++--
 object.h                         |   1 +
 sequencer.c                      |  70 +--
 sequencer.h                      |  30 ++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 884 +++++++++++++++++++++++++++++++
 10 files changed, 1665 insertions(+), 71 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: 5b2471720c93ee30e5764a19f3d3b3ae9ec9712a
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v12
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v12
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v11:

 1:  dd1deb5e5b = 1:  20e050a0ad history: extract helper for a commit's parent tree
 2:  7309f64485 = 2:  b99867a0d4 history: give commit_tree_ext a message template
 3:  0762589e22 = 3:  352db997e9 sequencer: share the squash message marker helpers and flags
 4:  7abda3643c ! 4:  33d3eca6db history: add squash subcommand to fold a range
     @@ Commit message
          a "git reset --soft" to the merge base followed by "git commit --amend".
      
          Add "git history squash <revision-range>" to do this directly. It folds
     -    every commit in the range into one commit, preserving the authorship of
     +    every selected commit into one, preserving the authorship and parents of
          the oldest commit and taking the tree of the tip, then replays commits
     -    above the range. The editor opens with every folded message in the same
     -    template used by "git rebase -i --autosquash". With --no-edit, the
     -    oldest message is kept, or the last amend! replacement that targets it.
     +    above the range. By default an editor opens with every folded message in
     +    the same template used by "git rebase -i --autosquash". With --no-edit,
     +    the selected message is used without opening an editor.
      
     -    A fixup!, squash! or amend! commit is refused unless its target is also
     -    in the range, so the fold does not silently absorb a marker intended for
     -    another commit. As an exception, a range made up entirely of markers for
     -    one target is combined, allowing a batch of related fixups to be
     -    consolidated.
     +    Resolve fixup!, squash! and amend! subjects directly while walking the
     +    selected commits. A marker is rejected unless its fixed target is also
     +    selected, except that a range made up entirely of related markers can be
     +    consolidated. Without editing, refuse any squash! or amend! whose message
     +    would be discarded.
      
     -    The range is read like the arguments to "git rev-list", so several
     -    revisions such as "HEAD~3..HEAD ^topic" may be given, and rev-list
     -    options are accepted too. Walk-order options needed by the fold are
     -    restored after setup_revisions(), with a warning when an option changed
     -    them. The selected graph must have one actual boundary and one actual
     -    tip and must not reach a root. A merge inside the range is folded when
     -    all selected history reaches the same boundary; otherwise the range has
     -    more than one base and is rejected.
     +    Read the range like arguments to "git rev-list" and accept multiple
     +    revisions and rev-list options. Restore the walk settings required by the
     +    fold after setup_revisions(), warning when an option changed them. The
     +    range must name a bottom commit, must not reach a root, and must have one
     +    tip. Every parent after the oldest commit must be selected or also be a
     +    parent of the oldest commit. This permits internal merges and preserves
     +    all parents when the oldest commit is itself a merge.
      
     -    By default the command refuses when a local branch points inside the
     -    range, because that branch cannot be replayed as a descendant of the
     -    result. Tags and remote-tracking refs are left unchanged. Use
     -    --update-refs=head to leave interior branches unchanged as well.
     +    By default, refuse when a local branch descends from the selected commits
     +    but cannot remain a descendant of the result. Tags and remote-tracking
     +    refs are left unchanged. Use --update-refs=head to leave such local
     +    branches unchanged as well.
      
          Inspired-by: Sergey Chernov <serega.morph@gmail.com>
     +    Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
       ## Documentation/config/advice.adoc ##
     @@ Documentation/git-history.adoc: at once.
      +This command does not (yet) replay merge commits onto the rewritten
      +history: if a commit that would be replayed is a merge, the operation is
      +rejected, and you should use linkgit:git-rebase[1] with the
     -+`--rebase-merges` flag instead. The `squash` subcommand can still fold a
     -+merge that lies inside the range, as long as the range has a single base.
     ++`--rebase-merges` flag instead. The `squash` subcommand can still fold merges
     ++that lie inside the selected range, subject to the restrictions below.
       
       Furthermore, the command does not support operations that can result in merge
       conflicts. This limitation is by design as history rewrites are not intended to
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      +already on `topic`. Rev-list options may also be given, but any that would
      +change how the range is walked are overridden with a warning.
      ++
     -+An editor opens pre-filled with the messages of all the folded commits so
     -+you can combine them. With `--no-edit`, the oldest commit's message is
     -+preserved instead, except that an `amend!` commit targeting it replaces its
     -+message. A merge commit inside the range is folded like any other, but the
     -+range must have a single base and a single tip. A range that reaches more
     -+than one entry point (for example a side branch that forked before the range
     -+and was later merged into it), or that selects two unmerged tips, is rejected.
     ++An editor opens pre-filled with the messages of all the folded commits so you
     ++can combine them. With `--no-edit`, the oldest commit's message is preserved
     ++instead, except that an `amend!` commit targeting it replaces its message.
     +++
     ++The selected commits must form a connected graph with a single tip and must
     ++not include a root commit. Every parent of a commit after the oldest one must
     ++either be selected or also be a parent of the oldest commit. When the oldest
     ++commit is a merge, all of its parents are preserved in the squashed commit.
      ++
      +A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
      +targets is also in the range, so the fold does not silently absorb a
      +marker meant for a commit outside it. As an exception, a range made up entirely
      +of markers for one target is combined into a single commit. With `--no-edit`,
     -+the last `amend!` message is used if there is one.
     ++the last `amend!` message is used if there is one; a `squash!` or `amend!` is
     ++otherwise refused if folding it would discard its message.
      ++
     -+The template mirrors `git rebase -i --autosquash`: each `fixup!`, `squash!`,
     -+or `amend!` is grouped under the commit it targets rather than shown in
     -+commit order. A `fixup!` message is dropped (commented out in full), a
     -+`squash!` keeps its body with only the marker subject commented, and an
     ++The editor template mirrors `git rebase -i --autosquash`: each `fixup!`,
     ++`squash!`, or `amend!` is grouped under the commit it targets rather than
     ++shown in commit order. A `fixup!` message is dropped (commented out in full),
     ++a `squash!` keeps its body with only the marker subject commented, and an
      +`amend!` replaces its target's message, unless a `squash!` folded into that
      +target first, in which case it keeps its body like a `squash!`.
      ++
     -+A local branch that points at a commit inside the range cannot be rewritten
     -+as a descendant of the result, so with the default `--update-refs=branches`
     -+the command refuses. Rerun with `--update-refs=head` to rewrite only the
     -+current branch and leave such branches pointing at the old commits. Tags and
     -+remote-tracking refs are always left unchanged.
     ++A local branch descended from a selected commit but not from the range tip
     ++cannot be rewritten as a descendant of the result, so with the default
     ++`--update-refs=branches` the command refuses. Rerun with `--update-refs=head`
     ++to rewrite only the current branch and leave such branches unchanged. Tags
     ++and remote-tracking refs are always left unchanged.
      +
       OPTIONS
       -------
     @@ Documentation/git-history.adoc: OPTIONS
      +`--edit`::
      +`--no-edit`::
      +	For `squash`, open an editor to combine the messages of the folded commits.
     -+	This is the default; use `--no-edit` to keep the selected message
     -+	without opening an editor.
     ++	This is the default; use `--no-edit` to keep the selected message without
     ++	opening an editor.
      +
       `--reedit-message`::
       	Open an editor to modify the target commit's message.
     @@ builtin/history.c
       #include "cache-tree.h"
       #include "commit.h"
       #include "commit-reach.h"
     +@@
     + #include "path.h"
     + #include "read-cache.h"
     + #include "refs.h"
     ++#include "ref-filter.h"
     + #include "replay.h"
     + #include "reset.h"
     + #include "revision.h"
      @@
       	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
       #define GIT_HISTORY_SPLIT_USAGE \
     @@ builtin/history.c: out:
       	return ret;
       }
       
     ++/*Remember to update object flag allocation in object.h */
     ++#define SQUASH_SEEN (1u << 11)
     ++#define SQUASH_TIP (1u << 12)
     ++#define SQUASH_AMEND_TARGET (1u << 13)
     ++
     ++static bool is_autosquash_subject(const char *s)
     ++{
     ++	return starts_with(s, "amend!") || starts_with(s, "fixup!") ||
     ++		starts_with(s, "squash!");
     ++}
     ++
     ++static bool skip_one_autosquash_prefix(const char *s, const char **out)
     ++{
     ++	if (skip_prefix(s, "amend!", out) || skip_prefix(s, "fixup!", out) ||
     ++	    skip_prefix(s, "squash!", out)) {
     ++		while (**out == ' ')
     ++			(*out)++;
     ++		return true;
     ++	}
     ++	return false;
     ++}
     ++
     ++static void truncate_message_to_subject(struct strbuf *msg)
     ++{
     ++	const char *eos = strstr(msg->buf, "\n\n");
     ++
     ++	if (eos)
     ++		strbuf_setlen(msg, eos - msg->buf + 1);
     ++}
     ++
     ++struct subject_data {
     ++	struct strintmap subjects;
     ++	struct strbuf subject;
     ++	struct strbuf squash_message;
     ++	const char *message;
     ++	bool edit_message;
     ++};
     ++
     ++#define SUBJECT_DATA_INIT {		\
     ++	.subjects = STRINTMAP_INIT,	\
     ++	.subject = STRBUF_INIT,		\
     ++	.squash_message = STRBUF_INIT,	\
     ++}
     ++
     ++static void subject_data_clear(struct subject_data *data)
     ++{
     ++	strintmap_clear(&data->subjects);
     ++	strbuf_release(&data->subject);
     ++	strbuf_release(&data->squash_message);
     ++}
     ++
     ++static int squash_amend_message(struct repository *repo,
     ++				struct commit *commit,
     ++				struct subject_data *data,
     ++				unsigned flags)
     ++{
     ++	const char *body = data->message + data->subject.len;
     ++
     ++	while (isspace(*body))
     ++		body++;
     ++
     ++	if (!*body) {
     ++		warning(_("ignoring %s (%s): message body is empty"),
     ++			repo_find_unique_abbrev(repo, &commit->object.oid,
     ++						DEFAULT_ABBREV),
     ++			data->subject.buf);
     ++		return 0;
     ++	}
     ++
     ++	if (data->edit_message) {
     ++		return 0;
     ++	} else if (flags & SQUASH_AMEND_TARGET) {
     ++		if (starts_with(data->squash_message.buf, "squash!"))
     ++			return error(_("squashing %s (%s) would overwrite "
     ++				       "'squash!' message, please combine them "
     ++				       "using '--edit'"),
     ++				     repo_find_unique_abbrev(repo,
     ++							     &commit->object.oid,
     ++							     DEFAULT_ABBREV),
     ++				     data->subject.buf);
     ++		if (starts_with(data->squash_message.buf, "fixup!"))
     ++			strbuf_splice(&data->squash_message, 0, 5, "amend!", 5);
     ++		if (starts_with(data->squash_message.buf, "amend!")) {
     ++			truncate_message_to_subject(&data->squash_message);
     ++			strbuf_addch(&data->squash_message, '\n');
     ++		} else {
     ++			strbuf_reset(&data->squash_message);
     ++		}
     ++		strbuf_addstr(&data->squash_message, body);
     ++		strbuf_complete_line(&data->squash_message);
     ++	} else {
     ++		return error(_("cannot squash %s (%s) that does not target "
     ++			       "base commit without '--edit'"),
     ++			     repo_find_unique_abbrev(repo, &commit->object.oid,
     ++						     DEFAULT_ABBREV),
     ++			     data->subject.buf);
     ++	}
     ++	return 0;
     ++}
     ++
     ++static int squash_squash_message(struct repository *repo,
     ++				struct commit *commit,
     ++				struct subject_data *data,
     ++				unsigned flags)
     ++{
     ++	const char *body = data->message + data->subject.len;
     ++
     ++	while (isspace(*body))
     ++		body++;
     ++
     ++	if (data->edit_message) {
     ++		return 0;
     ++	} else if (flags & SQUASH_AMEND_TARGET) {
     ++		if (starts_with(data->squash_message.buf, "fixup!")) {
     ++			truncate_message_to_subject(&data->squash_message);
     ++			strbuf_splice(&data->squash_message, 0, 5, "squash", 6);
     ++		}
     ++		if (starts_with(data->squash_message.buf, "squash!")) {
     ++			strbuf_addch(&data->squash_message, '\n');
     ++			strbuf_addstr(&data->squash_message, body);
     ++			strbuf_complete_line(&data->squash_message);
     ++		} else {
     ++			return error(_("squashing %s (%s) would discard its "
     ++				       "message, please combine them using "
     ++				       "'--edit'"),
     ++				     repo_find_unique_abbrev(repo,
     ++							     &commit->object.oid,
     ++							     DEFAULT_ABBREV),
     ++				     data->subject.buf);
     ++		}
     ++	} else {
     ++		return error(_("cannot squash %s (%s) that does not target "
     ++			       "base commit without '--edit'"),
     ++			      repo_find_unique_abbrev(repo, &commit->object.oid,
     ++						      DEFAULT_ABBREV),
     ++			      data->subject.buf);
     ++	}
     ++	return 0;
     ++}
     ++
     ++static int squash_check_can_autosquash(struct repository *repo,
     ++				       struct commit *commit,
     ++				       struct subject_data *data,
     ++				       unsigned flags)
     ++{
     ++	commit->object.flags |= flags & SQUASH_AMEND_TARGET;
     ++	if (starts_with(data->subject.buf, "amend!"))
     ++		return squash_amend_message(repo, commit, data, flags);
     ++	else if (starts_with(data->subject.buf, "squash!"))
     ++		return squash_squash_message(repo, commit, data, flags);
     ++
     ++	return 0;
     ++}
     ++
     ++static int squash_check_autosquash_subject(struct repository *repo,
     ++					   struct commit *commit,
     ++					   struct subject_data *data)
     ++{
     ++	const char* s = data->subject.buf;
     ++	struct commit *target;
     ++	struct hashmap_iter iter;
     ++	struct strmap_entry *entry;
     ++	/* Try skipping autosquash prefixes one at a time to allow
     ++	 * squashing
     ++	 *     a commit
     ++	 *     fixup! fixup! a commit
     ++	 *
     ++	 * where we may have started with
     ++	 *     a commit
     ++	 *     fixup! a commit
     ++	 *     fixup! fixup! a commit
     ++	 *
     ++	 * and squashed the first fixup separately from the second
     ++	 */
     ++	while (skip_one_autosquash_prefix(s, &s)) {
     ++		unsigned flags = strintmap_get(&data->subjects, s);
     ++		if (flags)
     ++			return squash_check_can_autosquash(repo, commit, data, flags);
     ++	}
     ++	/*
     ++	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
     ++	 * "fixup! main". If the target is not being squshed check the subject
     ++	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
     ++	 * squashed together.
     ++	 */
     ++	target = lookup_commit_reference_by_name(s);
     ++	if (target && istarts_with(oid_to_hex(&target->object.oid), s)) {
     ++		unsigned flags =
     ++			target->object.flags & (SQUASH_SEEN | SQUASH_AMEND_TARGET);
     ++		if (!flags) {
     ++			const char *subject_start;
     ++			const char *buffer = repo_logmsg_reencode(repo, target,
     ++								  NULL, NULL);
     ++			size_t subject_len = find_commit_subject(buffer,
     ++								 &subject_start);
     ++			char *subject = xmemdupz(subject_start, subject_len);
     ++
     ++			flags = strintmap_get(&data->subjects, subject);
     ++			free(subject);
     ++			repo_unuse_commit_buffer(repo, target, buffer);
     ++		}
     ++		if (flags)
     ++			return squash_check_can_autosquash(repo, commit,
     ++							   data, flags);
     ++	}
     ++	/* Try subject prefix matches */
     ++	strintmap_for_each_entry(&data->subjects, &iter, entry) {
     ++		s = data->subject.buf;
     ++		while(skip_one_autosquash_prefix(s, &s)) {
     ++			if (starts_with(entry->key, s)) {
     ++				unsigned value = (intptr_t)entry->value;
     ++
     ++				return squash_check_can_autosquash(repo, commit,
     ++								   data, value);
     ++			}
     ++		}
     ++	}
     ++	return error(_("cannot squash %s (%s): its target is not being "
     ++		       "squashed"),
     ++		       repo_find_unique_abbrev(repo, &commit->object.oid,
     ++					       DEFAULT_ABBREV),
     ++		       data->subject.buf);
     ++}
     ++
     ++static int squash_check_subject(struct repository *repo,
     ++				struct commit *commit,
     ++				struct subject_data *data)
     ++{
     ++	int ret = 0;
     ++	const char *buf = repo_logmsg_reencode(repo, commit, NULL, NULL);
     ++	size_t subject_len = find_commit_subject(buf, &data->message);
     ++
     ++	strbuf_reset(&data->subject);
     ++	strbuf_add(&data->subject, data->message, subject_len);
     ++
     ++	if (!strintmap_get_size(&data->subjects)) {
     ++		const char *s;
     ++
     ++		strbuf_addstr(&data->squash_message, data->message);
     ++		strbuf_complete_line(&data->squash_message);
     ++		/*
     ++		 * Strip a single autosquash prefix to allow squashing
     ++		 *     fixup! base
     ++		 *     amend! base
     ++		 */
     ++		s = data->subject.buf;
     ++		skip_one_autosquash_prefix(s, &s);
     ++		strintmap_set(&data->subjects, s, SQUASH_AMEND_TARGET | SQUASH_SEEN);
     ++		commit->object.flags |= SQUASH_AMEND_TARGET;
     ++	} else if (is_autosquash_subject(data->subject.buf)) {
     ++		ret = squash_check_autosquash_subject(repo, commit, data);
     ++	} else {
     ++		strintmap_set(&data->subjects, data->subject.buf, SQUASH_SEEN);
     ++	}
     ++	repo_unuse_commit_buffer(repo, commit, buf);
     ++	return ret;
     ++}
     ++
     ++static int build_squash_message(struct repository *repo,
     ++				const struct strbuf *todo_buf,
     ++				struct strbuf *out);
     ++
      +/*
      + * Resolve a "<base>..<tip>" revision range into the base commit just outside
      + * the range (which becomes the parent of the squashed commit), the oldest
     @@ builtin/history.c: out:
      + * but the range must have a single base and must not reach a root commit.
      + */
      +static int resolve_squash_range(struct repository *repo,
     -+				const char **argv,
     -+				struct commit **base_out,
     ++				bool update_branches,
     ++				bool edit_message,
     ++				int argc, const char **argv,
      +				struct commit **oldest_out,
      +				struct commit **tip_out,
     -+				struct oidset *interior_out)
     ++				char **message_out)
      +{
      +	struct rev_info revs;
     -+	struct commit *commit, *base = NULL, *oldest = NULL, *tip = NULL;
     -+	struct commit_list *boundaries = NULL, *commits = NULL, *iter,
     -+		**commits_tail = &commits;
     -+	struct oidset selected = OIDSET_INIT, has_children = OIDSET_INIT;
     -+	struct strvec args = STRVEC_INIT;
     -+	bool reaches_root = false;
     ++	struct subject_data subject_data = SUBJECT_DATA_INIT;
     ++	struct commit *commit, *oldest = NULL, *tip = NULL;
     ++	struct strbuf todo_buf = STRBUF_INIT;
      +	size_t i;
     -+	int ret;
     ++	int ret, tip_count = 0;
     ++	struct ref_filter filter = REF_FILTER_INIT;
     ++	struct ref_array refs = { 0 };
      +
      +	repo_init_revisions(repo, &revs, NULL);
     ++	subject_data.edit_message = edit_message;
      +	revs.reverse = 1;
      +	revs.topo_order = 1;
      +	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
      +	revs.simplify_history = 0;
     -+	revs.boundary = 1;
     -+
     -+	strvec_push(&args, "ignored");
     -+	strvec_push(&args, "--ancestry-path");
     -+	strvec_pushv(&args, argv);
     -+	setup_revisions_from_strvec(&args, &revs, NULL);
     -+	if (args.nr != 1) {
     -+		ret = error(_("unrecognized argument: %s"), args.v[1]);
     ++	revs.ancestry_path = 1;
     ++	revs.limited = 1;
     ++	revs.ancestry_path_implicit_bottoms = 1;
     ++
     ++	argc = setup_revisions(argc, argv, &revs, NULL);
     ++	if (argc > 1) {
     ++		ret = error(_("unrecognized argument: %s"), argv[1]);
      +		goto out;
      +	}
      +
      +	if (revs.reverse != 1 || revs.topo_order != 1 ||
      +	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
     -+	    revs.simplify_history != 0 || revs.boundary != 1) {
     ++	    revs.simplify_history != 0 || revs.boundary == 1 ||
     ++	    revs.ancestry_path != 1 || revs.limited != 1 ||
     ++	    revs.ancestry_path_implicit_bottoms != 1) {
      +		warning(_("ignoring rev-list options that would change how the "
      +			  "range is walked"));
      +		revs.reverse = 1;
      +		revs.topo_order = 1;
      +		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
      +		revs.simplify_history = 0;
     -+		revs.boundary = 1;
     ++		revs.boundary = 0;
     ++		revs.ancestry_path = 1;
     ++		revs.limited = 1;
     ++		revs.ancestry_path_implicit_bottoms = 1;
      +	}
      +
     -+	/* A squash range must name a bottom revision to reparent onto. */
     ++	/*
     ++	 * A squash needs a base to reparent onto, so the range has to exclude
     ++	 * something, as in "<base>..<tip>". A revision range with no such
     ++	 * bottom commit cannot be squashed.
     ++	 */
      +	for (i = 0; i < revs.cmdline.nr; i++)
      +		if (revs.cmdline.rev[i].flags & BOTTOM)
      +			break;
     @@ builtin/history.c: out:
      +		ret = error(_("error preparing revisions"));
      +		goto out;
      +	}
     -+
     -+	/* Set boundary commits aside for the base check below. */
      +	while ((commit = get_revision(&revs))) {
     -+		if (commit->object.flags & BOUNDARY) {
     -+			commit_list_insert(commit, &boundaries);
     -+			continue;
     ++		struct commit_list *p;
     ++
     ++		if (edit_message)
     ++			strbuf_addf(&todo_buf, "pick %s\n",
     ++				    oid_to_hex(&commit->object.oid));
     ++
     ++		if (!commit->parents) {
     ++			ret = error(_("cannot squash down to root commit"));
     ++			goto out;
     ++		}
     ++		for (p = commit->parents; oldest && p; p = p->next) {
     ++			struct commit_list *q;
     ++			struct object *o;
     ++			bool seen;
     ++
     ++			if (repo_parse_commit(repo, p->item)) {
     ++				ret = error(_("cannot parse commit"));
     ++				goto out;
     ++			}
     ++			o = &p->item->object;
     ++			seen = o->flags & SQUASH_SEEN;
     ++			/*
     ++			 * Allow parents that match the parents of the
     ++			 * squashed commit.
     ++			 */
     ++			for (q = oldest->parents; !seen && q; q = q->next) {
     ++				if (p->item == q->item) {
     ++					seen = true;
     ++					commit_list_insert(commit, &filter.with_commit);
     ++				}
     ++			}
     ++			if (!seen) {
     ++				ret = error(_("parent %s of commit %s is "
     ++					      "outside the revision range"),
     ++					    repo_find_unique_abbrev(repo, &o->oid,
     ++								    DEFAULT_ABBREV),
     ++					    repo_find_unique_abbrev(repo, &commit->object.oid,
     ++								    DEFAULT_ABBREV));
     ++				goto out;
     ++			}
     ++			if (o->flags & SQUASH_TIP) {
     ++				tip_count--;
     ++				o->flags &= ~SQUASH_TIP;
     ++			}
      +		}
     -+		if (!oldest)
     ++		if (!oldest) {
     ++			commit_list_insert(commit, &filter.with_commit);
      +			oldest = commit;
     -+		oidset_insert(&selected, &commit->object.oid);
     -+		commits_tail = commit_list_append(commit, commits_tail);
     ++		}
     ++		if (squash_check_subject(repo, commit, &subject_data)) {
     ++			ret = -1;
     ++			goto out;
     ++		}
     ++		tip = commit;
     ++		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
     ++		tip_count++;
      +	}
     -+
     -+	if (!oldest) {
     ++	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP | SQUASH_AMEND_TARGET);
     ++	reset_revision_walk();
     ++	if (!tip_count) {
      +		ret = error(_("the revision range is empty"));
      +		goto out;
     -+	} else if (!commits->next) {
     ++	} else if (tip_count != 1) {
     ++		  ret = error(_("the revision range contains more than one tip "
     ++				"commit"));
     ++		  goto out;
     ++	  } else if (oldest == tip) {
      +		ret = error(_("the revision range holds a single commit; "
      +			      "nothing to squash"));
      +		goto out;
     ++	} else if (!oldest->parents) {
     ++		BUG("an in-range commit must have a parent");
      +	}
     -+
     -+	/*
     -+	 * Find the selected commits that have selected children. The only
     -+	 * remaining commit must be the tip whose tree becomes the result.
     -+	 */
     -+	for (iter = commits; iter; iter = iter->next) {
     -+		struct commit_list *p;
     -+
     -+		if (!iter->item->parents)
     -+			reaches_root = true;
     -+		for (p = iter->item->parents; p; p = p->next)
     -+			if (oidset_contains(&selected, &p->item->object.oid))
     -+				oidset_insert(&has_children,
     -+					      &p->item->object.oid);
     -+	}
     -+	if (reaches_root) {
     -+		ret = error(_("the revision range reaches a root commit; "
     -+			      "cannot squash"));
     ++	commit_list_insert(tip, &filter.no_commit);
     ++	filter.kind = FILTER_REFS_BRANCHES;
     ++	if (update_branches &&
     ++	    filter_refs(&refs, &filter, filter.kind)) {
     ++		ret = error(_("could not filter refs"));
      +		goto out;
      +	}
     -+	for (iter = commits; iter; iter = iter->next) {
     -+		if (oidset_contains(&has_children, &iter->item->object.oid))
     -+			continue;
     -+		if (tip) {
     -+			ret = error(_("the revision range has more than one tip; "
     -+				      "cannot squash"));
     -+			goto out;
     -+		}
     -+		tip = iter->item;
     -+	}
     -+
     -+	/* The range must reach exactly one commit outside it. */
     -+	if (!boundaries) {
     -+		ret = error(_("the revision range has no base; cannot squash"));
     ++	if (refs.nr) {
     ++		/*
     ++		 * TODO: list the branches and also check HEADS from other worktrees
     ++		 */
     ++		ret = error(_("a branch points to a commit that is being squashed"));
     ++		advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
     ++				  _("Use --update-refs=head to rewrite only "
     ++				    "the current branch and leave such refs "
     ++				    "untouched."));
      +		goto out;
      +	}
     -+	base = boundaries->item;
     -+	for (iter = boundaries; iter; iter = iter->next) {
     -+		if (iter->item != base) {
     -+			ret = error(_("the revision range has more than one base; "
     -+				      "cannot squash"));
     ++	if (edit_message) {
     ++		strbuf_reset(&subject_data.squash_message);
     ++		ret = build_squash_message(repo, &todo_buf,
     ++					   &subject_data.squash_message);
     ++		if (ret < 0)
      +			goto out;
     -+		}
      +	}
     -+
     -+	for (iter = commits; iter; iter = iter->next)
     -+		if (iter->item != tip)
     -+			oidset_insert(interior_out, &iter->item->object.oid);
     -+
     -+	*base_out = base;
      +	*oldest_out = oldest;
      +	*tip_out = tip;
     ++	*message_out = strbuf_detach(&subject_data.squash_message, NULL);
      +	ret = 0;
      +
      +out:
     -+	commit_list_free(boundaries);
     -+	commit_list_free(commits);
     -+	oidset_clear(&selected);
     -+	oidset_clear(&has_children);
     -+	reset_revision_walk();
     ++	strbuf_release(&todo_buf);
     ++	subject_data_clear(&subject_data);
      +	release_revisions(&revs);
     -+	strvec_clear(&args);
     ++	ref_filter_clear(&filter);
     ++	ref_array_clear(&refs);
      +	return ret;
      +}
      +
     -+static const char *autosquash_target(const char *subject)
     -+{
     -+	const char *rest;
     -+
     -+	while (skip_prefix(subject, "fixup! ", &rest) ||
     -+	       skip_prefix(subject, "squash! ", &rest) ||
     -+	       skip_prefix(subject, "amend! ", &rest))
     -+		subject = rest;
     -+	return subject;
     -+}
     -+
     -+static int reject_dangling_fixups(struct repository *repo,
     -+				  struct commit *base,
     -+				  struct commit *tip,
     -+				  struct commit **amend_source)
     -+{
     -+	struct todo_list todo = TODO_LIST_INIT;
     -+	struct replay_opts opts = REPLAY_OPTS_INIT;
     -+	struct rev_info revs;
     -+	struct commit *commit, *last_amend = NULL;
     -+	struct strvec args = STRVEC_INIT;
     -+	char *dangling_subject = NULL, *dangling_target = NULL;
     -+	bool mixed_target = false, all_fixups_one_target;
     -+	bool past_oldest_group = false;
     -+	int i, ret, nr_dangling = 0;
     -+
     -+	*amend_source = NULL;
     -+
     -+	repo_init_revisions(repo, &revs, NULL);
     -+	strvec_push(&args, "ignored");
     -+	strvec_push(&args, "--reverse");
     -+	strvec_push(&args, "--topo-order");
     -+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
     -+		     oid_to_hex(&tip->object.oid));
     -+	setup_revisions_from_strvec(&args, &revs, NULL);
     -+
     -+	if (prepare_revision_walk(&revs) < 0) {
     -+		ret = error(_("error preparing revisions"));
     -+		goto out;
     -+	}
     -+	while ((commit = get_revision(&revs)))
     -+		strbuf_addf(&todo.buf, "pick %s\n",
     -+			    oid_to_hex(&commit->object.oid));
     -+
     -+	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
     -+	    todo_list_rearrange_squash(&todo) < 0) {
     -+		ret = error(_("could not check the range for fixups"));
     -+		goto out;
     -+	}
     -+
     -+	for (i = 0; i < todo.nr; i++) {
     -+		const char *message, *subject_start, *target;
     -+		char *subject;
     -+		size_t sublen;
     -+
     -+		message = repo_logmsg_reencode(repo, todo.items[i].commit,
     -+					       NULL, NULL);
     -+		sublen = find_commit_subject(message, &subject_start);
     -+
     -+		if (todo.items[i].command != TODO_PICK) {
     -+			if (!past_oldest_group &&
     -+			    starts_with(subject_start, "amend! "))
     -+				*amend_source = todo.items[i].commit;
     -+			repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
     -+			continue;
     -+		}
     -+		if (i)
     -+			past_oldest_group = true;
     -+
     -+		subject = xmemdupz(subject_start, sublen);
     -+		target = autosquash_target(subject);
     -+		if (target != subject) {
     -+			nr_dangling++;
     -+			if (!dangling_target) {
     -+				dangling_target = xstrdup(target);
     -+				dangling_subject = xstrdup(subject);
     -+			} else if (strcmp(dangling_target, target)) {
     -+				mixed_target = true;
     -+			}
     -+			if (starts_with(subject, "amend! "))
     -+				last_amend = todo.items[i].commit;
     -+		}
     -+		free(subject);
     -+		repo_unuse_commit_buffer(repo, todo.items[i].commit, message);
     -+	}
     -+
     -+	all_fixups_one_target = nr_dangling == todo.nr && !mixed_target;
     -+	if (nr_dangling && !all_fixups_one_target) {
     -+		ret = error(_("cannot squash '%s': its target is not in the "
     -+			      "range"), dangling_subject);
     -+	} else {
     -+		if (last_amend)
     -+			*amend_source = last_amend;
     -+		ret = 0;
     -+	}
     -+
     -+out:
     -+	free(dangling_subject);
     -+	free(dangling_target);
     -+	todo_list_release(&todo);
     -+	replay_opts_release(&opts);
     -+	reset_revision_walk();
     -+	release_revisions(&revs);
     -+	strvec_clear(&args);
     -+	return ret;
     -+}
     -+
     -+struct interior_ref_cb {
     -+	const struct oidset *interior;
     -+	const char *name;
     -+};
     -+
     -+static int find_interior_ref(const struct reference *ref, void *cb_data)
     -+{
     -+	struct interior_ref_cb *data = cb_data;
     -+
     -+	if (oidset_contains(data->interior, ref->oid)) {
     -+		data->name = xstrdup(ref->name);
     -+		return 1;
     -+	}
     -+
     -+	return 0;
     -+}
     -+
      +static bool amend_replaces_target(struct todo_list *todo, int target)
      +{
      +	int i;
     @@ builtin/history.c: out:
      +}
      +
      +static int build_squash_message(struct repository *repo,
     -+				struct commit *base,
     -+				struct commit *tip,
     ++				const struct strbuf *todo_buf,
      +				struct strbuf *out)
      +{
     -+	struct rev_info revs;
     -+	struct commit *commit;
     -+	struct strvec args = STRVEC_INIT;
      +	struct todo_list todo = TODO_LIST_INIT;
      +	struct replay_opts opts = REPLAY_OPTS_INIT;
      +	int i, nr_commits, ret;
      +
     -+	repo_init_revisions(repo, &revs, NULL);
     -+	strvec_push(&args, "ignored");
     -+	strvec_push(&args, "--reverse");
     -+	strvec_push(&args, "--topo-order");
     -+	strvec_pushf(&args, "%s..%s", oid_to_hex(&base->object.oid),
     -+		     oid_to_hex(&tip->object.oid));
     -+	setup_revisions_from_strvec(&args, &revs, NULL);
     -+
     -+	if (prepare_revision_walk(&revs) < 0) {
     -+		ret = error(_("error preparing revisions"));
     -+		goto out;
     -+	}
     -+
     -+	while ((commit = get_revision(&revs)))
     -+		strbuf_addf(&todo.buf, "pick %s\n",
     -+			    oid_to_hex(&commit->object.oid));
     -+
     -+	if (todo_list_parse_insn_buffer(repo, &opts, todo.buf.buf, &todo) < 0 ||
     ++	if (todo_list_parse_insn_buffer(repo, &opts, todo_buf->buf, &todo) < 0 ||
      +	    todo_list_rearrange_squash(&todo) < 0) {
      +		ret = error(_("could not prepare the squash message"));
      +		goto out;
     @@ builtin/history.c: out:
      +out:
      +	todo_list_release(&todo);
      +	replay_opts_release(&opts);
     -+	reset_revision_walk();
     -+	release_revisions(&revs);
     -+	strvec_clear(&args);
      +	return ret;
      +}
      +
     @@ builtin/history.c: out:
      +		NULL,
      +	};
      +	enum ref_action action = REF_ACTION_DEFAULT;
     -+	enum commit_tree_flags flags = 0;
      +	int dry_run = 0;
      +	int edit = 1;
      +	struct option options[] = {
     @@ builtin/history.c: out:
      +		OPT_END(),
      +	};
      +	struct strbuf reflog_msg = STRBUF_INIT;
     -+	struct strbuf message = STRBUF_INIT;
     -+	struct oidset interior = OIDSET_INIT;
     -+	struct commit *base = NULL, *oldest = NULL, *tip = NULL, *rewritten,
     -+		*amend_source = NULL;
     ++	struct commit *oldest, *tip, *rewritten;
      +	const struct object_id *base_tree_oid, *tip_tree_oid;
     -+	const char *message_template = NULL;
     -+	struct commit_list *parents = NULL;
     ++	char *message_template = NULL;
      +	struct rev_info revs = { 0 };
      +	int ret;
      +
      +	argc = parse_options(argc, argv, prefix, options, usage,
     -+			     PARSE_OPT_KEEP_UNKNOWN_OPT);
     -+	if (!argc) {
     ++			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
     ++	if (argc < 2) {
      +		ret = error(_("command expects a revision range"));
      +		goto out;
      +	}
     @@ builtin/history.c: out:
      +	if (action == REF_ACTION_DEFAULT)
      +		action = REF_ACTION_BRANCHES;
      +
     -+	ret = resolve_squash_range(repo, argv, &base, &oldest, &tip,
     -+				   &interior);
     -+	if (ret < 0)
     -+		goto out;
     ++	strbuf_addstr(&reflog_msg, "squash: updating ");
     ++	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
      +
     -+	ret = reject_dangling_fixups(repo, base, tip, &amend_source);
     ++	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
     ++				   edit,
     ++				   argc, argv, &oldest, &tip,
     ++				   &message_template);
      +	if (ret < 0)
      +		goto out;
     -+	if (!edit && amend_source) {
     -+		const char *amend_message, *body;
     -+
     -+		amend_message = repo_logmsg_reencode(repo, amend_source,
     -+						     NULL, NULL);
     -+		find_commit_subject(amend_message, &body);
     -+		body = skip_blank_lines(body + commit_subject_length(body));
     -+		strbuf_addstr(&message, body);
     -+		message_template = message.buf;
     -+		repo_unuse_commit_buffer(repo, amend_source, amend_message);
     -+	}
     -+
     -+	if (action == REF_ACTION_BRANCHES) {
     -+		struct interior_ref_cb cb = { .interior = &interior };
     -+
     -+		refs_for_each_branch_ref(get_main_ref_store(repo),
     -+					 find_interior_ref, &cb);
     -+		if (cb.name) {
     -+			ret = error(_("'%s' points into the squashed range"),
     -+				    cb.name);
     -+			advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
     -+					  _("Use --update-refs=head to rewrite only "
     -+					    "the current branch and leave such refs "
     -+					    "untouched."));
     -+			free((char *)cb.name);
     -+			goto out;
     -+		}
     -+	}
     -+
     -+	if (edit) {
     -+		ret = build_squash_message(repo, base, tip, &message);
     -+		if (ret < 0)
     -+			goto out;
     -+		message_template = message.buf;
     -+		flags |= COMMIT_TREE_EDIT_MESSAGE;
     -+	}
      +
      +	ret = setup_revwalk(repo, action, tip, &revs);
      +	if (ret < 0)
      +		goto out;
      +
     -+	base_tree_oid = &repo_get_commit_tree(repo, base)->object.oid;
     ++	base_tree_oid = &repo_get_commit_tree(repo,
     ++					oldest->parents->item)->object.oid;
      +	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
     -+	commit_list_append(base, &parents);
      +
      +	ret = commit_tree_ext(repo, "squash", oldest, message_template,
     -+			      parents,
     -+			      base_tree_oid, tip_tree_oid, &rewritten, flags);
     ++			      oldest->parents, base_tree_oid, tip_tree_oid,
     ++			      &rewritten,
     ++			      edit ? COMMIT_TREE_EDIT_MESSAGE : 0);
      +	if (ret < 0) {
      +		ret = error(_("failed writing squashed commit"));
      +		goto out;
      +	}
      +
     -+	strbuf_addstr(&reflog_msg, "squash: updating ");
     -+	strbuf_join_argv(&reflog_msg, argc, argv, ' ');
     -+
      +	ret = handle_reference_updates(&revs, action, tip, rewritten,
      +				       reflog_msg.buf, dry_run,
      +				       REPLAY_EMPTY_COMMIT_ABORT);
     @@ builtin/history.c: out:
      +
      +out:
      +	strbuf_release(&reflog_msg);
     -+	strbuf_release(&message);
     -+	oidset_clear(&interior);
     -+	commit_list_free(parents);
      +	release_revisions(&revs);
     ++	free(message_template);
      +	return ret;
      +}
      +
     @@ builtin/history.c: int cmd_history(int argc,
       	};
       
      
     + ## object.h ##
     +@@ object.h: void object_array_init(struct object_array *array);
     +  * bisect.c:                                        16
     +  * bundle.c:                                        16
     +  * http-push.c:                          11-----14
     ++ * builtin/history.c:                    11---13
     +  * commit-graph.c:                                15
     +  * commit-reach.c:                                  16-------20
     +  * builtin/last-modified.c:                         1617
     +
       ## t/meson.build ##
      @@ t/meson.build: integration_tests = [
         't3452-history-split.sh',
     @@ t/t3455-history-squash.sh (new)
      +	test_cmp expect actual
      +}
      +
     ++# Checks that the author data of two commits matches
     ++# Usage: check_commit_author <rev1> <rev2>
     ++check_commit_author () {
     ++	git show -s --format="%an <%ae> %ad" "$1" >expect &&
     ++	git show -s --format="%an <%ae> %ad" "$2" >actual &&
     ++	test_cmp expect actual
     ++}
     ++
      +test_expect_success 'setup linear history touching two files' '
     -+	test_commit base file a &&
     -+	git tag start &&
     -+	GIT_AUTHOR_NAME=Squasher GIT_AUTHOR_EMAIL=squash@example.com \
     -+		test_commit --no-tag one other x &&
     -+	test_commit --no-tag two file c &&
     -+	test_commit three file d
     ++	test_commit base file a start &&
     ++	GIT_AUTHOR_NAME=One GIT_AUTHOR_EMAIL=one@example.com \
     ++		test_commit one other x &&
     ++	GIT_AUTHOR_NAME=Two GIT_AUTHOR_EMAIL=two@example.com \
     ++		test_commit two file c &&
     ++	GIT_AUTHOR_NAME=Three GIT_AUTHOR_EMAIL=three@example.com \
     ++		test_commit three file d
      +'
      +
      +test_expect_success 'errors on missing range argument' '
     @@ t/t3455-history-squash.sh (new)
      +	test_cmp_rev "$head_before" HEAD
      +'
      +
     ++test_expect_success 'rejects root commit' '
     ++	# create a disconnected root commit
     ++	oid=$(git commit-tree -m root three^{tree}) &&
     ++	# because we pass --ancestry-path when calling setup_revs() it the
     ++	# revision walk will only include commits decended from $oid so
     ++	# we need to give it another --ancestry-path commit to actually walk
     ++	# any commits.
     ++	test_must_fail git history squash --ancestry-path=start $oid..three 2>err &&
     ++	echo "error: cannot squash down to root commit" >expect &&
     ++	test_cmp expect err
     ++'
     ++
     ++test_expect_success 'rejects multiple tips' '
     ++	oid=$(git commit-tree -m tip -p start^0 three^{tree}) &&
     ++	test_must_fail git history squash ^start $oid three~1 2>err &&
     ++	echo "error: the revision range contains more than one tip commit" >expect &&
     ++	test_cmp expect err &&
     ++
     ++	git reset --hard three &&
     ++	git history squash --no-edit ^start three~1 three &&
     ++	test_cmp_rev HEAD~1 start^0 &&
     ++	test_cmp_rev HEAD^{tree} three^{tree}
     ++'
     ++
      +test_expect_success 'accepts multiple revision arguments with an exclusion' '
      +	git reset --hard three &&
      +	git branch -f keep HEAD~2 &&
     @@ t/t3455-history-squash.sh (new)
      +	git branch -D keep
      +'
      +
     -+test_expect_success 'refuses a range with more than one tip' '
     -+	git reset --hard start &&
     -+	main=$(git symbolic-ref --short HEAD) &&
     -+	test_commit --no-tag main-one file b &&
     -+	test_commit --no-tag main-two file c &&
     -+	git checkout -b other-tip start &&
     -+	test_commit --no-tag other-tip other d &&
     -+	git checkout "$main" &&
     -+	main_before=$(git rev-parse HEAD) &&
     -+	other_before=$(git rev-parse other-tip) &&
     -+
     -+	test_must_fail git history squash ^start HEAD other-tip 2>err &&
     -+	test_grep "more than one tip" err &&
     -+	test_cmp_rev "$main_before" HEAD &&
     -+	test_cmp_rev "$other_before" other-tip &&
     -+
     -+	git branch -D other-tip
     -+'
     -+
     -+test_expect_success 'refuses a range that reaches a root commit' '
     -+	git reset --hard three &&
     -+	root=$(printf "unrelated root\n" |
     -+		git commit-tree "$(git rev-parse HEAD^{tree})") &&
     -+	head_before=$(git rev-parse HEAD) &&
     -+
     -+	test_must_fail git history squash --ancestry-path="$root" \
     -+		^start HEAD "$root" 2>err &&
     -+	test_grep "reaches a root commit" err &&
     -+	test_cmp_rev "$head_before" HEAD
     -+'
     -+
      +test_expect_success 'squashes a branch the current branch is not on' '
      +	git reset --hard three &&
      +	main=$(git symbolic-ref --short HEAD) &&
     @@ t/t3455-history-squash.sh (new)
      +	git branch -D off-history
      +'
      +
     -+test_expect_success 'squashes a range preserving its tree and oldest authorship' '
     ++test_expect_success 'squashes a range into a single commit without changing the tree' '
      +	git reset --hard three &&
      +	head_before=$(git rev-parse HEAD) &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	git history squash --dry-run start.. >out &&
     ++	git history squash --no-edit --dry-run start.. >out &&
      +	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
      +	test_cmp_rev "$head_before" HEAD &&
      +
     -+	git history squash start.. &&
     ++	git history squash --no-edit start.. &&
      +
      +	test "$predicted" = "$(git rev-parse HEAD)" &&
      +	check_commit_count start..HEAD 1 &&
     @@ t/t3455-history-squash.sh (new)
      +	check_log_subjects -1 <<-\EOF &&
      +	one
      +	EOF
     -+	git log -1 --format="%an <%ae>" >actual &&
     -+	echo "Squasher <squash@example.com>" >expect &&
     -+	test_cmp expect actual &&
      +	git reflog >reflog &&
      +	test_grep "squash: updating" reflog
      +'
     @@ t/t3455-history-squash.sh (new)
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
      +'
      +
     ++test_expect_success 'squashing a mix of fixups' '
     ++	git reset --hard three &&
     ++	echo fix >file &&
     ++	git commit --fixup=two -a &&
     ++	echo really fix >file &&
     ++	git commit --fixup=one -a &&
     ++	echo really really fix >file &&
     ++	git commit --fixup=HEAD~1 -a && # fixup! two
     ++	echo really really really fix >file &&
     ++	git commit --fixup=HEAD~1 -a && # fixup! one
     ++
     ++	# squashing fixup! with a target that is not being squashed fails
     ++	test_must_fail git history squash one.. 2>err &&
     ++	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
     ++
     ++	# squashing fixup! into fixup! with a different target fails
     ++	test_must_fail git history squash HEAD~4.. 2>err && # HEAD~4 is fixup! two
     ++	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
     ++
     ++	# squashing a sequence of fixup! commits into their targets
     ++	git history squash --no-edit start..HEAD~1 &&
     ++	test_cmp_rev start HEAD~2 &&
     ++	check_commit_author one HEAD~1 &&
     ++	test_commit_message HEAD~1 -m one &&
      +
     -+test_expect_success 'folds fixups whose target is in the range' '
     -+	git reset --hard start &&
     -+	test_commit --no-tag target file b &&
     -+	git commit --allow-empty -m "fixup! target" &&
     -+	git commit --allow-empty -m "fixup! target" &&
     -+	test_commit --no-tag later file c &&
     -+
     ++	# squashing "fixup! fixup! <target>" into "<target>"
      +	git history squash --no-edit start.. &&
     -+
     -+	check_commit_count start..HEAD 1 &&
     -+	check_log_subjects -1 <<-\EOF
     -+	target
     -+	EOF
     ++	test_cmp_rev start HEAD~1 &&
     ++	check_commit_author one HEAD &&
     ++	test_commit_message HEAD -m one
      +'
      +
     -+test_expect_success 'refuses a below-range fixup! after an in-range commit' '
     -+	git reset --hard start &&
     -+	test_commit --no-tag inside file b &&
     -+	test_commit --no-tag "fixup! outside" file c &&
     -+	head_before=$(git rev-parse HEAD) &&
     -+
     -+	test_must_fail git history squash start.. 2>err &&
     -+	test_grep "target is not in the range" err &&
     -+	test_cmp_rev "$head_before" HEAD
     -+'
     ++test_expect_success 'squashing "squash!" messages' '
     ++	git reset --hard two &&
     ++	echo fix >file &&
     ++	git commit --fixup=HEAD -a &&
     ++	oldest=$(git rev-parse HEAD) &&
     ++	echo better fix >file &&
     ++	git commit -a -F - <<-EOF &&
     ++	squash! $(git rev-parse two)
      +
     -+test_expect_success 'combines a run of fixups for one commit below the range' '
     -+	git reset --hard start &&
     -+	stage_file b && git commit -m "fixup! base" &&
     -+	stage_file c && git commit -m "fixup! base" &&
     ++	Append this
     ++	EOF
      +
     -+	git history squash --no-edit start.. &&
     ++	echo an even better fix >file &&
     ++	git commit -a -F - <<-EOF &&
     ++	squash! squash! two
      +
     -+	check_commit_count start..HEAD 1 &&
     -+	check_log_subjects -1 <<-\EOF
     -+	fixup! base
     ++	Append this as well
      +	EOF
     -+'
      +
     -+test_expect_success 'combining below-range markers offers every message' '
     -+	git reset --hard start &&
     -+	stage_file b && git commit -m "fixup! base" &&
     -+	stage_file c &&
     -+	commit_with_message "amend! base\n\namended body\n" &&
     ++	# must edit when squashing "squash!" into its target
     ++	test_must_fail git history squash --no-edit two^.. 2>err &&
     ++	test_grep "^error: squashing .* (squash! [a-f0-9]*) would discard its message" err &&
      +
     -+	git history squash start.. &&
     ++	# squashing "squash!" into "fixup!" appends messages and changes
     ++	# subject prefix
     ++	git history squash --no-edit two.. &&
     ++	test_cmp_rev HEAD^ two &&
     ++	test_commit_message HEAD <<-\EOF &&
     ++	squash! two
      +
     -+	check_commit_count start..HEAD 1 &&
     -+	check_log_messages -1 <<-\EOF
     -+	fixup! base
     ++	Append this
      +
     -+	amend! base
     ++	Append this as well
     ++	EOF
     ++	check_commit_author "$oldest" HEAD &&
      +
     -+	amended body
     ++	git commit --allow-empty -F - <<-\EOF &&
     ++	amend! two
      +
     ++	A new message
      +	EOF
     ++
     ++	# "amend!" does not replace "squash!"
     ++	test_must_fail git history squash --no-edit HEAD~2.. 2>err &&
     ++	test_grep "^error: squashing .* (amend! two) would overwrite .squash!. message" err
      +'
      +
     -+test_expect_success 'refuses fixups for two different commits below the range' '
     -+	git reset --hard start &&
     -+	stage_file b && git commit -m "fixup! aaa" &&
     -+	stage_file c && git commit -m "fixup! bbb" &&
     -+	head_before=$(git rev-parse HEAD) &&
     ++test_expect_success '--no-edit uses last "amend!" message without an editor' '
     ++	git reset --hard three &&
     ++	write_script editor <<-\EOF &&
     ++	exit 1
     ++	EOF
     ++	test_set_editor "$(pwd)/editor" &&
     ++	echo fix >file &&
     ++	git commit --author="Fix Me <fix.me@example.com>" --fixup=HEAD -a &&
     ++	git commit --allow-empty -F - <<-EOF &&
     ++	amend! $(git rev-parse --short HEAD)
      +
     -+	test_must_fail git history squash start.. 2>err &&
     -+	test_grep "target is not in the range" err &&
     -+	test_cmp_rev "$head_before" HEAD
     -+'
     ++	The first reword
      +
     -+test_expect_success 'does not discard squash! or amend! message bodies' '
     -+	git reset --hard start &&
     -+	test_commit --no-tag marker-oldest file b &&
     -+	git commit --allow-empty -m "squash! marker-oldest" &&
     -+	commit_with_message "amend! marker-oldest\n\nearlier message\n" &&
     -+	commit_with_message \
     -+		"amend! marker-oldest\n\namended subject\n\namended body\n" &&
     -+	test_commit --no-tag marker-later file c &&
     -+	commit_with_message "amend! marker-later\n\nwrong message\n" &&
     ++	More detail
     ++	EOF
      +
     -+	git history squash start.. &&
     ++	git commit --allow-empty -F - <<-\EOF &&
     ++	amend! three
      +
     -+	check_commit_count start..HEAD 1 &&
     -+	check_log_messages -1 <<-\EOF
     -+	marker-oldest
     ++	The second reword
      +
     -+	earlier message
     ++	Extra detail
     ++	EOF
      +
     -+	amended subject
     ++	test_commit WIP &&
      +
     -+	amended body
     ++	cat >msg <<-EOF &&
     ++	amend! $(git rev-parse HEAD^ | tr a-f A-F)
      +
     -+	wrong message
     ++	The third reword
      +
     ++	Excruciating detail
      +	EOF
     -+'
     -+
     -+test_expect_success '--no-edit keeps the selected message without an editor' '
     -+	git reset --hard start &&
     -+	test_commit --no-tag no-edit-target file b &&
     -+	git commit --allow-empty -m "squash! no-edit-target" &&
     -+	commit_with_message "amend! no-edit-target\n\namended subject\n\namended body\n" &&
      +
     -+	write_script editor <<-\EOF &&
     -+	exit 1
     ++	git commit --author="Someone Else <s.else@example.com>" --allow-empty \
     ++		-F msg &&
     ++
     ++	# squashing amend! updates the commit message
     ++	git history squash --no-edit three^.. &&
     ++	sed -e 1,2d msg | test_commit_message HEAD &&
     ++	check_commit_author three HEAD &&
     ++	test_cmp_rev HEAD^ three^ &&
     ++
     ++	# squashing amend! into fixup! updates subject prefix
     ++	git reset --hard HEAD@{1} &&
     ++	git history squash --no-edit three.. &&
     ++	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
     ++	check_commit_author HEAD@{1}~4 HEAD &&
     ++	test_cmp_rev HEAD^ three &&
     ++
     ++	# squashing amend! into amend! keeps original subject line
     ++	git reset --hard HEAD@{1} &&
     ++	git history squash --no-edit HEAD~3.. &&
     ++	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
     ++	test_cmp_rev HEAD~3 three &&
     ++
     ++	# all amend! messages must target the first commit
     ++	git reset --hard HEAD@{1} &&
     ++	git commit --allow-empty -F - <<-\EOF &&
     ++	amend! WIP
     ++
     ++	The real message
      +	EOF
     -+	test_set_editor "$(pwd)/editor" &&
     -+	git history squash --no-edit start.. &&
      +
     -+	check_log_messages -1 <<-\EOF &&
     -+	amended subject
     ++	test_must_fail git history squash --no-edit HEAD~4.. 2>err &&
     ++	test_grep "^error: cannot squash .* that does not target" err &&
      +
     -+	amended body
     ++	# amend! message that targets commit that is not in range is rejected
     ++	test_must_fail git history squash --no-edit HEAD~3.. 2>err &&
     ++	test_grep "^error: cannot squash .* target is not being squashed" err &&
     ++	test_set_editor :
     ++'
      +
     ++test_expect_success 'squashing fixups into a merge' '
     ++	test_when_finished \
     ++		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
     ++		 git branch -D feature" &&
     ++	git checkout -f start &&
     ++	test_commit F1 &&
     ++	git checkout -b feature start &&
     ++	test_commit F2 &&
     ++	git merge F1 &&
     ++	echo fixed >F1.t &&
     ++	cat >msg <<-EOF &&
     ++	amend! $(git rev-parse HEAD)
     ++
     ++	merge F1 and F2
     ++
     ++	reworded
      +	EOF
     -+	test_set_editor :
     ++
     ++	git commit -a -F msg &&
     ++	git history squash --no-edit HEAD^^! HEAD &&
     ++	test_cmp_rev HEAD^1 F2 &&
     ++	test_cmp_rev HEAD^2 F1 &&
     ++	test_cmp_rev HEAD@{1}^{tree} HEAD^{tree} &&
     ++	sed 1,2d msg | test_commit_message HEAD
      +'
      +
      +test_expect_success 'edits every message and aborts on an empty result' '
     @@ t/t3455-history-squash.sh (new)
      +	EOF
      +'
      +
     -+test_expect_success 'handles fixup!, squash! and amend! messages like rebase' '
     ++test_expect_success 'handles fixup!, squash! and amend! like rebase' '
      +	git reset --hard start &&
      +	test_commit --no-tag mark-base file b &&
      +	stage_file c &&
     @@ t/t3455-history-squash.sh (new)
      +	EOF
      +'
      +
     -+test_expect_success 'handles branches pointing at the squashed range' '
     ++test_expect_success '--update-refs=head only moves HEAD' '
      +	git reset --hard three &&
      +	git branch -f other HEAD &&
     -+	git branch -f mid HEAD~1 &&
      +	other_before=$(git rev-parse other) &&
     -+	mid_before=$(git rev-parse mid) &&
     -+	head_before=$(git rev-parse HEAD) &&
     ++
     ++	git history squash --no-edit --update-refs=head start.. &&
     ++
     ++	check_commit_count start..HEAD 1 &&
     ++	test_cmp_rev "$other_before" other
     ++'
     ++
     ++test_expect_success 'refuses to fold a range a branch points into' '
     ++	test_when_finished \
     ++		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
     ++		 git branch -D feature" &&
     ++	git checkout -f -b feature start &&
     ++	test_commit C1 &&
     ++	test_commit C2 &&
     ++	git checkout -b topic-1 start &&
     ++	test_commit C3 &&
     ++	test_commit C4 &&
     ++	git checkout C3 &&
     ++	test_commit C5 &&
     ++	git checkout feature &&
     ++	git merge C5 &&
     ++	test_commit C6 &&
     ++	git checkout -b topic-2 C2 &&
     ++	test_commit C7 &&
     ++	git checkout feature &&
      +
      +	test_must_fail git history squash start.. 2>err &&
     -+	test_grep "error: .* points into the squashed range" err &&
     -+	test_grep "hint: .*--update-refs=head" err &&
     -+	test_cmp_rev "$head_before" HEAD &&
     ++	# TODO: check the branch names when we print them (topic-1 & topic-2)
     ++	test_grep "^error: a branch points to" err &&
     ++	test_grep "^hint: .* --update-refs=head" err &&
     ++	test_cmp_rev C6 HEAD &&
     ++
     ++	# squash succeeds with --update-refs=head
     ++	git history squash --no-edit --update-refs=head start.. &&
     ++	test_cmp_rev start HEAD^ &&
     ++	test_cmp_rev C6^{tree} HEAD^{tree} &&
     ++	test_cmp_rev C6 HEAD@{1}
     ++'
     ++
     ++test_expect_success 'advice.historyUpdateRefs silences the hint' '
     ++	git reset --hard three &&
     ++	git branch -f mid HEAD~1 &&
     ++	head_before=$(git rev-parse HEAD) &&
      +
      +	test_must_fail git -c advice.historyUpdateRefs=false \
      +		history squash start.. 2>err &&
     -+	test_grep "points into the squashed range" err &&
     ++	test_grep "^error: a branch points to" err &&
      +	test_grep ! "hint:" err &&
      +	test_cmp_rev "$head_before" HEAD &&
      +
     -+	git history squash --no-edit --update-refs=head start.. &&
     -+
     -+	check_commit_count start..HEAD 1 &&
     -+	test_cmp_rev "$other_before" other &&
     -+	test_cmp_rev "$mid_before" mid &&
     -+
     -+	git branch -D other mid
     ++	git branch -D mid
      +'
      +
      +test_expect_success 'leaves tags and remote-tracking refs unchanged' '
     @@ t/t3455-history-squash.sh (new)
      +	git update-ref -d refs/remotes/origin/mark
      +'
      +
     -+test_expect_success 'handles a branch pointing at an internal merge' '
     ++test_expect_success 'squashes a range whose internal merge has a single base' '
      +	git reset --hard start &&
      +	main=$(git symbolic-ref --short HEAD) &&
      +	test_commit --no-tag before-side file b &&
     @@ t/t3455-history-squash.sh (new)
      +	test_commit --no-tag after-side file c &&
      +	git merge --no-ff -m merge inner-side &&
      +	git branch -D inner-side &&
     -+	git branch at-merge HEAD &&
      +	test_commit --no-tag after-merge file d &&
     -+	head_before=$(git rev-parse HEAD) &&
      +	tip_tree=$(git rev-parse HEAD^{tree}) &&
      +
     -+	test_must_fail git history squash start.. 2>err &&
     -+	test_grep "at-merge" err &&
     -+	test_grep "points into the squashed range" err &&
     -+	test_cmp_rev "$head_before" HEAD &&
     -+	git branch -D at-merge &&
     -+
      +	git history squash --no-edit start.. &&
      +
      +	check_commit_count start..HEAD 1 &&
     @@ t/t3455-history-squash.sh (new)
      +	merged=$(git rev-parse HEAD) &&
      +
      +	test_must_fail git history squash "$base.." 2>err &&
     -+	test_grep "more than one base" err &&
     ++	test_grep "parent .* of commit .* is outside the revision range" err &&
      +	test_cmp_rev "$merged" HEAD
      +'
      +
     @@ t/t3455-history-squash.sh (new)
      +	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
      +'
      +
     ++test_expect_success 'folds a range with two interior merges' '
     ++	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
     ++	test_commit --no-tag two-merge-a file a1 &&
     ++	git checkout -b two-merge-s1 &&
     ++	test_commit --no-tag two-merge-s1 s1 x &&
     ++	git checkout "$main" &&
     ++	git merge --no-ff -m "merge s1" two-merge-s1 &&
     ++	test_commit --no-tag two-merge-b file b1 &&
     ++	git checkout -b two-merge-s2 &&
     ++	test_commit --no-tag two-merge-s2 s2 y &&
     ++	git checkout "$main" &&
     ++	git merge --no-ff -m "merge s2" two-merge-s2 &&
     ++	git branch -D two-merge-s1 two-merge-s2 &&
     ++	tip_tree=$(git rev-parse HEAD^{tree}) &&
     ++
     ++	git history squash --no-edit start.. &&
     ++
     ++	check_commit_count start..HEAD 1 &&
     ++	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
     ++	test_path_is_file s1 &&
     ++	test_path_is_file s2
     ++'
     ++
      +test_expect_success 'folds a range with a nested merge' '
      +	git reset --hard start &&
      +	main=$(git symbolic-ref --short HEAD) &&
     @@ t/t3455-history-squash.sh (new)
      +	git branch -D octo-pre octo-within &&
      +
      +	test_must_fail git history squash "$octo_base.." 2>err &&
     -+	test_grep "more than one base" err &&
     ++	test_grep "parent .* of commit .* is outside the revision range" err &&
      +	test_cmp_rev "$merged" HEAD
      +'
      +
     @@ t/t3455-history-squash.sh (new)
      +	test_cmp_rev "$head_before" HEAD
      +'
      +
     ++test_expect_success 'refuses to fold a range a ref points into at a merge' '
     ++	git reset --hard start &&
     ++	main=$(git symbolic-ref --short HEAD) &&
     ++	test_commit --no-tag refmerge-base file b &&
     ++	git checkout -b refmerge-side &&
     ++	test_commit --no-tag refmerge-side side x &&
     ++	git checkout "$main" &&
     ++	test_commit --no-tag refmerge-main file c &&
     ++	git merge --no-ff -m "interior merge" refmerge-side &&
     ++	git branch -D refmerge-side &&
     ++	git branch at-merge HEAD &&
     ++	test_commit --no-tag refmerge-tail file d &&
     ++	head_before=$(git rev-parse HEAD) &&
     ++
     ++	test_must_fail git history squash start.. 2>err &&
     ++	# TODO: test for branch nome "at-merge"
     ++	test_grep "a branch points to a commit" err &&
     ++	test_cmp_rev "$head_before" HEAD &&
     ++
     ++	git branch -D at-merge
     ++'
     ++
      +test_done

-- 
gitgitgadget

[PATCH v12 1/4] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 000155ad9c..c22715d848 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -164,6 +164,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -171,21 +190,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -475,18 +484,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -830,16 +831,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v12 2/4] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index c22715d848..a60e8dbcd0 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -108,6 +108,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -137,13 +138,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -196,7 +200,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -675,7 +679,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -886,7 +890,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -903,7 +907,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v12 3/4] sequencer: share the squash message marker helpers and flags

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

When "git rebase -i" squashes commits it builds an editor template with a
"This is a combination of N commits." banner, a "This is the 1st/Nth
commit message:" header above each kept message (or a "will be skipped"
header for a dropped one), and a commented-out subject for any fixup!,
squash! or amend! commit. The banner, the headers and the
subject-commenting all live in static helpers in sequencer.c wired to the
rebase state, so no other command can present a squash the same way.

Pull the three pieces out into add_squash_combination_header(),
add_squash_message_header() (which takes a flag for the "will be skipped"
variant) and squash_subject_comment_len(), and use them from
update_squash_messages() and append_squash_message(). Also move the
todo_item_flags enum to the header, so a caller reading the output of
todo_list_rearrange_squash() can tell an amend! (TODO_REPLACE_FIXUP_MSG)
from a plain fixup!. A later change reuses all of this to give "git
history squash" the same template.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 sequencer.c | 70 +++++++++++++++++++++++++++++------------------------
 sequencer.h | 30 +++++++++++++++++++++++
 2 files changed, 69 insertions(+), 31 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 82ab3c536f..642dfa9d91 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1880,18 +1880,38 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
-enum todo_item_flags {
-	TODO_EDIT_MERGE_MSG    = (1 << 0),
-	TODO_REPLACE_FIXUP_MSG = (1 << 1),
-	TODO_EDIT_FIXUP_MSG    = (1 << 2),
-};
-
 static const char first_commit_msg_str[] = N_("This is the 1st commit message:");
 static const char nth_commit_msg_fmt[] = N_("This is the commit message #%d:");
 static const char skip_first_commit_msg_str[] = N_("The 1st commit message will be skipped:");
 static const char skip_nth_commit_msg_fmt[] = N_("The commit message #%d will be skipped:");
 static const char combined_commit_msg_fmt[] = N_("This is a combination of %d commits.");
 
+void add_squash_combination_header(struct strbuf *buf, int n)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	strbuf_addf(buf, _(combined_commit_msg_fmt), n);
+}
+
+void add_squash_message_header(struct strbuf *buf, int n, int skip)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	if (n == 1)
+		strbuf_addstr(buf, skip ? _(skip_first_commit_msg_str) :
+				   _(first_commit_msg_str));
+	else
+		strbuf_addf(buf, skip ? _(skip_nth_commit_msg_fmt) :
+			    _(nth_commit_msg_fmt), n);
+}
+
+size_t squash_subject_comment_len(const char *body, int squashing)
+{
+	if (starts_with(body, "amend!") ||
+	    (squashing && (starts_with(body, "squash!") ||
+			   starts_with(body, "fixup!"))))
+		return commit_subject_length(body);
+	return 0;
+}
+
 static int is_fixup_flag(enum todo_command command, unsigned flag)
 {
 	return command == TODO_FIXUP && ((flag & TODO_REPLACE_FIXUP_MSG) ||
@@ -2005,20 +2025,13 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 {
 	struct replay_ctx *ctx = opts->ctx;
 	const char *fixup_msg;
-	size_t commented_len = 0, fixup_off;
-	/*
-	 * amend is non-interactive and not normally used with fixup!
-	 * or squash! commits, so only comment out those subjects when
-	 * squashing commit messages.
-	 */
-	if (starts_with(body, "amend!") ||
-	    ((command == TODO_SQUASH || seen_squash(ctx)) &&
-	     (starts_with(body, "squash!") || starts_with(body, "fixup!"))))
-		commented_len = commit_subject_length(body);
+	size_t commented_len, fixup_off;
+
+	commented_len = squash_subject_comment_len(body,
+				command == TODO_SQUASH || seen_squash(ctx));
 
-	strbuf_addf(buf, "\n%s ", comment_line_str);
-	strbuf_addf(buf, _(nth_commit_msg_fmt),
-		    ++ctx->current_fixup_count + 1);
+	strbuf_addch(buf, '\n');
+	add_squash_message_header(buf, ++ctx->current_fixup_count + 1, 0);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len, comment_line_str);
 	/* buf->buf may be reallocated so store an offset into the buffer */
@@ -2083,9 +2096,8 @@ static int update_squash_messages(struct repository *r,
 		eol = !starts_with(buf.buf, comment_line_str) ?
 			buf.buf : strchrnul(buf.buf, '\n');
 
-		strbuf_addf(&header, "%s ", comment_line_str);
-		strbuf_addf(&header, _(combined_commit_msg_fmt),
-			    ctx->current_fixup_count + 2);
+		add_squash_combination_header(&header,
+					      ctx->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);
 		if (is_fixup_flag(command, flag) && !seen_squash(ctx))
@@ -2109,12 +2121,9 @@ static int update_squash_messages(struct repository *r,
 			repo_unuse_commit_buffer(r, head_commit, head_message);
 			return error(_("cannot write '%s'"), rebase_path_fixup_msg());
 		}
-		strbuf_addf(&buf, "%s ", comment_line_str);
-		strbuf_addf(&buf, _(combined_commit_msg_fmt), 2);
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addstr(&buf, is_fixup_flag(command, flag) ?
-			      _(skip_first_commit_msg_str) :
-			      _(first_commit_msg_str));
+		add_squash_combination_header(&buf, 2);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, 1, is_fixup_flag(command, flag));
 		strbuf_addstr(&buf, "\n\n");
 		if (is_fixup_flag(command, flag))
 			strbuf_add_commented_lines(&buf, body, strlen(body),
@@ -2133,9 +2142,8 @@ static int update_squash_messages(struct repository *r,
 	if (command == TODO_SQUASH || is_fixup_flag(command, flag)) {
 		res = append_squash_message(&buf, body, command, opts, flag);
 	} else if (command == TODO_FIXUP) {
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),
-			    ++ctx->current_fixup_count + 1);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, ++ctx->current_fixup_count + 1, 1);
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body),
 					   comment_line_str);
diff --git a/sequencer.h b/sequencer.h
index 64a9c7fb1b..b01f897020 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,6 +119,13 @@ enum todo_command {
 	TODO_COMMENT
 };
 
+/* Bits for the "flags" member of struct todo_item */
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG    = (1 << 0),
+	TODO_REPLACE_FIXUP_MSG = (1 << 1),
+	TODO_EDIT_FIXUP_MSG    = (1 << 2),
+};
+
 struct todo_item {
 	enum todo_command command;
 	struct commit *commit;
@@ -208,6 +215,29 @@ int todo_list_rearrange_squash(struct todo_list *todo_list);
  */
 void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
 
+/*
+ * Append the "This is a combination of N commits." banner that "git rebase
+ * -i" writes at the top of a squashed commit's message, commented out with
+ * the comment character.
+ */
+void add_squash_combination_header(struct strbuf *buf, int n);
+
+/*
+ * Append the header (1-based N) that "git rebase -i" writes above each message
+ * when squashing, commented out with the comment character. With SKIP it reads
+ * "The ... commit message will be skipped" for a message that is dropped (a
+ * fixup), otherwise "This is the ... commit message".
+ */
+void add_squash_message_header(struct strbuf *buf, int n, int skip);
+
+/*
+ * Return the length of the leading subject of BODY when it should be commented
+ * out in a squash message, or 0 otherwise. An "amend!" subject always
+ * qualifies; "squash!" and "fixup!" subjects only when SQUASHING, since a
+ * plain fixup chain keeps them.
+ */
+size_t squash_subject_comment_len(const char *body, int squashing);
+
 void append_conflicts_hint(struct index_state *istate,
 		struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
 enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,
-- 
gitgitgadget

[PATCH v12 4/4] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Folding a series of commits into one required either an interactive
rebase where each commit after the first was hand-edited to "fixup", or
a "git reset --soft" to the merge base followed by "git commit --amend".

Add "git history squash <revision-range>" to do this directly. It folds
every selected commit into one, preserving the authorship and parents of
the oldest commit and taking the tree of the tip, then replays commits
above the range. By default an editor opens with every folded message in
the same template used by "git rebase -i --autosquash". With --no-edit,
the selected message is used without opening an editor.

Resolve fixup!, squash! and amend! subjects directly while walking the
selected commits. A marker is rejected unless its fixed target is also
selected, except that a range made up entirely of related markers can be
consolidated. Without editing, refuse any squash! or amend! whose message
would be discarded.

Read the range like arguments to "git rev-list" and accept multiple
revisions and rev-list options. Restore the walk settings required by the
fold after setup_revisions(), warning when an option changed them. The
range must name a bottom commit, must not reach a root, and must have one
tip. Every parent after the oldest commit must be selected or also be a
parent of the oldest commit. This permits internal merges and preserves
all parents when the oldest commit is itself a merge.

By default, refuse when a local branch descends from the selected commits
but cannot remain a descendant of the result. Tags and remote-tracking
refs are left unchanged. Use --update-refs=head to leave such local
branches unchanged as well.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  59 ++-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 611 +++++++++++++++++++++
 object.h                         |   1 +
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 884 +++++++++++++++++++++++++++++++
 8 files changed, 1560 insertions(+), 2 deletions(-)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 81f80a9274..e2a3487778 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -59,6 +59,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a ref points
+		into the range being folded, to tell the user about
+		`--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 28b477cd37..2e2e31f521 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -12,6 +12,7 @@ git history drop <commit> [--dry-run] [--update-refs=(branches|head)] [--empty=(
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>
 
 DESCRIPTION
 -----------
@@ -43,8 +44,11 @@ at once.
 LIMITATIONS
 -----------
 
-This command does not (yet) work with histories that contain merges. You
-should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
+This command does not (yet) replay merge commits onto the rewritten
+history: if a commit that would be replayed is a merge, the operation is
+rejected, and you should use linkgit:git-rebase[1] with the
+`--rebase-merges` flag instead. The `squash` subcommand can still fold merges
+that lie inside the selected range, subject to the restrictions below.
 
 Furthermore, the command does not support operations that can result in merge
 conflicts. This limitation is by design as history rewrites are not intended to
@@ -113,6 +117,51 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's authorship and
+	takes the tree of the range's newest commit, so the whole range
+	collapses into a single commit. Commits above the range are replayed
+	on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash HEAD~3..HEAD` folds the three most recent commits into
+one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
+while leaving the two newest commits in place. Several revisions may be
+given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
+already on `topic`. Rev-list options may also be given, but any that would
+change how the range is walked are overridden with a warning.
++
+An editor opens pre-filled with the messages of all the folded commits so you
+can combine them. With `--no-edit`, the oldest commit's message is preserved
+instead, except that an `amend!` commit targeting it replaces its message.
++
+The selected commits must form a connected graph with a single tip and must
+not include a root commit. Every parent of a commit after the oldest one must
+either be selected or also be a parent of the oldest commit. When the oldest
+commit is a merge, all of its parents are preserved in the squashed commit.
++
+A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
+targets is also in the range, so the fold does not silently absorb a
+marker meant for a commit outside it. As an exception, a range made up entirely
+of markers for one target is combined into a single commit. With `--no-edit`,
+the last `amend!` message is used if there is one; a `squash!` or `amend!` is
+otherwise refused if folding it would discard its message.
++
+The editor template mirrors `git rebase -i --autosquash`: each `fixup!`,
+`squash!`, or `amend!` is grouped under the commit it targets rather than
+shown in commit order. A `fixup!` message is dropped (commented out in full),
+a `squash!` keeps its body with only the marker subject commented, and an
+`amend!` replaces its target's message, unless a `squash!` folded into that
+target first, in which case it keeps its body like a `squash!`.
++
+A local branch descended from a selected commit but not from the range tip
+cannot be rewritten as a descendant of the result, so with the default
+`--update-refs=branches` the command refuses. Rerun with `--update-refs=head`
+to rewrite only the current branch and leave such branches unchanged. Tags
+and remote-tracking refs are always left unchanged.
+
 OPTIONS
 -------
 
@@ -122,6 +171,12 @@ OPTIONS
 	objects will be written into the repository, so applying these printed
 	ref updates is generally safe.
 
+`--edit`::
+`--no-edit`::
+	For `squash`, open an editor to combine the messages of the folded commits.
+	This is the default; use `--no-edit` to keep the selected message without
+	opening an editor.
+
 `--reedit-message`::
 	Open an editor to modify the target commit's message.
 
diff --git a/advice.c b/advice.c
index 63bf8b0c5f..401d047391 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 66f6cd6a77..3f0b4f0485 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index a60e8dbcd0..4c1f089d9f 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -16,6 +17,7 @@
 #include "path.h"
 #include "read-cache.h"
 #include "refs.h"
+#include "ref-filter.h"
 #include "replay.h"
 #include "reset.h"
 #include "revision.h"
@@ -34,6 +36,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -1004,6 +1008,611 @@ out:
 	return ret;
 }
 
+/*Remember to update object flag allocation in object.h */
+#define SQUASH_SEEN (1u << 11)
+#define SQUASH_TIP (1u << 12)
+#define SQUASH_AMEND_TARGET (1u << 13)
+
+static bool is_autosquash_subject(const char *s)
+{
+	return starts_with(s, "amend!") || starts_with(s, "fixup!") ||
+		starts_with(s, "squash!");
+}
+
+static bool skip_one_autosquash_prefix(const char *s, const char **out)
+{
+	if (skip_prefix(s, "amend!", out) || skip_prefix(s, "fixup!", out) ||
+	    skip_prefix(s, "squash!", out)) {
+		while (**out == ' ')
+			(*out)++;
+		return true;
+	}
+	return false;
+}
+
+static void truncate_message_to_subject(struct strbuf *msg)
+{
+	const char *eos = strstr(msg->buf, "\n\n");
+
+	if (eos)
+		strbuf_setlen(msg, eos - msg->buf + 1);
+}
+
+struct subject_data {
+	struct strintmap subjects;
+	struct strbuf subject;
+	struct strbuf squash_message;
+	const char *message;
+	bool edit_message;
+};
+
+#define SUBJECT_DATA_INIT {		\
+	.subjects = STRINTMAP_INIT,	\
+	.subject = STRBUF_INIT,		\
+	.squash_message = STRBUF_INIT,	\
+}
+
+static void subject_data_clear(struct subject_data *data)
+{
+	strintmap_clear(&data->subjects);
+	strbuf_release(&data->subject);
+	strbuf_release(&data->squash_message);
+}
+
+static int squash_amend_message(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data,
+				unsigned flags)
+{
+	const char *body = data->message + data->subject.len;
+
+	while (isspace(*body))
+		body++;
+
+	if (!*body) {
+		warning(_("ignoring %s (%s): message body is empty"),
+			repo_find_unique_abbrev(repo, &commit->object.oid,
+						DEFAULT_ABBREV),
+			data->subject.buf);
+		return 0;
+	}
+
+	if (data->edit_message) {
+		return 0;
+	} else if (flags & SQUASH_AMEND_TARGET) {
+		if (starts_with(data->squash_message.buf, "squash!"))
+			return error(_("squashing %s (%s) would overwrite "
+				       "'squash!' message, please combine them "
+				       "using '--edit'"),
+				     repo_find_unique_abbrev(repo,
+							     &commit->object.oid,
+							     DEFAULT_ABBREV),
+				     data->subject.buf);
+		if (starts_with(data->squash_message.buf, "fixup!"))
+			strbuf_splice(&data->squash_message, 0, 5, "amend!", 5);
+		if (starts_with(data->squash_message.buf, "amend!")) {
+			truncate_message_to_subject(&data->squash_message);
+			strbuf_addch(&data->squash_message, '\n');
+		} else {
+			strbuf_reset(&data->squash_message);
+		}
+		strbuf_addstr(&data->squash_message, body);
+		strbuf_complete_line(&data->squash_message);
+	} else {
+		return error(_("cannot squash %s (%s) that does not target "
+			       "base commit without '--edit'"),
+			     repo_find_unique_abbrev(repo, &commit->object.oid,
+						     DEFAULT_ABBREV),
+			     data->subject.buf);
+	}
+	return 0;
+}
+
+static int squash_squash_message(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data,
+				unsigned flags)
+{
+	const char *body = data->message + data->subject.len;
+
+	while (isspace(*body))
+		body++;
+
+	if (data->edit_message) {
+		return 0;
+	} else if (flags & SQUASH_AMEND_TARGET) {
+		if (starts_with(data->squash_message.buf, "fixup!")) {
+			truncate_message_to_subject(&data->squash_message);
+			strbuf_splice(&data->squash_message, 0, 5, "squash", 6);
+		}
+		if (starts_with(data->squash_message.buf, "squash!")) {
+			strbuf_addch(&data->squash_message, '\n');
+			strbuf_addstr(&data->squash_message, body);
+			strbuf_complete_line(&data->squash_message);
+		} else {
+			return error(_("squashing %s (%s) would discard its "
+				       "message, please combine them using "
+				       "'--edit'"),
+				     repo_find_unique_abbrev(repo,
+							     &commit->object.oid,
+							     DEFAULT_ABBREV),
+				     data->subject.buf);
+		}
+	} else {
+		return error(_("cannot squash %s (%s) that does not target "
+			       "base commit without '--edit'"),
+			      repo_find_unique_abbrev(repo, &commit->object.oid,
+						      DEFAULT_ABBREV),
+			      data->subject.buf);
+	}
+	return 0;
+}
+
+static int squash_check_can_autosquash(struct repository *repo,
+				       struct commit *commit,
+				       struct subject_data *data,
+				       unsigned flags)
+{
+	commit->object.flags |= flags & SQUASH_AMEND_TARGET;
+	if (starts_with(data->subject.buf, "amend!"))
+		return squash_amend_message(repo, commit, data, flags);
+	else if (starts_with(data->subject.buf, "squash!"))
+		return squash_squash_message(repo, commit, data, flags);
+
+	return 0;
+}
+
+static int squash_check_autosquash_subject(struct repository *repo,
+					   struct commit *commit,
+					   struct subject_data *data)
+{
+	const char* s = data->subject.buf;
+	struct commit *target;
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+	/* Try skipping autosquash prefixes one at a time to allow
+	 * squashing
+	 *     a commit
+	 *     fixup! fixup! a commit
+	 *
+	 * where we may have started with
+	 *     a commit
+	 *     fixup! a commit
+	 *     fixup! fixup! a commit
+	 *
+	 * and squashed the first fixup separately from the second
+	 */
+	while (skip_one_autosquash_prefix(s, &s)) {
+		unsigned flags = strintmap_get(&data->subjects, s);
+		if (flags)
+			return squash_check_can_autosquash(repo, commit, data, flags);
+	}
+	/*
+	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
+	 * "fixup! main". If the target is not being squshed check the subject
+	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
+	 * squashed together.
+	 */
+	target = lookup_commit_reference_by_name(s);
+	if (target && istarts_with(oid_to_hex(&target->object.oid), s)) {
+		unsigned flags =
+			target->object.flags & (SQUASH_SEEN | SQUASH_AMEND_TARGET);
+		if (!flags) {
+			const char *subject_start;
+			const char *buffer = repo_logmsg_reencode(repo, target,
+								  NULL, NULL);
+			size_t subject_len = find_commit_subject(buffer,
+								 &subject_start);
+			char *subject = xmemdupz(subject_start, subject_len);
+
+			flags = strintmap_get(&data->subjects, subject);
+			free(subject);
+			repo_unuse_commit_buffer(repo, target, buffer);
+		}
+		if (flags)
+			return squash_check_can_autosquash(repo, commit,
+							   data, flags);
+	}
+	/* Try subject prefix matches */
+	strintmap_for_each_entry(&data->subjects, &iter, entry) {
+		s = data->subject.buf;
+		while(skip_one_autosquash_prefix(s, &s)) {
+			if (starts_with(entry->key, s)) {
+				unsigned value = (intptr_t)entry->value;
+
+				return squash_check_can_autosquash(repo, commit,
+								   data, value);
+			}
+		}
+	}
+	return error(_("cannot squash %s (%s): its target is not being "
+		       "squashed"),
+		       repo_find_unique_abbrev(repo, &commit->object.oid,
+					       DEFAULT_ABBREV),
+		       data->subject.buf);
+}
+
+static int squash_check_subject(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data)
+{
+	int ret = 0;
+	const char *buf = repo_logmsg_reencode(repo, commit, NULL, NULL);
+	size_t subject_len = find_commit_subject(buf, &data->message);
+
+	strbuf_reset(&data->subject);
+	strbuf_add(&data->subject, data->message, subject_len);
+
+	if (!strintmap_get_size(&data->subjects)) {
+		const char *s;
+
+		strbuf_addstr(&data->squash_message, data->message);
+		strbuf_complete_line(&data->squash_message);
+		/*
+		 * Strip a single autosquash prefix to allow squashing
+		 *     fixup! base
+		 *     amend! base
+		 */
+		s = data->subject.buf;
+		skip_one_autosquash_prefix(s, &s);
+		strintmap_set(&data->subjects, s, SQUASH_AMEND_TARGET | SQUASH_SEEN);
+		commit->object.flags |= SQUASH_AMEND_TARGET;
+	} else if (is_autosquash_subject(data->subject.buf)) {
+		ret = squash_check_autosquash_subject(repo, commit, data);
+	} else {
+		strintmap_set(&data->subjects, data->subject.buf, SQUASH_SEEN);
+	}
+	repo_unuse_commit_buffer(repo, commit, buf);
+	return ret;
+}
+
+static int build_squash_message(struct repository *repo,
+				const struct strbuf *todo_buf,
+				struct strbuf *out);
+
+/*
+ * Resolve a "<base>..<tip>" revision range into the base commit just outside
+ * the range (which becomes the parent of the squashed commit), the oldest
+ * commit contained in the range (whose message the squash reuses), and the
+ * range tip (whose tree becomes the result). A merge inside the range is fine,
+ * but the range must have a single base and must not reach a root commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				bool update_branches,
+				bool edit_message,
+				int argc, const char **argv,
+				struct commit **oldest_out,
+				struct commit **tip_out,
+				char **message_out)
+{
+	struct rev_info revs;
+	struct subject_data subject_data = SUBJECT_DATA_INIT;
+	struct commit *commit, *oldest = NULL, *tip = NULL;
+	struct strbuf todo_buf = STRBUF_INIT;
+	size_t i;
+	int ret, tip_count = 0;
+	struct ref_filter filter = REF_FILTER_INIT;
+	struct ref_array refs = { 0 };
+
+	repo_init_revisions(repo, &revs, NULL);
+	subject_data.edit_message = edit_message;
+	revs.reverse = 1;
+	revs.topo_order = 1;
+	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+	revs.simplify_history = 0;
+	revs.ancestry_path = 1;
+	revs.limited = 1;
+	revs.ancestry_path_implicit_bottoms = 1;
+
+	argc = setup_revisions(argc, argv, &revs, NULL);
+	if (argc > 1) {
+		ret = error(_("unrecognized argument: %s"), argv[1]);
+		goto out;
+	}
+
+	if (revs.reverse != 1 || revs.topo_order != 1 ||
+	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
+	    revs.simplify_history != 0 || revs.boundary == 1 ||
+	    revs.ancestry_path != 1 || revs.limited != 1 ||
+	    revs.ancestry_path_implicit_bottoms != 1) {
+		warning(_("ignoring rev-list options that would change how the "
+			  "range is walked"));
+		revs.reverse = 1;
+		revs.topo_order = 1;
+		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+		revs.simplify_history = 0;
+		revs.boundary = 0;
+		revs.ancestry_path = 1;
+		revs.limited = 1;
+		revs.ancestry_path_implicit_bottoms = 1;
+	}
+
+	/*
+	 * A squash needs a base to reparent onto, so the range has to exclude
+	 * something, as in "<base>..<tip>". A revision range with no such
+	 * bottom commit cannot be squashed.
+	 */
+	for (i = 0; i < revs.cmdline.nr; i++)
+		if (revs.cmdline.rev[i].flags & BOTTOM)
+			break;
+	if (i == revs.cmdline.nr) {
+		ret = error(_("not a '<base>..<tip>' revision range"));
+		goto out;
+	}
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+	while ((commit = get_revision(&revs))) {
+		struct commit_list *p;
+
+		if (edit_message)
+			strbuf_addf(&todo_buf, "pick %s\n",
+				    oid_to_hex(&commit->object.oid));
+
+		if (!commit->parents) {
+			ret = error(_("cannot squash down to root commit"));
+			goto out;
+		}
+		for (p = commit->parents; oldest && p; p = p->next) {
+			struct commit_list *q;
+			struct object *o;
+			bool seen;
+
+			if (repo_parse_commit(repo, p->item)) {
+				ret = error(_("cannot parse commit"));
+				goto out;
+			}
+			o = &p->item->object;
+			seen = o->flags & SQUASH_SEEN;
+			/*
+			 * Allow parents that match the parents of the
+			 * squashed commit.
+			 */
+			for (q = oldest->parents; !seen && q; q = q->next) {
+				if (p->item == q->item) {
+					seen = true;
+					commit_list_insert(commit, &filter.with_commit);
+				}
+			}
+			if (!seen) {
+				ret = error(_("parent %s of commit %s is "
+					      "outside the revision range"),
+					    repo_find_unique_abbrev(repo, &o->oid,
+								    DEFAULT_ABBREV),
+					    repo_find_unique_abbrev(repo, &commit->object.oid,
+								    DEFAULT_ABBREV));
+				goto out;
+			}
+			if (o->flags & SQUASH_TIP) {
+				tip_count--;
+				o->flags &= ~SQUASH_TIP;
+			}
+		}
+		if (!oldest) {
+			commit_list_insert(commit, &filter.with_commit);
+			oldest = commit;
+		}
+		if (squash_check_subject(repo, commit, &subject_data)) {
+			ret = -1;
+			goto out;
+		}
+		tip = commit;
+		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
+		tip_count++;
+	}
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP | SQUASH_AMEND_TARGET);
+	reset_revision_walk();
+	if (!tip_count) {
+		ret = error(_("the revision range is empty"));
+		goto out;
+	} else if (tip_count != 1) {
+		  ret = error(_("the revision range contains more than one tip "
+				"commit"));
+		  goto out;
+	  } else if (oldest == tip) {
+		ret = error(_("the revision range holds a single commit; "
+			      "nothing to squash"));
+		goto out;
+	} else if (!oldest->parents) {
+		BUG("an in-range commit must have a parent");
+	}
+	commit_list_insert(tip, &filter.no_commit);
+	filter.kind = FILTER_REFS_BRANCHES;
+	if (update_branches &&
+	    filter_refs(&refs, &filter, filter.kind)) {
+		ret = error(_("could not filter refs"));
+		goto out;
+	}
+	if (refs.nr) {
+		/*
+		 * TODO: list the branches and also check HEADS from other worktrees
+		 */
+		ret = error(_("a branch points to a commit that is being squashed"));
+		advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+				  _("Use --update-refs=head to rewrite only "
+				    "the current branch and leave such refs "
+				    "untouched."));
+		goto out;
+	}
+	if (edit_message) {
+		strbuf_reset(&subject_data.squash_message);
+		ret = build_squash_message(repo, &todo_buf,
+					   &subject_data.squash_message);
+		if (ret < 0)
+			goto out;
+	}
+	*oldest_out = oldest;
+	*tip_out = tip;
+	*message_out = strbuf_detach(&subject_data.squash_message, NULL);
+	ret = 0;
+
+out:
+	strbuf_release(&todo_buf);
+	subject_data_clear(&subject_data);
+	release_revisions(&revs);
+	ref_filter_clear(&filter);
+	ref_array_clear(&refs);
+	return ret;
+}
+
+static bool amend_replaces_target(struct todo_list *todo, int target)
+{
+	int i;
+
+	for (i = target + 1; i < todo->nr &&
+			     todo->items[i].command != TODO_PICK; i++) {
+		if (todo->items[i].command == TODO_SQUASH)
+			return false;
+		if (todo->items[i].flags & TODO_REPLACE_FIXUP_MSG)
+			return true;
+	}
+	return false;
+}
+
+static int build_squash_message(struct repository *repo,
+				const struct strbuf *todo_buf,
+				struct strbuf *out)
+{
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	int i, nr_commits, ret;
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo_buf->buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not prepare the squash message"));
+		goto out;
+	}
+
+	nr_commits = todo.nr;
+	for (i = 0; i < nr_commits; i++) {
+		struct todo_item *item = &todo.items[i];
+		const char *message, *body;
+		size_t commented_len;
+		bool skip, squashing;
+
+		squashing = item->command == TODO_SQUASH ||
+			    (item->flags & TODO_REPLACE_FIXUP_MSG);
+		if (item->command == TODO_PICK)
+			skip = amend_replaces_target(&todo, i);
+		else
+			skip = !squashing;
+
+		message = repo_logmsg_reencode(repo, item->commit, NULL, NULL);
+		find_commit_subject(message, &body);
+
+		if (skip)
+			commented_len = strlen(body);
+		else if (squashing)
+			commented_len = squash_subject_comment_len(body, 1);
+		else
+			commented_len = 0;
+
+		if (!i)
+			add_squash_combination_header(out, nr_commits);
+		strbuf_addch(out, '\n');
+		add_squash_message_header(out, i + 1, skip);
+		strbuf_addstr(out, "\n\n");
+		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
+		strbuf_addstr(out, body + commented_len);
+		strbuf_complete_line(out);
+
+		repo_unuse_commit_buffer(repo, item->commit, message);
+	}
+
+	ret = 0;
+
+out:
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	return ret;
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	int dry_run = 0;
+	int edit = 1;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BOOL('e', "edit", &edit,
+			 N_("edit the commit message")),
+		OPT_END(),
+	};
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct commit *oldest, *tip, *rewritten;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	char *message_template = NULL;
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage,
+			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
+	if (argc < 2) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
+
+	strbuf_addstr(&reflog_msg, "squash: updating ");
+	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
+
+	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
+				   edit,
+				   argc, argv, &oldest, &tip,
+				   &message_template);
+	if (ret < 0)
+		goto out;
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo,
+					oldest->parents->item)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+
+	ret = commit_tree_ext(repo, "squash", oldest, message_template,
+			      oldest->parents, base_tree_oid, tip_tree_oid,
+			      &rewritten,
+			      edit ? COMMIT_TREE_EDIT_MESSAGE : 0);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
+
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	release_revisions(&revs);
+	free(message_template);
+	return ret;
+}
+
 static int update_worktree(struct repository *repo,
 			   const struct commit *old_head,
 			   const struct commit *new_head,
@@ -1192,6 +1801,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -1200,6 +1810,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
diff --git a/object.h b/object.h
index 8fb03ff90a..46cade33fb 100644
--- a/object.h
+++ b/object.h
@@ -74,6 +74,7 @@ void object_array_init(struct object_array *array);
  * bisect.c:                                        16
  * bundle.c:                                        16
  * http-push.c:                          11-----14
+ * builtin/history.c:                    11---13
  * commit-graph.c:                                15
  * commit-reach.c:                                  16-------20
  * builtin/last-modified.c:                         1617
diff --git a/t/meson.build b/t/meson.build
index a25f37d2f5..78b8ea54ad 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -406,6 +406,7 @@ integration_tests = [
   't3452-history-split.sh',
   't3453-history-fixup.sh',
   't3454-history-drop.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..8638d56dd6
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,884 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+stage_file () {
+	printf "%s\n" "$1" >file &&
+	git add file
+}
+
+commit_with_message () {
+	printf "%b" "$1" >msg &&
+	git commit --allow-empty -qF msg
+}
+
+check_commit_count () {
+	git rev-list --count "$1" >actual &&
+	echo "$2" >expect &&
+	test_cmp expect actual
+}
+
+check_log_subjects () {
+	git log --format="%s" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+check_log_messages () {
+	git log --format="%B" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+# Checks that the author data of two commits matches
+# Usage: check_commit_author <rev1> <rev2>
+check_commit_author () {
+	git show -s --format="%an <%ae> %ad" "$1" >expect &&
+	git show -s --format="%an <%ae> %ad" "$2" >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'setup linear history touching two files' '
+	test_commit base file a start &&
+	GIT_AUTHOR_NAME=One GIT_AUTHOR_EMAIL=one@example.com \
+		test_commit one other x &&
+	GIT_AUTHOR_NAME=Two GIT_AUTHOR_EMAIL=two@example.com \
+		test_commit two file c &&
+	GIT_AUTHOR_NAME=Three GIT_AUTHOR_EMAIL=three@example.com \
+		test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "expects a revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the revision range is empty" err
+'
+
+test_expect_success 'errors on a single revision that is not a range' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "not a .*range" err &&
+	test_must_fail git history squash HEAD~1 2>err &&
+	test_grep "not a .*range" err
+'
+
+test_expect_success 'errors on a range holding a single commit' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "HEAD^!" 2>err &&
+	test_grep "single commit; nothing to squash" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'rejects root commit' '
+	# create a disconnected root commit
+	oid=$(git commit-tree -m root three^{tree}) &&
+	# because we pass --ancestry-path when calling setup_revs() it the
+	# revision walk will only include commits decended from $oid so
+	# we need to give it another --ancestry-path commit to actually walk
+	# any commits.
+	test_must_fail git history squash --ancestry-path=start $oid..three 2>err &&
+	echo "error: cannot squash down to root commit" >expect &&
+	test_cmp expect err
+'
+
+test_expect_success 'rejects multiple tips' '
+	oid=$(git commit-tree -m tip -p start^0 three^{tree}) &&
+	test_must_fail git history squash ^start $oid three~1 2>err &&
+	echo "error: the revision range contains more than one tip commit" >expect &&
+	test_cmp expect err &&
+
+	git reset --hard three &&
+	git history squash --no-edit ^start three~1 three &&
+	test_cmp_rev HEAD~1 start^0 &&
+	test_cmp_rev HEAD^{tree} three^{tree}
+'
+
+test_expect_success 'accepts multiple revision arguments with an exclusion' '
+	git reset --hard three &&
+	git branch -f keep HEAD~2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start..HEAD ^keep &&
+
+	git reflog -1 --format=%gs >actual &&
+	echo "squash: updating start..HEAD ^keep" >expect &&
+	test_cmp expect actual &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	two
+	one
+	EOF
+	test_cmp_rev keep HEAD~1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git branch -D keep
+'
+
+test_expect_success 'squashes a branch the current branch is not on' '
+	git reset --hard three &&
+	main=$(git symbolic-ref --short HEAD) &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b off-history start &&
+	test_commit --no-tag off-one off a &&
+	test_commit --no-tag off-two off b &&
+	git checkout "$main" &&
+
+	git history squash --no-edit start..off-history &&
+
+	check_commit_count start..off-history 1 &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D off-history
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash --no-edit start.. &&
+
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	check_log_subjects -1 <<-\EOF &&
+	one
+	EOF
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'sanitizes rev-list walk options, before and after --' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit --date-order start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git reset --hard three &&
+	git history squash --no-edit -- --reverse start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start..@~1 &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	three
+	one
+	EOF
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit "$root.." &&
+
+	check_commit_count "$root..HEAD" 1 &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashing a mix of fixups' '
+	git reset --hard three &&
+	echo fix >file &&
+	git commit --fixup=two -a &&
+	echo really fix >file &&
+	git commit --fixup=one -a &&
+	echo really really fix >file &&
+	git commit --fixup=HEAD~1 -a && # fixup! two
+	echo really really really fix >file &&
+	git commit --fixup=HEAD~1 -a && # fixup! one
+
+	# squashing fixup! with a target that is not being squashed fails
+	test_must_fail git history squash one.. 2>err &&
+	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
+
+	# squashing fixup! into fixup! with a different target fails
+	test_must_fail git history squash HEAD~4.. 2>err && # HEAD~4 is fixup! two
+	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
+
+	# squashing a sequence of fixup! commits into their targets
+	git history squash --no-edit start..HEAD~1 &&
+	test_cmp_rev start HEAD~2 &&
+	check_commit_author one HEAD~1 &&
+	test_commit_message HEAD~1 -m one &&
+
+	# squashing "fixup! fixup! <target>" into "<target>"
+	git history squash --no-edit start.. &&
+	test_cmp_rev start HEAD~1 &&
+	check_commit_author one HEAD &&
+	test_commit_message HEAD -m one
+'
+
+test_expect_success 'squashing "squash!" messages' '
+	git reset --hard two &&
+	echo fix >file &&
+	git commit --fixup=HEAD -a &&
+	oldest=$(git rev-parse HEAD) &&
+	echo better fix >file &&
+	git commit -a -F - <<-EOF &&
+	squash! $(git rev-parse two)
+
+	Append this
+	EOF
+
+	echo an even better fix >file &&
+	git commit -a -F - <<-EOF &&
+	squash! squash! two
+
+	Append this as well
+	EOF
+
+	# must edit when squashing "squash!" into its target
+	test_must_fail git history squash --no-edit two^.. 2>err &&
+	test_grep "^error: squashing .* (squash! [a-f0-9]*) would discard its message" err &&
+
+	# squashing "squash!" into "fixup!" appends messages and changes
+	# subject prefix
+	git history squash --no-edit two.. &&
+	test_cmp_rev HEAD^ two &&
+	test_commit_message HEAD <<-\EOF &&
+	squash! two
+
+	Append this
+
+	Append this as well
+	EOF
+	check_commit_author "$oldest" HEAD &&
+
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! two
+
+	A new message
+	EOF
+
+	# "amend!" does not replace "squash!"
+	test_must_fail git history squash --no-edit HEAD~2.. 2>err &&
+	test_grep "^error: squashing .* (amend! two) would overwrite .squash!. message" err
+'
+
+test_expect_success '--no-edit uses last "amend!" message without an editor' '
+	git reset --hard three &&
+	write_script editor <<-\EOF &&
+	exit 1
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	echo fix >file &&
+	git commit --author="Fix Me <fix.me@example.com>" --fixup=HEAD -a &&
+	git commit --allow-empty -F - <<-EOF &&
+	amend! $(git rev-parse --short HEAD)
+
+	The first reword
+
+	More detail
+	EOF
+
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! three
+
+	The second reword
+
+	Extra detail
+	EOF
+
+	test_commit WIP &&
+
+	cat >msg <<-EOF &&
+	amend! $(git rev-parse HEAD^ | tr a-f A-F)
+
+	The third reword
+
+	Excruciating detail
+	EOF
+
+	git commit --author="Someone Else <s.else@example.com>" --allow-empty \
+		-F msg &&
+
+	# squashing amend! updates the commit message
+	git history squash --no-edit three^.. &&
+	sed -e 1,2d msg | test_commit_message HEAD &&
+	check_commit_author three HEAD &&
+	test_cmp_rev HEAD^ three^ &&
+
+	# squashing amend! into fixup! updates subject prefix
+	git reset --hard HEAD@{1} &&
+	git history squash --no-edit three.. &&
+	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
+	check_commit_author HEAD@{1}~4 HEAD &&
+	test_cmp_rev HEAD^ three &&
+
+	# squashing amend! into amend! keeps original subject line
+	git reset --hard HEAD@{1} &&
+	git history squash --no-edit HEAD~3.. &&
+	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
+	test_cmp_rev HEAD~3 three &&
+
+	# all amend! messages must target the first commit
+	git reset --hard HEAD@{1} &&
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! WIP
+
+	The real message
+	EOF
+
+	test_must_fail git history squash --no-edit HEAD~4.. 2>err &&
+	test_grep "^error: cannot squash .* that does not target" err &&
+
+	# amend! message that targets commit that is not in range is rejected
+	test_must_fail git history squash --no-edit HEAD~3.. 2>err &&
+	test_grep "^error: cannot squash .* target is not being squashed" err &&
+	test_set_editor :
+'
+
+test_expect_success 'squashing fixups into a merge' '
+	test_when_finished \
+		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
+		 git branch -D feature" &&
+	git checkout -f start &&
+	test_commit F1 &&
+	git checkout -b feature start &&
+	test_commit F2 &&
+	git merge F1 &&
+	echo fixed >F1.t &&
+	cat >msg <<-EOF &&
+	amend! $(git rev-parse HEAD)
+
+	merge F1 and F2
+
+	reworded
+	EOF
+
+	git commit -a -F msg &&
+	git history squash --no-edit HEAD^^! HEAD &&
+	test_cmp_rev HEAD^1 F2 &&
+	test_cmp_rev HEAD^2 F1 &&
+	test_cmp_rev HEAD@{1}^{tree} HEAD^{tree} &&
+	sed 1,2d msg | test_commit_message HEAD
+'
+
+test_expect_success 'edits every message and aborts on an empty result' '
+	git reset --hard start &&
+	stage_file b &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script empty-editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/empty-editor" &&
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "Aborting commit due to empty commit message" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# This is the 1st commit message:
+
+	re-one subject
+
+	re-one body line
+
+	# This is the commit message #2:
+
+	re-two
+
+	# This is the commit message #3:
+
+	re-three
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_subjects -1 <<-\EOF
+	combined
+	EOF
+'
+
+test_expect_success 'handles fixup!, squash! and amend! like rebase' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "fixup! mark-base\n\nfixup body\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+	stage_file e &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	mark-base
+
+	# The commit message #2 will be skipped:
+
+	# fixup! mark-base
+	#
+	# fixup body
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# This is the commit message #4:
+
+	# amend! mark-base
+
+	amended message
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	mark-base
+
+	squash remark
+
+	amended message
+
+	EOF
+'
+
+test_expect_success 'groups fixups under their targets in the editor' '
+	git reset --hard start &&
+	test_commit --no-tag alpha file a1 &&
+	test_commit --no-tag beta file b1 &&
+	stage_file a2 &&
+	commit_with_message "fixup! alpha\n" &&
+	stage_file b2 &&
+	commit_with_message "fixup! beta\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	alpha
+
+	# The commit message #2 will be skipped:
+
+	# fixup! alpha
+
+	# This is the commit message #3:
+
+	beta
+
+	# The commit message #4 will be skipped:
+
+	# fixup! beta
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited
+'
+
+test_expect_success 'lets amend! replace its target message in the editor' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# The 1st commit message will be skipped:
+
+	# mark-base
+
+	# This is the commit message #2:
+
+	# amend! mark-base
+
+	amended message
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	amended message
+
+	squash remark
+
+	EOF
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --no-edit --update-refs=head start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success 'refuses to fold a range a branch points into' '
+	test_when_finished \
+		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
+		 git branch -D feature" &&
+	git checkout -f -b feature start &&
+	test_commit C1 &&
+	test_commit C2 &&
+	git checkout -b topic-1 start &&
+	test_commit C3 &&
+	test_commit C4 &&
+	git checkout C3 &&
+	test_commit C5 &&
+	git checkout feature &&
+	git merge C5 &&
+	test_commit C6 &&
+	git checkout -b topic-2 C2 &&
+	test_commit C7 &&
+	git checkout feature &&
+
+	test_must_fail git history squash start.. 2>err &&
+	# TODO: check the branch names when we print them (topic-1 & topic-2)
+	test_grep "^error: a branch points to" err &&
+	test_grep "^hint: .* --update-refs=head" err &&
+	test_cmp_rev C6 HEAD &&
+
+	# squash succeeds with --update-refs=head
+	git history squash --no-edit --update-refs=head start.. &&
+	test_cmp_rev start HEAD^ &&
+	test_cmp_rev C6^{tree} HEAD^{tree} &&
+	test_cmp_rev C6 HEAD@{1}
+'
+
+test_expect_success 'advice.historyUpdateRefs silences the hint' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "^error: a branch points to" err &&
+	test_grep ! "hint:" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D mid
+'
+
+test_expect_success 'leaves tags and remote-tracking refs unchanged' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	git update-ref refs/remotes/origin/mark HEAD~1 &&
+	mark_before=$(git rev-parse mark) &&
+
+	git history squash --no-edit start.. &&
+
+	test_cmp_rev "$mark_before" mark &&
+	test_cmp_rev "$mark_before" refs/remotes/origin/mark &&
+
+	git tag -d mark &&
+	git update-ref -d refs/remotes/origin/mark
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout "$main" &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	test_commit --no-tag after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF &&
+	before-side
+	EOF
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a merge of a branch that forked at the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b base-fork-side &&
+	test_commit --no-tag base-fork-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag base-fork-main file b &&
+	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
+	git branch -D base-fork-side &&
+	test_commit --no-tag base-fork-tail file c &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'refuses a merge whose other parent is outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "parent .* of commit .* is outside the revision range" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit "$base.." &&
+
+	check_commit_count "$base..HEAD" 1 &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'folds a range with two interior merges' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag two-merge-a file a1 &&
+	git checkout -b two-merge-s1 &&
+	test_commit --no-tag two-merge-s1 s1 x &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s1" two-merge-s1 &&
+	test_commit --no-tag two-merge-b file b1 &&
+	git checkout -b two-merge-s2 &&
+	test_commit --no-tag two-merge-s2 s2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s2" two-merge-s2 &&
+	git branch -D two-merge-s1 two-merge-s2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file s1 &&
+	test_path_is_file s2
+'
+
+test_expect_success 'folds a range with a nested merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b nested-outer &&
+	test_commit --no-tag nested-outer outer x &&
+	git checkout -b nested-inner &&
+	test_commit --no-tag nested-inner inner y &&
+	git checkout nested-outer &&
+	git merge --no-ff -m "merge inner" nested-inner &&
+	git checkout "$main" &&
+	test_commit --no-tag nested-main file b1 &&
+	git merge --no-ff -m "merge outer" nested-outer &&
+	git branch -D nested-outer nested-inner &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file outer &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range with an octopus merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag octo-base file a1 &&
+	git checkout -b octo-1 &&
+	test_commit --no-tag octo-1 o1 x &&
+	git checkout "$main" &&
+	git checkout -b octo-2 &&
+	test_commit --no-tag octo-2 o2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-1 octo-2 &&
+	git branch -D octo-1 octo-2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file o1 &&
+	test_path_is_file o2
+'
+
+test_expect_success 'refuses an octopus merge with an arm forked before the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b octo-pre &&
+	test_commit octo-pre-side pside x &&
+	git checkout "$main" &&
+	test_commit octo-pre-main file b1 &&
+	octo_base=$(git rev-parse HEAD) &&
+	git checkout -b octo-within &&
+	test_commit --no-tag octo-within wside y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-pre octo-within &&
+	merged=$(git rev-parse HEAD) &&
+	git branch -D octo-pre octo-within &&
+
+	test_must_fail git history squash "$octo_base.." 2>err &&
+	test_grep "parent .* of commit .* is outside the revision range" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'refuses when a descendant above the range is a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag desc-one file b &&
+	test_commit --no-tag desc-two file c &&
+	git tag desc-tip &&
+	git checkout -b desc-above &&
+	test_commit --no-tag desc-above above x &&
+	git checkout "$main" &&
+	test_commit --no-tag desc-main file d &&
+	git merge --no-ff -m "merge desc-above" desc-above &&
+	git branch -D desc-above &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash --no-edit start..desc-tip 2>err &&
+	test_grep "merge commits is not supported" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'refuses to fold a range a ref points into at a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag refmerge-base file b &&
+	git checkout -b refmerge-side &&
+	test_commit --no-tag refmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag refmerge-main file c &&
+	git merge --no-ff -m "interior merge" refmerge-side &&
+	git branch -D refmerge-side &&
+	git branch at-merge HEAD &&
+	test_commit --no-tag refmerge-tail file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	# TODO: test for branch nome "at-merge"
+	test_grep "a branch points to a commit" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D at-merge
+'
+
+test_done
-- 
gitgitgadget

[PATCH v13 0/8] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v13:

 * Split the squash implementation into five patches covering parsing, range
   validation, branch protection, commit creation, and message editing.
 * Print the sorted names of local branches that prevent a squash, with
   clearer advice for --update-refs=head.
 * Isolate --no-edit behavior from the final patch that enables default
   editor-based message combining.

Changes in v12:

 * Incorporated fixups from Phillip:
   * Reworks range validation into a single walk that rejects roots and
     multiple tips while preserving every parent when squashing into a
     merge.
   * Resolves fixup!, squash! and amend! targets directly, preserving
     message intent and safely consolidating related markers.
   * Builds the editor template from the exact selected revisions, including
     exclusions, while retaining --no-edit behavior.
   * Protects descendant local branches while leaving tags and
     remote-tracking refs unchanged.

Changes in v11:

 * Make message editing the default with the autosquash-style template, add
   --no-edit instead of squash-specific --reedit-message.
 * Validate one actual boundary and tip, rejecting root-reaching and
   multi-tip ranges.
 * Protect only interior local branches, leaving tags and remote-tracking
   refs unchanged.
 * Move sequencer preparation before squash and fold the later
   message-editing patch into the feature commit.

Changes in v10:

 * Record the full revision expression in squash reflog.
 * Preserve the boundary-walk invariant when sanitizing rev-list options.
 * Clarify amend! and --reedit-message documentation.

Changes in v9:

 * Use the last amend! targeting the oldest folded commit as the default
   squashed message. Ignore amend! markers targeting later commits while
   selecting that replacement message.
 * Improve tests.

Changes in v8:

 * --reedit-message now builds the same editor template as git rebase -i
   --autosquash: fixup!, squash! and amend! commits are grouped under the
   commit they target instead of shown in commit order, and an amend!
   replaces its target's message.
 * A fixup!, squash! or amend! is refused only when its target is outside
   the range, so several fixups for an in-range commit fold together. A
   range that is entirely markers for one below-range target is combined
   into a single commit, keeping the last amend! message.
 * Merges inside the range are folded when the range has a single base, with
   no dedicated opt-in flag, --ancestry-path ensures only commits descended
   from the base are folded, and a range reaching more than one base is
   rejected.
 * Rev-list options are accepted and sanitized the way git replay does,
   forcing the walk order back with a warning, which also fixes git history
   squash -- --reverse slipping past the previous option check.
 * Kept this as an explicit squash subcommand rather than making
   --reedit-message the default or renaming the command.

Changes in v7:

 * --reedit-message now builds the same editor template git rebase -i shows
   for a squash (a combination of N commits banner with each folded message
   under its own header) and follows autosquash for markers: a fixup!
   message falls out (commented under a will be skipped header), while a
   squash! or amend! keeps its body with only the marker subject commented
   so its remark can be reworded in. Only the message text is affected,
   every commit's changes are always folded in.
 * Reuse git rebase -i's squash-message code: a preparatory sequencer:
   commit extracts the banner, header and marker-comment helpers so both
   rebase and git history squash build the identical template from one
   source.
 * Refuse a range whose oldest commit is a fixup!, squash! or amend!, since
   the marker's target cannot be inside the range.
 * Reorder the squash usage so dashed options come before <revision-range>,
   and spell out HEAD instead of @ in the documentation and examples.
 * Expand the squash commit message and documentation with this overview,
   and scope the merge limitation so it no longer contradicts squash folding
   a single-base interior merge.

Changes in v6:

 * git history squash now accepts multiple revision arguments, read like the
   arguments to git-rev-list, so a compound range such as @~3.. ^topic
   works.
 * The base to reparent onto is now the oldest in-range commit's parent; a
   boundary other than that base means the range has more than one base and
   is rejected. This also fixes the earlier overly-restrictive handling of
   merges and side branches.
 * A single-commit range (e.g. @^!) is rejected with "nothing to squash"
   (this also covers the @^!-style example that previously succeeded
   silently).
 * Commit messages reworded: the squash commit now gives an overview of
   fixup!/squash!/amend! handling, rewording, merge-parent and ref behavior.

Changes in v5:

 * The range walk now uses --ancestry-path, so only commits descended from
   the base are folded; a single revision such as HEAD or HEAD~1 is now
   rejected as "not a <base>..<tip> range" rather than treated as a squash
   down to the root.
 * This adopts the --ancestry-path suggestion; the multi-base rejection is
   unchanged, so a side branch that forked before the base and merged in is
   still refused.
 * Added tests covering more merge topologies: two interior merges, a nested
   merge, an octopus merge, an octopus arm forked before the base, a merge
   among the descendants replayed above the range, and a ref pointing at an
   interior merge commit.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (8):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  sequencer: share the squash message marker helpers and flags
  history: add skeleton for squash subcommand
  history: validate squash revision ranges
  history: protect branches when squashing a range
  history: create squashed commits without editing
  history: support editing squashed commit messages

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  59 +-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 720 +++++++++++++++++++++++--
 object.h                         |   1 +
 sequencer.c                      |  70 +--
 sequencer.h                      |  30 ++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 886 +++++++++++++++++++++++++++++++
 10 files changed, 1702 insertions(+), 71 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: 2c78326f810173a4f3aefd8021f1e07575412481
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v13
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v13
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v12:

 1:  20e050a0ad = 1:  b175bdca54 history: extract helper for a commit's parent tree
 2:  b99867a0d4 = 2:  965074f9e8 history: give commit_tree_ext a message template
 3:  352db997e9 = 3:  cdbdd766b2 sequencer: share the squash message marker helpers and flags
 -:  ---------- > 4:  f7d953b081 history: add skeleton for squash subcommand
 -:  ---------- > 5:  dbbf66ba02 history: validate squash revision ranges
 -:  ---------- > 6:  e71a8adfbe history: protect branches when squashing a range
 4:  33d3eca6db ! 7:  8b3551d0d4 history: add squash subcommand to fold a range
     @@ Metadata
      Author: Harald Nordgren <haraldnordgren@gmail.com>
      
       ## Commit message ##
     -    history: add squash subcommand to fold a range
     +    history: create squashed commits without editing
      
     -    Folding a series of commits into one required either an interactive
     -    rebase where each commit after the first was hand-edited to "fixup", or
     -    a "git reset --soft" to the merge base followed by "git commit --amend".
     +    Create one replacement commit from the resolved range when --no-edit is
     +    selected. Preserve the authorship and all parents of the oldest commit,
     +    use the tip tree, and replay descendants through the existing history
     +    rewrite machinery. Record the complete revision expression in the
     +    reflog and retain dry-run and update-refs behavior.
      
     -    Add "git history squash <revision-range>" to do this directly. It folds
     -    every selected commit into one, preserving the authorship and parents of
     -    the oldest commit and taking the tree of the tip, then replays commits
     -    above the range. By default an editor opens with every folded message in
     -    the same template used by "git rebase -i --autosquash". With --no-edit,
     -    the selected message is used without opening an editor.
     -
     -    Resolve fixup!, squash! and amend! subjects directly while walking the
     -    selected commits. A marker is rejected unless its fixed target is also
     -    selected, except that a range made up entirely of related markers can be
     -    consolidated. Without editing, refuse any squash! or amend! whose message
     -    would be discarded.
     -
     -    Read the range like arguments to "git rev-list" and accept multiple
     -    revisions and rev-list options. Restore the walk settings required by the
     -    fold after setup_revisions(), warning when an option changed them. The
     -    range must name a bottom commit, must not reach a root, and must have one
     -    tip. Every parent after the oldest commit must be selected or also be a
     -    parent of the oldest commit. This permits internal merges and preserves
     -    all parents when the oldest commit is itself a merge.
     -
     -    By default, refuse when a local branch descends from the selected commits
     -    but cannot remain a descendant of the result. Tags and remote-tracking
     -    refs are left unchanged. Use --update-refs=head to leave such local
     -    branches unchanged as well.
     +    Resolve fixup!, squash! and amend! subjects while walking the range.
     +    Reject markers whose targets are not selected and refuse any no-edit
     +    fold that would discard a squash! or amend! message. A range made
     +    entirely from related markers can still be consolidated, with the last
     +    applicable amend! body supplying the message.
      
          Inspired-by: Sergey Chernov <serega.morph@gmail.com>
          Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
     - ## Documentation/config/advice.adoc ##
     -@@ Documentation/config/advice.adoc: all advice messages.
     - 	forceDeleteBranch::
     - 		Shown when the user tries to delete a not fully merged
     - 		branch without the force option set.
     -+	historyUpdateRefs::
     -+		Shown when `git history squash` refuses because a ref points
     -+		into the range being folded, to tell the user about
     -+		`--update-refs=head`.
     - 	ignoredHook::
     - 		Shown when a hook is ignored because the hook is not
     - 		set as executable.
     -
       ## Documentation/git-history.adoc ##
     -@@ Documentation/git-history.adoc: git history drop <commit> [--dry-run] [--update-refs=(branches|head)] [--empty=(
     - git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
     - git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
     - git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
     -+git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>
     - 
     - DESCRIPTION
     - -----------
      @@ Documentation/git-history.adoc: at once.
       LIMITATIONS
       -----------
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      +already on `topic`. Rev-list options may also be given, but any that would
      +change how the range is walked are overridden with a warning.
      ++
     -+An editor opens pre-filled with the messages of all the folded commits so you
     -+can combine them. With `--no-edit`, the oldest commit's message is preserved
     -+instead, except that an `amend!` commit targeting it replaces its message.
     ++With `--no-edit`, the oldest commit's message is preserved, except that an
     ++`amend!` commit targeting it replaces its message.
      ++
      +The selected commits must form a connected graph with a single tip and must
      +not include a root commit. Every parent of a commit after the oldest one must
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
      +the last `amend!` message is used if there is one; a `squash!` or `amend!` is
      +otherwise refused if folding it would discard its message.
      ++
     -+The editor template mirrors `git rebase -i --autosquash`: each `fixup!`,
     -+`squash!`, or `amend!` is grouped under the commit it targets rather than
     -+shown in commit order. A `fixup!` message is dropped (commented out in full),
     -+a `squash!` keeps its body with only the marker subject commented, and an
     -+`amend!` replaces its target's message, unless a `squash!` folded into that
     -+target first, in which case it keeps its body like a `squash!`.
     -++
      +A local branch descended from a selected commit but not from the range tip
      +cannot be rewritten as a descendant of the result, so with the default
      +`--update-refs=branches` the command refuses. Rerun with `--update-refs=head`
     @@ Documentation/git-history.adoc: linkgit:gitglossary[7].
       OPTIONS
       -------
       
     -@@ Documentation/git-history.adoc: OPTIONS
     - 	objects will be written into the repository, so applying these printed
     - 	ref updates is generally safe.
     - 
     -+`--edit`::
     -+`--no-edit`::
     -+	For `squash`, open an editor to combine the messages of the folded commits.
     -+	This is the default; use `--no-edit` to keep the selected message without
     -+	opening an editor.
     -+
     - `--reedit-message`::
     - 	Open an editor to modify the target commit's message.
     - 
     -
     - ## advice.c ##
     -@@ advice.c: static struct {
     - 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
     - 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
     - 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
     -+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
     - 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
     - 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
     - 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
     -
     - ## advice.h ##
     -@@ advice.h: enum advice_type {
     - 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
     - 	ADVICE_FORCE_DELETE_BRANCH,
     - 	ADVICE_GRAFT_FILE_DEPRECATED,
     -+	ADVICE_HISTORY_UPDATE_REFS,
     - 	ADVICE_IGNORED_HOOK,
     - 	ADVICE_IMPLICIT_IDENTITY,
     - 	ADVICE_MERGE_CONFLICT,
      
       ## builtin/history.c ##
     -@@
     - #define USE_THE_REPOSITORY_VARIABLE
     - 
     - #include "builtin.h"
     -+#include "advice.h"
     - #include "cache-tree.h"
     - #include "commit.h"
     - #include "commit-reach.h"
     -@@
     - #include "path.h"
     - #include "read-cache.h"
     - #include "refs.h"
     -+#include "ref-filter.h"
     - #include "replay.h"
     - #include "reset.h"
     - #include "revision.h"
     -@@
     - 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
     - #define GIT_HISTORY_SPLIT_USAGE \
     - 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
     -+#define GIT_HISTORY_SQUASH_USAGE \
     -+	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>")
     - 
     - static void change_data_free(void *util, const char *str UNUSED)
     - {
      @@ builtin/history.c: out:
     - 	return ret;
     - }
       
     -+/*Remember to update object flag allocation in object.h */
     -+#define SQUASH_SEEN (1u << 11)
     -+#define SQUASH_TIP (1u << 12)
     + #define SQUASH_SEEN (1u << 11)
     + #define SQUASH_TIP (1u << 12)
      +#define SQUASH_AMEND_TARGET (1u << 13)
      +
      +static bool is_autosquash_subject(const char *s)
     @@ builtin/history.c: out:
      +	repo_unuse_commit_buffer(repo, commit, buf);
      +	return ret;
      +}
     -+
     -+static int build_squash_message(struct repository *repo,
     -+				const struct strbuf *todo_buf,
     -+				struct strbuf *out);
     -+
     -+/*
     -+ * Resolve a "<base>..<tip>" revision range into the base commit just outside
     -+ * the range (which becomes the parent of the squashed commit), the oldest
     -+ * commit contained in the range (whose message the squash reuses), and the
     -+ * range tip (whose tree becomes the result). A merge inside the range is fine,
     -+ * but the range must have a single base and must not reach a root commit.
     -+ */
     -+static int resolve_squash_range(struct repository *repo,
     -+				bool update_branches,
     -+				bool edit_message,
     -+				int argc, const char **argv,
     -+				struct commit **oldest_out,
     + 
     + static int setup_squash_revisions(struct repository *repo,
     + 				  int argc, const char **argv,
     +@@ builtin/history.c: static int resolve_squash_range(struct repository *repo,
     + 				bool update_branches,
     + 				int argc, const char **argv,
     + 				struct commit **oldest_out,
     +-				struct commit **tip_out)
      +				struct commit **tip_out,
      +				char **message_out)
     -+{
     -+	struct rev_info revs;
     + {
     + 	struct rev_info revs;
      +	struct subject_data subject_data = SUBJECT_DATA_INIT;
     -+	struct commit *commit, *oldest = NULL, *tip = NULL;
     -+	struct strbuf todo_buf = STRBUF_INIT;
     -+	size_t i;
     -+	int ret, tip_count = 0;
     -+	struct ref_filter filter = REF_FILTER_INIT;
     -+	struct ref_array refs = { 0 };
     -+
     -+	repo_init_revisions(repo, &revs, NULL);
     -+	subject_data.edit_message = edit_message;
     -+	revs.reverse = 1;
     -+	revs.topo_order = 1;
     -+	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
     -+	revs.simplify_history = 0;
     -+	revs.ancestry_path = 1;
     -+	revs.limited = 1;
     -+	revs.ancestry_path_implicit_bottoms = 1;
     -+
     -+	argc = setup_revisions(argc, argv, &revs, NULL);
     -+	if (argc > 1) {
     -+		ret = error(_("unrecognized argument: %s"), argv[1]);
     -+		goto out;
     -+	}
     -+
     -+	if (revs.reverse != 1 || revs.topo_order != 1 ||
     -+	    revs.sort_order != REV_SORT_IN_GRAPH_ORDER ||
     -+	    revs.simplify_history != 0 || revs.boundary == 1 ||
     -+	    revs.ancestry_path != 1 || revs.limited != 1 ||
     -+	    revs.ancestry_path_implicit_bottoms != 1) {
     -+		warning(_("ignoring rev-list options that would change how the "
     -+			  "range is walked"));
     -+		revs.reverse = 1;
     -+		revs.topo_order = 1;
     -+		revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
     -+		revs.simplify_history = 0;
     -+		revs.boundary = 0;
     -+		revs.ancestry_path = 1;
     -+		revs.limited = 1;
     -+		revs.ancestry_path_implicit_bottoms = 1;
     -+	}
     -+
     -+	/*
     -+	 * A squash needs a base to reparent onto, so the range has to exclude
     -+	 * something, as in "<base>..<tip>". A revision range with no such
     -+	 * bottom commit cannot be squashed.
     -+	 */
     -+	for (i = 0; i < revs.cmdline.nr; i++)
     -+		if (revs.cmdline.rev[i].flags & BOTTOM)
     -+			break;
     -+	if (i == revs.cmdline.nr) {
     -+		ret = error(_("not a '<base>..<tip>' revision range"));
     -+		goto out;
     -+	}
     -+
     -+	if (prepare_revision_walk(&revs) < 0) {
     -+		ret = error(_("error preparing revisions"));
     -+		goto out;
     -+	}
     -+	while ((commit = get_revision(&revs))) {
     -+		struct commit_list *p;
     -+
     -+		if (edit_message)
     -+			strbuf_addf(&todo_buf, "pick %s\n",
     -+				    oid_to_hex(&commit->object.oid));
     -+
     -+		if (!commit->parents) {
     -+			ret = error(_("cannot squash down to root commit"));
     -+			goto out;
     -+		}
     -+		for (p = commit->parents; oldest && p; p = p->next) {
     -+			struct commit_list *q;
     -+			struct object *o;
     -+			bool seen;
     -+
     -+			if (repo_parse_commit(repo, p->item)) {
     -+				ret = error(_("cannot parse commit"));
     -+				goto out;
     -+			}
     -+			o = &p->item->object;
     -+			seen = o->flags & SQUASH_SEEN;
     -+			/*
     -+			 * Allow parents that match the parents of the
     -+			 * squashed commit.
     -+			 */
     -+			for (q = oldest->parents; !seen && q; q = q->next) {
     -+				if (p->item == q->item) {
     -+					seen = true;
     -+					commit_list_insert(commit, &filter.with_commit);
     -+				}
     -+			}
     -+			if (!seen) {
     -+				ret = error(_("parent %s of commit %s is "
     -+					      "outside the revision range"),
     -+					    repo_find_unique_abbrev(repo, &o->oid,
     -+								    DEFAULT_ABBREV),
     -+					    repo_find_unique_abbrev(repo, &commit->object.oid,
     -+								    DEFAULT_ABBREV));
     -+				goto out;
     -+			}
     -+			if (o->flags & SQUASH_TIP) {
     -+				tip_count--;
     -+				o->flags &= ~SQUASH_TIP;
     -+			}
     -+		}
     -+		if (!oldest) {
     -+			commit_list_insert(commit, &filter.with_commit);
     -+			oldest = commit;
     -+		}
     + 	struct commit *commit, *oldest = NULL, *tip = NULL;
     + 	int ret, tip_count = 0;
     + 	bool walk_started = false;
     +@@ builtin/history.c: static int resolve_squash_range(struct repository *repo,
     + 			commit_list_insert(commit, &filter.with_commit);
     + 			oldest = commit;
     + 		}
      +		if (squash_check_subject(repo, commit, &subject_data)) {
      +			ret = -1;
      +			goto out;
      +		}
     -+		tip = commit;
     -+		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
     -+		tip_count++;
     -+	}
     -+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP | SQUASH_AMEND_TARGET);
     -+	reset_revision_walk();
     -+	if (!tip_count) {
     -+		ret = error(_("the revision range is empty"));
     -+		goto out;
     -+	} else if (tip_count != 1) {
     -+		  ret = error(_("the revision range contains more than one tip "
     -+				"commit"));
     -+		  goto out;
     -+	  } else if (oldest == tip) {
     -+		ret = error(_("the revision range holds a single commit; "
     -+			      "nothing to squash"));
     -+		goto out;
     -+	} else if (!oldest->parents) {
     -+		BUG("an in-range commit must have a parent");
     -+	}
     -+	commit_list_insert(tip, &filter.no_commit);
     -+	filter.kind = FILTER_REFS_BRANCHES;
     -+	if (update_branches &&
     -+	    filter_refs(&refs, &filter, filter.kind)) {
     -+		ret = error(_("could not filter refs"));
     -+		goto out;
     -+	}
     -+	if (refs.nr) {
     -+		/*
     -+		 * TODO: list the branches and also check HEADS from other worktrees
     -+		 */
     -+		ret = error(_("a branch points to a commit that is being squashed"));
     -+		advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
     -+				  _("Use --update-refs=head to rewrite only "
     -+				    "the current branch and leave such refs "
     -+				    "untouched."));
     -+		goto out;
     -+	}
     -+	if (edit_message) {
     -+		strbuf_reset(&subject_data.squash_message);
     -+		ret = build_squash_message(repo, &todo_buf,
     -+					   &subject_data.squash_message);
     -+		if (ret < 0)
     -+			goto out;
     -+	}
     -+	*oldest_out = oldest;
     -+	*tip_out = tip;
     + 		tip = commit;
     + 		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
     + 		tip_count++;
     +@@ builtin/history.c: static int resolve_squash_range(struct repository *repo,
     + 
     + 	*oldest_out = oldest;
     + 	*tip_out = tip;
      +	*message_out = strbuf_detach(&subject_data.squash_message, NULL);
     -+	ret = 0;
     -+
     -+out:
     -+	strbuf_release(&todo_buf);
     + 	ret = 0;
     + 
     + out:
     +-	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
     ++	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP |
     ++			   SQUASH_AMEND_TARGET);
     + 	if (walk_started)
     + 		reset_revision_walk();
      +	subject_data_clear(&subject_data);
     -+	release_revisions(&revs);
     -+	ref_filter_clear(&filter);
     -+	ref_array_clear(&refs);
     -+	return ret;
     -+}
     -+
     -+static bool amend_replaces_target(struct todo_list *todo, int target)
     -+{
     -+	int i;
     -+
     -+	for (i = target + 1; i < todo->nr &&
     -+			     todo->items[i].command != TODO_PICK; i++) {
     -+		if (todo->items[i].command == TODO_SQUASH)
     -+			return false;
     -+		if (todo->items[i].flags & TODO_REPLACE_FIXUP_MSG)
     -+			return true;
     -+	}
     -+	return false;
     -+}
     -+
     -+static int build_squash_message(struct repository *repo,
     -+				const struct strbuf *todo_buf,
     -+				struct strbuf *out)
     -+{
     -+	struct todo_list todo = TODO_LIST_INIT;
     -+	struct replay_opts opts = REPLAY_OPTS_INIT;
     -+	int i, nr_commits, ret;
     -+
     -+	if (todo_list_parse_insn_buffer(repo, &opts, todo_buf->buf, &todo) < 0 ||
     -+	    todo_list_rearrange_squash(&todo) < 0) {
     -+		ret = error(_("could not prepare the squash message"));
     -+		goto out;
     -+	}
     -+
     -+	nr_commits = todo.nr;
     -+	for (i = 0; i < nr_commits; i++) {
     -+		struct todo_item *item = &todo.items[i];
     -+		const char *message, *body;
     -+		size_t commented_len;
     -+		bool skip, squashing;
     -+
     -+		squashing = item->command == TODO_SQUASH ||
     -+			    (item->flags & TODO_REPLACE_FIXUP_MSG);
     -+		if (item->command == TODO_PICK)
     -+			skip = amend_replaces_target(&todo, i);
     -+		else
     -+			skip = !squashing;
     -+
     -+		message = repo_logmsg_reencode(repo, item->commit, NULL, NULL);
     -+		find_commit_subject(message, &body);
     -+
     -+		if (skip)
     -+			commented_len = strlen(body);
     -+		else if (squashing)
     -+			commented_len = squash_subject_comment_len(body, 1);
     -+		else
     -+			commented_len = 0;
     -+
     -+		if (!i)
     -+			add_squash_combination_header(out, nr_commits);
     -+		strbuf_addch(out, '\n');
     -+		add_squash_message_header(out, i + 1, skip);
     -+		strbuf_addstr(out, "\n\n");
     -+		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
     -+		strbuf_addstr(out, body + commented_len);
     -+		strbuf_complete_line(out);
     -+
     -+		repo_unuse_commit_buffer(repo, item->commit, message);
     -+	}
     -+
     -+	ret = 0;
     -+
     -+out:
     -+	todo_list_release(&todo);
     -+	replay_opts_release(&opts);
     -+	return ret;
     -+}
     -+
     -+static int cmd_history_squash(int argc,
     -+			      const char **argv,
     -+			      const char *prefix,
     -+			      struct repository *repo)
     -+{
     -+	const char * const usage[] = {
     -+		GIT_HISTORY_SQUASH_USAGE,
     -+		NULL,
     -+	};
     -+	enum ref_action action = REF_ACTION_DEFAULT;
     -+	int dry_run = 0;
     -+	int edit = 1;
     -+	struct option options[] = {
     -+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
     -+			       N_("control which refs should be updated"),
     -+			       PARSE_OPT_NONEG, parse_ref_action),
     -+		OPT_BOOL('n', "dry-run", &dry_run,
     -+			 N_("perform a dry-run without updating any refs")),
     -+		OPT_BOOL('e', "edit", &edit,
     -+			 N_("edit the commit message")),
     -+		OPT_END(),
     -+	};
     + 	release_revisions(&revs);
     + 	ref_filter_clear(&filter);
     + 	ref_array_clear(&refs);
     +@@ builtin/history.c: static int cmd_history_squash(int argc,
     + 			 N_("edit the commit message")),
     + 		OPT_END(),
     + 	};
     +-	struct commit *oldest, *tip;
      +	struct strbuf reflog_msg = STRBUF_INIT;
      +	struct commit *oldest, *tip, *rewritten;
      +	const struct object_id *base_tree_oid, *tip_tree_oid;
      +	char *message_template = NULL;
      +	struct rev_info revs = { 0 };
     -+	int ret;
     -+
     -+	argc = parse_options(argc, argv, prefix, options, usage,
     -+			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
     + 	int ret;
     + 
     + 	argc = parse_options(argc, argv, prefix, options, usage,
     + 			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
     +-	if (argc < 2)
     +-		return error(_("command expects a revision range"));
      +	if (argc < 2) {
      +		ret = error(_("command expects a revision range"));
      +		goto out;
      +	}
     -+	repo_config(repo, git_default_config, NULL);
     -+
     -+	if (action == REF_ACTION_DEFAULT)
     -+		action = REF_ACTION_BRANCHES;
     + 	repo_config(repo, git_default_config, NULL);
      +
     + 	if (action == REF_ACTION_DEFAULT)
     + 		action = REF_ACTION_BRANCHES;
     + 
      +	strbuf_addstr(&reflog_msg, "squash: updating ");
      +	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
      +
     -+	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
     -+				   edit,
     + 	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
     +-				   argc, argv, &oldest, &tip);
      +				   argc, argv, &oldest, &tip,
      +				   &message_template);
     -+	if (ret < 0)
     + 	if (ret < 0)
     +-		return ret;
     ++		goto out;
     ++	if (edit) {
     ++		ret = error(_("message editing is not supported yet; use '--no-edit'"));
      +		goto out;
     ++	}
      +
      +	ret = setup_revwalk(repo, action, tip, &revs);
      +	if (ret < 0)
     @@ builtin/history.c: out:
      +
      +	ret = commit_tree_ext(repo, "squash", oldest, message_template,
      +			      oldest->parents, base_tree_oid, tip_tree_oid,
     -+			      &rewritten,
     -+			      edit ? COMMIT_TREE_EDIT_MESSAGE : 0);
     ++			      &rewritten, 0);
      +	if (ret < 0) {
      +		ret = error(_("failed writing squashed commit"));
      +		goto out;
     @@ builtin/history.c: out:
      +		ret = error(_("failed replaying descendants"));
      +		goto out;
      +	}
     -+
     + 
     +-	return error(_("squashing commits is not implemented yet"));
      +	ret = 0;
      +
      +out:
     @@ builtin/history.c: out:
      +	release_revisions(&revs);
      +	free(message_template);
      +	return ret;
     -+}
     -+
     - static int update_worktree(struct repository *repo,
     - 			   const struct commit *old_head,
     - 			   const struct commit *new_head,
     -@@ builtin/history.c: int cmd_history(int argc,
     - 		GIT_HISTORY_FIXUP_USAGE,
     - 		GIT_HISTORY_REWORD_USAGE,
     - 		GIT_HISTORY_SPLIT_USAGE,
     -+		GIT_HISTORY_SQUASH_USAGE,
     - 		NULL,
     - 	};
     - 	parse_opt_subcommand_fn *fn = NULL;
     -@@ builtin/history.c: int cmd_history(int argc,
     - 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
     - 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
     - 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
     -+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
     - 		OPT_END(),
     - 	};
     + }
       
     + static int update_worktree(struct repository *repo,
      
       ## object.h ##
      @@ object.h: void object_array_init(struct object_array *array);
        * bisect.c:                                        16
        * bundle.c:                                        16
        * http-push.c:                          11-----14
     +- * builtin/history.c:                    1112
      + * builtin/history.c:                    11---13
        * commit-graph.c:                                15
        * commit-reach.c:                                  16-------20
        * builtin/last-modified.c:                         1617
      
     - ## t/meson.build ##
     -@@ t/meson.build: integration_tests = [
     -   't3452-history-split.sh',
     -   't3453-history-fixup.sh',
     -   't3454-history-drop.sh',
     -+  't3455-history-squash.sh',
     -   't3500-cherry.sh',
     -   't3501-revert-cherry-pick.sh',
     -   't3502-cherry-pick-merge.sh',
     -
     - ## t/t3455-history-squash.sh (new) ##
     -@@
     -+#!/bin/sh
     -+
     -+test_description='tests for git-history squash subcommand'
     -+
     -+. ./test-lib.sh
     -+
     + ## t/t3455-history-squash.sh ##
     +@@ t/t3455-history-squash.sh: test_description='tests for git-history squash subcommand'
     + 
     + . ./test-lib.sh
     + 
     +-test_expect_success 'setup linear history' '
      +stage_file () {
      +	printf "%s\n" "$1" >file &&
      +	git add file
     @@ t/t3455-history-squash.sh (new)
      +}
      +
      +test_expect_success 'setup linear history touching two files' '
     -+	test_commit base file a start &&
     + 	test_commit base file a start &&
     +-	test_commit one file b &&
     +-	test_commit two file c &&
     +-	test_commit three file d
      +	GIT_AUTHOR_NAME=One GIT_AUTHOR_EMAIL=one@example.com \
      +		test_commit one other x &&
      +	GIT_AUTHOR_NAME=Two GIT_AUTHOR_EMAIL=two@example.com \
      +		test_commit two file c &&
      +	GIT_AUTHOR_NAME=Three GIT_AUTHOR_EMAIL=three@example.com \
      +		test_commit three file d
     -+'
     -+
     -+test_expect_success 'errors on missing range argument' '
     -+	test_must_fail git history squash 2>err &&
     -+	test_grep "expects a revision range" err
     -+'
     -+
     -+test_expect_success 'errors on an empty range' '
     -+	test_must_fail git history squash HEAD..HEAD 2>err &&
     -+	test_grep "the revision range is empty" err
     -+'
     -+
     -+test_expect_success 'errors on a single revision that is not a range' '
     -+	test_must_fail git history squash HEAD 2>err &&
     -+	test_grep "not a .*range" err &&
     -+	test_must_fail git history squash HEAD~1 2>err &&
     -+	test_grep "not a .*range" err
     -+'
     -+
     -+test_expect_success 'errors on a range holding a single commit' '
     + '
     + 
     + test_expect_success 'errors on missing range argument' '
     +@@ t/t3455-history-squash.sh: test_expect_success 'errors on a single revision that is not a range' '
     + '
     + 
     + test_expect_success 'errors on a range holding a single commit' '
      +	git reset --hard three &&
      +	head_before=$(git rev-parse HEAD) &&
      +
     -+	test_must_fail git history squash "HEAD^!" 2>err &&
     + 	test_must_fail git history squash "HEAD^!" 2>err &&
     +-	test_grep "single commit; nothing to squash" err
      +	test_grep "single commit; nothing to squash" err &&
      +	test_cmp_rev "$head_before" HEAD
     -+'
     -+
     + '
     + 
     +-test_expect_success 'rejects a root commit' '
      +test_expect_success 'rejects root commit' '
      +	# create a disconnected root commit
     -+	oid=$(git commit-tree -m root three^{tree}) &&
     + 	oid=$(git commit-tree -m root three^{tree}) &&
     +-	test_must_fail git history squash \
     +-		--ancestry-path=start "$oid..three" 2>err &&
     +-	test_grep "cannot squash down to root commit" err
      +	# because we pass --ancestry-path when calling setup_revs() it the
      +	# revision walk will only include commits decended from $oid so
      +	# we need to give it another --ancestry-path commit to actually walk
     @@ t/t3455-history-squash.sh (new)
      +	test_must_fail git history squash --ancestry-path=start $oid..three 2>err &&
      +	echo "error: cannot squash down to root commit" >expect &&
      +	test_cmp expect err
     -+'
     -+
     -+test_expect_success 'rejects multiple tips' '
     -+	oid=$(git commit-tree -m tip -p start^0 three^{tree}) &&
     + '
     + 
     + test_expect_success 'rejects multiple tips' '
     + 	oid=$(git commit-tree -m tip -p start^0 three^{tree}) &&
     +-	test_must_fail git history squash ^start "$oid" three~1 2>err &&
     +-	test_grep "revision range contains more than one tip" err
      +	test_must_fail git history squash ^start $oid three~1 2>err &&
      +	echo "error: the revision range contains more than one tip commit" >expect &&
      +	test_cmp expect err &&
     @@ t/t3455-history-squash.sh (new)
      +	git history squash --no-edit ^start three~1 three &&
      +	test_cmp_rev HEAD~1 start^0 &&
      +	test_cmp_rev HEAD^{tree} three^{tree}
     -+'
     -+
     + '
     + 
     +-test_expect_success 'rejects a merge parent outside the range' '
     +-	git reset --hard start &&
      +test_expect_success 'accepts multiple revision arguments with an exclusion' '
      +	git reset --hard three &&
      +	git branch -f keep HEAD~2 &&
     @@ t/t3455-history-squash.sh (new)
      +
      +test_expect_success 'squashes a branch the current branch is not on' '
      +	git reset --hard three &&
     -+	main=$(git symbolic-ref --short HEAD) &&
     + 	main=$(git symbolic-ref --short HEAD) &&
     +-	git checkout -b outside-parent &&
     +-	test_commit --no-tag outside-parent outside x &&
      +	head_before=$(git rev-parse HEAD) &&
      +	git checkout -b off-history start &&
      +	test_commit --no-tag off-one off a &&
      +	test_commit --no-tag off-two off b &&
     -+	git checkout "$main" &&
     -+
     + 	git checkout "$main" &&
     +-	test_commit --no-tag outside-main file b &&
     +-	base=$(git rev-parse HEAD) &&
     +-	test_commit --no-tag outside-mid file c &&
     +-	git merge --no-ff -m "merge outside-parent" outside-parent &&
     +-	git branch -D outside-parent &&
     + 
     +-	test_must_fail git history squash "$base.." 2>err &&
     +-	test_grep "parent .* of commit .* is outside the revision range" err
      +	git history squash --no-edit start..off-history &&
      +
      +	check_commit_count start..off-history 1 &&
     @@ t/t3455-history-squash.sh (new)
      +	test_must_fail git history squash --no-edit HEAD~3.. 2>err &&
      +	test_grep "^error: cannot squash .* target is not being squashed" err &&
      +	test_set_editor :
     -+'
     -+
     + '
     + 
     +-test_expect_success 'prints branches that cannot follow the squash' '
      +test_expect_success 'squashing fixups into a merge' '
      +	test_when_finished \
      +		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
     @@ t/t3455-history-squash.sh (new)
      +	sed 1,2d msg | test_commit_message HEAD
      +'
      +
     -+test_expect_success 'edits every message and aborts on an empty result' '
     -+	git reset --hard start &&
     -+	stage_file b &&
     -+	git commit -m "re-one subject" -m "re-one body line" &&
     -+	test_commit --no-tag re-two file c &&
     -+	test_commit re-three file d &&
     -+	head_before=$(git rev-parse HEAD) &&
     -+
     -+	write_script empty-editor <<-\EOF &&
     -+	>"$1"
     -+	EOF
     -+	test_set_editor "$(pwd)/empty-editor" &&
     -+	test_must_fail git history squash start.. 2>err &&
     -+	test_grep "Aborting commit due to empty commit message" err &&
     -+	test_cmp_rev "$head_before" HEAD &&
     -+
     -+	write_script editor <<-\EOF &&
     -+	cat "$1" >edited &&
     -+	echo combined >"$1"
     -+	EOF
     -+	test_set_editor "$(pwd)/editor" &&
     -+	git history squash start.. &&
     -+
     -+	cat >expect <<-EOF &&
     -+	# This is a combination of 3 commits.
     -+	# This is the 1st commit message:
     -+
     -+	re-one subject
     -+
     -+	re-one body line
     -+
     -+	# This is the commit message #2:
     -+
     -+	re-two
     -+
     -+	# This is the commit message #3:
     -+
     -+	re-three
     -+
     -+	# Please enter the commit message for the squash changes. Lines starting
     -+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     -+	# Changes to be committed:
     -+	#	modified:   file
     -+	#
     -+	EOF
     -+	test_cmp expect edited &&
     -+	check_log_subjects -1 <<-\EOF
     -+	combined
     -+	EOF
     -+'
     -+
     -+test_expect_success 'handles fixup!, squash! and amend! like rebase' '
     -+	git reset --hard start &&
     -+	test_commit --no-tag mark-base file b &&
     -+	stage_file c &&
     -+	commit_with_message "fixup! mark-base\n\nfixup body\n" &&
     -+	stage_file d &&
     -+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
     -+	stage_file e &&
     -+	commit_with_message "amend! mark-base\n\namended message\n" &&
     -+
     -+	write_script editor <<-\EOF &&
     -+	cat "$1" >edited
     -+	EOF
     -+	test_set_editor "$(pwd)/editor" &&
     -+	git history squash start.. &&
     -+
     -+	cat >expect <<-EOF &&
     -+	# This is a combination of 4 commits.
     -+	# This is the 1st commit message:
     -+
     -+	mark-base
     -+
     -+	# The commit message #2 will be skipped:
     -+
     -+	# fixup! mark-base
     -+	#
     -+	# fixup body
     -+
     -+	# This is the commit message #3:
     -+
     -+	# squash! mark-base
     -+
     -+	squash remark
     -+
     -+	# This is the commit message #4:
     -+
     -+	# amend! mark-base
     -+
     -+	amended message
     -+
     -+	# Please enter the commit message for the squash changes. Lines starting
     -+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     -+	# Changes to be committed:
     -+	#	modified:   file
     -+	#
     -+	EOF
     -+	test_cmp expect edited &&
     -+	check_log_messages -1 <<-\EOF
     -+	mark-base
     -+
     -+	squash remark
     -+
     -+	amended message
     -+
     -+	EOF
     -+'
     -+
     -+test_expect_success 'groups fixups under their targets in the editor' '
     -+	git reset --hard start &&
     -+	test_commit --no-tag alpha file a1 &&
     -+	test_commit --no-tag beta file b1 &&
     -+	stage_file a2 &&
     -+	commit_with_message "fixup! alpha\n" &&
     -+	stage_file b2 &&
     -+	commit_with_message "fixup! beta\n" &&
     -+
     -+	write_script editor <<-\EOF &&
     -+	cat "$1" >edited
     -+	EOF
     -+	test_set_editor "$(pwd)/editor" &&
     -+	git history squash start.. &&
     -+
     -+	cat >expect <<-EOF &&
     -+	# This is a combination of 4 commits.
     -+	# This is the 1st commit message:
     -+
     -+	alpha
     -+
     -+	# The commit message #2 will be skipped:
     -+
     -+	# fixup! alpha
     -+
     -+	# This is the commit message #3:
     -+
     -+	beta
     -+
     -+	# The commit message #4 will be skipped:
     -+
     -+	# fixup! beta
     -+
     -+	# Please enter the commit message for the squash changes. Lines starting
     -+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     -+	# Changes to be committed:
     -+	#	modified:   file
     -+	#
     -+	EOF
     -+	test_cmp expect edited
     -+'
     -+
     -+test_expect_success 'lets amend! replace its target message in the editor' '
     -+	git reset --hard start &&
     -+	test_commit --no-tag mark-base file b &&
     -+	stage_file c &&
     -+	commit_with_message "amend! mark-base\n\namended message\n" &&
     -+	stage_file d &&
     -+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
     -+
     -+	write_script editor <<-\EOF &&
     -+	cat "$1" >edited
     -+	EOF
     -+	test_set_editor "$(pwd)/editor" &&
     -+	git history squash start.. &&
     -+
     -+	cat >expect <<-EOF &&
     -+	# This is a combination of 3 commits.
     -+	# The 1st commit message will be skipped:
     -+
     -+	# mark-base
     -+
     -+	# This is the commit message #2:
     -+
     -+	# amend! mark-base
     -+
     -+	amended message
     -+
     -+	# This is the commit message #3:
     -+
     -+	# squash! mark-base
     -+
     -+	squash remark
     -+
     -+	# Please enter the commit message for the squash changes. Lines starting
     -+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
     -+	# Changes to be committed:
     -+	#	modified:   file
     -+	#
     -+	EOF
     -+	test_cmp expect edited &&
     -+	check_log_messages -1 <<-\EOF
     -+	amended message
     -+
     -+	squash remark
     -+
     -+	EOF
     -+'
     -+
      +test_expect_success '--update-refs=head only moves HEAD' '
      +	git reset --hard three &&
      +	git branch -f other HEAD &&
     @@ t/t3455-history-squash.sh (new)
      +'
      +
      +test_expect_success 'refuses to fold a range a branch points into' '
     -+	test_when_finished \
     -+		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
     -+		 git branch -D feature" &&
     -+	git checkout -f -b feature start &&
     -+	test_commit C1 &&
     -+	test_commit C2 &&
     -+	git checkout -b topic-1 start &&
     -+	test_commit C3 &&
     -+	test_commit C4 &&
     -+	git checkout C3 &&
     -+	test_commit C5 &&
     -+	git checkout feature &&
     -+	git merge C5 &&
     -+	test_commit C6 &&
     -+	git checkout -b topic-2 C2 &&
     -+	test_commit C7 &&
     -+	git checkout feature &&
     -+
     -+	test_must_fail git history squash start.. 2>err &&
     -+	# TODO: check the branch names when we print them (topic-1 & topic-2)
     -+	test_grep "^error: a branch points to" err &&
     + 	test_when_finished \
     + 		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
     + 		 git branch -D feature" &&
     +@@ t/t3455-history-squash.sh: test_expect_success 'prints branches that cannot follow the squash' '
     + 	test_grep "^error: the following branches cannot be rewritten" err &&
     + 	test_grep "^  topic-1$" err &&
     + 	test_grep "^  topic-2$" err &&
     +-	test_grep "^hint: .* --update-refs=head" err
      +	test_grep "^hint: .* --update-refs=head" err &&
      +	test_cmp_rev C6 HEAD &&
      +
     @@ t/t3455-history-squash.sh (new)
      +	test_cmp_rev start HEAD^ &&
      +	test_cmp_rev C6^{tree} HEAD^{tree} &&
      +	test_cmp_rev C6 HEAD@{1}
     -+'
     -+
     -+test_expect_success 'advice.historyUpdateRefs silences the hint' '
     -+	git reset --hard three &&
     -+	git branch -f mid HEAD~1 &&
     + '
     + 
     + test_expect_success 'advice.historyUpdateRefs silences the hint' '
     + 	git reset --hard three &&
     + 	git branch -f mid HEAD~1 &&
      +	head_before=$(git rev-parse HEAD) &&
     -+
     -+	test_must_fail git -c advice.historyUpdateRefs=false \
     -+		history squash start.. 2>err &&
     -+	test_grep "^error: a branch points to" err &&
     -+	test_grep ! "hint:" err &&
     + 
     + 	test_must_fail git -c advice.historyUpdateRefs=false \
     + 		history squash start.. 2>err &&
     + 	test_grep "^error: the following branches cannot be rewritten" err &&
     + 	test_grep "^  mid$" err &&
     + 	test_grep ! "hint:" err &&
      +	test_cmp_rev "$head_before" HEAD &&
     -+
     -+	git branch -D mid
     -+'
     -+
     + 
     + 	git branch -D mid
     + '
     + 
      +test_expect_success 'leaves tags and remote-tracking refs unchanged' '
      +	git reset --hard three &&
      +	git tag -f mark HEAD~1 &&
     @@ t/t3455-history-squash.sh (new)
      +	head_before=$(git rev-parse HEAD) &&
      +
      +	test_must_fail git history squash start.. 2>err &&
     -+	# TODO: test for branch nome "at-merge"
     -+	test_grep "a branch points to a commit" err &&
     ++	test_grep "^error: the following branches cannot be rewritten" err &&
     ++	test_grep "^  at-merge$" err &&
      +	test_cmp_rev "$head_before" HEAD &&
      +
      +	git branch -D at-merge
      +'
      +
     -+test_done
     + test_done
 -:  ---------- > 8:  821217ed7c history: support editing squashed commit messages

-- 
gitgitgadget

[PATCH v13 1/8] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 000155ad9c..c22715d848 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -164,6 +164,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -171,21 +190,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -475,18 +484,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -830,16 +831,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v13 2/8] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index c22715d848..a60e8dbcd0 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -108,6 +108,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -137,13 +138,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -196,7 +200,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -675,7 +679,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -886,7 +890,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -903,7 +907,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v13 3/8] sequencer: share the squash message marker helpers and flags

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

When "git rebase -i" squashes commits it builds an editor template with a
"This is a combination of N commits." banner, a "This is the 1st/Nth
commit message:" header above each kept message (or a "will be skipped"
header for a dropped one), and a commented-out subject for any fixup!,
squash! or amend! commit. The banner, the headers and the
subject-commenting all live in static helpers in sequencer.c wired to the
rebase state, so no other command can present a squash the same way.

Pull the three pieces out into add_squash_combination_header(),
add_squash_message_header() (which takes a flag for the "will be skipped"
variant) and squash_subject_comment_len(), and use them from
update_squash_messages() and append_squash_message(). Also move the
todo_item_flags enum to the header, so a caller reading the output of
todo_list_rearrange_squash() can tell an amend! (TODO_REPLACE_FIXUP_MSG)
from a plain fixup!. A later change reuses all of this to give "git
history squash" the same template.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 sequencer.c | 70 +++++++++++++++++++++++++++++------------------------
 sequencer.h | 30 +++++++++++++++++++++++
 2 files changed, 69 insertions(+), 31 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 83c3849205..4d2d59ecbe 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1880,18 +1880,38 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
-enum todo_item_flags {
-	TODO_EDIT_MERGE_MSG    = (1 << 0),
-	TODO_REPLACE_FIXUP_MSG = (1 << 1),
-	TODO_EDIT_FIXUP_MSG    = (1 << 2),
-};
-
 static const char first_commit_msg_str[] = N_("This is the 1st commit message:");
 static const char nth_commit_msg_fmt[] = N_("This is the commit message #%d:");
 static const char skip_first_commit_msg_str[] = N_("The 1st commit message will be skipped:");
 static const char skip_nth_commit_msg_fmt[] = N_("The commit message #%d will be skipped:");
 static const char combined_commit_msg_fmt[] = N_("This is a combination of %d commits.");
 
+void add_squash_combination_header(struct strbuf *buf, int n)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	strbuf_addf(buf, _(combined_commit_msg_fmt), n);
+}
+
+void add_squash_message_header(struct strbuf *buf, int n, int skip)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	if (n == 1)
+		strbuf_addstr(buf, skip ? _(skip_first_commit_msg_str) :
+				   _(first_commit_msg_str));
+	else
+		strbuf_addf(buf, skip ? _(skip_nth_commit_msg_fmt) :
+			    _(nth_commit_msg_fmt), n);
+}
+
+size_t squash_subject_comment_len(const char *body, int squashing)
+{
+	if (starts_with(body, "amend!") ||
+	    (squashing && (starts_with(body, "squash!") ||
+			   starts_with(body, "fixup!"))))
+		return commit_subject_length(body);
+	return 0;
+}
+
 static int is_fixup_flag(enum todo_command command, unsigned flag)
 {
 	return command == TODO_FIXUP && ((flag & TODO_REPLACE_FIXUP_MSG) ||
@@ -2012,20 +2032,13 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 {
 	struct replay_ctx *ctx = opts->ctx;
 	const char *fixup_msg;
-	size_t commented_len = 0, fixup_off;
-	/*
-	 * amend is non-interactive and not normally used with fixup!
-	 * or squash! commits, so only comment out those subjects when
-	 * squashing commit messages.
-	 */
-	if (starts_with(body, "amend!") ||
-	    ((command == TODO_SQUASH || seen_squash(ctx)) &&
-	     (starts_with(body, "squash!") || starts_with(body, "fixup!"))))
-		commented_len = commit_subject_length(body);
+	size_t commented_len, fixup_off;
+
+	commented_len = squash_subject_comment_len(body,
+				command == TODO_SQUASH || seen_squash(ctx));
 
-	strbuf_addf(buf, "\n%s ", comment_line_str);
-	strbuf_addf(buf, _(nth_commit_msg_fmt),
-		    ++ctx->current_fixup_count + 1);
+	strbuf_addch(buf, '\n');
+	add_squash_message_header(buf, ++ctx->current_fixup_count + 1, 0);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len, comment_line_str);
 	/* buf->buf may be reallocated so store an offset into the buffer */
@@ -2090,9 +2103,8 @@ static int update_squash_messages(struct repository *r,
 		eol = !starts_with(buf.buf, comment_line_str) ?
 			buf.buf : strchrnul(buf.buf, '\n');
 
-		strbuf_addf(&header, "%s ", comment_line_str);
-		strbuf_addf(&header, _(combined_commit_msg_fmt),
-			    ctx->current_fixup_count + 2);
+		add_squash_combination_header(&header,
+					      ctx->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);
 		if (is_fixup_flag(command, flag) && !seen_squash(ctx))
@@ -2116,12 +2128,9 @@ static int update_squash_messages(struct repository *r,
 			repo_unuse_commit_buffer(r, head_commit, head_message);
 			return error(_("cannot write '%s'"), rebase_path_fixup_msg());
 		}
-		strbuf_addf(&buf, "%s ", comment_line_str);
-		strbuf_addf(&buf, _(combined_commit_msg_fmt), 2);
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addstr(&buf, is_fixup_flag(command, flag) ?
-			      _(skip_first_commit_msg_str) :
-			      _(first_commit_msg_str));
+		add_squash_combination_header(&buf, 2);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, 1, is_fixup_flag(command, flag));
 		strbuf_addstr(&buf, "\n\n");
 		if (is_fixup_flag(command, flag))
 			strbuf_add_commented_lines(&buf, body, strlen(body),
@@ -2140,9 +2149,8 @@ static int update_squash_messages(struct repository *r,
 	if (command == TODO_SQUASH || is_fixup_flag(command, flag)) {
 		res = append_squash_message(&buf, body, command, opts, flag);
 	} else if (command == TODO_FIXUP) {
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),
-			    ++ctx->current_fixup_count + 1);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, ++ctx->current_fixup_count + 1, 1);
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body),
 					   comment_line_str);
diff --git a/sequencer.h b/sequencer.h
index 64a9c7fb1b..b01f897020 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,6 +119,13 @@ enum todo_command {
 	TODO_COMMENT
 };
 
+/* Bits for the "flags" member of struct todo_item */
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG    = (1 << 0),
+	TODO_REPLACE_FIXUP_MSG = (1 << 1),
+	TODO_EDIT_FIXUP_MSG    = (1 << 2),
+};
+
 struct todo_item {
 	enum todo_command command;
 	struct commit *commit;
@@ -208,6 +215,29 @@ int todo_list_rearrange_squash(struct todo_list *todo_list);
  */
 void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
 
+/*
+ * Append the "This is a combination of N commits." banner that "git rebase
+ * -i" writes at the top of a squashed commit's message, commented out with
+ * the comment character.
+ */
+void add_squash_combination_header(struct strbuf *buf, int n);
+
+/*
+ * Append the header (1-based N) that "git rebase -i" writes above each message
+ * when squashing, commented out with the comment character. With SKIP it reads
+ * "The ... commit message will be skipped" for a message that is dropped (a
+ * fixup), otherwise "This is the ... commit message".
+ */
+void add_squash_message_header(struct strbuf *buf, int n, int skip);
+
+/*
+ * Return the length of the leading subject of BODY when it should be commented
+ * out in a squash message, or 0 otherwise. An "amend!" subject always
+ * qualifies; "squash!" and "fixup!" subjects only when SQUASHING, since a
+ * plain fixup chain keeps them.
+ */
+size_t squash_subject_comment_len(const char *body, int squashing);
+
 void append_conflicts_hint(struct index_state *istate,
 		struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
 enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,
-- 
gitgitgadget

[PATCH v13 4/8] history: add skeleton for squash subcommand

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Add the entry point and option parsing for "git history squash". Pass
the remaining arguments through setup_revisions() so the command accepts
revision ranges and rev-list options, while restoring the ordering and
simplification settings required by the fold if an option changes them.

Require at least one BOTTOM revision. The squashed commit needs a commit
outside the selected range to serve as its base, so a single positive
revision is not a sufficient range.

Keep this step limited to defining the revision input contract so graph
validation and the rewrite can be added independently.

Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  1 +
 builtin/history.c              | 94 ++++++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 28b477cd37..b660baf94d 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -12,6 +12,7 @@ git history drop <commit> [--dry-run] [--update-refs=(branches|head)] [--empty=(
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>
 
 DESCRIPTION
 -----------
diff --git a/builtin/history.c b/builtin/history.c
index a60e8dbcd0..4f5a7a46ce 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -34,6 +34,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -1004,6 +1006,96 @@ out:
 	return ret;
 }
 
+static int setup_squash_revisions(struct repository *repo,
+				  int argc, const char **argv,
+				  struct rev_info *revs)
+{
+	repo_init_revisions(repo, revs, NULL);
+	revs->reverse = 1;
+	revs->topo_order = 1;
+	revs->sort_order = REV_SORT_IN_GRAPH_ORDER;
+	revs->simplify_history = 0;
+	revs->ancestry_path = 1;
+	revs->limited = 1;
+	revs->ancestry_path_implicit_bottoms = 1;
+
+	argc = setup_revisions(argc, argv, revs, NULL);
+	if (argc > 1)
+		return error(_("unrecognized argument: %s"), argv[1]);
+
+	if (revs->reverse != 1 || revs->topo_order != 1 ||
+	    revs->sort_order != REV_SORT_IN_GRAPH_ORDER ||
+	    revs->simplify_history != 0 || revs->boundary == 1 ||
+	    revs->ancestry_path != 1 || revs->limited != 1 ||
+	    revs->ancestry_path_implicit_bottoms != 1) {
+		warning(_("ignoring rev-list options that would change how the "
+			  "range is walked"));
+		revs->reverse = 1;
+		revs->topo_order = 1;
+		revs->sort_order = REV_SORT_IN_GRAPH_ORDER;
+		revs->simplify_history = 0;
+		revs->boundary = 0;
+		revs->ancestry_path = 1;
+		revs->limited = 1;
+		revs->ancestry_path_implicit_bottoms = 1;
+	}
+
+	/*
+	 * A squash needs a base to reparent onto, so the range has to exclude
+	 * something, as in "<base>..<tip>". A revision range with no such
+	 * bottom commit cannot be squashed.
+	 */
+	for (size_t i = 0; i < revs->cmdline.nr; i++)
+		if (revs->cmdline.rev[i].flags & BOTTOM)
+			return 0;
+
+	return error(_("not a '<base>..<tip>' revision range"));
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	int dry_run = 0;
+	int edit = 1;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BOOL('e', "edit", &edit,
+			 N_("edit the commit message")),
+		OPT_END(),
+	};
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage,
+			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
+	if (argc < 2) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	ret = setup_squash_revisions(repo, argc, argv, &revs);
+	if (ret < 0)
+		goto out;
+
+	ret = error(_("squashing commits is not implemented yet"));
+
+out:
+	release_revisions(&revs);
+	return ret;
+}
+
 static int update_worktree(struct repository *repo,
 			   const struct commit *old_head,
 			   const struct commit *new_head,
@@ -1192,6 +1284,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -1200,6 +1293,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
-- 
gitgitgadget

[PATCH v13 5/8] history: validate squash revision ranges

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Walk the selected commits in topological order from oldest to newest and
mark each one as it is seen. Every parent after the oldest commit must
already be selected or also be a parent of the oldest commit. This
accepts merges contained by the range while rejecting a merge arm that
entered it from elsewhere.

Track the remaining graph tips during the same walk and require exactly
one. Also reject empty and single-commit ranges and any selection that
reaches a root commit. These checks identify the oldest commit whose
parents will be preserved and the single tip whose tree will be used by
the rewrite.

Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c         | 119 ++++++++++++++++++++++++++++++++++----
 object.h                  |   1 +
 t/meson.build             |   1 +
 t/t3455-history-squash.sh |  65 +++++++++++++++++++++
 4 files changed, 174 insertions(+), 12 deletions(-)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/builtin/history.c b/builtin/history.c
index 4f5a7a46ce..6541a397e8 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1006,6 +1006,9 @@ out:
 	return ret;
 }
 
+#define SQUASH_SEEN (1u << 11)
+#define SQUASH_TIP (1u << 12)
+
 static int setup_squash_revisions(struct repository *repo,
 				  int argc, const char **argv,
 				  struct rev_info *revs)
@@ -1052,6 +1055,104 @@ static int setup_squash_revisions(struct repository *repo,
 	return error(_("not a '<base>..<tip>' revision range"));
 }
 
+/*
+ * Resolve a revision range into its oldest commit and single tip. Every
+ * parent after the oldest commit must either be selected or also be a parent
+ * of the oldest commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				int argc, const char **argv,
+				struct commit **oldest_out,
+				struct commit **tip_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *oldest = NULL, *tip = NULL;
+	int ret, tip_count = 0;
+	bool walk_started = false;
+
+	ret = setup_squash_revisions(repo, argc, argv, &revs);
+	if (ret < 0)
+		goto out;
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+	walk_started = true;
+	while ((commit = get_revision(&revs))) {
+		struct commit_list *p;
+
+		if (!commit->parents) {
+			ret = error(_("cannot squash down to root commit"));
+			goto out;
+		}
+		for (p = commit->parents; oldest && p; p = p->next) {
+			struct commit_list *q;
+			struct object *o;
+			bool seen;
+
+			if (repo_parse_commit(repo, p->item)) {
+				ret = error(_("cannot parse commit"));
+				goto out;
+			}
+			o = &p->item->object;
+			seen = o->flags & SQUASH_SEEN;
+			/*
+			 * Allow parents that match the parents of the
+			 * squashed commit.
+			 */
+			for (q = oldest->parents; !seen && q; q = q->next)
+				if (p->item == q->item)
+					seen = true;
+			if (!seen) {
+				ret = error(_("parent %s of commit %s is "
+					      "outside the revision range"),
+					    repo_find_unique_abbrev(repo, &o->oid,
+								    DEFAULT_ABBREV),
+					    repo_find_unique_abbrev(repo,
+								    &commit->object.oid,
+								    DEFAULT_ABBREV));
+				goto out;
+			}
+			if (o->flags & SQUASH_TIP) {
+				tip_count--;
+				o->flags &= ~SQUASH_TIP;
+			}
+		}
+		if (!oldest)
+			oldest = commit;
+		tip = commit;
+		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
+		tip_count++;
+	}
+
+	if (!tip_count) {
+		ret = error(_("the revision range is empty"));
+		goto out;
+	} else if (tip_count != 1) {
+		ret = error(_("the revision range contains more than one tip "
+			      "commit"));
+		goto out;
+	} else if (oldest == tip) {
+		ret = error(_("the revision range holds a single commit; "
+			      "nothing to squash"));
+		goto out;
+	} else if (!oldest->parents) {
+		BUG("an in-range commit must have a parent");
+	}
+
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
+	if (walk_started)
+		reset_revision_walk();
+	release_revisions(&revs);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1074,26 +1175,20 @@ static int cmd_history_squash(int argc,
 			 N_("edit the commit message")),
 		OPT_END(),
 	};
-	struct rev_info revs = { 0 };
+	struct commit *oldest, *tip;
 	int ret;
 
 	argc = parse_options(argc, argv, prefix, options, usage,
 			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
-	if (argc < 2) {
-		ret = error(_("command expects a revision range"));
-		goto out;
-	}
+	if (argc < 2)
+		return error(_("command expects a revision range"));
 	repo_config(repo, git_default_config, NULL);
 
-	ret = setup_squash_revisions(repo, argc, argv, &revs);
+	ret = resolve_squash_range(repo, argc, argv, &oldest, &tip);
 	if (ret < 0)
-		goto out;
-
-	ret = error(_("squashing commits is not implemented yet"));
+		return ret;
 
-out:
-	release_revisions(&revs);
-	return ret;
+	return error(_("squashing commits is not implemented yet"));
 }
 
 static int update_worktree(struct repository *repo,
diff --git a/object.h b/object.h
index 8fb03ff90a..dcf30156ca 100644
--- a/object.h
+++ b/object.h
@@ -74,6 +74,7 @@ void object_array_init(struct object_array *array);
  * bisect.c:                                        16
  * bundle.c:                                        16
  * http-push.c:                          11-----14
+ * builtin/history.c:                    1112
  * commit-graph.c:                                15
  * commit-reach.c:                                  16-------20
  * builtin/last-modified.c:                         1617
diff --git a/t/meson.build b/t/meson.build
index a25f37d2f5..78b8ea54ad 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -406,6 +406,7 @@ integration_tests = [
   't3452-history-split.sh',
   't3453-history-fixup.sh',
   't3454-history-drop.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..df92aa4f6c
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,65 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+test_expect_success 'setup linear history' '
+	test_commit base file a start &&
+	test_commit one file b &&
+	test_commit two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "expects a revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the revision range is empty" err
+'
+
+test_expect_success 'errors on a single revision that is not a range' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "not a .*range" err &&
+	test_must_fail git history squash HEAD~1 2>err &&
+	test_grep "not a .*range" err
+'
+
+test_expect_success 'errors on a range holding a single commit' '
+	test_must_fail git history squash "HEAD^!" 2>err &&
+	test_grep "single commit; nothing to squash" err
+'
+
+test_expect_success 'rejects a root commit' '
+	oid=$(git commit-tree -m root three^{tree}) &&
+	test_must_fail git history squash \
+		--ancestry-path=start "$oid..three" 2>err &&
+	test_grep "cannot squash down to root commit" err
+'
+
+test_expect_success 'rejects multiple tips' '
+	oid=$(git commit-tree -m tip -p start^0 three^{tree}) &&
+	test_must_fail git history squash ^start "$oid" three~1 2>err &&
+	test_grep "revision range contains more than one tip" err
+'
+
+test_expect_success 'rejects a merge parent outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "parent .* of commit .* is outside the revision range" err
+'
+
+test_done
-- 
gitgitgadget

[PATCH v13 6/8] history: protect branches when squashing a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

A local branch that descends from the selected graph without containing
its tip cannot be replayed as a descendant of the squashed commit. Find
those branches with ref-filter before creating any replacement objects
and refuse the operation unless --update-refs=head was requested.

Limit this protection to local branches, matching the refs that the
default history rewrite mode updates; tags and remote-tracking refs
remain untouched. Sort the blocking refs and print their short branch
names so the user can decide whether to move them or leave them behind.

Add advice.historyUpdateRefs for the hint that points to
--update-refs=head.

Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |  4 ++
 advice.c                         |  1 +
 advice.h                         |  1 +
 builtin/history.c                | 70 ++++++++++++++++++++++++++++++--
 t/t3455-history-squash.sh        | 39 ++++++++++++++++++
 5 files changed, 111 insertions(+), 4 deletions(-)

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 81f80a9274..3d91c90eda 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -59,6 +59,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a local branch
+		cannot be rewritten as a descendant of the squashed commit, to
+		tell the user about `--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/advice.c b/advice.c
index 63bf8b0c5f..401d047391 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 66f6cd6a77..3f0b4f0485 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index 6541a397e8..e65b76b59f 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -16,10 +17,12 @@
 #include "path.h"
 #include "read-cache.h"
 #include "refs.h"
+#include "ref-filter.h"
 #include "replay.h"
 #include "reset.h"
 #include "revision.h"
 #include "sequencer.h"
+#include "string-list.h"
 #include "strvec.h"
 #include "tree.h"
 #include "tree-walk.h"
@@ -1061,6 +1064,7 @@ static int setup_squash_revisions(struct repository *repo,
  * of the oldest commit.
  */
 static int resolve_squash_range(struct repository *repo,
+				bool update_branches,
 				int argc, const char **argv,
 				struct commit **oldest_out,
 				struct commit **tip_out)
@@ -1069,6 +1073,8 @@ static int resolve_squash_range(struct repository *repo,
 	struct commit *commit, *oldest = NULL, *tip = NULL;
 	int ret, tip_count = 0;
 	bool walk_started = false;
+	struct ref_filter filter = REF_FILTER_INIT;
+	struct ref_array refs = { 0 };
 
 	ret = setup_squash_revisions(repo, argc, argv, &revs);
 	if (ret < 0)
@@ -1101,9 +1107,12 @@ static int resolve_squash_range(struct repository *repo,
 			 * Allow parents that match the parents of the
 			 * squashed commit.
 			 */
-			for (q = oldest->parents; !seen && q; q = q->next)
-				if (p->item == q->item)
+			for (q = oldest->parents; !seen && q; q = q->next) {
+				if (p->item == q->item) {
 					seen = true;
+					commit_list_insert(commit, &filter.with_commit);
+				}
+			}
 			if (!seen) {
 				ret = error(_("parent %s of commit %s is "
 					      "outside the revision range"),
@@ -1119,12 +1128,17 @@ static int resolve_squash_range(struct repository *repo,
 				o->flags &= ~SQUASH_TIP;
 			}
 		}
-		if (!oldest)
+		if (!oldest) {
+			commit_list_insert(commit, &filter.with_commit);
 			oldest = commit;
+		}
 		tip = commit;
 		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
 		tip_count++;
 	}
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
+	reset_revision_walk();
+	walk_started = false;
 
 	if (!tip_count) {
 		ret = error(_("the revision range is empty"));
@@ -1141,6 +1155,49 @@ static int resolve_squash_range(struct repository *repo,
 		BUG("an in-range commit must have a parent");
 	}
 
+	commit_list_insert(tip, &filter.no_commit);
+	filter.kind = FILTER_REFS_BRANCHES;
+	if (update_branches &&
+	    filter_refs(&refs, &filter, filter.kind)) {
+		ret = error(_("could not filter refs"));
+		goto out;
+	}
+	if (refs.nr) {
+		struct ref_format format = REF_FORMAT_INIT;
+		struct ref_sorting *sorting;
+		struct string_list sorting_options = STRING_LIST_INIT_DUP;
+		struct strbuf branches = STRBUF_INIT;
+		struct strbuf err = STRBUF_INIT;
+
+		format.format = "%(refname:short)";
+		if (verify_ref_format(&format))
+			BUG("invalid branch format");
+		string_list_append(&sorting_options, "refname");
+		sorting = ref_sorting_options(&sorting_options);
+		ref_array_sort(sorting, &refs);
+		for (int i = 0; i < refs.nr; i++) {
+			strbuf_reset(&err);
+			strbuf_addstr(&branches, "\n  ");
+			if (format_ref_array_item(refs.items[i], &format,
+						  &branches, &err))
+				BUG("could not format branch name: %s", err.buf);
+		}
+		/*
+		 * TODO: also check HEADS from other worktrees.
+		 */
+		ret = error(_("the following branches cannot be rewritten as "
+			      "descendants of the squashed commit:%s"), branches.buf);
+		advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+				  _("Use --update-refs=head to rewrite only "
+				    "the current branch and leave such branches "
+				    "untouched."));
+		strbuf_release(&err);
+		strbuf_release(&branches);
+		ref_sorting_release(sorting);
+		string_list_clear(&sorting_options, 0);
+		goto out;
+	}
+
 	*oldest_out = oldest;
 	*tip_out = tip;
 	ret = 0;
@@ -1150,6 +1207,8 @@ out:
 	if (walk_started)
 		reset_revision_walk();
 	release_revisions(&revs);
+	ref_filter_clear(&filter);
+	ref_array_clear(&refs);
 	return ret;
 }
 
@@ -1183,8 +1242,11 @@ static int cmd_history_squash(int argc,
 	if (argc < 2)
 		return error(_("command expects a revision range"));
 	repo_config(repo, git_default_config, NULL);
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
 
-	ret = resolve_squash_range(repo, argc, argv, &oldest, &tip);
+	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
+				   argc, argv, &oldest, &tip);
 	if (ret < 0)
 		return ret;
 
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index df92aa4f6c..b1f65de5f5 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -62,4 +62,43 @@ test_expect_success 'rejects a merge parent outside the range' '
 	test_grep "parent .* of commit .* is outside the revision range" err
 '
 
+test_expect_success 'prints branches that cannot follow the squash' '
+	test_when_finished \
+		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
+		 git branch -D feature" &&
+	git checkout -f -b feature start &&
+	test_commit C1 &&
+	test_commit C2 &&
+	git checkout -b topic-1 start &&
+	test_commit C3 &&
+	test_commit C4 &&
+	git checkout C3 &&
+	test_commit C5 &&
+	git checkout feature &&
+	git merge C5 &&
+	test_commit C6 &&
+	git checkout -b topic-2 C2 &&
+	test_commit C7 &&
+	git checkout feature &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "^error: the following branches cannot be rewritten" err &&
+	test_grep "^  topic-1$" err &&
+	test_grep "^  topic-2$" err &&
+	test_grep "^hint: .* --update-refs=head" err
+'
+
+test_expect_success 'advice.historyUpdateRefs silences the hint' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "^error: the following branches cannot be rewritten" err &&
+	test_grep "^  mid$" err &&
+	test_grep ! "hint:" err &&
+
+	git branch -D mid
+'
+
 test_done
-- 
gitgitgadget

[PATCH v13 7/8] history: create squashed commits without editing

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Create one replacement commit from the resolved range when --no-edit is
selected. Preserve the authorship and all parents of the oldest commit,
use the tip tree, and replay descendants through the existing history
rewrite machinery. Record the complete revision expression in the
reflog and retain dry-run and update-refs behavior.

Resolve fixup!, squash! and amend! subjects while walking the range.
Reject markers whose targets are not selected and refuse any no-edit
fold that would discard a squash! or amend! message. A range made
entirely from related markers can still be consolidated, with the last
applicable amend! body supplying the message.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  44 ++-
 builtin/history.c              | 324 ++++++++++++++++-
 object.h                       |   2 +-
 t/t3455-history-squash.sh      | 633 +++++++++++++++++++++++++++++++--
 4 files changed, 968 insertions(+), 35 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index b660baf94d..fb04a67685 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -44,8 +44,11 @@ at once.
 LIMITATIONS
 -----------
 
-This command does not (yet) work with histories that contain merges. You
-should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
+This command does not (yet) replay merge commits onto the rewritten
+history: if a commit that would be replayed is a merge, the operation is
+rejected, and you should use linkgit:git-rebase[1] with the
+`--rebase-merges` flag instead. The `squash` subcommand can still fold merges
+that lie inside the selected range, subject to the restrictions below.
 
 Furthermore, the command does not support operations that can result in merge
 conflicts. This limitation is by design as history rewrites are not intended to
@@ -114,6 +117,43 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's authorship and
+	takes the tree of the range's newest commit, so the whole range
+	collapses into a single commit. Commits above the range are replayed
+	on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash HEAD~3..HEAD` folds the three most recent commits into
+one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
+while leaving the two newest commits in place. Several revisions may be
+given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
+already on `topic`. Rev-list options may also be given, but any that would
+change how the range is walked are overridden with a warning.
++
+With `--no-edit`, the oldest commit's message is preserved, except that an
+`amend!` commit targeting it replaces its message.
++
+The selected commits must form a connected graph with a single tip and must
+not include a root commit. Every parent of a commit after the oldest one must
+either be selected or also be a parent of the oldest commit. When the oldest
+commit is a merge, all of its parents are preserved in the squashed commit.
++
+A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
+targets is also in the range, so the fold does not silently absorb a
+marker meant for a commit outside it. As an exception, a range made up entirely
+of markers for one target is combined into a single commit. With `--no-edit`,
+the last `amend!` message is used if there is one; a `squash!` or `amend!` is
+otherwise refused if folding it would discard its message.
++
+A local branch descended from a selected commit but not from the range tip
+cannot be rewritten as a descendant of the result, so with the default
+`--update-refs=branches` the command refuses. Rerun with `--update-refs=head`
+to rewrite only the current branch and leave such branches unchanged. Tags
+and remote-tracking refs are always left unchanged.
+
 OPTIONS
 -------
 
diff --git a/builtin/history.c b/builtin/history.c
index e65b76b59f..915cfb0cb9 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1011,6 +1011,260 @@ out:
 
 #define SQUASH_SEEN (1u << 11)
 #define SQUASH_TIP (1u << 12)
+#define SQUASH_AMEND_TARGET (1u << 13)
+
+static bool is_autosquash_subject(const char *s)
+{
+	return starts_with(s, "amend!") || starts_with(s, "fixup!") ||
+		starts_with(s, "squash!");
+}
+
+static bool skip_one_autosquash_prefix(const char *s, const char **out)
+{
+	if (skip_prefix(s, "amend!", out) || skip_prefix(s, "fixup!", out) ||
+	    skip_prefix(s, "squash!", out)) {
+		while (**out == ' ')
+			(*out)++;
+		return true;
+	}
+	return false;
+}
+
+static void truncate_message_to_subject(struct strbuf *msg)
+{
+	const char *eos = strstr(msg->buf, "\n\n");
+
+	if (eos)
+		strbuf_setlen(msg, eos - msg->buf + 1);
+}
+
+struct subject_data {
+	struct strintmap subjects;
+	struct strbuf subject;
+	struct strbuf squash_message;
+	const char *message;
+	bool edit_message;
+};
+
+#define SUBJECT_DATA_INIT {		\
+	.subjects = STRINTMAP_INIT,	\
+	.subject = STRBUF_INIT,		\
+	.squash_message = STRBUF_INIT,	\
+}
+
+static void subject_data_clear(struct subject_data *data)
+{
+	strintmap_clear(&data->subjects);
+	strbuf_release(&data->subject);
+	strbuf_release(&data->squash_message);
+}
+
+static int squash_amend_message(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data,
+				unsigned flags)
+{
+	const char *body = data->message + data->subject.len;
+
+	while (isspace(*body))
+		body++;
+
+	if (!*body) {
+		warning(_("ignoring %s (%s): message body is empty"),
+			repo_find_unique_abbrev(repo, &commit->object.oid,
+						DEFAULT_ABBREV),
+			data->subject.buf);
+		return 0;
+	}
+
+	if (data->edit_message) {
+		return 0;
+	} else if (flags & SQUASH_AMEND_TARGET) {
+		if (starts_with(data->squash_message.buf, "squash!"))
+			return error(_("squashing %s (%s) would overwrite "
+				       "'squash!' message, please combine them "
+				       "using '--edit'"),
+				     repo_find_unique_abbrev(repo,
+							     &commit->object.oid,
+							     DEFAULT_ABBREV),
+				     data->subject.buf);
+		if (starts_with(data->squash_message.buf, "fixup!"))
+			strbuf_splice(&data->squash_message, 0, 5, "amend!", 5);
+		if (starts_with(data->squash_message.buf, "amend!")) {
+			truncate_message_to_subject(&data->squash_message);
+			strbuf_addch(&data->squash_message, '\n');
+		} else {
+			strbuf_reset(&data->squash_message);
+		}
+		strbuf_addstr(&data->squash_message, body);
+		strbuf_complete_line(&data->squash_message);
+	} else {
+		return error(_("cannot squash %s (%s) that does not target "
+			       "base commit without '--edit'"),
+			     repo_find_unique_abbrev(repo, &commit->object.oid,
+						     DEFAULT_ABBREV),
+			     data->subject.buf);
+	}
+	return 0;
+}
+
+static int squash_squash_message(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data,
+				unsigned flags)
+{
+	const char *body = data->message + data->subject.len;
+
+	while (isspace(*body))
+		body++;
+
+	if (data->edit_message) {
+		return 0;
+	} else if (flags & SQUASH_AMEND_TARGET) {
+		if (starts_with(data->squash_message.buf, "fixup!")) {
+			truncate_message_to_subject(&data->squash_message);
+			strbuf_splice(&data->squash_message, 0, 5, "squash", 6);
+		}
+		if (starts_with(data->squash_message.buf, "squash!")) {
+			strbuf_addch(&data->squash_message, '\n');
+			strbuf_addstr(&data->squash_message, body);
+			strbuf_complete_line(&data->squash_message);
+		} else {
+			return error(_("squashing %s (%s) would discard its "
+				       "message, please combine them using "
+				       "'--edit'"),
+				     repo_find_unique_abbrev(repo,
+							     &commit->object.oid,
+							     DEFAULT_ABBREV),
+				     data->subject.buf);
+		}
+	} else {
+		return error(_("cannot squash %s (%s) that does not target "
+			       "base commit without '--edit'"),
+			      repo_find_unique_abbrev(repo, &commit->object.oid,
+						      DEFAULT_ABBREV),
+			      data->subject.buf);
+	}
+	return 0;
+}
+
+static int squash_check_can_autosquash(struct repository *repo,
+				       struct commit *commit,
+				       struct subject_data *data,
+				       unsigned flags)
+{
+	commit->object.flags |= flags & SQUASH_AMEND_TARGET;
+	if (starts_with(data->subject.buf, "amend!"))
+		return squash_amend_message(repo, commit, data, flags);
+	else if (starts_with(data->subject.buf, "squash!"))
+		return squash_squash_message(repo, commit, data, flags);
+
+	return 0;
+}
+
+static int squash_check_autosquash_subject(struct repository *repo,
+					   struct commit *commit,
+					   struct subject_data *data)
+{
+	const char* s = data->subject.buf;
+	struct commit *target;
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+	/* Try skipping autosquash prefixes one at a time to allow
+	 * squashing
+	 *     a commit
+	 *     fixup! fixup! a commit
+	 *
+	 * where we may have started with
+	 *     a commit
+	 *     fixup! a commit
+	 *     fixup! fixup! a commit
+	 *
+	 * and squashed the first fixup separately from the second
+	 */
+	while (skip_one_autosquash_prefix(s, &s)) {
+		unsigned flags = strintmap_get(&data->subjects, s);
+		if (flags)
+			return squash_check_can_autosquash(repo, commit, data, flags);
+	}
+	/*
+	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
+	 * "fixup! main". If the target is not being squshed check the subject
+	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
+	 * squashed together.
+	 */
+	target = lookup_commit_reference_by_name(s);
+	if (target && istarts_with(oid_to_hex(&target->object.oid), s)) {
+		unsigned flags =
+			target->object.flags & (SQUASH_SEEN | SQUASH_AMEND_TARGET);
+		if (!flags) {
+			const char *subject_start;
+			const char *buffer = repo_logmsg_reencode(repo, target,
+								  NULL, NULL);
+			size_t subject_len = find_commit_subject(buffer,
+								 &subject_start);
+			char *subject = xmemdupz(subject_start, subject_len);
+
+			flags = strintmap_get(&data->subjects, subject);
+			free(subject);
+			repo_unuse_commit_buffer(repo, target, buffer);
+		}
+		if (flags)
+			return squash_check_can_autosquash(repo, commit,
+							   data, flags);
+	}
+	/* Try subject prefix matches */
+	strintmap_for_each_entry(&data->subjects, &iter, entry) {
+		s = data->subject.buf;
+		while(skip_one_autosquash_prefix(s, &s)) {
+			if (starts_with(entry->key, s)) {
+				unsigned value = (intptr_t)entry->value;
+
+				return squash_check_can_autosquash(repo, commit,
+								   data, value);
+			}
+		}
+	}
+	return error(_("cannot squash %s (%s): its target is not being "
+		       "squashed"),
+		       repo_find_unique_abbrev(repo, &commit->object.oid,
+					       DEFAULT_ABBREV),
+		       data->subject.buf);
+}
+
+static int squash_check_subject(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data)
+{
+	int ret = 0;
+	const char *buf = repo_logmsg_reencode(repo, commit, NULL, NULL);
+	size_t subject_len = find_commit_subject(buf, &data->message);
+
+	strbuf_reset(&data->subject);
+	strbuf_add(&data->subject, data->message, subject_len);
+
+	if (!strintmap_get_size(&data->subjects)) {
+		const char *s;
+
+		strbuf_addstr(&data->squash_message, data->message);
+		strbuf_complete_line(&data->squash_message);
+		/*
+		 * Strip a single autosquash prefix to allow squashing
+		 *     fixup! base
+		 *     amend! base
+		 */
+		s = data->subject.buf;
+		skip_one_autosquash_prefix(s, &s);
+		strintmap_set(&data->subjects, s, SQUASH_AMEND_TARGET | SQUASH_SEEN);
+		commit->object.flags |= SQUASH_AMEND_TARGET;
+	} else if (is_autosquash_subject(data->subject.buf)) {
+		ret = squash_check_autosquash_subject(repo, commit, data);
+	} else {
+		strintmap_set(&data->subjects, data->subject.buf, SQUASH_SEEN);
+	}
+	repo_unuse_commit_buffer(repo, commit, buf);
+	return ret;
+}
 
 static int setup_squash_revisions(struct repository *repo,
 				  int argc, const char **argv,
@@ -1067,9 +1321,11 @@ static int resolve_squash_range(struct repository *repo,
 				bool update_branches,
 				int argc, const char **argv,
 				struct commit **oldest_out,
-				struct commit **tip_out)
+				struct commit **tip_out,
+				char **message_out)
 {
 	struct rev_info revs;
+	struct subject_data subject_data = SUBJECT_DATA_INIT;
 	struct commit *commit, *oldest = NULL, *tip = NULL;
 	int ret, tip_count = 0;
 	bool walk_started = false;
@@ -1132,6 +1388,10 @@ static int resolve_squash_range(struct repository *repo,
 			commit_list_insert(commit, &filter.with_commit);
 			oldest = commit;
 		}
+		if (squash_check_subject(repo, commit, &subject_data)) {
+			ret = -1;
+			goto out;
+		}
 		tip = commit;
 		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
 		tip_count++;
@@ -1200,12 +1460,15 @@ static int resolve_squash_range(struct repository *repo,
 
 	*oldest_out = oldest;
 	*tip_out = tip;
+	*message_out = strbuf_detach(&subject_data.squash_message, NULL);
 	ret = 0;
 
 out:
-	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP |
+			   SQUASH_AMEND_TARGET);
 	if (walk_started)
 		reset_revision_walk();
+	subject_data_clear(&subject_data);
 	release_revisions(&revs);
 	ref_filter_clear(&filter);
 	ref_array_clear(&refs);
@@ -1234,23 +1497,68 @@ static int cmd_history_squash(int argc,
 			 N_("edit the commit message")),
 		OPT_END(),
 	};
-	struct commit *oldest, *tip;
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct commit *oldest, *tip, *rewritten;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	char *message_template = NULL;
+	struct rev_info revs = { 0 };
 	int ret;
 
 	argc = parse_options(argc, argv, prefix, options, usage,
 			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
-	if (argc < 2)
-		return error(_("command expects a revision range"));
+	if (argc < 2) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
 	repo_config(repo, git_default_config, NULL);
+
 	if (action == REF_ACTION_DEFAULT)
 		action = REF_ACTION_BRANCHES;
 
+	strbuf_addstr(&reflog_msg, "squash: updating ");
+	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
+
 	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
-				   argc, argv, &oldest, &tip);
+				   argc, argv, &oldest, &tip,
+				   &message_template);
 	if (ret < 0)
-		return ret;
+		goto out;
+	if (edit) {
+		ret = error(_("message editing is not supported yet; use '--no-edit'"));
+		goto out;
+	}
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo,
+					oldest->parents->item)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+
+	ret = commit_tree_ext(repo, "squash", oldest, message_template,
+			      oldest->parents, base_tree_oid, tip_tree_oid,
+			      &rewritten, 0);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
 
-	return error(_("squashing commits is not implemented yet"));
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	release_revisions(&revs);
+	free(message_template);
+	return ret;
 }
 
 static int update_worktree(struct repository *repo,
diff --git a/object.h b/object.h
index dcf30156ca..46cade33fb 100644
--- a/object.h
+++ b/object.h
@@ -74,7 +74,7 @@ void object_array_init(struct object_array *array);
  * bisect.c:                                        16
  * bundle.c:                                        16
  * http-push.c:                          11-----14
- * builtin/history.c:                    1112
+ * builtin/history.c:                    11---13
  * commit-graph.c:                                15
  * commit-reach.c:                                  16-------20
  * builtin/last-modified.c:                         1617
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index b1f65de5f5..d2d8e5fdb9 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -4,11 +4,50 @@ test_description='tests for git-history squash subcommand'
 
 . ./test-lib.sh
 
-test_expect_success 'setup linear history' '
+stage_file () {
+	printf "%s\n" "$1" >file &&
+	git add file
+}
+
+commit_with_message () {
+	printf "%b" "$1" >msg &&
+	git commit --allow-empty -qF msg
+}
+
+check_commit_count () {
+	git rev-list --count "$1" >actual &&
+	echo "$2" >expect &&
+	test_cmp expect actual
+}
+
+check_log_subjects () {
+	git log --format="%s" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+check_log_messages () {
+	git log --format="%B" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+# Checks that the author data of two commits matches
+# Usage: check_commit_author <rev1> <rev2>
+check_commit_author () {
+	git show -s --format="%an <%ae> %ad" "$1" >expect &&
+	git show -s --format="%an <%ae> %ad" "$2" >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'setup linear history touching two files' '
 	test_commit base file a start &&
-	test_commit one file b &&
-	test_commit two file c &&
-	test_commit three file d
+	GIT_AUTHOR_NAME=One GIT_AUTHOR_EMAIL=one@example.com \
+		test_commit one other x &&
+	GIT_AUTHOR_NAME=Two GIT_AUTHOR_EMAIL=two@example.com \
+		test_commit two file c &&
+	GIT_AUTHOR_NAME=Three GIT_AUTHOR_EMAIL=three@example.com \
+		test_commit three file d
 '
 
 test_expect_success 'errors on missing range argument' '
@@ -29,40 +68,331 @@ test_expect_success 'errors on a single revision that is not a range' '
 '
 
 test_expect_success 'errors on a range holding a single commit' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
 	test_must_fail git history squash "HEAD^!" 2>err &&
-	test_grep "single commit; nothing to squash" err
+	test_grep "single commit; nothing to squash" err &&
+	test_cmp_rev "$head_before" HEAD
 '
 
-test_expect_success 'rejects a root commit' '
+test_expect_success 'rejects root commit' '
+	# create a disconnected root commit
 	oid=$(git commit-tree -m root three^{tree}) &&
-	test_must_fail git history squash \
-		--ancestry-path=start "$oid..three" 2>err &&
-	test_grep "cannot squash down to root commit" err
+	# because we pass --ancestry-path when calling setup_revs() it the
+	# revision walk will only include commits decended from $oid so
+	# we need to give it another --ancestry-path commit to actually walk
+	# any commits.
+	test_must_fail git history squash --ancestry-path=start $oid..three 2>err &&
+	echo "error: cannot squash down to root commit" >expect &&
+	test_cmp expect err
 '
 
 test_expect_success 'rejects multiple tips' '
 	oid=$(git commit-tree -m tip -p start^0 three^{tree}) &&
-	test_must_fail git history squash ^start "$oid" three~1 2>err &&
-	test_grep "revision range contains more than one tip" err
+	test_must_fail git history squash ^start $oid three~1 2>err &&
+	echo "error: the revision range contains more than one tip commit" >expect &&
+	test_cmp expect err &&
+
+	git reset --hard three &&
+	git history squash --no-edit ^start three~1 three &&
+	test_cmp_rev HEAD~1 start^0 &&
+	test_cmp_rev HEAD^{tree} three^{tree}
 '
 
-test_expect_success 'rejects a merge parent outside the range' '
-	git reset --hard start &&
+test_expect_success 'accepts multiple revision arguments with an exclusion' '
+	git reset --hard three &&
+	git branch -f keep HEAD~2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start..HEAD ^keep &&
+
+	git reflog -1 --format=%gs >actual &&
+	echo "squash: updating start..HEAD ^keep" >expect &&
+	test_cmp expect actual &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	two
+	one
+	EOF
+	test_cmp_rev keep HEAD~1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git branch -D keep
+'
+
+test_expect_success 'squashes a branch the current branch is not on' '
+	git reset --hard three &&
 	main=$(git symbolic-ref --short HEAD) &&
-	git checkout -b outside-parent &&
-	test_commit --no-tag outside-parent outside x &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b off-history start &&
+	test_commit --no-tag off-one off a &&
+	test_commit --no-tag off-two off b &&
 	git checkout "$main" &&
-	test_commit --no-tag outside-main file b &&
-	base=$(git rev-parse HEAD) &&
-	test_commit --no-tag outside-mid file c &&
-	git merge --no-ff -m "merge outside-parent" outside-parent &&
-	git branch -D outside-parent &&
 
-	test_must_fail git history squash "$base.." 2>err &&
-	test_grep "parent .* of commit .* is outside the revision range" err
+	git history squash --no-edit start..off-history &&
+
+	check_commit_count start..off-history 1 &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D off-history
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash --no-edit start.. &&
+
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	check_log_subjects -1 <<-\EOF &&
+	one
+	EOF
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'sanitizes rev-list walk options, before and after --' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit --date-order start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git reset --hard three &&
+	git history squash --no-edit -- --reverse start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start..@~1 &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	three
+	one
+	EOF
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit "$root.." &&
+
+	check_commit_count "$root..HEAD" 1 &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashing a mix of fixups' '
+	git reset --hard three &&
+	echo fix >file &&
+	git commit --fixup=two -a &&
+	echo really fix >file &&
+	git commit --fixup=one -a &&
+	echo really really fix >file &&
+	git commit --fixup=HEAD~1 -a && # fixup! two
+	echo really really really fix >file &&
+	git commit --fixup=HEAD~1 -a && # fixup! one
+
+	# squashing fixup! with a target that is not being squashed fails
+	test_must_fail git history squash one.. 2>err &&
+	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
+
+	# squashing fixup! into fixup! with a different target fails
+	test_must_fail git history squash HEAD~4.. 2>err && # HEAD~4 is fixup! two
+	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
+
+	# squashing a sequence of fixup! commits into their targets
+	git history squash --no-edit start..HEAD~1 &&
+	test_cmp_rev start HEAD~2 &&
+	check_commit_author one HEAD~1 &&
+	test_commit_message HEAD~1 -m one &&
+
+	# squashing "fixup! fixup! <target>" into "<target>"
+	git history squash --no-edit start.. &&
+	test_cmp_rev start HEAD~1 &&
+	check_commit_author one HEAD &&
+	test_commit_message HEAD -m one
+'
+
+test_expect_success 'squashing "squash!" messages' '
+	git reset --hard two &&
+	echo fix >file &&
+	git commit --fixup=HEAD -a &&
+	oldest=$(git rev-parse HEAD) &&
+	echo better fix >file &&
+	git commit -a -F - <<-EOF &&
+	squash! $(git rev-parse two)
+
+	Append this
+	EOF
+
+	echo an even better fix >file &&
+	git commit -a -F - <<-EOF &&
+	squash! squash! two
+
+	Append this as well
+	EOF
+
+	# must edit when squashing "squash!" into its target
+	test_must_fail git history squash --no-edit two^.. 2>err &&
+	test_grep "^error: squashing .* (squash! [a-f0-9]*) would discard its message" err &&
+
+	# squashing "squash!" into "fixup!" appends messages and changes
+	# subject prefix
+	git history squash --no-edit two.. &&
+	test_cmp_rev HEAD^ two &&
+	test_commit_message HEAD <<-\EOF &&
+	squash! two
+
+	Append this
+
+	Append this as well
+	EOF
+	check_commit_author "$oldest" HEAD &&
+
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! two
+
+	A new message
+	EOF
+
+	# "amend!" does not replace "squash!"
+	test_must_fail git history squash --no-edit HEAD~2.. 2>err &&
+	test_grep "^error: squashing .* (amend! two) would overwrite .squash!. message" err
+'
+
+test_expect_success '--no-edit uses last "amend!" message without an editor' '
+	git reset --hard three &&
+	write_script editor <<-\EOF &&
+	exit 1
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	echo fix >file &&
+	git commit --author="Fix Me <fix.me@example.com>" --fixup=HEAD -a &&
+	git commit --allow-empty -F - <<-EOF &&
+	amend! $(git rev-parse --short HEAD)
+
+	The first reword
+
+	More detail
+	EOF
+
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! three
+
+	The second reword
+
+	Extra detail
+	EOF
+
+	test_commit WIP &&
+
+	cat >msg <<-EOF &&
+	amend! $(git rev-parse HEAD^ | tr a-f A-F)
+
+	The third reword
+
+	Excruciating detail
+	EOF
+
+	git commit --author="Someone Else <s.else@example.com>" --allow-empty \
+		-F msg &&
+
+	# squashing amend! updates the commit message
+	git history squash --no-edit three^.. &&
+	sed -e 1,2d msg | test_commit_message HEAD &&
+	check_commit_author three HEAD &&
+	test_cmp_rev HEAD^ three^ &&
+
+	# squashing amend! into fixup! updates subject prefix
+	git reset --hard HEAD@{1} &&
+	git history squash --no-edit three.. &&
+	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
+	check_commit_author HEAD@{1}~4 HEAD &&
+	test_cmp_rev HEAD^ three &&
+
+	# squashing amend! into amend! keeps original subject line
+	git reset --hard HEAD@{1} &&
+	git history squash --no-edit HEAD~3.. &&
+	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
+	test_cmp_rev HEAD~3 three &&
+
+	# all amend! messages must target the first commit
+	git reset --hard HEAD@{1} &&
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! WIP
+
+	The real message
+	EOF
+
+	test_must_fail git history squash --no-edit HEAD~4.. 2>err &&
+	test_grep "^error: cannot squash .* that does not target" err &&
+
+	# amend! message that targets commit that is not in range is rejected
+	test_must_fail git history squash --no-edit HEAD~3.. 2>err &&
+	test_grep "^error: cannot squash .* target is not being squashed" err &&
+	test_set_editor :
 '
 
-test_expect_success 'prints branches that cannot follow the squash' '
+test_expect_success 'squashing fixups into a merge' '
+	test_when_finished \
+		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
+		 git branch -D feature" &&
+	git checkout -f start &&
+	test_commit F1 &&
+	git checkout -b feature start &&
+	test_commit F2 &&
+	git merge F1 &&
+	echo fixed >F1.t &&
+	cat >msg <<-EOF &&
+	amend! $(git rev-parse HEAD)
+
+	merge F1 and F2
+
+	reworded
+	EOF
+
+	git commit -a -F msg &&
+	git history squash --no-edit HEAD^^! HEAD &&
+	test_cmp_rev HEAD^1 F2 &&
+	test_cmp_rev HEAD^2 F1 &&
+	test_cmp_rev HEAD@{1}^{tree} HEAD^{tree} &&
+	sed 1,2d msg | test_commit_message HEAD
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --no-edit --update-refs=head start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success 'refuses to fold a range a branch points into' '
 	test_when_finished \
 		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
 		 git branch -D feature" &&
@@ -85,20 +415,275 @@ test_expect_success 'prints branches that cannot follow the squash' '
 	test_grep "^error: the following branches cannot be rewritten" err &&
 	test_grep "^  topic-1$" err &&
 	test_grep "^  topic-2$" err &&
-	test_grep "^hint: .* --update-refs=head" err
+	test_grep "^hint: .* --update-refs=head" err &&
+	test_cmp_rev C6 HEAD &&
+
+	# squash succeeds with --update-refs=head
+	git history squash --no-edit --update-refs=head start.. &&
+	test_cmp_rev start HEAD^ &&
+	test_cmp_rev C6^{tree} HEAD^{tree} &&
+	test_cmp_rev C6 HEAD@{1}
 '
 
 test_expect_success 'advice.historyUpdateRefs silences the hint' '
 	git reset --hard three &&
 	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
 
 	test_must_fail git -c advice.historyUpdateRefs=false \
 		history squash start.. 2>err &&
 	test_grep "^error: the following branches cannot be rewritten" err &&
 	test_grep "^  mid$" err &&
 	test_grep ! "hint:" err &&
+	test_cmp_rev "$head_before" HEAD &&
 
 	git branch -D mid
 '
 
+test_expect_success 'leaves tags and remote-tracking refs unchanged' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	git update-ref refs/remotes/origin/mark HEAD~1 &&
+	mark_before=$(git rev-parse mark) &&
+
+	git history squash --no-edit start.. &&
+
+	test_cmp_rev "$mark_before" mark &&
+	test_cmp_rev "$mark_before" refs/remotes/origin/mark &&
+
+	git tag -d mark &&
+	git update-ref -d refs/remotes/origin/mark
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout "$main" &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	test_commit --no-tag after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF &&
+	before-side
+	EOF
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a merge of a branch that forked at the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b base-fork-side &&
+	test_commit --no-tag base-fork-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag base-fork-main file b &&
+	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
+	git branch -D base-fork-side &&
+	test_commit --no-tag base-fork-tail file c &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'refuses a merge whose other parent is outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "parent .* of commit .* is outside the revision range" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit "$base.." &&
+
+	check_commit_count "$base..HEAD" 1 &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'folds a range with two interior merges' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag two-merge-a file a1 &&
+	git checkout -b two-merge-s1 &&
+	test_commit --no-tag two-merge-s1 s1 x &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s1" two-merge-s1 &&
+	test_commit --no-tag two-merge-b file b1 &&
+	git checkout -b two-merge-s2 &&
+	test_commit --no-tag two-merge-s2 s2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s2" two-merge-s2 &&
+	git branch -D two-merge-s1 two-merge-s2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file s1 &&
+	test_path_is_file s2
+'
+
+test_expect_success 'folds a range with a nested merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b nested-outer &&
+	test_commit --no-tag nested-outer outer x &&
+	git checkout -b nested-inner &&
+	test_commit --no-tag nested-inner inner y &&
+	git checkout nested-outer &&
+	git merge --no-ff -m "merge inner" nested-inner &&
+	git checkout "$main" &&
+	test_commit --no-tag nested-main file b1 &&
+	git merge --no-ff -m "merge outer" nested-outer &&
+	git branch -D nested-outer nested-inner &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file outer &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range with an octopus merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag octo-base file a1 &&
+	git checkout -b octo-1 &&
+	test_commit --no-tag octo-1 o1 x &&
+	git checkout "$main" &&
+	git checkout -b octo-2 &&
+	test_commit --no-tag octo-2 o2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-1 octo-2 &&
+	git branch -D octo-1 octo-2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file o1 &&
+	test_path_is_file o2
+'
+
+test_expect_success 'refuses an octopus merge with an arm forked before the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b octo-pre &&
+	test_commit octo-pre-side pside x &&
+	git checkout "$main" &&
+	test_commit octo-pre-main file b1 &&
+	octo_base=$(git rev-parse HEAD) &&
+	git checkout -b octo-within &&
+	test_commit --no-tag octo-within wside y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-pre octo-within &&
+	merged=$(git rev-parse HEAD) &&
+	git branch -D octo-pre octo-within &&
+
+	test_must_fail git history squash "$octo_base.." 2>err &&
+	test_grep "parent .* of commit .* is outside the revision range" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'refuses when a descendant above the range is a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag desc-one file b &&
+	test_commit --no-tag desc-two file c &&
+	git tag desc-tip &&
+	git checkout -b desc-above &&
+	test_commit --no-tag desc-above above x &&
+	git checkout "$main" &&
+	test_commit --no-tag desc-main file d &&
+	git merge --no-ff -m "merge desc-above" desc-above &&
+	git branch -D desc-above &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash --no-edit start..desc-tip 2>err &&
+	test_grep "merge commits is not supported" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'refuses to fold a range a ref points into at a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag refmerge-base file b &&
+	git checkout -b refmerge-side &&
+	test_commit --no-tag refmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag refmerge-main file c &&
+	git merge --no-ff -m "interior merge" refmerge-side &&
+	git branch -D refmerge-side &&
+	git branch at-merge HEAD &&
+	test_commit --no-tag refmerge-tail file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "^error: the following branches cannot be rewritten" err &&
+	test_grep "^  at-merge$" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D at-merge
+'
+
 test_done
-- 
gitgitgadget

Re: [PATCH v13 7/8] history: create squashed commits without editing

[Junio C Hamano]

"Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:

> +test_expect_success '--no-edit uses last "amend!" message without an editor' '
> +	git reset --hard three &&
> +	write_script editor <<-\EOF &&
> +	exit 1
> +	EOF
> +	test_set_editor "$(pwd)/editor" &&
> +	echo fix >file &&
> +	git commit --author="Fix Me <fix.me@example.com>" --fixup=HEAD -a &&
> +	git commit --allow-empty -F - <<-EOF &&
> +	amend! $(git rev-parse --short HEAD)
> +
> +	The first reword
> +
> +	More detail
> +	EOF
> +
> +	git commit --allow-empty -F - <<-\EOF &&
> +	amend! three
> +
> +	The second reword
> +
> +	Extra detail
> +	EOF
> +
> +	test_commit WIP &&
> +
> +	cat >msg <<-EOF &&
> +	amend! $(git rev-parse HEAD^ | tr a-f A-F)
> +
> +	The third reword
> +
> +	Excruciating detail
> +	EOF

Care to explain why you need to (1) eat the exit status of the 'git
rev-parse' command and (2) munge the commit object name by piping it
into "tr"?

When another in-flight topic is in effect, this test will break due
to "amend!" followed by a string that is *not* an object name, as
the other topic declares that uppercase letters are not valid in a
hexadecimal string.

Thanks.

Re: [PATCH v13 7/8] history: create squashed commits without editing

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> "Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>> +test_expect_success '--no-edit uses last "amend!" message without an editor' '
>> +	git reset --hard three &&
>> +	write_script editor <<-\EOF &&
>> +	exit 1
>> +	EOF
>> +	test_set_editor "$(pwd)/editor" &&
>> +	echo fix >file &&
>> +	git commit --author="Fix Me <fix.me@example.com>" --fixup=HEAD -a &&
>> +	git commit --allow-empty -F - <<-EOF &&
>> +	amend! $(git rev-parse --short HEAD)
>> +
>> +	The first reword
>> +
>> +	More detail
>> +	EOF
>> +
>> +	git commit --allow-empty -F - <<-\EOF &&
>> +	amend! three
>> +
>> +	The second reword
>> +
>> +	Extra detail
>> +	EOF
>> +
>> +	test_commit WIP &&
>> +
>> +	cat >msg <<-EOF &&
>> +	amend! $(git rev-parse HEAD^ | tr a-f A-F)
>> +
>> +	The third reword
>> +
>> +	Excruciating detail
>> +	EOF
>
> Care to explain why you need to (1) eat the exit status of the 'git
> rev-parse' command and (2) munge the commit object name by piping it
> into "tr"?
>
> When another in-flight topic is in effect, this test will break due
> to "amend!" followed by a string that is *not* an object name, as
> the other topic declares that uppercase letters are not valid in a
> hexadecimal string.

In the meantime, I've queued the following on top of the series
before rebuilding 'seen'.


diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index 591463cb86..d21e9d9fc4 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -309,7 +309,7 @@ test_expect_success '--no-edit uses last "amend!" message without an editor' '
 	test_commit WIP &&
 
 	cat >msg <<-EOF &&
-	amend! $(git rev-parse HEAD^ | tr a-f A-F)
+	amend! $(git rev-parse --short HEAD^)
 
 	The third reword
 
-- 
2.55.0-758-g31b934252d

Re: [PATCH v13 7/8] history: create squashed commits without editing

[Phillip Wood]

On 13/08/2026 18:28, Junio C Hamano wrote:

 > "Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:
 >
 >> Inspired-by: Sergey Chernov <serega.morph@gmail.com>
 >> Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
 >> Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>

Thanks for the Helped-by: trailer, but this and several of the other 
patches are missing my sign off from the fixup patches I sent. My sign 
off should come above yours to reflect the chain of custody.

>> +test_expect_success '--no-edit uses last "amend!" message without an editor' '
>> +	git reset --hard three &&
>> +	write_script editor <<-\EOF &&
>> +	exit 1
>> +	EOF
>> +	test_set_editor "$(pwd)/editor" &&
>> +	echo fix >file &&
>> +	git commit --author="Fix Me <fix.me@example.com>" --fixup=HEAD -a &&
>> +	git commit --allow-empty -F - <<-EOF &&
>> +	amend! $(git rev-parse --short HEAD)
>> +
>> +	The first reword
>> +
>> +	More detail
>> +	EOF
>> +
>> +	git commit --allow-empty -F - <<-\EOF &&
>> +	amend! three
>> +
>> +	The second reword
>> +
>> +	Extra detail
>> +	EOF
>> +
>> +	test_commit WIP &&
>> +
>> +	cat >msg <<-EOF &&
>> +	amend! $(git rev-parse HEAD^ | tr a-f A-F)
>> +
>> +	The third reword
>> +
>> +	Excruciating detail
>> +	EOF
> 
> Care to explain why you need to (1) eat the exit status of the 'git
> rev-parse' command and (2) munge the commit object name by piping it
> into "tr"?

I chose to put the command substitution in the here doc, rather than 
move it out and use a variable because it was more convenient and it 
clearly shows what's going to be in the subject line. To me the benefits 
of that outweigh the minute risk that we'll miss a bug, that's not 
triggered elsewhere in the test suite, where "git rev-parse" produces 
the correct output but does not exit cleanly.

It's piped into "tr" to check that

	target = lookup_commit_reference_by_name(s);
	if (target && istarts_with(oid_to_hex(&target->object.oid), s))

uses istarts_with() so that we accept uppercase object ids.

> When another in-flight topic is in effect, this test will break due
> to "amend!" followed by a string that is *not* an object name, as
> the other topic declares that uppercase letters are not valid in a
> hexadecimal string.

I've just had a quick look at that other thread, it would be more 
convincing to me if there was some explanation of the security issues 
that accepting uppercase object ids causes. While I appreciate brian may 
not be able to talk about specific vulnerabilities in particular 
products, it would help to outline the security issues in general terms.

Thanks

Phillip

Re: [PATCH v13 7/8] history: create squashed commits without editing

[Junio C Hamano]

Phillip Wood <phillip.wood123@gmail.com> writes:

> It's piped into "tr" to check that
>
> 	target = lookup_commit_reference_by_name(s);
> 	if (target && istarts_with(oid_to_hex(&target->object.oid), s))
>
> uses istarts_with() so that we accept uppercase object ids.

You should check in with brian about istarts_with() that is used
here, as I suspect he missed it in his effort to declare uppercase
hexadecimal literals invalid.  In the meantime, '| tr' must be
removed if this topic wants to play nicely with the
'bc/restrict-hex-to-lowercase' topic.  In my fixup patch, I changed
it to use 'rev-parse --short' to test at least the "starts with"
aspect of this code.

> I've just had a quick look at that other thread, it would be more 
> convincing to me if there was some explanation of the security issues 
> that accepting uppercase object ids causes. While I appreciate brian may 
> not be able to talk about specific vulnerabilities in particular 
> products, it would help to outline the security issues in general terms.

True.


Thanks.

Re: [PATCH v13 7/8] history: create squashed commits without editing

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> Phillip Wood <phillip.wood123@gmail.com> writes:
>
>> It's piped into "tr" to check that
>>
>> 	target = lookup_commit_reference_by_name(s);
>> 	if (target && istarts_with(oid_to_hex(&target->object.oid), s))
>>
>> uses istarts_with() so that we accept uppercase object ids.
>
> You should check in with brian about istarts_with() that is used
> here, as I suspect he missed it in his effort to declare uppercase
> hexadecimal literals invalid.

Ah no, no, no.  This is a new code introduced by this series.

And as I said, I do not see why we want to be case insensitive with
this comparison.

Re: [PATCH v13 7/8] history: create squashed commits without editing

[Junio C Hamano]

Phillip Wood <phillip.wood123@gmail.com> writes:

> I've just had a quick look at that other thread, it would be more 
> convincing to me if there was some explanation of the security issues 
> that accepting uppercase object ids causes. While I appreciate brian may 
> not be able to talk about specific vulnerabilities in particular 
> products, it would help to outline the security issues in general terms.

In any case, I do not see any new use of istarts_with() in the patch
to deliberately allow upppercase hexadecimal.  It is not like there
is an existing machinery that has generated uppercase hexadecimal
for a long time and we need to support their output, or anything
like that.

Re: [PATCH v13 7/8] history: create squashed commits without editing

[Junio C Hamano]

Phillip Wood <phillip.wood123@gmail.com> writes:

> I've just had a quick look at that other thread, it would be more 
> convincing to me if there was some explanation of the security issues 
> that accepting uppercase object ids causes. While I appreciate brian may 
> not be able to talk about specific vulnerabilities in particular 
> products, it would help to outline the security issues in general terms.

In any case, I do not see any reason to use istarts_with() in the
patch to deliberately allow upppercase hexadecimal.  It is not like
there is an existing machinery that has generated uppercase
hexadecimal for a long time and we need to support their output, or
anything like that.

Re: [PATCH v13 7/8] history: create squashed commits without editing

[Harald Nordgren]

>  >> Inspired-by: Sergey Chernov <serega.morph@gmail.com>
>  >> Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
>  >> Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
>
> Thanks for the Helped-by: trailer, but this and several of the other
> patches are missing my sign off from the fixup patches I sent. My sign
> off should come above yours to reflect the chain of custody.

Got it, should I use both headers?

    Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
    Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
    Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>


Harald

Re: [PATCH v13 7/8] history: create squashed commits without editing

[Kristoffer Haugsbakk]

On Mon, Aug 17, 2026, at 19:38, Harald Nordgren wrote:
>>  >> Inspired-by: Sergey Chernov <serega.morph@gmail.com>
>>  >> Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
>>  >> Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
>>
>> Thanks for the Helped-by: trailer, but this and several of the other
>> patches are missing my sign off from the fixup patches I sent. My sign
>> off should come above yours to reflect the chain of custody.
>
> Got it, should I use both headers?
>
>     Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
>     Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
>     Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>

In general swapping the first and second makes more sense.

    S: PW
    H: PW
    S: HN

Because as a chain of custody this says: Phillip
signed off, then Harald said that PW helped him,
then Harald signed off on what he got from PW
with perhaps his own changes mixed in.

sent from mobile

[PATCH v13 8/8] history: support editing squashed commit messages

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Open the editor by default when squashing and provide --no-edit as the
opt-out. Record the exact commits selected by the revision walk,
rearrange that todo list with the sequencer's autosquash machinery, and
build the message template from the resulting order.

Match interactive rebase's treatment of marker messages: comment out
fixup! messages, retain squash! bodies, and let amend! replace its target
unless a preceding squash! requires both bodies. This keeps message
editing aligned with the marker validation used by the no-edit path.

Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  18 ++-
 builtin/history.c              |  97 +++++++++++++++-
 t/t3455-history-squash.sh      | 197 +++++++++++++++++++++++++++++++++
 3 files changed, 305 insertions(+), 7 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index fb04a67685..2e2e31f521 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -133,8 +133,9 @@ given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
 already on `topic`. Rev-list options may also be given, but any that would
 change how the range is walked are overridden with a warning.
 +
-With `--no-edit`, the oldest commit's message is preserved, except that an
-`amend!` commit targeting it replaces its message.
+An editor opens pre-filled with the messages of all the folded commits so you
+can combine them. With `--no-edit`, the oldest commit's message is preserved
+instead, except that an `amend!` commit targeting it replaces its message.
 +
 The selected commits must form a connected graph with a single tip and must
 not include a root commit. Every parent of a commit after the oldest one must
@@ -148,6 +149,13 @@ of markers for one target is combined into a single commit. With `--no-edit`,
 the last `amend!` message is used if there is one; a `squash!` or `amend!` is
 otherwise refused if folding it would discard its message.
 +
+The editor template mirrors `git rebase -i --autosquash`: each `fixup!`,
+`squash!`, or `amend!` is grouped under the commit it targets rather than
+shown in commit order. A `fixup!` message is dropped (commented out in full),
+a `squash!` keeps its body with only the marker subject commented, and an
+`amend!` replaces its target's message, unless a `squash!` folded into that
+target first, in which case it keeps its body like a `squash!`.
++
 A local branch descended from a selected commit but not from the range tip
 cannot be rewritten as a descendant of the result, so with the default
 `--update-refs=branches` the command refuses. Rerun with `--update-refs=head`
@@ -163,6 +171,12 @@ OPTIONS
 	objects will be written into the repository, so applying these printed
 	ref updates is generally safe.
 
+`--edit`::
+`--no-edit`::
+	For `squash`, open an editor to combine the messages of the folded commits.
+	This is the default; use `--no-edit` to keep the selected message without
+	opening an editor.
+
 `--reedit-message`::
 	Open an editor to modify the target commit's message.
 
diff --git a/builtin/history.c b/builtin/history.c
index 915cfb0cb9..db35a7451a 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1266,6 +1266,10 @@ static int squash_check_subject(struct repository *repo,
 	return ret;
 }
 
+static int build_squash_message(struct repository *repo,
+				const struct strbuf *todo_buf,
+				struct strbuf *out);
+
 static int setup_squash_revisions(struct repository *repo,
 				  int argc, const char **argv,
 				  struct rev_info *revs)
@@ -1319,6 +1323,7 @@ static int setup_squash_revisions(struct repository *repo,
  */
 static int resolve_squash_range(struct repository *repo,
 				bool update_branches,
+				bool edit_message,
 				int argc, const char **argv,
 				struct commit **oldest_out,
 				struct commit **tip_out,
@@ -1327,11 +1332,13 @@ static int resolve_squash_range(struct repository *repo,
 	struct rev_info revs;
 	struct subject_data subject_data = SUBJECT_DATA_INIT;
 	struct commit *commit, *oldest = NULL, *tip = NULL;
+	struct strbuf todo_buf = STRBUF_INIT;
 	int ret, tip_count = 0;
 	bool walk_started = false;
 	struct ref_filter filter = REF_FILTER_INIT;
 	struct ref_array refs = { 0 };
 
+	subject_data.edit_message = edit_message;
 	ret = setup_squash_revisions(repo, argc, argv, &revs);
 	if (ret < 0)
 		goto out;
@@ -1344,6 +1351,10 @@ static int resolve_squash_range(struct repository *repo,
 	while ((commit = get_revision(&revs))) {
 		struct commit_list *p;
 
+		if (edit_message)
+			strbuf_addf(&todo_buf, "pick %s\n",
+				    oid_to_hex(&commit->object.oid));
+
 		if (!commit->parents) {
 			ret = error(_("cannot squash down to root commit"));
 			goto out;
@@ -1457,6 +1468,13 @@ static int resolve_squash_range(struct repository *repo,
 		string_list_clear(&sorting_options, 0);
 		goto out;
 	}
+	if (edit_message) {
+		strbuf_reset(&subject_data.squash_message);
+		ret = build_squash_message(repo, &todo_buf,
+					   &subject_data.squash_message);
+		if (ret < 0)
+			goto out;
+	}
 
 	*oldest_out = oldest;
 	*tip_out = tip;
@@ -1464,6 +1482,7 @@ static int resolve_squash_range(struct repository *repo,
 	ret = 0;
 
 out:
+	strbuf_release(&todo_buf);
 	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP |
 			   SQUASH_AMEND_TARGET);
 	if (walk_started)
@@ -1475,6 +1494,76 @@ out:
 	return ret;
 }
 
+static bool amend_replaces_target(struct todo_list *todo, int target)
+{
+	for (int i = target + 1; i < todo->nr &&
+				 todo->items[i].command != TODO_PICK; i++) {
+		if (todo->items[i].command == TODO_SQUASH)
+			return false;
+		if (todo->items[i].flags & TODO_REPLACE_FIXUP_MSG)
+			return true;
+	}
+	return false;
+}
+
+static int build_squash_message(struct repository *repo,
+				const struct strbuf *todo_buf,
+				struct strbuf *out)
+{
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	int nr_commits, ret;
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo_buf->buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not prepare the squash message"));
+		goto out;
+	}
+
+	nr_commits = todo.nr;
+	for (int i = 0; i < nr_commits; i++) {
+		struct todo_item *item = &todo.items[i];
+		const char *message, *body;
+		size_t commented_len;
+		bool skip, squashing;
+
+		squashing = item->command == TODO_SQUASH ||
+			    (item->flags & TODO_REPLACE_FIXUP_MSG);
+		if (item->command == TODO_PICK)
+			skip = amend_replaces_target(&todo, i);
+		else
+			skip = !squashing;
+
+		message = repo_logmsg_reencode(repo, item->commit, NULL, NULL);
+		find_commit_subject(message, &body);
+
+		if (skip)
+			commented_len = strlen(body);
+		else if (squashing)
+			commented_len = squash_subject_comment_len(body, 1);
+		else
+			commented_len = 0;
+
+		if (!i)
+			add_squash_combination_header(out, nr_commits);
+		strbuf_addch(out, '\n');
+		add_squash_message_header(out, i + 1, skip);
+		strbuf_addstr(out, "\n\n");
+		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
+		strbuf_addstr(out, body + commented_len);
+		strbuf_complete_line(out);
+
+		repo_unuse_commit_buffer(repo, item->commit, message);
+	}
+
+	ret = 0;
+
+out:
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1519,14 +1608,11 @@ static int cmd_history_squash(int argc,
 	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
 
 	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
+				   edit,
 				   argc, argv, &oldest, &tip,
 				   &message_template);
 	if (ret < 0)
 		goto out;
-	if (edit) {
-		ret = error(_("message editing is not supported yet; use '--no-edit'"));
-		goto out;
-	}
 
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
@@ -1538,7 +1624,8 @@ static int cmd_history_squash(int argc,
 
 	ret = commit_tree_ext(repo, "squash", oldest, message_template,
 			      oldest->parents, base_tree_oid, tip_tree_oid,
-			      &rewritten, 0);
+			      &rewritten,
+			      edit ? COMMIT_TREE_EDIT_MESSAGE : 0);
 	if (ret < 0) {
 		ret = error(_("failed writing squashed commit"));
 		goto out;
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index d2d8e5fdb9..591463cb86 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -381,6 +381,203 @@ test_expect_success 'squashing fixups into a merge' '
 	sed 1,2d msg | test_commit_message HEAD
 '
 
+test_expect_success 'edits every message and aborts on an empty result' '
+	git reset --hard start &&
+	stage_file b &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script empty-editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/empty-editor" &&
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "Aborting commit due to empty commit message" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# This is the 1st commit message:
+
+	re-one subject
+
+	re-one body line
+
+	# This is the commit message #2:
+
+	re-two
+
+	# This is the commit message #3:
+
+	re-three
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_subjects -1 <<-\EOF
+	combined
+	EOF
+'
+
+test_expect_success 'handles fixup!, squash! and amend! like rebase' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "fixup! mark-base\n\nfixup body\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+	stage_file e &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	mark-base
+
+	# The commit message #2 will be skipped:
+
+	# fixup! mark-base
+	#
+	# fixup body
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# This is the commit message #4:
+
+	# amend! mark-base
+
+	amended message
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	mark-base
+
+	squash remark
+
+	amended message
+
+	EOF
+'
+
+test_expect_success 'groups fixups under their targets in the editor' '
+	git reset --hard start &&
+	test_commit --no-tag alpha file a1 &&
+	test_commit --no-tag beta file b1 &&
+	stage_file a2 &&
+	commit_with_message "fixup! alpha\n" &&
+	stage_file b2 &&
+	commit_with_message "fixup! beta\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	alpha
+
+	# The commit message #2 will be skipped:
+
+	# fixup! alpha
+
+	# This is the commit message #3:
+
+	beta
+
+	# The commit message #4 will be skipped:
+
+	# fixup! beta
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited
+'
+
+test_expect_success 'lets amend! replace its target message in the editor' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# The 1st commit message will be skipped:
+
+	# mark-base
+
+	# This is the commit message #2:
+
+	# amend! mark-base
+
+	amended message
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	amended message
+
+	squash remark
+
+	EOF
+'
+
 test_expect_success '--update-refs=head only moves HEAD' '
 	git reset --hard three &&
 	git branch -f other HEAD &&
-- 
gitgitgadget

[PATCH v14 0/8] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v14:

 * Update commit message trailers.
 * Simplify rev-parse and tr complexity in the tests.

Changes in v13:

 * Split the squash implementation into five patches covering parsing, range
   validation, branch protection, commit creation, and message editing.
 * Print the sorted names of local branches that prevent a squash, with
   clearer advice for --update-refs=head.
 * Isolate --no-edit behavior from the final patch that enables default
   editor-based message combining.

Changes in v12:

 * Incorporated fixups from Phillip:
   * Reworks range validation into a single walk that rejects roots and
     multiple tips while preserving every parent when squashing into a
     merge.
   * Resolves fixup!, squash! and amend! targets directly, preserving
     message intent and safely consolidating related markers.
   * Builds the editor template from the exact selected revisions, including
     exclusions, while retaining --no-edit behavior.
   * Protects descendant local branches while leaving tags and
     remote-tracking refs unchanged.

Changes in v11:

 * Make message editing the default with the autosquash-style template, add
   --no-edit instead of squash-specific --reedit-message.
 * Validate one actual boundary and tip, rejecting root-reaching and
   multi-tip ranges.
 * Protect only interior local branches, leaving tags and remote-tracking
   refs unchanged.
 * Move sequencer preparation before squash and fold the later
   message-editing patch into the feature commit.

Changes in v10:

 * Record the full revision expression in squash reflog.
 * Preserve the boundary-walk invariant when sanitizing rev-list options.
 * Clarify amend! and --reedit-message documentation.

Changes in v9:

 * Use the last amend! targeting the oldest folded commit as the default
   squashed message. Ignore amend! markers targeting later commits while
   selecting that replacement message.
 * Improve tests.

Changes in v8:

 * --reedit-message now builds the same editor template as git rebase -i
   --autosquash: fixup!, squash! and amend! commits are grouped under the
   commit they target instead of shown in commit order, and an amend!
   replaces its target's message.
 * A fixup!, squash! or amend! is refused only when its target is outside
   the range, so several fixups for an in-range commit fold together. A
   range that is entirely markers for one below-range target is combined
   into a single commit, keeping the last amend! message.
 * Merges inside the range are folded when the range has a single base, with
   no dedicated opt-in flag, --ancestry-path ensures only commits descended
   from the base are folded, and a range reaching more than one base is
   rejected.
 * Rev-list options are accepted and sanitized the way git replay does,
   forcing the walk order back with a warning, which also fixes git history
   squash -- --reverse slipping past the previous option check.
 * Kept this as an explicit squash subcommand rather than making
   --reedit-message the default or renaming the command.

Changes in v7:

 * --reedit-message now builds the same editor template git rebase -i shows
   for a squash (a combination of N commits banner with each folded message
   under its own header) and follows autosquash for markers: a fixup!
   message falls out (commented under a will be skipped header), while a
   squash! or amend! keeps its body with only the marker subject commented
   so its remark can be reworded in. Only the message text is affected,
   every commit's changes are always folded in.
 * Reuse git rebase -i's squash-message code: a preparatory sequencer:
   commit extracts the banner, header and marker-comment helpers so both
   rebase and git history squash build the identical template from one
   source.
 * Refuse a range whose oldest commit is a fixup!, squash! or amend!, since
   the marker's target cannot be inside the range.
 * Reorder the squash usage so dashed options come before <revision-range>,
   and spell out HEAD instead of @ in the documentation and examples.
 * Expand the squash commit message and documentation with this overview,
   and scope the merge limitation so it no longer contradicts squash folding
   a single-base interior merge.

Changes in v6:

 * git history squash now accepts multiple revision arguments, read like the
   arguments to git-rev-list, so a compound range such as @~3.. ^topic
   works.
 * The base to reparent onto is now the oldest in-range commit's parent; a
   boundary other than that base means the range has more than one base and
   is rejected. This also fixes the earlier overly-restrictive handling of
   merges and side branches.
 * A single-commit range (e.g. @^!) is rejected with "nothing to squash"
   (this also covers the @^!-style example that previously succeeded
   silently).
 * Commit messages reworded: the squash commit now gives an overview of
   fixup!/squash!/amend! handling, rewording, merge-parent and ref behavior.

Changes in v5:

 * The range walk now uses --ancestry-path, so only commits descended from
   the base are folded; a single revision such as HEAD or HEAD~1 is now
   rejected as "not a <base>..<tip> range" rather than treated as a squash
   down to the root.
 * This adopts the --ancestry-path suggestion; the multi-base rejection is
   unchanged, so a side branch that forked before the base and merged in is
   still refused.
 * Added tests covering more merge topologies: two interior merges, a nested
   merge, an octopus merge, an octopus arm forked before the base, a merge
   among the descendants replayed above the range, and a ref pointing at an
   interior merge commit.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (8):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  sequencer: share the squash message marker helpers and flags
  history: add skeleton for squash subcommand
  history: validate squash revision ranges
  history: protect branches when squashing a range
  history: create squashed commits without editing
  history: support editing squashed commit messages

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  59 +-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 720 +++++++++++++++++++++++--
 object.h                         |   1 +
 sequencer.c                      |  70 +--
 sequencer.h                      |  30 ++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 886 +++++++++++++++++++++++++++++++
 10 files changed, 1702 insertions(+), 71 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: 18e66859d87fb4b76599f73460b54f0848c76b16
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v14
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v14
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v13:

 1:  b175bdca54 = 1:  19c5e311a3 history: extract helper for a commit's parent tree
 2:  965074f9e8 = 2:  aadb7a5df4 history: give commit_tree_ext a message template
 3:  cdbdd766b2 = 3:  e1621f656e sequencer: share the squash message marker helpers and flags
 4:  f7d953b081 ! 4:  016ae0fd42 history: add skeleton for squash subcommand
     @@ Commit message
          Keep this step limited to defining the revision input contract so graph
          validation and the rewrite can be added independently.
      
     +    Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
 5:  dbbf66ba02 ! 5:  4992d14ce4 history: validate squash revision ranges
     @@ Commit message
          parents will be preserved and the single tip whose tree will be used by
          the rewrite.
      
     +    Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
 6:  e71a8adfbe ! 6:  b862a5b4c3 history: protect branches when squashing a range
     @@ Commit message
          Add advice.historyUpdateRefs for the hint that points to
          --update-refs=head.
      
     +    Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
 7:  8b3551d0d4 ! 7:  03528d3b34 history: create squashed commits without editing
     @@ Commit message
          applicable amend! body supplying the message.
      
          Inspired-by: Sergey Chernov <serega.morph@gmail.com>
     +    Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      
     @@ t/t3455-history-squash.sh: test_expect_success 'errors on a single revision that
      +	test_commit WIP &&
      +
      +	cat >msg <<-EOF &&
     -+	amend! $(git rev-parse HEAD^ | tr a-f A-F)
     ++	amend! $(git rev-parse --short HEAD^)
      +
      +	The third reword
      +
 8:  821217ed7c ! 8:  98aa3922cb history: support editing squashed commit messages
     @@ Commit message
          unless a preceding squash! requires both bodies. This keeps message
          editing aligned with the marker validation used by the no-edit path.
      
     +    Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
          Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
      

-- 
gitgitgadget

[PATCH v14 1/8] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 000155ad9c..c22715d848 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -164,6 +164,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -171,21 +190,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -475,18 +484,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -830,16 +831,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v14 2/8] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index c22715d848..a60e8dbcd0 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -108,6 +108,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -137,13 +138,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -196,7 +200,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -675,7 +679,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -886,7 +890,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -903,7 +907,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v14 3/8] sequencer: share the squash message marker helpers and flags

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

When "git rebase -i" squashes commits it builds an editor template with a
"This is a combination of N commits." banner, a "This is the 1st/Nth
commit message:" header above each kept message (or a "will be skipped"
header for a dropped one), and a commented-out subject for any fixup!,
squash! or amend! commit. The banner, the headers and the
subject-commenting all live in static helpers in sequencer.c wired to the
rebase state, so no other command can present a squash the same way.

Pull the three pieces out into add_squash_combination_header(),
add_squash_message_header() (which takes a flag for the "will be skipped"
variant) and squash_subject_comment_len(), and use them from
update_squash_messages() and append_squash_message(). Also move the
todo_item_flags enum to the header, so a caller reading the output of
todo_list_rearrange_squash() can tell an amend! (TODO_REPLACE_FIXUP_MSG)
from a plain fixup!. A later change reuses all of this to give "git
history squash" the same template.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 sequencer.c | 70 +++++++++++++++++++++++++++++------------------------
 sequencer.h | 30 +++++++++++++++++++++++
 2 files changed, 69 insertions(+), 31 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 83c3849205..4d2d59ecbe 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1880,18 +1880,38 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
-enum todo_item_flags {
-	TODO_EDIT_MERGE_MSG    = (1 << 0),
-	TODO_REPLACE_FIXUP_MSG = (1 << 1),
-	TODO_EDIT_FIXUP_MSG    = (1 << 2),
-};
-
 static const char first_commit_msg_str[] = N_("This is the 1st commit message:");
 static const char nth_commit_msg_fmt[] = N_("This is the commit message #%d:");
 static const char skip_first_commit_msg_str[] = N_("The 1st commit message will be skipped:");
 static const char skip_nth_commit_msg_fmt[] = N_("The commit message #%d will be skipped:");
 static const char combined_commit_msg_fmt[] = N_("This is a combination of %d commits.");
 
+void add_squash_combination_header(struct strbuf *buf, int n)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	strbuf_addf(buf, _(combined_commit_msg_fmt), n);
+}
+
+void add_squash_message_header(struct strbuf *buf, int n, int skip)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	if (n == 1)
+		strbuf_addstr(buf, skip ? _(skip_first_commit_msg_str) :
+				   _(first_commit_msg_str));
+	else
+		strbuf_addf(buf, skip ? _(skip_nth_commit_msg_fmt) :
+			    _(nth_commit_msg_fmt), n);
+}
+
+size_t squash_subject_comment_len(const char *body, int squashing)
+{
+	if (starts_with(body, "amend!") ||
+	    (squashing && (starts_with(body, "squash!") ||
+			   starts_with(body, "fixup!"))))
+		return commit_subject_length(body);
+	return 0;
+}
+
 static int is_fixup_flag(enum todo_command command, unsigned flag)
 {
 	return command == TODO_FIXUP && ((flag & TODO_REPLACE_FIXUP_MSG) ||
@@ -2012,20 +2032,13 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 {
 	struct replay_ctx *ctx = opts->ctx;
 	const char *fixup_msg;
-	size_t commented_len = 0, fixup_off;
-	/*
-	 * amend is non-interactive and not normally used with fixup!
-	 * or squash! commits, so only comment out those subjects when
-	 * squashing commit messages.
-	 */
-	if (starts_with(body, "amend!") ||
-	    ((command == TODO_SQUASH || seen_squash(ctx)) &&
-	     (starts_with(body, "squash!") || starts_with(body, "fixup!"))))
-		commented_len = commit_subject_length(body);
+	size_t commented_len, fixup_off;
+
+	commented_len = squash_subject_comment_len(body,
+				command == TODO_SQUASH || seen_squash(ctx));
 
-	strbuf_addf(buf, "\n%s ", comment_line_str);
-	strbuf_addf(buf, _(nth_commit_msg_fmt),
-		    ++ctx->current_fixup_count + 1);
+	strbuf_addch(buf, '\n');
+	add_squash_message_header(buf, ++ctx->current_fixup_count + 1, 0);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len, comment_line_str);
 	/* buf->buf may be reallocated so store an offset into the buffer */
@@ -2090,9 +2103,8 @@ static int update_squash_messages(struct repository *r,
 		eol = !starts_with(buf.buf, comment_line_str) ?
 			buf.buf : strchrnul(buf.buf, '\n');
 
-		strbuf_addf(&header, "%s ", comment_line_str);
-		strbuf_addf(&header, _(combined_commit_msg_fmt),
-			    ctx->current_fixup_count + 2);
+		add_squash_combination_header(&header,
+					      ctx->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);
 		if (is_fixup_flag(command, flag) && !seen_squash(ctx))
@@ -2116,12 +2128,9 @@ static int update_squash_messages(struct repository *r,
 			repo_unuse_commit_buffer(r, head_commit, head_message);
 			return error(_("cannot write '%s'"), rebase_path_fixup_msg());
 		}
-		strbuf_addf(&buf, "%s ", comment_line_str);
-		strbuf_addf(&buf, _(combined_commit_msg_fmt), 2);
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addstr(&buf, is_fixup_flag(command, flag) ?
-			      _(skip_first_commit_msg_str) :
-			      _(first_commit_msg_str));
+		add_squash_combination_header(&buf, 2);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, 1, is_fixup_flag(command, flag));
 		strbuf_addstr(&buf, "\n\n");
 		if (is_fixup_flag(command, flag))
 			strbuf_add_commented_lines(&buf, body, strlen(body),
@@ -2140,9 +2149,8 @@ static int update_squash_messages(struct repository *r,
 	if (command == TODO_SQUASH || is_fixup_flag(command, flag)) {
 		res = append_squash_message(&buf, body, command, opts, flag);
 	} else if (command == TODO_FIXUP) {
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),
-			    ++ctx->current_fixup_count + 1);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, ++ctx->current_fixup_count + 1, 1);
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body),
 					   comment_line_str);
diff --git a/sequencer.h b/sequencer.h
index 64a9c7fb1b..b01f897020 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,6 +119,13 @@ enum todo_command {
 	TODO_COMMENT
 };
 
+/* Bits for the "flags" member of struct todo_item */
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG    = (1 << 0),
+	TODO_REPLACE_FIXUP_MSG = (1 << 1),
+	TODO_EDIT_FIXUP_MSG    = (1 << 2),
+};
+
 struct todo_item {
 	enum todo_command command;
 	struct commit *commit;
@@ -208,6 +215,29 @@ int todo_list_rearrange_squash(struct todo_list *todo_list);
  */
 void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
 
+/*
+ * Append the "This is a combination of N commits." banner that "git rebase
+ * -i" writes at the top of a squashed commit's message, commented out with
+ * the comment character.
+ */
+void add_squash_combination_header(struct strbuf *buf, int n);
+
+/*
+ * Append the header (1-based N) that "git rebase -i" writes above each message
+ * when squashing, commented out with the comment character. With SKIP it reads
+ * "The ... commit message will be skipped" for a message that is dropped (a
+ * fixup), otherwise "This is the ... commit message".
+ */
+void add_squash_message_header(struct strbuf *buf, int n, int skip);
+
+/*
+ * Return the length of the leading subject of BODY when it should be commented
+ * out in a squash message, or 0 otherwise. An "amend!" subject always
+ * qualifies; "squash!" and "fixup!" subjects only when SQUASHING, since a
+ * plain fixup chain keeps them.
+ */
+size_t squash_subject_comment_len(const char *body, int squashing);
+
 void append_conflicts_hint(struct index_state *istate,
 		struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
 enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,
-- 
gitgitgadget

[PATCH v14 4/8] history: add skeleton for squash subcommand

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Add the entry point and option parsing for "git history squash". Pass
the remaining arguments through setup_revisions() so the command accepts
revision ranges and rev-list options, while restoring the ordering and
simplification settings required by the fold if an option changes them.

Require at least one BOTTOM revision. The squashed commit needs a commit
outside the selected range to serve as its base, so a single positive
revision is not a sufficient range.

Keep this step limited to defining the revision input contract so graph
validation and the rewrite can be added independently.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  1 +
 builtin/history.c              | 94 ++++++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 28b477cd37..b660baf94d 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -12,6 +12,7 @@ git history drop <commit> [--dry-run] [--update-refs=(branches|head)] [--empty=(
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>
 
 DESCRIPTION
 -----------
diff --git a/builtin/history.c b/builtin/history.c
index a60e8dbcd0..4f5a7a46ce 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -34,6 +34,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -1004,6 +1006,96 @@ out:
 	return ret;
 }
 
+static int setup_squash_revisions(struct repository *repo,
+				  int argc, const char **argv,
+				  struct rev_info *revs)
+{
+	repo_init_revisions(repo, revs, NULL);
+	revs->reverse = 1;
+	revs->topo_order = 1;
+	revs->sort_order = REV_SORT_IN_GRAPH_ORDER;
+	revs->simplify_history = 0;
+	revs->ancestry_path = 1;
+	revs->limited = 1;
+	revs->ancestry_path_implicit_bottoms = 1;
+
+	argc = setup_revisions(argc, argv, revs, NULL);
+	if (argc > 1)
+		return error(_("unrecognized argument: %s"), argv[1]);
+
+	if (revs->reverse != 1 || revs->topo_order != 1 ||
+	    revs->sort_order != REV_SORT_IN_GRAPH_ORDER ||
+	    revs->simplify_history != 0 || revs->boundary == 1 ||
+	    revs->ancestry_path != 1 || revs->limited != 1 ||
+	    revs->ancestry_path_implicit_bottoms != 1) {
+		warning(_("ignoring rev-list options that would change how the "
+			  "range is walked"));
+		revs->reverse = 1;
+		revs->topo_order = 1;
+		revs->sort_order = REV_SORT_IN_GRAPH_ORDER;
+		revs->simplify_history = 0;
+		revs->boundary = 0;
+		revs->ancestry_path = 1;
+		revs->limited = 1;
+		revs->ancestry_path_implicit_bottoms = 1;
+	}
+
+	/*
+	 * A squash needs a base to reparent onto, so the range has to exclude
+	 * something, as in "<base>..<tip>". A revision range with no such
+	 * bottom commit cannot be squashed.
+	 */
+	for (size_t i = 0; i < revs->cmdline.nr; i++)
+		if (revs->cmdline.rev[i].flags & BOTTOM)
+			return 0;
+
+	return error(_("not a '<base>..<tip>' revision range"));
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	int dry_run = 0;
+	int edit = 1;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BOOL('e', "edit", &edit,
+			 N_("edit the commit message")),
+		OPT_END(),
+	};
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage,
+			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
+	if (argc < 2) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	ret = setup_squash_revisions(repo, argc, argv, &revs);
+	if (ret < 0)
+		goto out;
+
+	ret = error(_("squashing commits is not implemented yet"));
+
+out:
+	release_revisions(&revs);
+	return ret;
+}
+
 static int update_worktree(struct repository *repo,
 			   const struct commit *old_head,
 			   const struct commit *new_head,
@@ -1192,6 +1284,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -1200,6 +1293,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
-- 
gitgitgadget

[PATCH v14 5/8] history: validate squash revision ranges

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Walk the selected commits in topological order from oldest to newest and
mark each one as it is seen. Every parent after the oldest commit must
already be selected or also be a parent of the oldest commit. This
accepts merges contained by the range while rejecting a merge arm that
entered it from elsewhere.

Track the remaining graph tips during the same walk and require exactly
one. Also reject empty and single-commit ranges and any selection that
reaches a root commit. These checks identify the oldest commit whose
parents will be preserved and the single tip whose tree will be used by
the rewrite.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c         | 119 ++++++++++++++++++++++++++++++++++----
 object.h                  |   1 +
 t/meson.build             |   1 +
 t/t3455-history-squash.sh |  65 +++++++++++++++++++++
 4 files changed, 174 insertions(+), 12 deletions(-)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/builtin/history.c b/builtin/history.c
index 4f5a7a46ce..6541a397e8 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1006,6 +1006,9 @@ out:
 	return ret;
 }
 
+#define SQUASH_SEEN (1u << 11)
+#define SQUASH_TIP (1u << 12)
+
 static int setup_squash_revisions(struct repository *repo,
 				  int argc, const char **argv,
 				  struct rev_info *revs)
@@ -1052,6 +1055,104 @@ static int setup_squash_revisions(struct repository *repo,
 	return error(_("not a '<base>..<tip>' revision range"));
 }
 
+/*
+ * Resolve a revision range into its oldest commit and single tip. Every
+ * parent after the oldest commit must either be selected or also be a parent
+ * of the oldest commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				int argc, const char **argv,
+				struct commit **oldest_out,
+				struct commit **tip_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *oldest = NULL, *tip = NULL;
+	int ret, tip_count = 0;
+	bool walk_started = false;
+
+	ret = setup_squash_revisions(repo, argc, argv, &revs);
+	if (ret < 0)
+		goto out;
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+	walk_started = true;
+	while ((commit = get_revision(&revs))) {
+		struct commit_list *p;
+
+		if (!commit->parents) {
+			ret = error(_("cannot squash down to root commit"));
+			goto out;
+		}
+		for (p = commit->parents; oldest && p; p = p->next) {
+			struct commit_list *q;
+			struct object *o;
+			bool seen;
+
+			if (repo_parse_commit(repo, p->item)) {
+				ret = error(_("cannot parse commit"));
+				goto out;
+			}
+			o = &p->item->object;
+			seen = o->flags & SQUASH_SEEN;
+			/*
+			 * Allow parents that match the parents of the
+			 * squashed commit.
+			 */
+			for (q = oldest->parents; !seen && q; q = q->next)
+				if (p->item == q->item)
+					seen = true;
+			if (!seen) {
+				ret = error(_("parent %s of commit %s is "
+					      "outside the revision range"),
+					    repo_find_unique_abbrev(repo, &o->oid,
+								    DEFAULT_ABBREV),
+					    repo_find_unique_abbrev(repo,
+								    &commit->object.oid,
+								    DEFAULT_ABBREV));
+				goto out;
+			}
+			if (o->flags & SQUASH_TIP) {
+				tip_count--;
+				o->flags &= ~SQUASH_TIP;
+			}
+		}
+		if (!oldest)
+			oldest = commit;
+		tip = commit;
+		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
+		tip_count++;
+	}
+
+	if (!tip_count) {
+		ret = error(_("the revision range is empty"));
+		goto out;
+	} else if (tip_count != 1) {
+		ret = error(_("the revision range contains more than one tip "
+			      "commit"));
+		goto out;
+	} else if (oldest == tip) {
+		ret = error(_("the revision range holds a single commit; "
+			      "nothing to squash"));
+		goto out;
+	} else if (!oldest->parents) {
+		BUG("an in-range commit must have a parent");
+	}
+
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
+	if (walk_started)
+		reset_revision_walk();
+	release_revisions(&revs);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1074,26 +1175,20 @@ static int cmd_history_squash(int argc,
 			 N_("edit the commit message")),
 		OPT_END(),
 	};
-	struct rev_info revs = { 0 };
+	struct commit *oldest, *tip;
 	int ret;
 
 	argc = parse_options(argc, argv, prefix, options, usage,
 			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
-	if (argc < 2) {
-		ret = error(_("command expects a revision range"));
-		goto out;
-	}
+	if (argc < 2)
+		return error(_("command expects a revision range"));
 	repo_config(repo, git_default_config, NULL);
 
-	ret = setup_squash_revisions(repo, argc, argv, &revs);
+	ret = resolve_squash_range(repo, argc, argv, &oldest, &tip);
 	if (ret < 0)
-		goto out;
-
-	ret = error(_("squashing commits is not implemented yet"));
+		return ret;
 
-out:
-	release_revisions(&revs);
-	return ret;
+	return error(_("squashing commits is not implemented yet"));
 }
 
 static int update_worktree(struct repository *repo,
diff --git a/object.h b/object.h
index 8fb03ff90a..dcf30156ca 100644
--- a/object.h
+++ b/object.h
@@ -74,6 +74,7 @@ void object_array_init(struct object_array *array);
  * bisect.c:                                        16
  * bundle.c:                                        16
  * http-push.c:                          11-----14
+ * builtin/history.c:                    1112
  * commit-graph.c:                                15
  * commit-reach.c:                                  16-------20
  * builtin/last-modified.c:                         1617
diff --git a/t/meson.build b/t/meson.build
index 2133c840da..a349bb73b5 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -407,6 +407,7 @@ integration_tests = [
   't3452-history-split.sh',
   't3453-history-fixup.sh',
   't3454-history-drop.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..df92aa4f6c
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,65 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+test_expect_success 'setup linear history' '
+	test_commit base file a start &&
+	test_commit one file b &&
+	test_commit two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "expects a revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the revision range is empty" err
+'
+
+test_expect_success 'errors on a single revision that is not a range' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "not a .*range" err &&
+	test_must_fail git history squash HEAD~1 2>err &&
+	test_grep "not a .*range" err
+'
+
+test_expect_success 'errors on a range holding a single commit' '
+	test_must_fail git history squash "HEAD^!" 2>err &&
+	test_grep "single commit; nothing to squash" err
+'
+
+test_expect_success 'rejects a root commit' '
+	oid=$(git commit-tree -m root three^{tree}) &&
+	test_must_fail git history squash \
+		--ancestry-path=start "$oid..three" 2>err &&
+	test_grep "cannot squash down to root commit" err
+'
+
+test_expect_success 'rejects multiple tips' '
+	oid=$(git commit-tree -m tip -p start^0 three^{tree}) &&
+	test_must_fail git history squash ^start "$oid" three~1 2>err &&
+	test_grep "revision range contains more than one tip" err
+'
+
+test_expect_success 'rejects a merge parent outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "parent .* of commit .* is outside the revision range" err
+'
+
+test_done
-- 
gitgitgadget

[PATCH v14 6/8] history: protect branches when squashing a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

A local branch that descends from the selected graph without containing
its tip cannot be replayed as a descendant of the squashed commit. Find
those branches with ref-filter before creating any replacement objects
and refuse the operation unless --update-refs=head was requested.

Limit this protection to local branches, matching the refs that the
default history rewrite mode updates; tags and remote-tracking refs
remain untouched. Sort the blocking refs and print their short branch
names so the user can decide whether to move them or leave them behind.

Add advice.historyUpdateRefs for the hint that points to
--update-refs=head.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |  4 ++
 advice.c                         |  1 +
 advice.h                         |  1 +
 builtin/history.c                | 70 ++++++++++++++++++++++++++++++--
 t/t3455-history-squash.sh        | 39 ++++++++++++++++++
 5 files changed, 111 insertions(+), 4 deletions(-)

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 81f80a9274..3d91c90eda 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -59,6 +59,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a local branch
+		cannot be rewritten as a descendant of the squashed commit, to
+		tell the user about `--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/advice.c b/advice.c
index 63bf8b0c5f..401d047391 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 66f6cd6a77..3f0b4f0485 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index 6541a397e8..e65b76b59f 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -16,10 +17,12 @@
 #include "path.h"
 #include "read-cache.h"
 #include "refs.h"
+#include "ref-filter.h"
 #include "replay.h"
 #include "reset.h"
 #include "revision.h"
 #include "sequencer.h"
+#include "string-list.h"
 #include "strvec.h"
 #include "tree.h"
 #include "tree-walk.h"
@@ -1061,6 +1064,7 @@ static int setup_squash_revisions(struct repository *repo,
  * of the oldest commit.
  */
 static int resolve_squash_range(struct repository *repo,
+				bool update_branches,
 				int argc, const char **argv,
 				struct commit **oldest_out,
 				struct commit **tip_out)
@@ -1069,6 +1073,8 @@ static int resolve_squash_range(struct repository *repo,
 	struct commit *commit, *oldest = NULL, *tip = NULL;
 	int ret, tip_count = 0;
 	bool walk_started = false;
+	struct ref_filter filter = REF_FILTER_INIT;
+	struct ref_array refs = { 0 };
 
 	ret = setup_squash_revisions(repo, argc, argv, &revs);
 	if (ret < 0)
@@ -1101,9 +1107,12 @@ static int resolve_squash_range(struct repository *repo,
 			 * Allow parents that match the parents of the
 			 * squashed commit.
 			 */
-			for (q = oldest->parents; !seen && q; q = q->next)
-				if (p->item == q->item)
+			for (q = oldest->parents; !seen && q; q = q->next) {
+				if (p->item == q->item) {
 					seen = true;
+					commit_list_insert(commit, &filter.with_commit);
+				}
+			}
 			if (!seen) {
 				ret = error(_("parent %s of commit %s is "
 					      "outside the revision range"),
@@ -1119,12 +1128,17 @@ static int resolve_squash_range(struct repository *repo,
 				o->flags &= ~SQUASH_TIP;
 			}
 		}
-		if (!oldest)
+		if (!oldest) {
+			commit_list_insert(commit, &filter.with_commit);
 			oldest = commit;
+		}
 		tip = commit;
 		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
 		tip_count++;
 	}
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
+	reset_revision_walk();
+	walk_started = false;
 
 	if (!tip_count) {
 		ret = error(_("the revision range is empty"));
@@ -1141,6 +1155,49 @@ static int resolve_squash_range(struct repository *repo,
 		BUG("an in-range commit must have a parent");
 	}
 
+	commit_list_insert(tip, &filter.no_commit);
+	filter.kind = FILTER_REFS_BRANCHES;
+	if (update_branches &&
+	    filter_refs(&refs, &filter, filter.kind)) {
+		ret = error(_("could not filter refs"));
+		goto out;
+	}
+	if (refs.nr) {
+		struct ref_format format = REF_FORMAT_INIT;
+		struct ref_sorting *sorting;
+		struct string_list sorting_options = STRING_LIST_INIT_DUP;
+		struct strbuf branches = STRBUF_INIT;
+		struct strbuf err = STRBUF_INIT;
+
+		format.format = "%(refname:short)";
+		if (verify_ref_format(&format))
+			BUG("invalid branch format");
+		string_list_append(&sorting_options, "refname");
+		sorting = ref_sorting_options(&sorting_options);
+		ref_array_sort(sorting, &refs);
+		for (int i = 0; i < refs.nr; i++) {
+			strbuf_reset(&err);
+			strbuf_addstr(&branches, "\n  ");
+			if (format_ref_array_item(refs.items[i], &format,
+						  &branches, &err))
+				BUG("could not format branch name: %s", err.buf);
+		}
+		/*
+		 * TODO: also check HEADS from other worktrees.
+		 */
+		ret = error(_("the following branches cannot be rewritten as "
+			      "descendants of the squashed commit:%s"), branches.buf);
+		advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+				  _("Use --update-refs=head to rewrite only "
+				    "the current branch and leave such branches "
+				    "untouched."));
+		strbuf_release(&err);
+		strbuf_release(&branches);
+		ref_sorting_release(sorting);
+		string_list_clear(&sorting_options, 0);
+		goto out;
+	}
+
 	*oldest_out = oldest;
 	*tip_out = tip;
 	ret = 0;
@@ -1150,6 +1207,8 @@ out:
 	if (walk_started)
 		reset_revision_walk();
 	release_revisions(&revs);
+	ref_filter_clear(&filter);
+	ref_array_clear(&refs);
 	return ret;
 }
 
@@ -1183,8 +1242,11 @@ static int cmd_history_squash(int argc,
 	if (argc < 2)
 		return error(_("command expects a revision range"));
 	repo_config(repo, git_default_config, NULL);
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
 
-	ret = resolve_squash_range(repo, argc, argv, &oldest, &tip);
+	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
+				   argc, argv, &oldest, &tip);
 	if (ret < 0)
 		return ret;
 
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index df92aa4f6c..b1f65de5f5 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -62,4 +62,43 @@ test_expect_success 'rejects a merge parent outside the range' '
 	test_grep "parent .* of commit .* is outside the revision range" err
 '
 
+test_expect_success 'prints branches that cannot follow the squash' '
+	test_when_finished \
+		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
+		 git branch -D feature" &&
+	git checkout -f -b feature start &&
+	test_commit C1 &&
+	test_commit C2 &&
+	git checkout -b topic-1 start &&
+	test_commit C3 &&
+	test_commit C4 &&
+	git checkout C3 &&
+	test_commit C5 &&
+	git checkout feature &&
+	git merge C5 &&
+	test_commit C6 &&
+	git checkout -b topic-2 C2 &&
+	test_commit C7 &&
+	git checkout feature &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "^error: the following branches cannot be rewritten" err &&
+	test_grep "^  topic-1$" err &&
+	test_grep "^  topic-2$" err &&
+	test_grep "^hint: .* --update-refs=head" err
+'
+
+test_expect_success 'advice.historyUpdateRefs silences the hint' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "^error: the following branches cannot be rewritten" err &&
+	test_grep "^  mid$" err &&
+	test_grep ! "hint:" err &&
+
+	git branch -D mid
+'
+
 test_done
-- 
gitgitgadget

[PATCH v14 7/8] history: create squashed commits without editing

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Create one replacement commit from the resolved range when --no-edit is
selected. Preserve the authorship and all parents of the oldest commit,
use the tip tree, and replay descendants through the existing history
rewrite machinery. Record the complete revision expression in the
reflog and retain dry-run and update-refs behavior.

Resolve fixup!, squash! and amend! subjects while walking the range.
Reject markers whose targets are not selected and refuse any no-edit
fold that would discard a squash! or amend! message. A range made
entirely from related markers can still be consolidated, with the last
applicable amend! body supplying the message.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  44 ++-
 builtin/history.c              | 324 ++++++++++++++++-
 object.h                       |   2 +-
 t/t3455-history-squash.sh      | 633 +++++++++++++++++++++++++++++++--
 4 files changed, 968 insertions(+), 35 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index b660baf94d..fb04a67685 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -44,8 +44,11 @@ at once.
 LIMITATIONS
 -----------
 
-This command does not (yet) work with histories that contain merges. You
-should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
+This command does not (yet) replay merge commits onto the rewritten
+history: if a commit that would be replayed is a merge, the operation is
+rejected, and you should use linkgit:git-rebase[1] with the
+`--rebase-merges` flag instead. The `squash` subcommand can still fold merges
+that lie inside the selected range, subject to the restrictions below.
 
 Furthermore, the command does not support operations that can result in merge
 conflicts. This limitation is by design as history rewrites are not intended to
@@ -114,6 +117,43 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's authorship and
+	takes the tree of the range's newest commit, so the whole range
+	collapses into a single commit. Commits above the range are replayed
+	on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash HEAD~3..HEAD` folds the three most recent commits into
+one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
+while leaving the two newest commits in place. Several revisions may be
+given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
+already on `topic`. Rev-list options may also be given, but any that would
+change how the range is walked are overridden with a warning.
++
+With `--no-edit`, the oldest commit's message is preserved, except that an
+`amend!` commit targeting it replaces its message.
++
+The selected commits must form a connected graph with a single tip and must
+not include a root commit. Every parent of a commit after the oldest one must
+either be selected or also be a parent of the oldest commit. When the oldest
+commit is a merge, all of its parents are preserved in the squashed commit.
++
+A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
+targets is also in the range, so the fold does not silently absorb a
+marker meant for a commit outside it. As an exception, a range made up entirely
+of markers for one target is combined into a single commit. With `--no-edit`,
+the last `amend!` message is used if there is one; a `squash!` or `amend!` is
+otherwise refused if folding it would discard its message.
++
+A local branch descended from a selected commit but not from the range tip
+cannot be rewritten as a descendant of the result, so with the default
+`--update-refs=branches` the command refuses. Rerun with `--update-refs=head`
+to rewrite only the current branch and leave such branches unchanged. Tags
+and remote-tracking refs are always left unchanged.
+
 OPTIONS
 -------
 
diff --git a/builtin/history.c b/builtin/history.c
index e65b76b59f..915cfb0cb9 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1011,6 +1011,260 @@ out:
 
 #define SQUASH_SEEN (1u << 11)
 #define SQUASH_TIP (1u << 12)
+#define SQUASH_AMEND_TARGET (1u << 13)
+
+static bool is_autosquash_subject(const char *s)
+{
+	return starts_with(s, "amend!") || starts_with(s, "fixup!") ||
+		starts_with(s, "squash!");
+}
+
+static bool skip_one_autosquash_prefix(const char *s, const char **out)
+{
+	if (skip_prefix(s, "amend!", out) || skip_prefix(s, "fixup!", out) ||
+	    skip_prefix(s, "squash!", out)) {
+		while (**out == ' ')
+			(*out)++;
+		return true;
+	}
+	return false;
+}
+
+static void truncate_message_to_subject(struct strbuf *msg)
+{
+	const char *eos = strstr(msg->buf, "\n\n");
+
+	if (eos)
+		strbuf_setlen(msg, eos - msg->buf + 1);
+}
+
+struct subject_data {
+	struct strintmap subjects;
+	struct strbuf subject;
+	struct strbuf squash_message;
+	const char *message;
+	bool edit_message;
+};
+
+#define SUBJECT_DATA_INIT {		\
+	.subjects = STRINTMAP_INIT,	\
+	.subject = STRBUF_INIT,		\
+	.squash_message = STRBUF_INIT,	\
+}
+
+static void subject_data_clear(struct subject_data *data)
+{
+	strintmap_clear(&data->subjects);
+	strbuf_release(&data->subject);
+	strbuf_release(&data->squash_message);
+}
+
+static int squash_amend_message(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data,
+				unsigned flags)
+{
+	const char *body = data->message + data->subject.len;
+
+	while (isspace(*body))
+		body++;
+
+	if (!*body) {
+		warning(_("ignoring %s (%s): message body is empty"),
+			repo_find_unique_abbrev(repo, &commit->object.oid,
+						DEFAULT_ABBREV),
+			data->subject.buf);
+		return 0;
+	}
+
+	if (data->edit_message) {
+		return 0;
+	} else if (flags & SQUASH_AMEND_TARGET) {
+		if (starts_with(data->squash_message.buf, "squash!"))
+			return error(_("squashing %s (%s) would overwrite "
+				       "'squash!' message, please combine them "
+				       "using '--edit'"),
+				     repo_find_unique_abbrev(repo,
+							     &commit->object.oid,
+							     DEFAULT_ABBREV),
+				     data->subject.buf);
+		if (starts_with(data->squash_message.buf, "fixup!"))
+			strbuf_splice(&data->squash_message, 0, 5, "amend!", 5);
+		if (starts_with(data->squash_message.buf, "amend!")) {
+			truncate_message_to_subject(&data->squash_message);
+			strbuf_addch(&data->squash_message, '\n');
+		} else {
+			strbuf_reset(&data->squash_message);
+		}
+		strbuf_addstr(&data->squash_message, body);
+		strbuf_complete_line(&data->squash_message);
+	} else {
+		return error(_("cannot squash %s (%s) that does not target "
+			       "base commit without '--edit'"),
+			     repo_find_unique_abbrev(repo, &commit->object.oid,
+						     DEFAULT_ABBREV),
+			     data->subject.buf);
+	}
+	return 0;
+}
+
+static int squash_squash_message(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data,
+				unsigned flags)
+{
+	const char *body = data->message + data->subject.len;
+
+	while (isspace(*body))
+		body++;
+
+	if (data->edit_message) {
+		return 0;
+	} else if (flags & SQUASH_AMEND_TARGET) {
+		if (starts_with(data->squash_message.buf, "fixup!")) {
+			truncate_message_to_subject(&data->squash_message);
+			strbuf_splice(&data->squash_message, 0, 5, "squash", 6);
+		}
+		if (starts_with(data->squash_message.buf, "squash!")) {
+			strbuf_addch(&data->squash_message, '\n');
+			strbuf_addstr(&data->squash_message, body);
+			strbuf_complete_line(&data->squash_message);
+		} else {
+			return error(_("squashing %s (%s) would discard its "
+				       "message, please combine them using "
+				       "'--edit'"),
+				     repo_find_unique_abbrev(repo,
+							     &commit->object.oid,
+							     DEFAULT_ABBREV),
+				     data->subject.buf);
+		}
+	} else {
+		return error(_("cannot squash %s (%s) that does not target "
+			       "base commit without '--edit'"),
+			      repo_find_unique_abbrev(repo, &commit->object.oid,
+						      DEFAULT_ABBREV),
+			      data->subject.buf);
+	}
+	return 0;
+}
+
+static int squash_check_can_autosquash(struct repository *repo,
+				       struct commit *commit,
+				       struct subject_data *data,
+				       unsigned flags)
+{
+	commit->object.flags |= flags & SQUASH_AMEND_TARGET;
+	if (starts_with(data->subject.buf, "amend!"))
+		return squash_amend_message(repo, commit, data, flags);
+	else if (starts_with(data->subject.buf, "squash!"))
+		return squash_squash_message(repo, commit, data, flags);
+
+	return 0;
+}
+
+static int squash_check_autosquash_subject(struct repository *repo,
+					   struct commit *commit,
+					   struct subject_data *data)
+{
+	const char* s = data->subject.buf;
+	struct commit *target;
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+	/* Try skipping autosquash prefixes one at a time to allow
+	 * squashing
+	 *     a commit
+	 *     fixup! fixup! a commit
+	 *
+	 * where we may have started with
+	 *     a commit
+	 *     fixup! a commit
+	 *     fixup! fixup! a commit
+	 *
+	 * and squashed the first fixup separately from the second
+	 */
+	while (skip_one_autosquash_prefix(s, &s)) {
+		unsigned flags = strintmap_get(&data->subjects, s);
+		if (flags)
+			return squash_check_can_autosquash(repo, commit, data, flags);
+	}
+	/*
+	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
+	 * "fixup! main". If the target is not being squshed check the subject
+	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
+	 * squashed together.
+	 */
+	target = lookup_commit_reference_by_name(s);
+	if (target && istarts_with(oid_to_hex(&target->object.oid), s)) {
+		unsigned flags =
+			target->object.flags & (SQUASH_SEEN | SQUASH_AMEND_TARGET);
+		if (!flags) {
+			const char *subject_start;
+			const char *buffer = repo_logmsg_reencode(repo, target,
+								  NULL, NULL);
+			size_t subject_len = find_commit_subject(buffer,
+								 &subject_start);
+			char *subject = xmemdupz(subject_start, subject_len);
+
+			flags = strintmap_get(&data->subjects, subject);
+			free(subject);
+			repo_unuse_commit_buffer(repo, target, buffer);
+		}
+		if (flags)
+			return squash_check_can_autosquash(repo, commit,
+							   data, flags);
+	}
+	/* Try subject prefix matches */
+	strintmap_for_each_entry(&data->subjects, &iter, entry) {
+		s = data->subject.buf;
+		while(skip_one_autosquash_prefix(s, &s)) {
+			if (starts_with(entry->key, s)) {
+				unsigned value = (intptr_t)entry->value;
+
+				return squash_check_can_autosquash(repo, commit,
+								   data, value);
+			}
+		}
+	}
+	return error(_("cannot squash %s (%s): its target is not being "
+		       "squashed"),
+		       repo_find_unique_abbrev(repo, &commit->object.oid,
+					       DEFAULT_ABBREV),
+		       data->subject.buf);
+}
+
+static int squash_check_subject(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data)
+{
+	int ret = 0;
+	const char *buf = repo_logmsg_reencode(repo, commit, NULL, NULL);
+	size_t subject_len = find_commit_subject(buf, &data->message);
+
+	strbuf_reset(&data->subject);
+	strbuf_add(&data->subject, data->message, subject_len);
+
+	if (!strintmap_get_size(&data->subjects)) {
+		const char *s;
+
+		strbuf_addstr(&data->squash_message, data->message);
+		strbuf_complete_line(&data->squash_message);
+		/*
+		 * Strip a single autosquash prefix to allow squashing
+		 *     fixup! base
+		 *     amend! base
+		 */
+		s = data->subject.buf;
+		skip_one_autosquash_prefix(s, &s);
+		strintmap_set(&data->subjects, s, SQUASH_AMEND_TARGET | SQUASH_SEEN);
+		commit->object.flags |= SQUASH_AMEND_TARGET;
+	} else if (is_autosquash_subject(data->subject.buf)) {
+		ret = squash_check_autosquash_subject(repo, commit, data);
+	} else {
+		strintmap_set(&data->subjects, data->subject.buf, SQUASH_SEEN);
+	}
+	repo_unuse_commit_buffer(repo, commit, buf);
+	return ret;
+}
 
 static int setup_squash_revisions(struct repository *repo,
 				  int argc, const char **argv,
@@ -1067,9 +1321,11 @@ static int resolve_squash_range(struct repository *repo,
 				bool update_branches,
 				int argc, const char **argv,
 				struct commit **oldest_out,
-				struct commit **tip_out)
+				struct commit **tip_out,
+				char **message_out)
 {
 	struct rev_info revs;
+	struct subject_data subject_data = SUBJECT_DATA_INIT;
 	struct commit *commit, *oldest = NULL, *tip = NULL;
 	int ret, tip_count = 0;
 	bool walk_started = false;
@@ -1132,6 +1388,10 @@ static int resolve_squash_range(struct repository *repo,
 			commit_list_insert(commit, &filter.with_commit);
 			oldest = commit;
 		}
+		if (squash_check_subject(repo, commit, &subject_data)) {
+			ret = -1;
+			goto out;
+		}
 		tip = commit;
 		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
 		tip_count++;
@@ -1200,12 +1460,15 @@ static int resolve_squash_range(struct repository *repo,
 
 	*oldest_out = oldest;
 	*tip_out = tip;
+	*message_out = strbuf_detach(&subject_data.squash_message, NULL);
 	ret = 0;
 
 out:
-	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP |
+			   SQUASH_AMEND_TARGET);
 	if (walk_started)
 		reset_revision_walk();
+	subject_data_clear(&subject_data);
 	release_revisions(&revs);
 	ref_filter_clear(&filter);
 	ref_array_clear(&refs);
@@ -1234,23 +1497,68 @@ static int cmd_history_squash(int argc,
 			 N_("edit the commit message")),
 		OPT_END(),
 	};
-	struct commit *oldest, *tip;
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct commit *oldest, *tip, *rewritten;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	char *message_template = NULL;
+	struct rev_info revs = { 0 };
 	int ret;
 
 	argc = parse_options(argc, argv, prefix, options, usage,
 			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
-	if (argc < 2)
-		return error(_("command expects a revision range"));
+	if (argc < 2) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
 	repo_config(repo, git_default_config, NULL);
+
 	if (action == REF_ACTION_DEFAULT)
 		action = REF_ACTION_BRANCHES;
 
+	strbuf_addstr(&reflog_msg, "squash: updating ");
+	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
+
 	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
-				   argc, argv, &oldest, &tip);
+				   argc, argv, &oldest, &tip,
+				   &message_template);
 	if (ret < 0)
-		return ret;
+		goto out;
+	if (edit) {
+		ret = error(_("message editing is not supported yet; use '--no-edit'"));
+		goto out;
+	}
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo,
+					oldest->parents->item)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+
+	ret = commit_tree_ext(repo, "squash", oldest, message_template,
+			      oldest->parents, base_tree_oid, tip_tree_oid,
+			      &rewritten, 0);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
 
-	return error(_("squashing commits is not implemented yet"));
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	release_revisions(&revs);
+	free(message_template);
+	return ret;
 }
 
 static int update_worktree(struct repository *repo,
diff --git a/object.h b/object.h
index dcf30156ca..46cade33fb 100644
--- a/object.h
+++ b/object.h
@@ -74,7 +74,7 @@ void object_array_init(struct object_array *array);
  * bisect.c:                                        16
  * bundle.c:                                        16
  * http-push.c:                          11-----14
- * builtin/history.c:                    1112
+ * builtin/history.c:                    11---13
  * commit-graph.c:                                15
  * commit-reach.c:                                  16-------20
  * builtin/last-modified.c:                         1617
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index b1f65de5f5..fb06637aaf 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -4,11 +4,50 @@ test_description='tests for git-history squash subcommand'
 
 . ./test-lib.sh
 
-test_expect_success 'setup linear history' '
+stage_file () {
+	printf "%s\n" "$1" >file &&
+	git add file
+}
+
+commit_with_message () {
+	printf "%b" "$1" >msg &&
+	git commit --allow-empty -qF msg
+}
+
+check_commit_count () {
+	git rev-list --count "$1" >actual &&
+	echo "$2" >expect &&
+	test_cmp expect actual
+}
+
+check_log_subjects () {
+	git log --format="%s" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+check_log_messages () {
+	git log --format="%B" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+# Checks that the author data of two commits matches
+# Usage: check_commit_author <rev1> <rev2>
+check_commit_author () {
+	git show -s --format="%an <%ae> %ad" "$1" >expect &&
+	git show -s --format="%an <%ae> %ad" "$2" >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'setup linear history touching two files' '
 	test_commit base file a start &&
-	test_commit one file b &&
-	test_commit two file c &&
-	test_commit three file d
+	GIT_AUTHOR_NAME=One GIT_AUTHOR_EMAIL=one@example.com \
+		test_commit one other x &&
+	GIT_AUTHOR_NAME=Two GIT_AUTHOR_EMAIL=two@example.com \
+		test_commit two file c &&
+	GIT_AUTHOR_NAME=Three GIT_AUTHOR_EMAIL=three@example.com \
+		test_commit three file d
 '
 
 test_expect_success 'errors on missing range argument' '
@@ -29,40 +68,331 @@ test_expect_success 'errors on a single revision that is not a range' '
 '
 
 test_expect_success 'errors on a range holding a single commit' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
 	test_must_fail git history squash "HEAD^!" 2>err &&
-	test_grep "single commit; nothing to squash" err
+	test_grep "single commit; nothing to squash" err &&
+	test_cmp_rev "$head_before" HEAD
 '
 
-test_expect_success 'rejects a root commit' '
+test_expect_success 'rejects root commit' '
+	# create a disconnected root commit
 	oid=$(git commit-tree -m root three^{tree}) &&
-	test_must_fail git history squash \
-		--ancestry-path=start "$oid..three" 2>err &&
-	test_grep "cannot squash down to root commit" err
+	# because we pass --ancestry-path when calling setup_revs() it the
+	# revision walk will only include commits decended from $oid so
+	# we need to give it another --ancestry-path commit to actually walk
+	# any commits.
+	test_must_fail git history squash --ancestry-path=start $oid..three 2>err &&
+	echo "error: cannot squash down to root commit" >expect &&
+	test_cmp expect err
 '
 
 test_expect_success 'rejects multiple tips' '
 	oid=$(git commit-tree -m tip -p start^0 three^{tree}) &&
-	test_must_fail git history squash ^start "$oid" three~1 2>err &&
-	test_grep "revision range contains more than one tip" err
+	test_must_fail git history squash ^start $oid three~1 2>err &&
+	echo "error: the revision range contains more than one tip commit" >expect &&
+	test_cmp expect err &&
+
+	git reset --hard three &&
+	git history squash --no-edit ^start three~1 three &&
+	test_cmp_rev HEAD~1 start^0 &&
+	test_cmp_rev HEAD^{tree} three^{tree}
 '
 
-test_expect_success 'rejects a merge parent outside the range' '
-	git reset --hard start &&
+test_expect_success 'accepts multiple revision arguments with an exclusion' '
+	git reset --hard three &&
+	git branch -f keep HEAD~2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start..HEAD ^keep &&
+
+	git reflog -1 --format=%gs >actual &&
+	echo "squash: updating start..HEAD ^keep" >expect &&
+	test_cmp expect actual &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	two
+	one
+	EOF
+	test_cmp_rev keep HEAD~1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git branch -D keep
+'
+
+test_expect_success 'squashes a branch the current branch is not on' '
+	git reset --hard three &&
 	main=$(git symbolic-ref --short HEAD) &&
-	git checkout -b outside-parent &&
-	test_commit --no-tag outside-parent outside x &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b off-history start &&
+	test_commit --no-tag off-one off a &&
+	test_commit --no-tag off-two off b &&
 	git checkout "$main" &&
-	test_commit --no-tag outside-main file b &&
-	base=$(git rev-parse HEAD) &&
-	test_commit --no-tag outside-mid file c &&
-	git merge --no-ff -m "merge outside-parent" outside-parent &&
-	git branch -D outside-parent &&
 
-	test_must_fail git history squash "$base.." 2>err &&
-	test_grep "parent .* of commit .* is outside the revision range" err
+	git history squash --no-edit start..off-history &&
+
+	check_commit_count start..off-history 1 &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D off-history
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash --no-edit start.. &&
+
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	check_log_subjects -1 <<-\EOF &&
+	one
+	EOF
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'sanitizes rev-list walk options, before and after --' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit --date-order start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git reset --hard three &&
+	git history squash --no-edit -- --reverse start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start..@~1 &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	three
+	one
+	EOF
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit "$root.." &&
+
+	check_commit_count "$root..HEAD" 1 &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashing a mix of fixups' '
+	git reset --hard three &&
+	echo fix >file &&
+	git commit --fixup=two -a &&
+	echo really fix >file &&
+	git commit --fixup=one -a &&
+	echo really really fix >file &&
+	git commit --fixup=HEAD~1 -a && # fixup! two
+	echo really really really fix >file &&
+	git commit --fixup=HEAD~1 -a && # fixup! one
+
+	# squashing fixup! with a target that is not being squashed fails
+	test_must_fail git history squash one.. 2>err &&
+	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
+
+	# squashing fixup! into fixup! with a different target fails
+	test_must_fail git history squash HEAD~4.. 2>err && # HEAD~4 is fixup! two
+	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
+
+	# squashing a sequence of fixup! commits into their targets
+	git history squash --no-edit start..HEAD~1 &&
+	test_cmp_rev start HEAD~2 &&
+	check_commit_author one HEAD~1 &&
+	test_commit_message HEAD~1 -m one &&
+
+	# squashing "fixup! fixup! <target>" into "<target>"
+	git history squash --no-edit start.. &&
+	test_cmp_rev start HEAD~1 &&
+	check_commit_author one HEAD &&
+	test_commit_message HEAD -m one
+'
+
+test_expect_success 'squashing "squash!" messages' '
+	git reset --hard two &&
+	echo fix >file &&
+	git commit --fixup=HEAD -a &&
+	oldest=$(git rev-parse HEAD) &&
+	echo better fix >file &&
+	git commit -a -F - <<-EOF &&
+	squash! $(git rev-parse two)
+
+	Append this
+	EOF
+
+	echo an even better fix >file &&
+	git commit -a -F - <<-EOF &&
+	squash! squash! two
+
+	Append this as well
+	EOF
+
+	# must edit when squashing "squash!" into its target
+	test_must_fail git history squash --no-edit two^.. 2>err &&
+	test_grep "^error: squashing .* (squash! [a-f0-9]*) would discard its message" err &&
+
+	# squashing "squash!" into "fixup!" appends messages and changes
+	# subject prefix
+	git history squash --no-edit two.. &&
+	test_cmp_rev HEAD^ two &&
+	test_commit_message HEAD <<-\EOF &&
+	squash! two
+
+	Append this
+
+	Append this as well
+	EOF
+	check_commit_author "$oldest" HEAD &&
+
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! two
+
+	A new message
+	EOF
+
+	# "amend!" does not replace "squash!"
+	test_must_fail git history squash --no-edit HEAD~2.. 2>err &&
+	test_grep "^error: squashing .* (amend! two) would overwrite .squash!. message" err
+'
+
+test_expect_success '--no-edit uses last "amend!" message without an editor' '
+	git reset --hard three &&
+	write_script editor <<-\EOF &&
+	exit 1
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	echo fix >file &&
+	git commit --author="Fix Me <fix.me@example.com>" --fixup=HEAD -a &&
+	git commit --allow-empty -F - <<-EOF &&
+	amend! $(git rev-parse --short HEAD)
+
+	The first reword
+
+	More detail
+	EOF
+
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! three
+
+	The second reword
+
+	Extra detail
+	EOF
+
+	test_commit WIP &&
+
+	cat >msg <<-EOF &&
+	amend! $(git rev-parse --short HEAD^)
+
+	The third reword
+
+	Excruciating detail
+	EOF
+
+	git commit --author="Someone Else <s.else@example.com>" --allow-empty \
+		-F msg &&
+
+	# squashing amend! updates the commit message
+	git history squash --no-edit three^.. &&
+	sed -e 1,2d msg | test_commit_message HEAD &&
+	check_commit_author three HEAD &&
+	test_cmp_rev HEAD^ three^ &&
+
+	# squashing amend! into fixup! updates subject prefix
+	git reset --hard HEAD@{1} &&
+	git history squash --no-edit three.. &&
+	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
+	check_commit_author HEAD@{1}~4 HEAD &&
+	test_cmp_rev HEAD^ three &&
+
+	# squashing amend! into amend! keeps original subject line
+	git reset --hard HEAD@{1} &&
+	git history squash --no-edit HEAD~3.. &&
+	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
+	test_cmp_rev HEAD~3 three &&
+
+	# all amend! messages must target the first commit
+	git reset --hard HEAD@{1} &&
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! WIP
+
+	The real message
+	EOF
+
+	test_must_fail git history squash --no-edit HEAD~4.. 2>err &&
+	test_grep "^error: cannot squash .* that does not target" err &&
+
+	# amend! message that targets commit that is not in range is rejected
+	test_must_fail git history squash --no-edit HEAD~3.. 2>err &&
+	test_grep "^error: cannot squash .* target is not being squashed" err &&
+	test_set_editor :
 '
 
-test_expect_success 'prints branches that cannot follow the squash' '
+test_expect_success 'squashing fixups into a merge' '
+	test_when_finished \
+		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
+		 git branch -D feature" &&
+	git checkout -f start &&
+	test_commit F1 &&
+	git checkout -b feature start &&
+	test_commit F2 &&
+	git merge F1 &&
+	echo fixed >F1.t &&
+	cat >msg <<-EOF &&
+	amend! $(git rev-parse HEAD)
+
+	merge F1 and F2
+
+	reworded
+	EOF
+
+	git commit -a -F msg &&
+	git history squash --no-edit HEAD^^! HEAD &&
+	test_cmp_rev HEAD^1 F2 &&
+	test_cmp_rev HEAD^2 F1 &&
+	test_cmp_rev HEAD@{1}^{tree} HEAD^{tree} &&
+	sed 1,2d msg | test_commit_message HEAD
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --no-edit --update-refs=head start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success 'refuses to fold a range a branch points into' '
 	test_when_finished \
 		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
 		 git branch -D feature" &&
@@ -85,20 +415,275 @@ test_expect_success 'prints branches that cannot follow the squash' '
 	test_grep "^error: the following branches cannot be rewritten" err &&
 	test_grep "^  topic-1$" err &&
 	test_grep "^  topic-2$" err &&
-	test_grep "^hint: .* --update-refs=head" err
+	test_grep "^hint: .* --update-refs=head" err &&
+	test_cmp_rev C6 HEAD &&
+
+	# squash succeeds with --update-refs=head
+	git history squash --no-edit --update-refs=head start.. &&
+	test_cmp_rev start HEAD^ &&
+	test_cmp_rev C6^{tree} HEAD^{tree} &&
+	test_cmp_rev C6 HEAD@{1}
 '
 
 test_expect_success 'advice.historyUpdateRefs silences the hint' '
 	git reset --hard three &&
 	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
 
 	test_must_fail git -c advice.historyUpdateRefs=false \
 		history squash start.. 2>err &&
 	test_grep "^error: the following branches cannot be rewritten" err &&
 	test_grep "^  mid$" err &&
 	test_grep ! "hint:" err &&
+	test_cmp_rev "$head_before" HEAD &&
 
 	git branch -D mid
 '
 
+test_expect_success 'leaves tags and remote-tracking refs unchanged' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	git update-ref refs/remotes/origin/mark HEAD~1 &&
+	mark_before=$(git rev-parse mark) &&
+
+	git history squash --no-edit start.. &&
+
+	test_cmp_rev "$mark_before" mark &&
+	test_cmp_rev "$mark_before" refs/remotes/origin/mark &&
+
+	git tag -d mark &&
+	git update-ref -d refs/remotes/origin/mark
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout "$main" &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	test_commit --no-tag after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF &&
+	before-side
+	EOF
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a merge of a branch that forked at the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b base-fork-side &&
+	test_commit --no-tag base-fork-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag base-fork-main file b &&
+	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
+	git branch -D base-fork-side &&
+	test_commit --no-tag base-fork-tail file c &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'refuses a merge whose other parent is outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "parent .* of commit .* is outside the revision range" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit "$base.." &&
+
+	check_commit_count "$base..HEAD" 1 &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'folds a range with two interior merges' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag two-merge-a file a1 &&
+	git checkout -b two-merge-s1 &&
+	test_commit --no-tag two-merge-s1 s1 x &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s1" two-merge-s1 &&
+	test_commit --no-tag two-merge-b file b1 &&
+	git checkout -b two-merge-s2 &&
+	test_commit --no-tag two-merge-s2 s2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s2" two-merge-s2 &&
+	git branch -D two-merge-s1 two-merge-s2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file s1 &&
+	test_path_is_file s2
+'
+
+test_expect_success 'folds a range with a nested merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b nested-outer &&
+	test_commit --no-tag nested-outer outer x &&
+	git checkout -b nested-inner &&
+	test_commit --no-tag nested-inner inner y &&
+	git checkout nested-outer &&
+	git merge --no-ff -m "merge inner" nested-inner &&
+	git checkout "$main" &&
+	test_commit --no-tag nested-main file b1 &&
+	git merge --no-ff -m "merge outer" nested-outer &&
+	git branch -D nested-outer nested-inner &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file outer &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range with an octopus merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag octo-base file a1 &&
+	git checkout -b octo-1 &&
+	test_commit --no-tag octo-1 o1 x &&
+	git checkout "$main" &&
+	git checkout -b octo-2 &&
+	test_commit --no-tag octo-2 o2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-1 octo-2 &&
+	git branch -D octo-1 octo-2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file o1 &&
+	test_path_is_file o2
+'
+
+test_expect_success 'refuses an octopus merge with an arm forked before the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b octo-pre &&
+	test_commit octo-pre-side pside x &&
+	git checkout "$main" &&
+	test_commit octo-pre-main file b1 &&
+	octo_base=$(git rev-parse HEAD) &&
+	git checkout -b octo-within &&
+	test_commit --no-tag octo-within wside y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-pre octo-within &&
+	merged=$(git rev-parse HEAD) &&
+	git branch -D octo-pre octo-within &&
+
+	test_must_fail git history squash "$octo_base.." 2>err &&
+	test_grep "parent .* of commit .* is outside the revision range" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'refuses when a descendant above the range is a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag desc-one file b &&
+	test_commit --no-tag desc-two file c &&
+	git tag desc-tip &&
+	git checkout -b desc-above &&
+	test_commit --no-tag desc-above above x &&
+	git checkout "$main" &&
+	test_commit --no-tag desc-main file d &&
+	git merge --no-ff -m "merge desc-above" desc-above &&
+	git branch -D desc-above &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash --no-edit start..desc-tip 2>err &&
+	test_grep "merge commits is not supported" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'refuses to fold a range a ref points into at a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag refmerge-base file b &&
+	git checkout -b refmerge-side &&
+	test_commit --no-tag refmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag refmerge-main file c &&
+	git merge --no-ff -m "interior merge" refmerge-side &&
+	git branch -D refmerge-side &&
+	git branch at-merge HEAD &&
+	test_commit --no-tag refmerge-tail file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "^error: the following branches cannot be rewritten" err &&
+	test_grep "^  at-merge$" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D at-merge
+'
+
 test_done
-- 
gitgitgadget

Re: [PATCH v14 7/8] history: create squashed commits without editing

[Junio C Hamano]

"Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:

> +	/*
> +	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
> +	 * "fixup! main". If the target is not being squshed check the subject
> +	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
> +	 * squashed together.
> +	 */
> +	target = lookup_commit_reference_by_name(s);
> +	if (target && istarts_with(oid_to_hex(&target->object.oid), s)) {

Why istarts_with()?  "fixup! ABCdef" should not be accepted, should it?

Re: [PATCH v14 7/8] history: create squashed commits without editing

[Phillip Wood]

On 20/08/2026 21:10, Junio C Hamano wrote:
> "Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> +	/*
>> +	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
>> +	 * "fixup! main". If the target is not being squshed check the subject
>> +	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
>> +	 * squashed together.
>> +	 */
>> +	target = lookup_commit_reference_by_name(s);
>> +	if (target && istarts_with(oid_to_hex(&target->object.oid), s)) {
> 
> Why istarts_with()?  "fixup! ABCdef" should not be accepted, should it?

I agree there isn't really a compelling case for mixed case oids, but 
accepting all uppercase, or all lowercase seems reasonable, or are we 
planning to completely ban uppercase oids as brain has suggested? The 
aim here is to accept any oid that rebase would, but not accept ref names.

Thanks

Phillip

Re: [PATCH v14 7/8] history: create squashed commits without editing

[Junio C Hamano]

Phillip Wood <phillip.wood123@gmail.com> writes:

> On 20/08/2026 21:10, Junio C Hamano wrote:
>> "Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:
>> 
>>> +	/*
>>> +	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
>>> +	 * "fixup! main". If the target is not being squshed check the subject
>>> +	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
>>> +	 * squashed together.
>>> +	 */
>>> +	target = lookup_commit_reference_by_name(s);
>>> +	if (target && istarts_with(oid_to_hex(&target->object.oid), s)) {
>> 
>> Why istarts_with()?  "fixup! ABCdef" should not be accepted, should it?
>
> I agree there isn't really a compelling case for mixed case oids, but 
> accepting all uppercase, or all lowercase seems reasonable, or are we 

Tell that to brian who wrote the bc/restrict-hex-to-lowercase topic
in <20260729233215.398654-7-sandals@crustytoothpaste.net>.

> planning to completely ban uppercase oids as brain has suggested? The 
> aim here is to accept any oid that rebase would, but not accept ref names.

I understand that we never emitted hexadecimal containing uppercase
letters ourselves, so 'commit --fixup' and friends wouldn't have
added anything that requires istarts_with().  So accepting any oid
that we would have given the users after "fixup!" but not refnames
can be achieved by starts_with() just fine, no?

Re: [PATCH v14 7/8] history: create squashed commits without editing

[Phillip Wood]

On 24/08/2026 16:07, Junio C Hamano wrote:
> Phillip Wood <phillip.wood123@gmail.com> writes:
> 
>> On 20/08/2026 21:10, Junio C Hamano wrote:
>>> "Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:
>>>
>>>> +	/*
>>>> +	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
>>>> +	 * "fixup! main". If the target is not being squshed check the subject
>>>> +	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
>>>> +	 * squashed together.
>>>> +	 */
>>>> +	target = lookup_commit_reference_by_name(s);
>>>> +	if (target && istarts_with(oid_to_hex(&target->object.oid), s)) {
>>>
>>> Why istarts_with()?  "fixup! ABCdef" should not be accepted, should it?
>>
>> I agree there isn't really a compelling case for mixed case oids, but
>> accepting all uppercase, or all lowercase seems reasonable, or are we
> 
> Tell that to brian who wrote the bc/restrict-hex-to-lowercase topic
> in <20260729233215.398654-7-sandals@crustytoothpaste.net>.
> >> planning to completely ban uppercase oids as brain has suggested? The
>> aim here is to accept any oid that rebase would, but not accept ref names.
> 
> I understand that we never emitted hexadecimal containing uppercase
> letters ourselves, so 'commit --fixup' and friends wouldn't have
> added anything that requires istarts_with().  So accepting any oid
> that we would have given the users after "fixup!" but not refnames
> can be achieved by starts_with() just fine, no?

If they're using "git commit --fixup" then yes. If we're going to reject 
uppercase hex everywhere then clearly we should be using starts_with() 
here, but if we keep accepting uppercase hex elsewhere why should we 
reject it here?

Thanks

Phillip

Re: [PATCH v14 7/8] history: create squashed commits without editing

[Junio C Hamano]

Phillip Wood <phillip.wood123@gmail.com> writes:

> On 24/08/2026 16:07, Junio C Hamano wrote:
>> Phillip Wood <phillip.wood123@gmail.com> writes:
>> 
>>> On 20/08/2026 21:10, Junio C Hamano wrote:
>>>> "Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:
>>>>
>>>>> +	/*
>>>>> +	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
>>>>> +	 * "fixup! main". If the target is not being squshed check the subject
>>>>> +	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
>>>>> +	 * squashed together.
>>>>> +	 */
>>>>> +	target = lookup_commit_reference_by_name(s);
>>>>> +	if (target && istarts_with(oid_to_hex(&target->object.oid), s)) {
>>>>
>>>> Why istarts_with()?  "fixup! ABCdef" should not be accepted, should it?
>>>
>>> I agree there isn't really a compelling case for mixed case oids, but
>>> accepting all uppercase, or all lowercase seems reasonable, or are we
>> 
>> Tell that to brian who wrote the bc/restrict-hex-to-lowercase topic
>> in <20260729233215.398654-7-sandals@crustytoothpaste.net>.
>> >> planning to completely ban uppercase oids as brain has suggested? The
>>> aim here is to accept any oid that rebase would, but not accept ref names.
>> 
>> I understand that we never emitted hexadecimal containing uppercase
>> letters ourselves, so 'commit --fixup' and friends wouldn't have
>> added anything that requires istarts_with().  So accepting any oid
>> that we would have given the users after "fixup!" but not refnames
>> can be achieved by starts_with() just fine, no?
>
> If they're using "git commit --fixup" then yes. If we're going to reject 
> uppercase hex everywhere then clearly we should be using starts_with() 
> here, but if we keep accepting uppercase hex elsewhere why should we 
> reject it here?

The point is not to add any *new* places that accept uppercase hex,
and this is to participate in the move to discourge the use of
uppercase hex.

[PATCH v14 8/8] history: support editing squashed commit messages

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Open the editor by default when squashing and provide --no-edit as the
opt-out. Record the exact commits selected by the revision walk,
rearrange that todo list with the sequencer's autosquash machinery, and
build the message template from the resulting order.

Match interactive rebase's treatment of marker messages: comment out
fixup! messages, retain squash! bodies, and let amend! replace its target
unless a preceding squash! requires both bodies. This keeps message
editing aligned with the marker validation used by the no-edit path.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  18 ++-
 builtin/history.c              |  97 +++++++++++++++-
 t/t3455-history-squash.sh      | 197 +++++++++++++++++++++++++++++++++
 3 files changed, 305 insertions(+), 7 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index fb04a67685..2e2e31f521 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -133,8 +133,9 @@ given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
 already on `topic`. Rev-list options may also be given, but any that would
 change how the range is walked are overridden with a warning.
 +
-With `--no-edit`, the oldest commit's message is preserved, except that an
-`amend!` commit targeting it replaces its message.
+An editor opens pre-filled with the messages of all the folded commits so you
+can combine them. With `--no-edit`, the oldest commit's message is preserved
+instead, except that an `amend!` commit targeting it replaces its message.
 +
 The selected commits must form a connected graph with a single tip and must
 not include a root commit. Every parent of a commit after the oldest one must
@@ -148,6 +149,13 @@ of markers for one target is combined into a single commit. With `--no-edit`,
 the last `amend!` message is used if there is one; a `squash!` or `amend!` is
 otherwise refused if folding it would discard its message.
 +
+The editor template mirrors `git rebase -i --autosquash`: each `fixup!`,
+`squash!`, or `amend!` is grouped under the commit it targets rather than
+shown in commit order. A `fixup!` message is dropped (commented out in full),
+a `squash!` keeps its body with only the marker subject commented, and an
+`amend!` replaces its target's message, unless a `squash!` folded into that
+target first, in which case it keeps its body like a `squash!`.
++
 A local branch descended from a selected commit but not from the range tip
 cannot be rewritten as a descendant of the result, so with the default
 `--update-refs=branches` the command refuses. Rerun with `--update-refs=head`
@@ -163,6 +171,12 @@ OPTIONS
 	objects will be written into the repository, so applying these printed
 	ref updates is generally safe.
 
+`--edit`::
+`--no-edit`::
+	For `squash`, open an editor to combine the messages of the folded commits.
+	This is the default; use `--no-edit` to keep the selected message without
+	opening an editor.
+
 `--reedit-message`::
 	Open an editor to modify the target commit's message.
 
diff --git a/builtin/history.c b/builtin/history.c
index 915cfb0cb9..db35a7451a 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1266,6 +1266,10 @@ static int squash_check_subject(struct repository *repo,
 	return ret;
 }
 
+static int build_squash_message(struct repository *repo,
+				const struct strbuf *todo_buf,
+				struct strbuf *out);
+
 static int setup_squash_revisions(struct repository *repo,
 				  int argc, const char **argv,
 				  struct rev_info *revs)
@@ -1319,6 +1323,7 @@ static int setup_squash_revisions(struct repository *repo,
  */
 static int resolve_squash_range(struct repository *repo,
 				bool update_branches,
+				bool edit_message,
 				int argc, const char **argv,
 				struct commit **oldest_out,
 				struct commit **tip_out,
@@ -1327,11 +1332,13 @@ static int resolve_squash_range(struct repository *repo,
 	struct rev_info revs;
 	struct subject_data subject_data = SUBJECT_DATA_INIT;
 	struct commit *commit, *oldest = NULL, *tip = NULL;
+	struct strbuf todo_buf = STRBUF_INIT;
 	int ret, tip_count = 0;
 	bool walk_started = false;
 	struct ref_filter filter = REF_FILTER_INIT;
 	struct ref_array refs = { 0 };
 
+	subject_data.edit_message = edit_message;
 	ret = setup_squash_revisions(repo, argc, argv, &revs);
 	if (ret < 0)
 		goto out;
@@ -1344,6 +1351,10 @@ static int resolve_squash_range(struct repository *repo,
 	while ((commit = get_revision(&revs))) {
 		struct commit_list *p;
 
+		if (edit_message)
+			strbuf_addf(&todo_buf, "pick %s\n",
+				    oid_to_hex(&commit->object.oid));
+
 		if (!commit->parents) {
 			ret = error(_("cannot squash down to root commit"));
 			goto out;
@@ -1457,6 +1468,13 @@ static int resolve_squash_range(struct repository *repo,
 		string_list_clear(&sorting_options, 0);
 		goto out;
 	}
+	if (edit_message) {
+		strbuf_reset(&subject_data.squash_message);
+		ret = build_squash_message(repo, &todo_buf,
+					   &subject_data.squash_message);
+		if (ret < 0)
+			goto out;
+	}
 
 	*oldest_out = oldest;
 	*tip_out = tip;
@@ -1464,6 +1482,7 @@ static int resolve_squash_range(struct repository *repo,
 	ret = 0;
 
 out:
+	strbuf_release(&todo_buf);
 	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP |
 			   SQUASH_AMEND_TARGET);
 	if (walk_started)
@@ -1475,6 +1494,76 @@ out:
 	return ret;
 }
 
+static bool amend_replaces_target(struct todo_list *todo, int target)
+{
+	for (int i = target + 1; i < todo->nr &&
+				 todo->items[i].command != TODO_PICK; i++) {
+		if (todo->items[i].command == TODO_SQUASH)
+			return false;
+		if (todo->items[i].flags & TODO_REPLACE_FIXUP_MSG)
+			return true;
+	}
+	return false;
+}
+
+static int build_squash_message(struct repository *repo,
+				const struct strbuf *todo_buf,
+				struct strbuf *out)
+{
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	int nr_commits, ret;
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo_buf->buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not prepare the squash message"));
+		goto out;
+	}
+
+	nr_commits = todo.nr;
+	for (int i = 0; i < nr_commits; i++) {
+		struct todo_item *item = &todo.items[i];
+		const char *message, *body;
+		size_t commented_len;
+		bool skip, squashing;
+
+		squashing = item->command == TODO_SQUASH ||
+			    (item->flags & TODO_REPLACE_FIXUP_MSG);
+		if (item->command == TODO_PICK)
+			skip = amend_replaces_target(&todo, i);
+		else
+			skip = !squashing;
+
+		message = repo_logmsg_reencode(repo, item->commit, NULL, NULL);
+		find_commit_subject(message, &body);
+
+		if (skip)
+			commented_len = strlen(body);
+		else if (squashing)
+			commented_len = squash_subject_comment_len(body, 1);
+		else
+			commented_len = 0;
+
+		if (!i)
+			add_squash_combination_header(out, nr_commits);
+		strbuf_addch(out, '\n');
+		add_squash_message_header(out, i + 1, skip);
+		strbuf_addstr(out, "\n\n");
+		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
+		strbuf_addstr(out, body + commented_len);
+		strbuf_complete_line(out);
+
+		repo_unuse_commit_buffer(repo, item->commit, message);
+	}
+
+	ret = 0;
+
+out:
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1519,14 +1608,11 @@ static int cmd_history_squash(int argc,
 	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
 
 	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
+				   edit,
 				   argc, argv, &oldest, &tip,
 				   &message_template);
 	if (ret < 0)
 		goto out;
-	if (edit) {
-		ret = error(_("message editing is not supported yet; use '--no-edit'"));
-		goto out;
-	}
 
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
@@ -1538,7 +1624,8 @@ static int cmd_history_squash(int argc,
 
 	ret = commit_tree_ext(repo, "squash", oldest, message_template,
 			      oldest->parents, base_tree_oid, tip_tree_oid,
-			      &rewritten, 0);
+			      &rewritten,
+			      edit ? COMMIT_TREE_EDIT_MESSAGE : 0);
 	if (ret < 0) {
 		ret = error(_("failed writing squashed commit"));
 		goto out;
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index fb06637aaf..d21e9d9fc4 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -381,6 +381,203 @@ test_expect_success 'squashing fixups into a merge' '
 	sed 1,2d msg | test_commit_message HEAD
 '
 
+test_expect_success 'edits every message and aborts on an empty result' '
+	git reset --hard start &&
+	stage_file b &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script empty-editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/empty-editor" &&
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "Aborting commit due to empty commit message" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# This is the 1st commit message:
+
+	re-one subject
+
+	re-one body line
+
+	# This is the commit message #2:
+
+	re-two
+
+	# This is the commit message #3:
+
+	re-three
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_subjects -1 <<-\EOF
+	combined
+	EOF
+'
+
+test_expect_success 'handles fixup!, squash! and amend! like rebase' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "fixup! mark-base\n\nfixup body\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+	stage_file e &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	mark-base
+
+	# The commit message #2 will be skipped:
+
+	# fixup! mark-base
+	#
+	# fixup body
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# This is the commit message #4:
+
+	# amend! mark-base
+
+	amended message
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	mark-base
+
+	squash remark
+
+	amended message
+
+	EOF
+'
+
+test_expect_success 'groups fixups under their targets in the editor' '
+	git reset --hard start &&
+	test_commit --no-tag alpha file a1 &&
+	test_commit --no-tag beta file b1 &&
+	stage_file a2 &&
+	commit_with_message "fixup! alpha\n" &&
+	stage_file b2 &&
+	commit_with_message "fixup! beta\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	alpha
+
+	# The commit message #2 will be skipped:
+
+	# fixup! alpha
+
+	# This is the commit message #3:
+
+	beta
+
+	# The commit message #4 will be skipped:
+
+	# fixup! beta
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited
+'
+
+test_expect_success 'lets amend! replace its target message in the editor' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# The 1st commit message will be skipped:
+
+	# mark-base
+
+	# This is the commit message #2:
+
+	# amend! mark-base
+
+	amended message
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	amended message
+
+	squash remark
+
+	EOF
+'
+
 test_expect_success '--update-refs=head only moves HEAD' '
 	git reset --hard three &&
 	git branch -f other HEAD &&
-- 
gitgitgadget

[PATCH v15 0/8] history: add squash subcommand to fold a range

[Harald Nordgren via GitGitGadget]

Adds git history squash <revision-range> to fold a range of commits.

Changes in v15:

 * Fixed istarts_with() → starts_with() in squash_check_autosquash_subject()
   so fixup! ABCdef (mixed/upper-case hex) is no longer accepted.
 * Fixed a typo in the adjacent comment (squshed → squashed).

Changes in v14:

 * Update commit message trailers.
 * Simplify rev-parse and tr complexity in the tests.

Changes in v13:

 * Split the squash implementation into five patches covering parsing, range
   validation, branch protection, commit creation, and message editing.
 * Print the sorted names of local branches that prevent a squash, with
   clearer advice for --update-refs=head.
 * Isolate --no-edit behavior from the final patch that enables default
   editor-based message combining.

Changes in v12:

 * Incorporated fixups from Phillip:
   * Reworks range validation into a single walk that rejects roots and
     multiple tips while preserving every parent when squashing into a
     merge.
   * Resolves fixup!, squash! and amend! targets directly, preserving
     message intent and safely consolidating related markers.
   * Builds the editor template from the exact selected revisions, including
     exclusions, while retaining --no-edit behavior.
   * Protects descendant local branches while leaving tags and
     remote-tracking refs unchanged.

Changes in v11:

 * Make message editing the default with the autosquash-style template, add
   --no-edit instead of squash-specific --reedit-message.
 * Validate one actual boundary and tip, rejecting root-reaching and
   multi-tip ranges.
 * Protect only interior local branches, leaving tags and remote-tracking
   refs unchanged.
 * Move sequencer preparation before squash and fold the later
   message-editing patch into the feature commit.

Changes in v10:

 * Record the full revision expression in squash reflog.
 * Preserve the boundary-walk invariant when sanitizing rev-list options.
 * Clarify amend! and --reedit-message documentation.

Changes in v9:

 * Use the last amend! targeting the oldest folded commit as the default
   squashed message. Ignore amend! markers targeting later commits while
   selecting that replacement message.
 * Improve tests.

Changes in v8:

 * --reedit-message now builds the same editor template as git rebase -i
   --autosquash: fixup!, squash! and amend! commits are grouped under the
   commit they target instead of shown in commit order, and an amend!
   replaces its target's message.
 * A fixup!, squash! or amend! is refused only when its target is outside
   the range, so several fixups for an in-range commit fold together. A
   range that is entirely markers for one below-range target is combined
   into a single commit, keeping the last amend! message.
 * Merges inside the range are folded when the range has a single base, with
   no dedicated opt-in flag, --ancestry-path ensures only commits descended
   from the base are folded, and a range reaching more than one base is
   rejected.
 * Rev-list options are accepted and sanitized the way git replay does,
   forcing the walk order back with a warning, which also fixes git history
   squash -- --reverse slipping past the previous option check.
 * Kept this as an explicit squash subcommand rather than making
   --reedit-message the default or renaming the command.

Changes in v7:

 * --reedit-message now builds the same editor template git rebase -i shows
   for a squash (a combination of N commits banner with each folded message
   under its own header) and follows autosquash for markers: a fixup!
   message falls out (commented under a will be skipped header), while a
   squash! or amend! keeps its body with only the marker subject commented
   so its remark can be reworded in. Only the message text is affected,
   every commit's changes are always folded in.
 * Reuse git rebase -i's squash-message code: a preparatory sequencer:
   commit extracts the banner, header and marker-comment helpers so both
   rebase and git history squash build the identical template from one
   source.
 * Refuse a range whose oldest commit is a fixup!, squash! or amend!, since
   the marker's target cannot be inside the range.
 * Reorder the squash usage so dashed options come before <revision-range>,
   and spell out HEAD instead of @ in the documentation and examples.
 * Expand the squash commit message and documentation with this overview,
   and scope the merge limitation so it no longer contradicts squash folding
   a single-base interior merge.

Changes in v6:

 * git history squash now accepts multiple revision arguments, read like the
   arguments to git-rev-list, so a compound range such as @~3.. ^topic
   works.
 * The base to reparent onto is now the oldest in-range commit's parent; a
   boundary other than that base means the range has more than one base and
   is rejected. This also fixes the earlier overly-restrictive handling of
   merges and side branches.
 * A single-commit range (e.g. @^!) is rejected with "nothing to squash"
   (this also covers the @^!-style example that previously succeeded
   silently).
 * Commit messages reworded: the squash commit now gives an overview of
   fixup!/squash!/amend! handling, rewording, merge-parent and ref behavior.

Changes in v5:

 * The range walk now uses --ancestry-path, so only commits descended from
   the base are folded; a single revision such as HEAD or HEAD~1 is now
   rejected as "not a <base>..<tip> range" rather than treated as a squash
   down to the root.
 * This adopts the --ancestry-path suggestion; the multi-base rejection is
   unchanged, so a side branch that forked before the base and merged in is
   still refused.
 * Added tests covering more merge topologies: two interior merges, a nested
   merge, an octopus merge, an octopus arm forked before the base, a merge
   among the descendants replayed above the range, and a ref pointing at an
   interior merge commit.

Changes in v4:

 * git history squash now detects when another ref points at a commit inside
   the range being folded and refuses, with an advice.historyUpdateRefs hint
   to use --update-refs=head.
 * A merge inside the range is folded fine as long as the range has a single
   base; a range with merge commit at the tip or base also folds correctly.
   Only a range with more than one base is rejected.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (8):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  sequencer: share the squash message marker helpers and flags
  history: add skeleton for squash subcommand
  history: validate squash revision ranges
  history: protect branches when squashing a range
  history: create squashed commits without editing
  history: support editing squashed commit messages

 Documentation/config/advice.adoc |   4 +
 Documentation/git-history.adoc   |  59 +-
 advice.c                         |   1 +
 advice.h                         |   1 +
 builtin/history.c                | 720 +++++++++++++++++++++++--
 object.h                         |   1 +
 sequencer.c                      |  70 +--
 sequencer.h                      |  30 ++
 t/meson.build                    |   1 +
 t/t3455-history-squash.sh        | 886 +++++++++++++++++++++++++++++++
 t/t9902-completion.sh            |   1 +
 11 files changed, 1703 insertions(+), 71 deletions(-)
 create mode 100755 t/t3455-history-squash.sh


base-commit: b8242b093d9e941a34460d715e3ce616a34ac3fe
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v15
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v15
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v14:

 1:  19c5e311a3 = 1:  98a1b756bc history: extract helper for a commit's parent tree
 2:  aadb7a5df4 = 2:  9d99354988 history: give commit_tree_ext a message template
 3:  e1621f656e = 3:  b7a1796838 sequencer: share the squash message marker helpers and flags
 4:  016ae0fd42 ! 4:  8ad1faaa9a history: add skeleton for squash subcommand
     @@ builtin/history.c: int cmd_history(int argc,
       		OPT_END(),
       	};
       
     +
     + ## t/t9902-completion.sh ##
     +@@ t/t9902-completion.sh: test_expect_success 'git history subcommands' '
     + 	fixup Z
     + 	reword Z
     + 	split Z
     ++	squash Z
     + 	EOF
     + 	test_completion "git history --" ""
     + '
 5:  4992d14ce4 = 5:  4389729c83 history: validate squash revision ranges
 6:  b862a5b4c3 = 6:  4d30ff1936 history: protect branches when squashing a range
 7:  03528d3b34 ! 7:  96349a802e history: create squashed commits without editing
     @@ builtin/history.c: out:
      +	}
      +	/*
      +	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
     -+	 * "fixup! main". If the target is not being squshed check the subject
     ++	 * "fixup! main". If the target is not being squashed check the subject
      +	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
      +	 * squashed together.
      +	 */
      +	target = lookup_commit_reference_by_name(s);
     -+	if (target && istarts_with(oid_to_hex(&target->object.oid), s)) {
     ++	if (target && starts_with(oid_to_hex(&target->object.oid), s)) {
      +		unsigned flags =
      +			target->object.flags & (SQUASH_SEEN | SQUASH_AMEND_TARGET);
      +		if (!flags) {
 8:  98aa3922cb = 8:  8da0333646 history: support editing squashed commit messages

-- 
gitgitgadget

[PATCH v15 1/8] history: extract helper for a commit's parent tree

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Three places resolve the tree of a commit's first parent, falling back
to the empty tree for a root commit, each repeating the same parse and
oidcpy dance. Extract a first_parent_tree_oid() helper and route the
existing callers through it.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 58 +++++++++++++++++++++--------------------------
 1 file changed, 26 insertions(+), 32 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index 000155ad9c..c22715d848 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -164,6 +164,25 @@ out:
 	return ret;
 }
 
+static int first_parent_tree_oid(struct repository *repo,
+				 struct commit *commit,
+				 struct object_id *out)
+{
+	struct commit *parent = commit->parents ? commit->parents->item : NULL;
+
+	if (!parent) {
+		oidcpy(out, repo->hash_algo->empty_tree);
+		return 0;
+	}
+
+	if (repo_parse_commit(repo, parent))
+		return error(_("unable to parse parent commit %s"),
+			     oid_to_hex(&parent->object.oid));
+
+	oidcpy(out, &repo_get_commit_tree(repo, parent)->object.oid);
+	return 0;
+}
+
 static int commit_tree_with_edited_message(struct repository *repo,
 					   const char *action,
 					   struct commit *original,
@@ -171,21 +190,11 @@ static int commit_tree_with_edited_message(struct repository *repo,
 {
 	struct object_id parent_tree_oid;
 	const struct object_id *tree_oid;
-	struct commit *parent;
 
 	tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	parent = original->parents ? original->parents->item : NULL;
-	if (parent) {
-		if (repo_parse_commit(repo, parent)) {
-			return error(_("unable to parse parent commit %s"),
-				     oid_to_hex(&parent->object.oid));
-		}
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return commit_tree_ext(repo, action, original, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
@@ -475,18 +484,10 @@ static int commit_became_empty(struct repository *repo,
 			       struct commit *original,
 			       struct tree *result)
 {
-	struct commit *parent = original->parents ? original->parents->item : NULL;
 	struct object_id parent_tree_oid;
 
-	if (parent) {
-		if (repo_parse_commit(repo, parent))
-			return error(_("unable to parse parent of %s"),
-				     oid_to_hex(&original->object.oid));
-
-		parent_tree_oid = repo_get_commit_tree(repo, parent)->object.oid;
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
-	}
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
+		return -1;
 
 	return oideq(&result->object.oid, &parent_tree_oid);
 }
@@ -830,16 +831,9 @@ static int split_commit(struct repository *repo,
 	struct tree *split_tree;
 	int ret;
 
-	if (original->parents) {
-		if (repo_parse_commit(repo, original->parents->item)) {
-			ret = error(_("unable to parse parent commit %s"),
-				    oid_to_hex(&original->parents->item->object.oid));
-			goto out;
-		}
-
-		parent_tree_oid = *get_commit_tree_oid(original->parents->item);
-	} else {
-		oidcpy(&parent_tree_oid, repo->hash_algo->empty_tree);
+	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0) {
+		ret = -1;
+		goto out;
 	}
 	original_commit_tree_oid = get_commit_tree_oid(original);
 
-- 
gitgitgadget

[PATCH v15 2/8] history: give commit_tree_ext a message template

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

commit_tree_ext() reuses the message of the commit it is handed. A
caller that folds several commits together wants to seed the message
from more than that single commit, so add an optional message_template
parameter. When NULL, the behavior is unchanged.

Pass NULL from the existing fixup and split callers.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/history.c b/builtin/history.c
index c22715d848..a60e8dbcd0 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -108,6 +108,7 @@ enum commit_tree_flags {
 static int commit_tree_ext(struct repository *repo,
 			   const char *action,
 			   struct commit *commit_with_message,
+			   const char *message_template,
 			   const struct commit_list *parents,
 			   const struct object_id *old_tree,
 			   const struct object_id *new_tree,
@@ -137,13 +138,16 @@ static int commit_tree_ext(struct repository *repo,
 		original_author = xmemdupz(ptr, len);
 	find_commit_subject(original_message, &original_body);
 
+	if (!message_template)
+		message_template = original_body;
+
 	if (flags & COMMIT_TREE_EDIT_MESSAGE) {
 		ret = fill_commit_message(repo, old_tree, new_tree,
-					  original_body, action, &commit_message);
+					  message_template, action, &commit_message);
 		if (ret < 0)
 			goto out;
 	} else {
-		strbuf_addstr(&commit_message, original_body);
+		strbuf_addstr(&commit_message, message_template);
 	}
 
 	original_extra_headers = read_commit_extra_headers(commit_with_message,
@@ -196,7 +200,7 @@ static int commit_tree_with_edited_message(struct repository *repo,
 	if (first_parent_tree_oid(repo, original, &parent_tree_oid) < 0)
 		return -1;
 
-	return commit_tree_ext(repo, action, original, original->parents,
+	return commit_tree_ext(repo, action, original, NULL, original->parents,
 			       &parent_tree_oid, tree_oid, out, COMMIT_TREE_EDIT_MESSAGE);
 }
 
@@ -675,7 +679,7 @@ static int cmd_history_fixup(int argc,
 		goto out;
 
 	if (!skip_commit) {
-		ret = commit_tree_ext(repo, "fixup", original, original->parents,
+		ret = commit_tree_ext(repo, "fixup", original, NULL, original->parents,
 				      &original_tree->object.oid, &merge_result.tree->object.oid,
 				      &rewritten, flags);
 		if (ret < 0) {
@@ -886,7 +890,7 @@ static int split_commit(struct repository *repo,
 	 * The first commit is constructed from the split-out tree. The base
 	 * that shall be diffed against is the parent of the original commit.
 	 */
-	ret = commit_tree_ext(repo, "split-out", original, original->parents, &parent_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, original->parents, &parent_tree_oid,
 			      &split_tree->object.oid, &first_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing first commit"));
@@ -903,7 +907,7 @@ static int split_commit(struct repository *repo,
 	old_tree_oid = &repo_get_commit_tree(repo, first_commit)->object.oid;
 	new_tree_oid = &repo_get_commit_tree(repo, original)->object.oid;
 
-	ret = commit_tree_ext(repo, "split-out", original, parents, old_tree_oid,
+	ret = commit_tree_ext(repo, "split-out", original, NULL, parents, old_tree_oid,
 			      new_tree_oid, &second_commit, COMMIT_TREE_EDIT_MESSAGE);
 	if (ret < 0) {
 		ret = error(_("failed writing second commit"));
-- 
gitgitgadget

[PATCH v15 3/8] sequencer: share the squash message marker helpers and flags

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

When "git rebase -i" squashes commits it builds an editor template with a
"This is a combination of N commits." banner, a "This is the 1st/Nth
commit message:" header above each kept message (or a "will be skipped"
header for a dropped one), and a commented-out subject for any fixup!,
squash! or amend! commit. The banner, the headers and the
subject-commenting all live in static helpers in sequencer.c wired to the
rebase state, so no other command can present a squash the same way.

Pull the three pieces out into add_squash_combination_header(),
add_squash_message_header() (which takes a flag for the "will be skipped"
variant) and squash_subject_comment_len(), and use them from
update_squash_messages() and append_squash_message(). Also move the
todo_item_flags enum to the header, so a caller reading the output of
todo_list_rearrange_squash() can tell an amend! (TODO_REPLACE_FIXUP_MSG)
from a plain fixup!. A later change reuses all of this to give "git
history squash" the same template.

No change in behavior.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 sequencer.c | 70 +++++++++++++++++++++++++++++------------------------
 sequencer.h | 30 +++++++++++++++++++++++
 2 files changed, 69 insertions(+), 31 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index 65afd100d9..557149d62f 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -1881,18 +1881,38 @@ static int is_pick_or_similar(enum todo_command command)
 	}
 }
 
-enum todo_item_flags {
-	TODO_EDIT_MERGE_MSG    = (1 << 0),
-	TODO_REPLACE_FIXUP_MSG = (1 << 1),
-	TODO_EDIT_FIXUP_MSG    = (1 << 2),
-};
-
 static const char first_commit_msg_str[] = N_("This is the 1st commit message:");
 static const char nth_commit_msg_fmt[] = N_("This is the commit message #%d:");
 static const char skip_first_commit_msg_str[] = N_("The 1st commit message will be skipped:");
 static const char skip_nth_commit_msg_fmt[] = N_("The commit message #%d will be skipped:");
 static const char combined_commit_msg_fmt[] = N_("This is a combination of %d commits.");
 
+void add_squash_combination_header(struct strbuf *buf, int n)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	strbuf_addf(buf, _(combined_commit_msg_fmt), n);
+}
+
+void add_squash_message_header(struct strbuf *buf, int n, int skip)
+{
+	strbuf_addf(buf, "%s ", comment_line_str);
+	if (n == 1)
+		strbuf_addstr(buf, skip ? _(skip_first_commit_msg_str) :
+				   _(first_commit_msg_str));
+	else
+		strbuf_addf(buf, skip ? _(skip_nth_commit_msg_fmt) :
+			    _(nth_commit_msg_fmt), n);
+}
+
+size_t squash_subject_comment_len(const char *body, int squashing)
+{
+	if (starts_with(body, "amend!") ||
+	    (squashing && (starts_with(body, "squash!") ||
+			   starts_with(body, "fixup!"))))
+		return commit_subject_length(body);
+	return 0;
+}
+
 static int is_fixup_flag(enum todo_command command, unsigned flag)
 {
 	return command == TODO_FIXUP && ((flag & TODO_REPLACE_FIXUP_MSG) ||
@@ -2013,20 +2033,13 @@ static int append_squash_message(struct strbuf *buf, const char *body,
 {
 	struct replay_ctx *ctx = opts->ctx;
 	const char *fixup_msg;
-	size_t commented_len = 0, fixup_off;
-	/*
-	 * amend is non-interactive and not normally used with fixup!
-	 * or squash! commits, so only comment out those subjects when
-	 * squashing commit messages.
-	 */
-	if (starts_with(body, "amend!") ||
-	    ((command == TODO_SQUASH || seen_squash(ctx)) &&
-	     (starts_with(body, "squash!") || starts_with(body, "fixup!"))))
-		commented_len = commit_subject_length(body);
+	size_t commented_len, fixup_off;
+
+	commented_len = squash_subject_comment_len(body,
+				command == TODO_SQUASH || seen_squash(ctx));
 
-	strbuf_addf(buf, "\n%s ", comment_line_str);
-	strbuf_addf(buf, _(nth_commit_msg_fmt),
-		    ++ctx->current_fixup_count + 1);
+	strbuf_addch(buf, '\n');
+	add_squash_message_header(buf, ++ctx->current_fixup_count + 1, 0);
 	strbuf_addstr(buf, "\n\n");
 	strbuf_add_commented_lines(buf, body, commented_len, comment_line_str);
 	/* buf->buf may be reallocated so store an offset into the buffer */
@@ -2091,9 +2104,8 @@ static int update_squash_messages(struct repository *r,
 		eol = !starts_with(buf.buf, comment_line_str) ?
 			buf.buf : strchrnul(buf.buf, '\n');
 
-		strbuf_addf(&header, "%s ", comment_line_str);
-		strbuf_addf(&header, _(combined_commit_msg_fmt),
-			    ctx->current_fixup_count + 2);
+		add_squash_combination_header(&header,
+					      ctx->current_fixup_count + 2);
 		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
 		strbuf_release(&header);
 		if (is_fixup_flag(command, flag) && !seen_squash(ctx))
@@ -2117,12 +2129,9 @@ static int update_squash_messages(struct repository *r,
 			repo_unuse_commit_buffer(r, head_commit, head_message);
 			return error(_("cannot write '%s'"), rebase_path_fixup_msg());
 		}
-		strbuf_addf(&buf, "%s ", comment_line_str);
-		strbuf_addf(&buf, _(combined_commit_msg_fmt), 2);
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addstr(&buf, is_fixup_flag(command, flag) ?
-			      _(skip_first_commit_msg_str) :
-			      _(first_commit_msg_str));
+		add_squash_combination_header(&buf, 2);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, 1, is_fixup_flag(command, flag));
 		strbuf_addstr(&buf, "\n\n");
 		if (is_fixup_flag(command, flag))
 			strbuf_add_commented_lines(&buf, body, strlen(body),
@@ -2141,9 +2150,8 @@ static int update_squash_messages(struct repository *r,
 	if (command == TODO_SQUASH || is_fixup_flag(command, flag)) {
 		res = append_squash_message(&buf, body, command, opts, flag);
 	} else if (command == TODO_FIXUP) {
-		strbuf_addf(&buf, "\n%s ", comment_line_str);
-		strbuf_addf(&buf, _(skip_nth_commit_msg_fmt),
-			    ++ctx->current_fixup_count + 1);
+		strbuf_addch(&buf, '\n');
+		add_squash_message_header(&buf, ++ctx->current_fixup_count + 1, 1);
 		strbuf_addstr(&buf, "\n\n");
 		strbuf_add_commented_lines(&buf, body, strlen(body),
 					   comment_line_str);
diff --git a/sequencer.h b/sequencer.h
index 64a9c7fb1b..b01f897020 100644
--- a/sequencer.h
+++ b/sequencer.h
@@ -119,6 +119,13 @@ enum todo_command {
 	TODO_COMMENT
 };
 
+/* Bits for the "flags" member of struct todo_item */
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG    = (1 << 0),
+	TODO_REPLACE_FIXUP_MSG = (1 << 1),
+	TODO_EDIT_FIXUP_MSG    = (1 << 2),
+};
+
 struct todo_item {
 	enum todo_command command;
 	struct commit *commit;
@@ -208,6 +215,29 @@ int todo_list_rearrange_squash(struct todo_list *todo_list);
  */
 void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag);
 
+/*
+ * Append the "This is a combination of N commits." banner that "git rebase
+ * -i" writes at the top of a squashed commit's message, commented out with
+ * the comment character.
+ */
+void add_squash_combination_header(struct strbuf *buf, int n);
+
+/*
+ * Append the header (1-based N) that "git rebase -i" writes above each message
+ * when squashing, commented out with the comment character. With SKIP it reads
+ * "The ... commit message will be skipped" for a message that is dropped (a
+ * fixup), otherwise "This is the ... commit message".
+ */
+void add_squash_message_header(struct strbuf *buf, int n, int skip);
+
+/*
+ * Return the length of the leading subject of BODY when it should be commented
+ * out in a squash message, or 0 otherwise. An "amend!" subject always
+ * qualifies; "squash!" and "fixup!" subjects only when SQUASHING, since a
+ * plain fixup chain keeps them.
+ */
+size_t squash_subject_comment_len(const char *body, int squashing);
+
 void append_conflicts_hint(struct index_state *istate,
 		struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode);
 enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,
-- 
gitgitgadget

[PATCH v15 4/8] history: add skeleton for squash subcommand

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Add the entry point and option parsing for "git history squash". Pass
the remaining arguments through setup_revisions() so the command accepts
revision ranges and rev-list options, while restoring the ordering and
simplification settings required by the fold if an option changes them.

Require at least one BOTTOM revision. The squashed commit needs a commit
outside the selected range to serve as its base, so a single positive
revision is not a sufficient range.

Keep this step limited to defining the revision input contract so graph
validation and the rewrite can be added independently.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  1 +
 builtin/history.c              | 94 ++++++++++++++++++++++++++++++++++
 t/t9902-completion.sh          |  1 +
 3 files changed, 96 insertions(+)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index 28b477cd37..b660baf94d 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -12,6 +12,7 @@ git history drop <commit> [--dry-run] [--update-refs=(branches|head)] [--empty=(
 git history fixup <commit> [--dry-run] [--update-refs=(branches|head)] [--reedit-message] [--empty=(drop|keep|abort)]
 git history reword <commit> [--dry-run] [--update-refs=(branches|head)]
 git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]
+git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>
 
 DESCRIPTION
 -----------
diff --git a/builtin/history.c b/builtin/history.c
index a60e8dbcd0..4f5a7a46ce 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -34,6 +34,8 @@
 	N_("git history reword <commit> [--dry-run] [--update-refs=(branches|head)]")
 #define GIT_HISTORY_SPLIT_USAGE \
 	N_("git history split <commit> [--dry-run] [--update-refs=(branches|head)] [--] [<pathspec>...]")
+#define GIT_HISTORY_SQUASH_USAGE \
+	N_("git history squash [--dry-run] [--update-refs=(branches|head)] [--[no-]edit] <revision-range>")
 
 static void change_data_free(void *util, const char *str UNUSED)
 {
@@ -1004,6 +1006,96 @@ out:
 	return ret;
 }
 
+static int setup_squash_revisions(struct repository *repo,
+				  int argc, const char **argv,
+				  struct rev_info *revs)
+{
+	repo_init_revisions(repo, revs, NULL);
+	revs->reverse = 1;
+	revs->topo_order = 1;
+	revs->sort_order = REV_SORT_IN_GRAPH_ORDER;
+	revs->simplify_history = 0;
+	revs->ancestry_path = 1;
+	revs->limited = 1;
+	revs->ancestry_path_implicit_bottoms = 1;
+
+	argc = setup_revisions(argc, argv, revs, NULL);
+	if (argc > 1)
+		return error(_("unrecognized argument: %s"), argv[1]);
+
+	if (revs->reverse != 1 || revs->topo_order != 1 ||
+	    revs->sort_order != REV_SORT_IN_GRAPH_ORDER ||
+	    revs->simplify_history != 0 || revs->boundary == 1 ||
+	    revs->ancestry_path != 1 || revs->limited != 1 ||
+	    revs->ancestry_path_implicit_bottoms != 1) {
+		warning(_("ignoring rev-list options that would change how the "
+			  "range is walked"));
+		revs->reverse = 1;
+		revs->topo_order = 1;
+		revs->sort_order = REV_SORT_IN_GRAPH_ORDER;
+		revs->simplify_history = 0;
+		revs->boundary = 0;
+		revs->ancestry_path = 1;
+		revs->limited = 1;
+		revs->ancestry_path_implicit_bottoms = 1;
+	}
+
+	/*
+	 * A squash needs a base to reparent onto, so the range has to exclude
+	 * something, as in "<base>..<tip>". A revision range with no such
+	 * bottom commit cannot be squashed.
+	 */
+	for (size_t i = 0; i < revs->cmdline.nr; i++)
+		if (revs->cmdline.rev[i].flags & BOTTOM)
+			return 0;
+
+	return error(_("not a '<base>..<tip>' revision range"));
+}
+
+static int cmd_history_squash(int argc,
+			      const char **argv,
+			      const char *prefix,
+			      struct repository *repo)
+{
+	const char * const usage[] = {
+		GIT_HISTORY_SQUASH_USAGE,
+		NULL,
+	};
+	enum ref_action action = REF_ACTION_DEFAULT;
+	int dry_run = 0;
+	int edit = 1;
+	struct option options[] = {
+		OPT_CALLBACK_F(0, "update-refs", &action, "(branches|head)",
+			       N_("control which refs should be updated"),
+			       PARSE_OPT_NONEG, parse_ref_action),
+		OPT_BOOL('n', "dry-run", &dry_run,
+			 N_("perform a dry-run without updating any refs")),
+		OPT_BOOL('e', "edit", &edit,
+			 N_("edit the commit message")),
+		OPT_END(),
+	};
+	struct rev_info revs = { 0 };
+	int ret;
+
+	argc = parse_options(argc, argv, prefix, options, usage,
+			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
+	if (argc < 2) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
+	repo_config(repo, git_default_config, NULL);
+
+	ret = setup_squash_revisions(repo, argc, argv, &revs);
+	if (ret < 0)
+		goto out;
+
+	ret = error(_("squashing commits is not implemented yet"));
+
+out:
+	release_revisions(&revs);
+	return ret;
+}
+
 static int update_worktree(struct repository *repo,
 			   const struct commit *old_head,
 			   const struct commit *new_head,
@@ -1192,6 +1284,7 @@ int cmd_history(int argc,
 		GIT_HISTORY_FIXUP_USAGE,
 		GIT_HISTORY_REWORD_USAGE,
 		GIT_HISTORY_SPLIT_USAGE,
+		GIT_HISTORY_SQUASH_USAGE,
 		NULL,
 	};
 	parse_opt_subcommand_fn *fn = NULL;
@@ -1200,6 +1293,7 @@ int cmd_history(int argc,
 		OPT_SUBCOMMAND("fixup", &fn, cmd_history_fixup),
 		OPT_SUBCOMMAND("reword", &fn, cmd_history_reword),
 		OPT_SUBCOMMAND("split", &fn, cmd_history_split),
+		OPT_SUBCOMMAND("squash", &fn, cmd_history_squash),
 		OPT_END(),
 	};
 
diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index 38cf221718..978c42c629 100755
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -3227,6 +3227,7 @@ test_expect_success 'git history subcommands' '
 	fixup Z
 	reword Z
 	split Z
+	squash Z
 	EOF
 	test_completion "git history --" ""
 '
-- 
gitgitgadget

Re: [PATCH v15 4/8] history: add skeleton for squash subcommand

[Junio C Hamano]

"Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Harald Nordgren <haraldnordgren@gmail.com>
>
> Add the entry point and option parsing for "git history squash". Pass
> the remaining arguments through setup_revisions() so the command accepts
> revision ranges and rev-list options, while restoring the ordering and
> simplification settings required by the fold if an option changes them.
>
> Require at least one BOTTOM revision. The squashed commit needs a commit
> outside the selected range to serve as its base, so a single positive
> revision is not a sufficient range.
>
> Keep this step limited to defining the revision input contract so graph
> validation and the rewrite can be added independently.
>
> Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
> Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
> Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
> ---
>  Documentation/git-history.adoc |  1 +
>  builtin/history.c              | 94 ++++++++++++++++++++++++++++++++++
>  t/t9902-completion.sh          |  1 +
>  3 files changed, 96 insertions(+)

Nice.  As the "complete 'git history'" topic is now in, with this part

> diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
> index 38cf221718..978c42c629 100755
> --- a/t/t9902-completion.sh
> +++ b/t/t9902-completion.sh
> @@ -3227,6 +3227,7 @@ test_expect_success 'git history subcommands' '
>  	fixup Z
>  	reword Z
>  	split Z
> +	squash Z
>  	EOF
>  	test_completion "git history --" ""
>  '

being a part of this series, I no longer need to worry about making
an evil merge for this ;-).

Thanks.

[PATCH v15 5/8] history: validate squash revision ranges

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Walk the selected commits in topological order from oldest to newest and
mark each one as it is seen. Every parent after the oldest commit must
already be selected or also be a parent of the oldest commit. This
accepts merges contained by the range while rejecting a merge arm that
entered it from elsewhere.

Track the remaining graph tips during the same walk and require exactly
one. Also reject empty and single-commit ranges and any selection that
reaches a root commit. These checks identify the oldest commit whose
parents will be preserved and the single tip whose tree will be used by
the rewrite.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 builtin/history.c         | 119 ++++++++++++++++++++++++++++++++++----
 object.h                  |   1 +
 t/meson.build             |   1 +
 t/t3455-history-squash.sh |  65 +++++++++++++++++++++
 4 files changed, 174 insertions(+), 12 deletions(-)
 create mode 100755 t/t3455-history-squash.sh

diff --git a/builtin/history.c b/builtin/history.c
index 4f5a7a46ce..6541a397e8 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1006,6 +1006,9 @@ out:
 	return ret;
 }
 
+#define SQUASH_SEEN (1u << 11)
+#define SQUASH_TIP (1u << 12)
+
 static int setup_squash_revisions(struct repository *repo,
 				  int argc, const char **argv,
 				  struct rev_info *revs)
@@ -1052,6 +1055,104 @@ static int setup_squash_revisions(struct repository *repo,
 	return error(_("not a '<base>..<tip>' revision range"));
 }
 
+/*
+ * Resolve a revision range into its oldest commit and single tip. Every
+ * parent after the oldest commit must either be selected or also be a parent
+ * of the oldest commit.
+ */
+static int resolve_squash_range(struct repository *repo,
+				int argc, const char **argv,
+				struct commit **oldest_out,
+				struct commit **tip_out)
+{
+	struct rev_info revs;
+	struct commit *commit, *oldest = NULL, *tip = NULL;
+	int ret, tip_count = 0;
+	bool walk_started = false;
+
+	ret = setup_squash_revisions(repo, argc, argv, &revs);
+	if (ret < 0)
+		goto out;
+
+	if (prepare_revision_walk(&revs) < 0) {
+		ret = error(_("error preparing revisions"));
+		goto out;
+	}
+	walk_started = true;
+	while ((commit = get_revision(&revs))) {
+		struct commit_list *p;
+
+		if (!commit->parents) {
+			ret = error(_("cannot squash down to root commit"));
+			goto out;
+		}
+		for (p = commit->parents; oldest && p; p = p->next) {
+			struct commit_list *q;
+			struct object *o;
+			bool seen;
+
+			if (repo_parse_commit(repo, p->item)) {
+				ret = error(_("cannot parse commit"));
+				goto out;
+			}
+			o = &p->item->object;
+			seen = o->flags & SQUASH_SEEN;
+			/*
+			 * Allow parents that match the parents of the
+			 * squashed commit.
+			 */
+			for (q = oldest->parents; !seen && q; q = q->next)
+				if (p->item == q->item)
+					seen = true;
+			if (!seen) {
+				ret = error(_("parent %s of commit %s is "
+					      "outside the revision range"),
+					    repo_find_unique_abbrev(repo, &o->oid,
+								    DEFAULT_ABBREV),
+					    repo_find_unique_abbrev(repo,
+								    &commit->object.oid,
+								    DEFAULT_ABBREV));
+				goto out;
+			}
+			if (o->flags & SQUASH_TIP) {
+				tip_count--;
+				o->flags &= ~SQUASH_TIP;
+			}
+		}
+		if (!oldest)
+			oldest = commit;
+		tip = commit;
+		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
+		tip_count++;
+	}
+
+	if (!tip_count) {
+		ret = error(_("the revision range is empty"));
+		goto out;
+	} else if (tip_count != 1) {
+		ret = error(_("the revision range contains more than one tip "
+			      "commit"));
+		goto out;
+	} else if (oldest == tip) {
+		ret = error(_("the revision range holds a single commit; "
+			      "nothing to squash"));
+		goto out;
+	} else if (!oldest->parents) {
+		BUG("an in-range commit must have a parent");
+	}
+
+	*oldest_out = oldest;
+	*tip_out = tip;
+	ret = 0;
+
+out:
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
+	if (walk_started)
+		reset_revision_walk();
+	release_revisions(&revs);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1074,26 +1175,20 @@ static int cmd_history_squash(int argc,
 			 N_("edit the commit message")),
 		OPT_END(),
 	};
-	struct rev_info revs = { 0 };
+	struct commit *oldest, *tip;
 	int ret;
 
 	argc = parse_options(argc, argv, prefix, options, usage,
 			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
-	if (argc < 2) {
-		ret = error(_("command expects a revision range"));
-		goto out;
-	}
+	if (argc < 2)
+		return error(_("command expects a revision range"));
 	repo_config(repo, git_default_config, NULL);
 
-	ret = setup_squash_revisions(repo, argc, argv, &revs);
+	ret = resolve_squash_range(repo, argc, argv, &oldest, &tip);
 	if (ret < 0)
-		goto out;
-
-	ret = error(_("squashing commits is not implemented yet"));
+		return ret;
 
-out:
-	release_revisions(&revs);
-	return ret;
+	return error(_("squashing commits is not implemented yet"));
 }
 
 static int update_worktree(struct repository *repo,
diff --git a/object.h b/object.h
index 8fb03ff90a..dcf30156ca 100644
--- a/object.h
+++ b/object.h
@@ -74,6 +74,7 @@ void object_array_init(struct object_array *array);
  * bisect.c:                                        16
  * bundle.c:                                        16
  * http-push.c:                          11-----14
+ * builtin/history.c:                    1112
  * commit-graph.c:                                15
  * commit-reach.c:                                  16-------20
  * builtin/last-modified.c:                         1617
diff --git a/t/meson.build b/t/meson.build
index 7f53cca7d1..ba6f33cdff 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -407,6 +407,7 @@ integration_tests = [
   't3452-history-split.sh',
   't3453-history-fixup.sh',
   't3454-history-drop.sh',
+  't3455-history-squash.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
new file mode 100755
index 0000000000..df92aa4f6c
--- /dev/null
+++ b/t/t3455-history-squash.sh
@@ -0,0 +1,65 @@
+#!/bin/sh
+
+test_description='tests for git-history squash subcommand'
+
+. ./test-lib.sh
+
+test_expect_success 'setup linear history' '
+	test_commit base file a start &&
+	test_commit one file b &&
+	test_commit two file c &&
+	test_commit three file d
+'
+
+test_expect_success 'errors on missing range argument' '
+	test_must_fail git history squash 2>err &&
+	test_grep "expects a revision range" err
+'
+
+test_expect_success 'errors on an empty range' '
+	test_must_fail git history squash HEAD..HEAD 2>err &&
+	test_grep "the revision range is empty" err
+'
+
+test_expect_success 'errors on a single revision that is not a range' '
+	test_must_fail git history squash HEAD 2>err &&
+	test_grep "not a .*range" err &&
+	test_must_fail git history squash HEAD~1 2>err &&
+	test_grep "not a .*range" err
+'
+
+test_expect_success 'errors on a range holding a single commit' '
+	test_must_fail git history squash "HEAD^!" 2>err &&
+	test_grep "single commit; nothing to squash" err
+'
+
+test_expect_success 'rejects a root commit' '
+	oid=$(git commit-tree -m root three^{tree}) &&
+	test_must_fail git history squash \
+		--ancestry-path=start "$oid..three" 2>err &&
+	test_grep "cannot squash down to root commit" err
+'
+
+test_expect_success 'rejects multiple tips' '
+	oid=$(git commit-tree -m tip -p start^0 three^{tree}) &&
+	test_must_fail git history squash ^start "$oid" three~1 2>err &&
+	test_grep "revision range contains more than one tip" err
+'
+
+test_expect_success 'rejects a merge parent outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "parent .* of commit .* is outside the revision range" err
+'
+
+test_done
-- 
gitgitgadget

[PATCH v15 6/8] history: protect branches when squashing a range

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

A local branch that descends from the selected graph without containing
its tip cannot be replayed as a descendant of the squashed commit. Find
those branches with ref-filter before creating any replacement objects
and refuse the operation unless --update-refs=head was requested.

Limit this protection to local branches, matching the refs that the
default history rewrite mode updates; tags and remote-tracking refs
remain untouched. Sort the blocking refs and print their short branch
names so the user can decide whether to move them or leave them behind.

Add advice.historyUpdateRefs for the hint that points to
--update-refs=head.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/config/advice.adoc |  4 ++
 advice.c                         |  1 +
 advice.h                         |  1 +
 builtin/history.c                | 70 ++++++++++++++++++++++++++++++--
 t/t3455-history-squash.sh        | 39 ++++++++++++++++++
 5 files changed, 111 insertions(+), 4 deletions(-)

diff --git a/Documentation/config/advice.adoc b/Documentation/config/advice.adoc
index 81f80a9274..3d91c90eda 100644
--- a/Documentation/config/advice.adoc
+++ b/Documentation/config/advice.adoc
@@ -59,6 +59,10 @@ all advice messages.
 	forceDeleteBranch::
 		Shown when the user tries to delete a not fully merged
 		branch without the force option set.
+	historyUpdateRefs::
+		Shown when `git history squash` refuses because a local branch
+		cannot be rewritten as a descendant of the squashed commit, to
+		tell the user about `--update-refs=head`.
 	ignoredHook::
 		Shown when a hook is ignored because the hook is not
 		set as executable.
diff --git a/advice.c b/advice.c
index 63bf8b0c5f..401d047391 100644
--- a/advice.c
+++ b/advice.c
@@ -58,6 +58,7 @@ static struct {
 	[ADVICE_FETCH_SHOW_FORCED_UPDATES]		= { "fetchShowForcedUpdates" },
 	[ADVICE_FORCE_DELETE_BRANCH]			= { "forceDeleteBranch" },
 	[ADVICE_GRAFT_FILE_DEPRECATED]			= { "graftFileDeprecated" },
+	[ADVICE_HISTORY_UPDATE_REFS]			= { "historyUpdateRefs" },
 	[ADVICE_IGNORED_HOOK]				= { "ignoredHook" },
 	[ADVICE_IMPLICIT_IDENTITY]			= { "implicitIdentity" },
 	[ADVICE_MERGE_CONFLICT]				= { "mergeConflict" },
diff --git a/advice.h b/advice.h
index 66f6cd6a77..3f0b4f0485 100644
--- a/advice.h
+++ b/advice.h
@@ -25,6 +25,7 @@ enum advice_type {
 	ADVICE_FETCH_SHOW_FORCED_UPDATES,
 	ADVICE_FORCE_DELETE_BRANCH,
 	ADVICE_GRAFT_FILE_DEPRECATED,
+	ADVICE_HISTORY_UPDATE_REFS,
 	ADVICE_IGNORED_HOOK,
 	ADVICE_IMPLICIT_IDENTITY,
 	ADVICE_MERGE_CONFLICT,
diff --git a/builtin/history.c b/builtin/history.c
index 6541a397e8..e65b76b59f 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1,6 +1,7 @@
 #define USE_THE_REPOSITORY_VARIABLE
 
 #include "builtin.h"
+#include "advice.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "commit-reach.h"
@@ -16,10 +17,12 @@
 #include "path.h"
 #include "read-cache.h"
 #include "refs.h"
+#include "ref-filter.h"
 #include "replay.h"
 #include "reset.h"
 #include "revision.h"
 #include "sequencer.h"
+#include "string-list.h"
 #include "strvec.h"
 #include "tree.h"
 #include "tree-walk.h"
@@ -1061,6 +1064,7 @@ static int setup_squash_revisions(struct repository *repo,
  * of the oldest commit.
  */
 static int resolve_squash_range(struct repository *repo,
+				bool update_branches,
 				int argc, const char **argv,
 				struct commit **oldest_out,
 				struct commit **tip_out)
@@ -1069,6 +1073,8 @@ static int resolve_squash_range(struct repository *repo,
 	struct commit *commit, *oldest = NULL, *tip = NULL;
 	int ret, tip_count = 0;
 	bool walk_started = false;
+	struct ref_filter filter = REF_FILTER_INIT;
+	struct ref_array refs = { 0 };
 
 	ret = setup_squash_revisions(repo, argc, argv, &revs);
 	if (ret < 0)
@@ -1101,9 +1107,12 @@ static int resolve_squash_range(struct repository *repo,
 			 * Allow parents that match the parents of the
 			 * squashed commit.
 			 */
-			for (q = oldest->parents; !seen && q; q = q->next)
-				if (p->item == q->item)
+			for (q = oldest->parents; !seen && q; q = q->next) {
+				if (p->item == q->item) {
 					seen = true;
+					commit_list_insert(commit, &filter.with_commit);
+				}
+			}
 			if (!seen) {
 				ret = error(_("parent %s of commit %s is "
 					      "outside the revision range"),
@@ -1119,12 +1128,17 @@ static int resolve_squash_range(struct repository *repo,
 				o->flags &= ~SQUASH_TIP;
 			}
 		}
-		if (!oldest)
+		if (!oldest) {
+			commit_list_insert(commit, &filter.with_commit);
 			oldest = commit;
+		}
 		tip = commit;
 		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
 		tip_count++;
 	}
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
+	reset_revision_walk();
+	walk_started = false;
 
 	if (!tip_count) {
 		ret = error(_("the revision range is empty"));
@@ -1141,6 +1155,49 @@ static int resolve_squash_range(struct repository *repo,
 		BUG("an in-range commit must have a parent");
 	}
 
+	commit_list_insert(tip, &filter.no_commit);
+	filter.kind = FILTER_REFS_BRANCHES;
+	if (update_branches &&
+	    filter_refs(&refs, &filter, filter.kind)) {
+		ret = error(_("could not filter refs"));
+		goto out;
+	}
+	if (refs.nr) {
+		struct ref_format format = REF_FORMAT_INIT;
+		struct ref_sorting *sorting;
+		struct string_list sorting_options = STRING_LIST_INIT_DUP;
+		struct strbuf branches = STRBUF_INIT;
+		struct strbuf err = STRBUF_INIT;
+
+		format.format = "%(refname:short)";
+		if (verify_ref_format(&format))
+			BUG("invalid branch format");
+		string_list_append(&sorting_options, "refname");
+		sorting = ref_sorting_options(&sorting_options);
+		ref_array_sort(sorting, &refs);
+		for (int i = 0; i < refs.nr; i++) {
+			strbuf_reset(&err);
+			strbuf_addstr(&branches, "\n  ");
+			if (format_ref_array_item(refs.items[i], &format,
+						  &branches, &err))
+				BUG("could not format branch name: %s", err.buf);
+		}
+		/*
+		 * TODO: also check HEADS from other worktrees.
+		 */
+		ret = error(_("the following branches cannot be rewritten as "
+			      "descendants of the squashed commit:%s"), branches.buf);
+		advise_if_enabled(ADVICE_HISTORY_UPDATE_REFS,
+				  _("Use --update-refs=head to rewrite only "
+				    "the current branch and leave such branches "
+				    "untouched."));
+		strbuf_release(&err);
+		strbuf_release(&branches);
+		ref_sorting_release(sorting);
+		string_list_clear(&sorting_options, 0);
+		goto out;
+	}
+
 	*oldest_out = oldest;
 	*tip_out = tip;
 	ret = 0;
@@ -1150,6 +1207,8 @@ out:
 	if (walk_started)
 		reset_revision_walk();
 	release_revisions(&revs);
+	ref_filter_clear(&filter);
+	ref_array_clear(&refs);
 	return ret;
 }
 
@@ -1183,8 +1242,11 @@ static int cmd_history_squash(int argc,
 	if (argc < 2)
 		return error(_("command expects a revision range"));
 	repo_config(repo, git_default_config, NULL);
+	if (action == REF_ACTION_DEFAULT)
+		action = REF_ACTION_BRANCHES;
 
-	ret = resolve_squash_range(repo, argc, argv, &oldest, &tip);
+	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
+				   argc, argv, &oldest, &tip);
 	if (ret < 0)
 		return ret;
 
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index df92aa4f6c..b1f65de5f5 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -62,4 +62,43 @@ test_expect_success 'rejects a merge parent outside the range' '
 	test_grep "parent .* of commit .* is outside the revision range" err
 '
 
+test_expect_success 'prints branches that cannot follow the squash' '
+	test_when_finished \
+		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
+		 git branch -D feature" &&
+	git checkout -f -b feature start &&
+	test_commit C1 &&
+	test_commit C2 &&
+	git checkout -b topic-1 start &&
+	test_commit C3 &&
+	test_commit C4 &&
+	git checkout C3 &&
+	test_commit C5 &&
+	git checkout feature &&
+	git merge C5 &&
+	test_commit C6 &&
+	git checkout -b topic-2 C2 &&
+	test_commit C7 &&
+	git checkout feature &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "^error: the following branches cannot be rewritten" err &&
+	test_grep "^  topic-1$" err &&
+	test_grep "^  topic-2$" err &&
+	test_grep "^hint: .* --update-refs=head" err
+'
+
+test_expect_success 'advice.historyUpdateRefs silences the hint' '
+	git reset --hard three &&
+	git branch -f mid HEAD~1 &&
+
+	test_must_fail git -c advice.historyUpdateRefs=false \
+		history squash start.. 2>err &&
+	test_grep "^error: the following branches cannot be rewritten" err &&
+	test_grep "^  mid$" err &&
+	test_grep ! "hint:" err &&
+
+	git branch -D mid
+'
+
 test_done
-- 
gitgitgadget

[PATCH v15 7/8] history: create squashed commits without editing

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Create one replacement commit from the resolved range when --no-edit is
selected. Preserve the authorship and all parents of the oldest commit,
use the tip tree, and replay descendants through the existing history
rewrite machinery. Record the complete revision expression in the
reflog and retain dry-run and update-refs behavior.

Resolve fixup!, squash! and amend! subjects while walking the range.
Reject markers whose targets are not selected and refuse any no-edit
fold that would discard a squash! or amend! message. A range made
entirely from related markers can still be consolidated, with the last
applicable amend! body supplying the message.

Inspired-by: Sergey Chernov <serega.morph@gmail.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  44 ++-
 builtin/history.c              | 324 ++++++++++++++++-
 object.h                       |   2 +-
 t/t3455-history-squash.sh      | 633 +++++++++++++++++++++++++++++++--
 4 files changed, 968 insertions(+), 35 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index b660baf94d..fb04a67685 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -44,8 +44,11 @@ at once.
 LIMITATIONS
 -----------
 
-This command does not (yet) work with histories that contain merges. You
-should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
+This command does not (yet) replay merge commits onto the rewritten
+history: if a commit that would be replayed is a merge, the operation is
+rejected, and you should use linkgit:git-rebase[1] with the
+`--rebase-merges` flag instead. The `squash` subcommand can still fold merges
+that lie inside the selected range, subject to the restrictions below.
 
 Furthermore, the command does not support operations that can result in merge
 conflicts. This limitation is by design as history rewrites are not intended to
@@ -114,6 +117,43 @@ linkgit:gitglossary[7].
 It is invalid to select either all or no hunks, as that would lead to
 one of the commits becoming empty.
 
+`squash <revision-range>`::
+	Fold all commits in _<revision-range>_ into the oldest commit of that
+	range. The resulting commit keeps the oldest commit's authorship and
+	takes the tree of the range's newest commit, so the whole range
+	collapses into a single commit. Commits above the range are replayed
+	on top of the result.
++
+The range is given in the usual `<base>..<tip>` form, where _<base>_ is
+the commit just below the oldest commit to squash. For example, `git
+history squash HEAD~3..HEAD` folds the three most recent commits into
+one, and `git history squash HEAD~5..HEAD~2` squashes an interior range
+while leaving the two newest commits in place. Several revisions may be
+given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
+already on `topic`. Rev-list options may also be given, but any that would
+change how the range is walked are overridden with a warning.
++
+With `--no-edit`, the oldest commit's message is preserved, except that an
+`amend!` commit targeting it replaces its message.
++
+The selected commits must form a connected graph with a single tip and must
+not include a root commit. Every parent of a commit after the oldest one must
+either be selected or also be a parent of the oldest commit. When the oldest
+commit is a merge, all of its parents are preserved in the squashed commit.
++
+A `fixup!`, `squash!`, or `amend!` commit is refused unless the commit it
+targets is also in the range, so the fold does not silently absorb a
+marker meant for a commit outside it. As an exception, a range made up entirely
+of markers for one target is combined into a single commit. With `--no-edit`,
+the last `amend!` message is used if there is one; a `squash!` or `amend!` is
+otherwise refused if folding it would discard its message.
++
+A local branch descended from a selected commit but not from the range tip
+cannot be rewritten as a descendant of the result, so with the default
+`--update-refs=branches` the command refuses. Rerun with `--update-refs=head`
+to rewrite only the current branch and leave such branches unchanged. Tags
+and remote-tracking refs are always left unchanged.
+
 OPTIONS
 -------
 
diff --git a/builtin/history.c b/builtin/history.c
index e65b76b59f..8176f6794e 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1011,6 +1011,260 @@ out:
 
 #define SQUASH_SEEN (1u << 11)
 #define SQUASH_TIP (1u << 12)
+#define SQUASH_AMEND_TARGET (1u << 13)
+
+static bool is_autosquash_subject(const char *s)
+{
+	return starts_with(s, "amend!") || starts_with(s, "fixup!") ||
+		starts_with(s, "squash!");
+}
+
+static bool skip_one_autosquash_prefix(const char *s, const char **out)
+{
+	if (skip_prefix(s, "amend!", out) || skip_prefix(s, "fixup!", out) ||
+	    skip_prefix(s, "squash!", out)) {
+		while (**out == ' ')
+			(*out)++;
+		return true;
+	}
+	return false;
+}
+
+static void truncate_message_to_subject(struct strbuf *msg)
+{
+	const char *eos = strstr(msg->buf, "\n\n");
+
+	if (eos)
+		strbuf_setlen(msg, eos - msg->buf + 1);
+}
+
+struct subject_data {
+	struct strintmap subjects;
+	struct strbuf subject;
+	struct strbuf squash_message;
+	const char *message;
+	bool edit_message;
+};
+
+#define SUBJECT_DATA_INIT {		\
+	.subjects = STRINTMAP_INIT,	\
+	.subject = STRBUF_INIT,		\
+	.squash_message = STRBUF_INIT,	\
+}
+
+static void subject_data_clear(struct subject_data *data)
+{
+	strintmap_clear(&data->subjects);
+	strbuf_release(&data->subject);
+	strbuf_release(&data->squash_message);
+}
+
+static int squash_amend_message(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data,
+				unsigned flags)
+{
+	const char *body = data->message + data->subject.len;
+
+	while (isspace(*body))
+		body++;
+
+	if (!*body) {
+		warning(_("ignoring %s (%s): message body is empty"),
+			repo_find_unique_abbrev(repo, &commit->object.oid,
+						DEFAULT_ABBREV),
+			data->subject.buf);
+		return 0;
+	}
+
+	if (data->edit_message) {
+		return 0;
+	} else if (flags & SQUASH_AMEND_TARGET) {
+		if (starts_with(data->squash_message.buf, "squash!"))
+			return error(_("squashing %s (%s) would overwrite "
+				       "'squash!' message, please combine them "
+				       "using '--edit'"),
+				     repo_find_unique_abbrev(repo,
+							     &commit->object.oid,
+							     DEFAULT_ABBREV),
+				     data->subject.buf);
+		if (starts_with(data->squash_message.buf, "fixup!"))
+			strbuf_splice(&data->squash_message, 0, 5, "amend!", 5);
+		if (starts_with(data->squash_message.buf, "amend!")) {
+			truncate_message_to_subject(&data->squash_message);
+			strbuf_addch(&data->squash_message, '\n');
+		} else {
+			strbuf_reset(&data->squash_message);
+		}
+		strbuf_addstr(&data->squash_message, body);
+		strbuf_complete_line(&data->squash_message);
+	} else {
+		return error(_("cannot squash %s (%s) that does not target "
+			       "base commit without '--edit'"),
+			     repo_find_unique_abbrev(repo, &commit->object.oid,
+						     DEFAULT_ABBREV),
+			     data->subject.buf);
+	}
+	return 0;
+}
+
+static int squash_squash_message(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data,
+				unsigned flags)
+{
+	const char *body = data->message + data->subject.len;
+
+	while (isspace(*body))
+		body++;
+
+	if (data->edit_message) {
+		return 0;
+	} else if (flags & SQUASH_AMEND_TARGET) {
+		if (starts_with(data->squash_message.buf, "fixup!")) {
+			truncate_message_to_subject(&data->squash_message);
+			strbuf_splice(&data->squash_message, 0, 5, "squash", 6);
+		}
+		if (starts_with(data->squash_message.buf, "squash!")) {
+			strbuf_addch(&data->squash_message, '\n');
+			strbuf_addstr(&data->squash_message, body);
+			strbuf_complete_line(&data->squash_message);
+		} else {
+			return error(_("squashing %s (%s) would discard its "
+				       "message, please combine them using "
+				       "'--edit'"),
+				     repo_find_unique_abbrev(repo,
+							     &commit->object.oid,
+							     DEFAULT_ABBREV),
+				     data->subject.buf);
+		}
+	} else {
+		return error(_("cannot squash %s (%s) that does not target "
+			       "base commit without '--edit'"),
+			      repo_find_unique_abbrev(repo, &commit->object.oid,
+						      DEFAULT_ABBREV),
+			      data->subject.buf);
+	}
+	return 0;
+}
+
+static int squash_check_can_autosquash(struct repository *repo,
+				       struct commit *commit,
+				       struct subject_data *data,
+				       unsigned flags)
+{
+	commit->object.flags |= flags & SQUASH_AMEND_TARGET;
+	if (starts_with(data->subject.buf, "amend!"))
+		return squash_amend_message(repo, commit, data, flags);
+	else if (starts_with(data->subject.buf, "squash!"))
+		return squash_squash_message(repo, commit, data, flags);
+
+	return 0;
+}
+
+static int squash_check_autosquash_subject(struct repository *repo,
+					   struct commit *commit,
+					   struct subject_data *data)
+{
+	const char* s = data->subject.buf;
+	struct commit *target;
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+	/* Try skipping autosquash prefixes one at a time to allow
+	 * squashing
+	 *     a commit
+	 *     fixup! fixup! a commit
+	 *
+	 * where we may have started with
+	 *     a commit
+	 *     fixup! a commit
+	 *     fixup! fixup! a commit
+	 *
+	 * and squashed the first fixup separately from the second
+	 */
+	while (skip_one_autosquash_prefix(s, &s)) {
+		unsigned flags = strintmap_get(&data->subjects, s);
+		if (flags)
+			return squash_check_can_autosquash(repo, commit, data, flags);
+	}
+	/*
+	 * Allow "fixup! <hex object id>", but not "fixup! HEAD^" or
+	 * "fixup! main". If the target is not being squashed check the subject
+	 * to allow "fixup! abc123" and "fixup! <subject of abc123>" to be
+	 * squashed together.
+	 */
+	target = lookup_commit_reference_by_name(s);
+	if (target && starts_with(oid_to_hex(&target->object.oid), s)) {
+		unsigned flags =
+			target->object.flags & (SQUASH_SEEN | SQUASH_AMEND_TARGET);
+		if (!flags) {
+			const char *subject_start;
+			const char *buffer = repo_logmsg_reencode(repo, target,
+								  NULL, NULL);
+			size_t subject_len = find_commit_subject(buffer,
+								 &subject_start);
+			char *subject = xmemdupz(subject_start, subject_len);
+
+			flags = strintmap_get(&data->subjects, subject);
+			free(subject);
+			repo_unuse_commit_buffer(repo, target, buffer);
+		}
+		if (flags)
+			return squash_check_can_autosquash(repo, commit,
+							   data, flags);
+	}
+	/* Try subject prefix matches */
+	strintmap_for_each_entry(&data->subjects, &iter, entry) {
+		s = data->subject.buf;
+		while(skip_one_autosquash_prefix(s, &s)) {
+			if (starts_with(entry->key, s)) {
+				unsigned value = (intptr_t)entry->value;
+
+				return squash_check_can_autosquash(repo, commit,
+								   data, value);
+			}
+		}
+	}
+	return error(_("cannot squash %s (%s): its target is not being "
+		       "squashed"),
+		       repo_find_unique_abbrev(repo, &commit->object.oid,
+					       DEFAULT_ABBREV),
+		       data->subject.buf);
+}
+
+static int squash_check_subject(struct repository *repo,
+				struct commit *commit,
+				struct subject_data *data)
+{
+	int ret = 0;
+	const char *buf = repo_logmsg_reencode(repo, commit, NULL, NULL);
+	size_t subject_len = find_commit_subject(buf, &data->message);
+
+	strbuf_reset(&data->subject);
+	strbuf_add(&data->subject, data->message, subject_len);
+
+	if (!strintmap_get_size(&data->subjects)) {
+		const char *s;
+
+		strbuf_addstr(&data->squash_message, data->message);
+		strbuf_complete_line(&data->squash_message);
+		/*
+		 * Strip a single autosquash prefix to allow squashing
+		 *     fixup! base
+		 *     amend! base
+		 */
+		s = data->subject.buf;
+		skip_one_autosquash_prefix(s, &s);
+		strintmap_set(&data->subjects, s, SQUASH_AMEND_TARGET | SQUASH_SEEN);
+		commit->object.flags |= SQUASH_AMEND_TARGET;
+	} else if (is_autosquash_subject(data->subject.buf)) {
+		ret = squash_check_autosquash_subject(repo, commit, data);
+	} else {
+		strintmap_set(&data->subjects, data->subject.buf, SQUASH_SEEN);
+	}
+	repo_unuse_commit_buffer(repo, commit, buf);
+	return ret;
+}
 
 static int setup_squash_revisions(struct repository *repo,
 				  int argc, const char **argv,
@@ -1067,9 +1321,11 @@ static int resolve_squash_range(struct repository *repo,
 				bool update_branches,
 				int argc, const char **argv,
 				struct commit **oldest_out,
-				struct commit **tip_out)
+				struct commit **tip_out,
+				char **message_out)
 {
 	struct rev_info revs;
+	struct subject_data subject_data = SUBJECT_DATA_INIT;
 	struct commit *commit, *oldest = NULL, *tip = NULL;
 	int ret, tip_count = 0;
 	bool walk_started = false;
@@ -1132,6 +1388,10 @@ static int resolve_squash_range(struct repository *repo,
 			commit_list_insert(commit, &filter.with_commit);
 			oldest = commit;
 		}
+		if (squash_check_subject(repo, commit, &subject_data)) {
+			ret = -1;
+			goto out;
+		}
 		tip = commit;
 		tip->object.flags |= SQUASH_SEEN | SQUASH_TIP;
 		tip_count++;
@@ -1200,12 +1460,15 @@ static int resolve_squash_range(struct repository *repo,
 
 	*oldest_out = oldest;
 	*tip_out = tip;
+	*message_out = strbuf_detach(&subject_data.squash_message, NULL);
 	ret = 0;
 
 out:
-	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP);
+	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP |
+			   SQUASH_AMEND_TARGET);
 	if (walk_started)
 		reset_revision_walk();
+	subject_data_clear(&subject_data);
 	release_revisions(&revs);
 	ref_filter_clear(&filter);
 	ref_array_clear(&refs);
@@ -1234,23 +1497,68 @@ static int cmd_history_squash(int argc,
 			 N_("edit the commit message")),
 		OPT_END(),
 	};
-	struct commit *oldest, *tip;
+	struct strbuf reflog_msg = STRBUF_INIT;
+	struct commit *oldest, *tip, *rewritten;
+	const struct object_id *base_tree_oid, *tip_tree_oid;
+	char *message_template = NULL;
+	struct rev_info revs = { 0 };
 	int ret;
 
 	argc = parse_options(argc, argv, prefix, options, usage,
 			     PARSE_OPT_KEEP_UNKNOWN_OPT | PARSE_OPT_KEEP_ARGV0);
-	if (argc < 2)
-		return error(_("command expects a revision range"));
+	if (argc < 2) {
+		ret = error(_("command expects a revision range"));
+		goto out;
+	}
 	repo_config(repo, git_default_config, NULL);
+
 	if (action == REF_ACTION_DEFAULT)
 		action = REF_ACTION_BRANCHES;
 
+	strbuf_addstr(&reflog_msg, "squash: updating ");
+	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
+
 	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
-				   argc, argv, &oldest, &tip);
+				   argc, argv, &oldest, &tip,
+				   &message_template);
 	if (ret < 0)
-		return ret;
+		goto out;
+	if (edit) {
+		ret = error(_("message editing is not supported yet; use '--no-edit'"));
+		goto out;
+	}
+
+	ret = setup_revwalk(repo, action, tip, &revs);
+	if (ret < 0)
+		goto out;
+
+	base_tree_oid = &repo_get_commit_tree(repo,
+					oldest->parents->item)->object.oid;
+	tip_tree_oid = &repo_get_commit_tree(repo, tip)->object.oid;
+
+	ret = commit_tree_ext(repo, "squash", oldest, message_template,
+			      oldest->parents, base_tree_oid, tip_tree_oid,
+			      &rewritten, 0);
+	if (ret < 0) {
+		ret = error(_("failed writing squashed commit"));
+		goto out;
+	}
+
+	ret = handle_reference_updates(&revs, action, tip, rewritten,
+				       reflog_msg.buf, dry_run,
+				       REPLAY_EMPTY_COMMIT_ABORT);
+	if (ret < 0) {
+		ret = error(_("failed replaying descendants"));
+		goto out;
+	}
 
-	return error(_("squashing commits is not implemented yet"));
+	ret = 0;
+
+out:
+	strbuf_release(&reflog_msg);
+	release_revisions(&revs);
+	free(message_template);
+	return ret;
 }
 
 static int update_worktree(struct repository *repo,
diff --git a/object.h b/object.h
index dcf30156ca..46cade33fb 100644
--- a/object.h
+++ b/object.h
@@ -74,7 +74,7 @@ void object_array_init(struct object_array *array);
  * bisect.c:                                        16
  * bundle.c:                                        16
  * http-push.c:                          11-----14
- * builtin/history.c:                    1112
+ * builtin/history.c:                    11---13
  * commit-graph.c:                                15
  * commit-reach.c:                                  16-------20
  * builtin/last-modified.c:                         1617
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index b1f65de5f5..fb06637aaf 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -4,11 +4,50 @@ test_description='tests for git-history squash subcommand'
 
 . ./test-lib.sh
 
-test_expect_success 'setup linear history' '
+stage_file () {
+	printf "%s\n" "$1" >file &&
+	git add file
+}
+
+commit_with_message () {
+	printf "%b" "$1" >msg &&
+	git commit --allow-empty -qF msg
+}
+
+check_commit_count () {
+	git rev-list --count "$1" >actual &&
+	echo "$2" >expect &&
+	test_cmp expect actual
+}
+
+check_log_subjects () {
+	git log --format="%s" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+check_log_messages () {
+	git log --format="%B" "$1" >actual &&
+	cat >expect &&
+	test_cmp expect actual
+}
+
+# Checks that the author data of two commits matches
+# Usage: check_commit_author <rev1> <rev2>
+check_commit_author () {
+	git show -s --format="%an <%ae> %ad" "$1" >expect &&
+	git show -s --format="%an <%ae> %ad" "$2" >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'setup linear history touching two files' '
 	test_commit base file a start &&
-	test_commit one file b &&
-	test_commit two file c &&
-	test_commit three file d
+	GIT_AUTHOR_NAME=One GIT_AUTHOR_EMAIL=one@example.com \
+		test_commit one other x &&
+	GIT_AUTHOR_NAME=Two GIT_AUTHOR_EMAIL=two@example.com \
+		test_commit two file c &&
+	GIT_AUTHOR_NAME=Three GIT_AUTHOR_EMAIL=three@example.com \
+		test_commit three file d
 '
 
 test_expect_success 'errors on missing range argument' '
@@ -29,40 +68,331 @@ test_expect_success 'errors on a single revision that is not a range' '
 '
 
 test_expect_success 'errors on a range holding a single commit' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+
 	test_must_fail git history squash "HEAD^!" 2>err &&
-	test_grep "single commit; nothing to squash" err
+	test_grep "single commit; nothing to squash" err &&
+	test_cmp_rev "$head_before" HEAD
 '
 
-test_expect_success 'rejects a root commit' '
+test_expect_success 'rejects root commit' '
+	# create a disconnected root commit
 	oid=$(git commit-tree -m root three^{tree}) &&
-	test_must_fail git history squash \
-		--ancestry-path=start "$oid..three" 2>err &&
-	test_grep "cannot squash down to root commit" err
+	# because we pass --ancestry-path when calling setup_revs() it the
+	# revision walk will only include commits decended from $oid so
+	# we need to give it another --ancestry-path commit to actually walk
+	# any commits.
+	test_must_fail git history squash --ancestry-path=start $oid..three 2>err &&
+	echo "error: cannot squash down to root commit" >expect &&
+	test_cmp expect err
 '
 
 test_expect_success 'rejects multiple tips' '
 	oid=$(git commit-tree -m tip -p start^0 three^{tree}) &&
-	test_must_fail git history squash ^start "$oid" three~1 2>err &&
-	test_grep "revision range contains more than one tip" err
+	test_must_fail git history squash ^start $oid three~1 2>err &&
+	echo "error: the revision range contains more than one tip commit" >expect &&
+	test_cmp expect err &&
+
+	git reset --hard three &&
+	git history squash --no-edit ^start three~1 three &&
+	test_cmp_rev HEAD~1 start^0 &&
+	test_cmp_rev HEAD^{tree} three^{tree}
 '
 
-test_expect_success 'rejects a merge parent outside the range' '
-	git reset --hard start &&
+test_expect_success 'accepts multiple revision arguments with an exclusion' '
+	git reset --hard three &&
+	git branch -f keep HEAD~2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start..HEAD ^keep &&
+
+	git reflog -1 --format=%gs >actual &&
+	echo "squash: updating start..HEAD ^keep" >expect &&
+	test_cmp expect actual &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	two
+	one
+	EOF
+	test_cmp_rev keep HEAD~1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git branch -D keep
+'
+
+test_expect_success 'squashes a branch the current branch is not on' '
+	git reset --hard three &&
 	main=$(git symbolic-ref --short HEAD) &&
-	git checkout -b outside-parent &&
-	test_commit --no-tag outside-parent outside x &&
+	head_before=$(git rev-parse HEAD) &&
+	git checkout -b off-history start &&
+	test_commit --no-tag off-one off a &&
+	test_commit --no-tag off-two off b &&
 	git checkout "$main" &&
-	test_commit --no-tag outside-main file b &&
-	base=$(git rev-parse HEAD) &&
-	test_commit --no-tag outside-mid file c &&
-	git merge --no-ff -m "merge outside-parent" outside-parent &&
-	git branch -D outside-parent &&
 
-	test_must_fail git history squash "$base.." 2>err &&
-	test_grep "parent .* of commit .* is outside the revision range" err
+	git history squash --no-edit start..off-history &&
+
+	check_commit_count start..off-history 1 &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D off-history
+'
+
+test_expect_success 'squashes a range into a single commit without changing the tree' '
+	git reset --hard three &&
+	head_before=$(git rev-parse HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit --dry-run start.. >out &&
+	predicted=$(awk "/^update refs\/heads\// {print \$3}" out) &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git history squash --no-edit start.. &&
+
+	test "$predicted" = "$(git rev-parse HEAD)" &&
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	check_log_subjects -1 <<-\EOF &&
+	one
+	EOF
+	git reflog >reflog &&
+	test_grep "squash: updating" reflog
+'
+
+test_expect_success 'sanitizes rev-list walk options, before and after --' '
+	git reset --hard three &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit --date-order start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+
+	git reset --hard three &&
+	git history squash --no-edit -- --reverse start.. 2>err &&
+	test_grep "ignoring rev-list options" err &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes an interior range and replays descendants verbatim' '
+	git reset --hard three &&
+	final_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start..@~1 &&
+
+	check_log_subjects start..HEAD <<-\EOF &&
+	three
+	one
+	EOF
+
+	test_cmp_rev start HEAD~2 &&
+	test "$final_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashes when the base is the root commit' '
+	git reset --hard three &&
+	root=$(git rev-list --max-parents=0 HEAD) &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit "$root.." &&
+
+	check_commit_count "$root..HEAD" 1 &&
+	test_cmp_rev "$root" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'squashing a mix of fixups' '
+	git reset --hard three &&
+	echo fix >file &&
+	git commit --fixup=two -a &&
+	echo really fix >file &&
+	git commit --fixup=one -a &&
+	echo really really fix >file &&
+	git commit --fixup=HEAD~1 -a && # fixup! two
+	echo really really really fix >file &&
+	git commit --fixup=HEAD~1 -a && # fixup! one
+
+	# squashing fixup! with a target that is not being squashed fails
+	test_must_fail git history squash one.. 2>err &&
+	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
+
+	# squashing fixup! into fixup! with a different target fails
+	test_must_fail git history squash HEAD~4.. 2>err && # HEAD~4 is fixup! two
+	test_grep "^error: cannot squash .* (fixup! one): its target is not being squashed" err &&
+
+	# squashing a sequence of fixup! commits into their targets
+	git history squash --no-edit start..HEAD~1 &&
+	test_cmp_rev start HEAD~2 &&
+	check_commit_author one HEAD~1 &&
+	test_commit_message HEAD~1 -m one &&
+
+	# squashing "fixup! fixup! <target>" into "<target>"
+	git history squash --no-edit start.. &&
+	test_cmp_rev start HEAD~1 &&
+	check_commit_author one HEAD &&
+	test_commit_message HEAD -m one
+'
+
+test_expect_success 'squashing "squash!" messages' '
+	git reset --hard two &&
+	echo fix >file &&
+	git commit --fixup=HEAD -a &&
+	oldest=$(git rev-parse HEAD) &&
+	echo better fix >file &&
+	git commit -a -F - <<-EOF &&
+	squash! $(git rev-parse two)
+
+	Append this
+	EOF
+
+	echo an even better fix >file &&
+	git commit -a -F - <<-EOF &&
+	squash! squash! two
+
+	Append this as well
+	EOF
+
+	# must edit when squashing "squash!" into its target
+	test_must_fail git history squash --no-edit two^.. 2>err &&
+	test_grep "^error: squashing .* (squash! [a-f0-9]*) would discard its message" err &&
+
+	# squashing "squash!" into "fixup!" appends messages and changes
+	# subject prefix
+	git history squash --no-edit two.. &&
+	test_cmp_rev HEAD^ two &&
+	test_commit_message HEAD <<-\EOF &&
+	squash! two
+
+	Append this
+
+	Append this as well
+	EOF
+	check_commit_author "$oldest" HEAD &&
+
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! two
+
+	A new message
+	EOF
+
+	# "amend!" does not replace "squash!"
+	test_must_fail git history squash --no-edit HEAD~2.. 2>err &&
+	test_grep "^error: squashing .* (amend! two) would overwrite .squash!. message" err
+'
+
+test_expect_success '--no-edit uses last "amend!" message without an editor' '
+	git reset --hard three &&
+	write_script editor <<-\EOF &&
+	exit 1
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	echo fix >file &&
+	git commit --author="Fix Me <fix.me@example.com>" --fixup=HEAD -a &&
+	git commit --allow-empty -F - <<-EOF &&
+	amend! $(git rev-parse --short HEAD)
+
+	The first reword
+
+	More detail
+	EOF
+
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! three
+
+	The second reword
+
+	Extra detail
+	EOF
+
+	test_commit WIP &&
+
+	cat >msg <<-EOF &&
+	amend! $(git rev-parse --short HEAD^)
+
+	The third reword
+
+	Excruciating detail
+	EOF
+
+	git commit --author="Someone Else <s.else@example.com>" --allow-empty \
+		-F msg &&
+
+	# squashing amend! updates the commit message
+	git history squash --no-edit three^.. &&
+	sed -e 1,2d msg | test_commit_message HEAD &&
+	check_commit_author three HEAD &&
+	test_cmp_rev HEAD^ three^ &&
+
+	# squashing amend! into fixup! updates subject prefix
+	git reset --hard HEAD@{1} &&
+	git history squash --no-edit three.. &&
+	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
+	check_commit_author HEAD@{1}~4 HEAD &&
+	test_cmp_rev HEAD^ three &&
+
+	# squashing amend! into amend! keeps original subject line
+	git reset --hard HEAD@{1} &&
+	git history squash --no-edit HEAD~3.. &&
+	sed "1s/.*/amend! three/" msg | test_commit_message HEAD &&
+	test_cmp_rev HEAD~3 three &&
+
+	# all amend! messages must target the first commit
+	git reset --hard HEAD@{1} &&
+	git commit --allow-empty -F - <<-\EOF &&
+	amend! WIP
+
+	The real message
+	EOF
+
+	test_must_fail git history squash --no-edit HEAD~4.. 2>err &&
+	test_grep "^error: cannot squash .* that does not target" err &&
+
+	# amend! message that targets commit that is not in range is rejected
+	test_must_fail git history squash --no-edit HEAD~3.. 2>err &&
+	test_grep "^error: cannot squash .* target is not being squashed" err &&
+	test_set_editor :
 '
 
-test_expect_success 'prints branches that cannot follow the squash' '
+test_expect_success 'squashing fixups into a merge' '
+	test_when_finished \
+		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
+		 git branch -D feature" &&
+	git checkout -f start &&
+	test_commit F1 &&
+	git checkout -b feature start &&
+	test_commit F2 &&
+	git merge F1 &&
+	echo fixed >F1.t &&
+	cat >msg <<-EOF &&
+	amend! $(git rev-parse HEAD)
+
+	merge F1 and F2
+
+	reworded
+	EOF
+
+	git commit -a -F msg &&
+	git history squash --no-edit HEAD^^! HEAD &&
+	test_cmp_rev HEAD^1 F2 &&
+	test_cmp_rev HEAD^2 F1 &&
+	test_cmp_rev HEAD@{1}^{tree} HEAD^{tree} &&
+	sed 1,2d msg | test_commit_message HEAD
+'
+
+test_expect_success '--update-refs=head only moves HEAD' '
+	git reset --hard three &&
+	git branch -f other HEAD &&
+	other_before=$(git rev-parse other) &&
+
+	git history squash --no-edit --update-refs=head start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev "$other_before" other
+'
+
+test_expect_success 'refuses to fold a range a branch points into' '
 	test_when_finished \
 		"git switch -f $GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME; \
 		 git branch -D feature" &&
@@ -85,20 +415,275 @@ test_expect_success 'prints branches that cannot follow the squash' '
 	test_grep "^error: the following branches cannot be rewritten" err &&
 	test_grep "^  topic-1$" err &&
 	test_grep "^  topic-2$" err &&
-	test_grep "^hint: .* --update-refs=head" err
+	test_grep "^hint: .* --update-refs=head" err &&
+	test_cmp_rev C6 HEAD &&
+
+	# squash succeeds with --update-refs=head
+	git history squash --no-edit --update-refs=head start.. &&
+	test_cmp_rev start HEAD^ &&
+	test_cmp_rev C6^{tree} HEAD^{tree} &&
+	test_cmp_rev C6 HEAD@{1}
 '
 
 test_expect_success 'advice.historyUpdateRefs silences the hint' '
 	git reset --hard three &&
 	git branch -f mid HEAD~1 &&
+	head_before=$(git rev-parse HEAD) &&
 
 	test_must_fail git -c advice.historyUpdateRefs=false \
 		history squash start.. 2>err &&
 	test_grep "^error: the following branches cannot be rewritten" err &&
 	test_grep "^  mid$" err &&
 	test_grep ! "hint:" err &&
+	test_cmp_rev "$head_before" HEAD &&
 
 	git branch -D mid
 '
 
+test_expect_success 'leaves tags and remote-tracking refs unchanged' '
+	git reset --hard three &&
+	git tag -f mark HEAD~1 &&
+	git update-ref refs/remotes/origin/mark HEAD~1 &&
+	mark_before=$(git rev-parse mark) &&
+
+	git history squash --no-edit start.. &&
+
+	test_cmp_rev "$mark_before" mark &&
+	test_cmp_rev "$mark_before" refs/remotes/origin/mark &&
+
+	git tag -d mark &&
+	git update-ref -d refs/remotes/origin/mark
+'
+
+test_expect_success 'squashes a range whose internal merge has a single base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag before-side file b &&
+	git checkout -b inner-side &&
+	test_commit --no-tag on-inner-side inner x &&
+	git checkout "$main" &&
+	test_commit --no-tag after-side file c &&
+	git merge --no-ff -m merge inner-side &&
+	git branch -D inner-side &&
+	test_commit --no-tag after-merge file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	check_log_subjects -1 <<-\EOF &&
+	before-side
+	EOF
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a merge of a branch that forked at the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b base-fork-side &&
+	test_commit --no-tag base-fork-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag base-fork-main file b &&
+	git merge --no-ff -m "merge base-fork-side" base-fork-side &&
+	git branch -D base-fork-side &&
+	test_commit --no-tag base-fork-tail file c &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test_cmp_rev start HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'refuses a merge whose other parent is outside the range' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b outside-parent &&
+	test_commit --no-tag outside-parent outside x &&
+	git checkout "$main" &&
+	test_commit --no-tag outside-main file b &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag outside-mid file c &&
+	git merge --no-ff -m "merge outside-parent" outside-parent &&
+	git branch -D outside-parent &&
+	merged=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash "$base.." 2>err &&
+	test_grep "parent .* of commit .* is outside the revision range" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'folds a range whose tip is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag tipmerge-base file b &&
+	git checkout -b tipmerge-side &&
+	test_commit --no-tag tipmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag tipmerge-main file c &&
+	git merge --no-ff -m "merge tipmerge-side" tipmerge-side &&
+	git branch -D tipmerge-side &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file side
+'
+
+test_expect_success 'folds a range whose base is a merge commit' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b basemerge-side &&
+	test_commit --no-tag basemerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag basemerge-main file b &&
+	git merge --no-ff -m "merge basemerge-side" basemerge-side &&
+	git branch -D basemerge-side &&
+	base=$(git rev-parse HEAD) &&
+	test_commit --no-tag basemerge-one file c &&
+	test_commit --no-tag basemerge-two file d &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit "$base.." &&
+
+	check_commit_count "$base..HEAD" 1 &&
+	test_cmp_rev "$base" HEAD^ &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})"
+'
+
+test_expect_success 'folds a range with two interior merges' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag two-merge-a file a1 &&
+	git checkout -b two-merge-s1 &&
+	test_commit --no-tag two-merge-s1 s1 x &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s1" two-merge-s1 &&
+	test_commit --no-tag two-merge-b file b1 &&
+	git checkout -b two-merge-s2 &&
+	test_commit --no-tag two-merge-s2 s2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m "merge s2" two-merge-s2 &&
+	git branch -D two-merge-s1 two-merge-s2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file s1 &&
+	test_path_is_file s2
+'
+
+test_expect_success 'folds a range with a nested merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b nested-outer &&
+	test_commit --no-tag nested-outer outer x &&
+	git checkout -b nested-inner &&
+	test_commit --no-tag nested-inner inner y &&
+	git checkout nested-outer &&
+	git merge --no-ff -m "merge inner" nested-inner &&
+	git checkout "$main" &&
+	test_commit --no-tag nested-main file b1 &&
+	git merge --no-ff -m "merge outer" nested-outer &&
+	git branch -D nested-outer nested-inner &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file outer &&
+	test_path_is_file inner
+'
+
+test_expect_success 'folds a range with an octopus merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag octo-base file a1 &&
+	git checkout -b octo-1 &&
+	test_commit --no-tag octo-1 o1 x &&
+	git checkout "$main" &&
+	git checkout -b octo-2 &&
+	test_commit --no-tag octo-2 o2 y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-1 octo-2 &&
+	git branch -D octo-1 octo-2 &&
+	tip_tree=$(git rev-parse HEAD^{tree}) &&
+
+	git history squash --no-edit start.. &&
+
+	check_commit_count start..HEAD 1 &&
+	test "$tip_tree" = "$(git rev-parse HEAD^{tree})" &&
+	test_path_is_file o1 &&
+	test_path_is_file o2
+'
+
+test_expect_success 'refuses an octopus merge with an arm forked before the base' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	git checkout -b octo-pre &&
+	test_commit octo-pre-side pside x &&
+	git checkout "$main" &&
+	test_commit octo-pre-main file b1 &&
+	octo_base=$(git rev-parse HEAD) &&
+	git checkout -b octo-within &&
+	test_commit --no-tag octo-within wside y &&
+	git checkout "$main" &&
+	git merge --no-ff -m octopus octo-pre octo-within &&
+	merged=$(git rev-parse HEAD) &&
+	git branch -D octo-pre octo-within &&
+
+	test_must_fail git history squash "$octo_base.." 2>err &&
+	test_grep "parent .* of commit .* is outside the revision range" err &&
+	test_cmp_rev "$merged" HEAD
+'
+
+test_expect_success 'refuses when a descendant above the range is a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag desc-one file b &&
+	test_commit --no-tag desc-two file c &&
+	git tag desc-tip &&
+	git checkout -b desc-above &&
+	test_commit --no-tag desc-above above x &&
+	git checkout "$main" &&
+	test_commit --no-tag desc-main file d &&
+	git merge --no-ff -m "merge desc-above" desc-above &&
+	git branch -D desc-above &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash --no-edit start..desc-tip 2>err &&
+	test_grep "merge commits is not supported" err &&
+	test_cmp_rev "$head_before" HEAD
+'
+
+test_expect_success 'refuses to fold a range a ref points into at a merge' '
+	git reset --hard start &&
+	main=$(git symbolic-ref --short HEAD) &&
+	test_commit --no-tag refmerge-base file b &&
+	git checkout -b refmerge-side &&
+	test_commit --no-tag refmerge-side side x &&
+	git checkout "$main" &&
+	test_commit --no-tag refmerge-main file c &&
+	git merge --no-ff -m "interior merge" refmerge-side &&
+	git branch -D refmerge-side &&
+	git branch at-merge HEAD &&
+	test_commit --no-tag refmerge-tail file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "^error: the following branches cannot be rewritten" err &&
+	test_grep "^  at-merge$" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	git branch -D at-merge
+'
+
 test_done
-- 
gitgitgadget

[PATCH v15 8/8] history: support editing squashed commit messages

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

Open the editor by default when squashing and provide --no-edit as the
opt-out. Record the exact commits selected by the revision walk,
rearrange that todo list with the sequencer's autosquash machinery, and
build the message template from the resulting order.

Match interactive rebase's treatment of marker messages: comment out
fixup! messages, retain squash! bodies, and let amend! replace its target
unless a preceding squash! requires both bodies. This keeps message
editing aligned with the marker validation used by the no-edit path.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-history.adoc |  18 ++-
 builtin/history.c              |  97 +++++++++++++++-
 t/t3455-history-squash.sh      | 197 +++++++++++++++++++++++++++++++++
 3 files changed, 305 insertions(+), 7 deletions(-)

diff --git a/Documentation/git-history.adoc b/Documentation/git-history.adoc
index fb04a67685..2e2e31f521 100644
--- a/Documentation/git-history.adoc
+++ b/Documentation/git-history.adoc
@@ -133,8 +133,9 @@ given, for example `HEAD~3..HEAD ^topic` to additionally exclude what is
 already on `topic`. Rev-list options may also be given, but any that would
 change how the range is walked are overridden with a warning.
 +
-With `--no-edit`, the oldest commit's message is preserved, except that an
-`amend!` commit targeting it replaces its message.
+An editor opens pre-filled with the messages of all the folded commits so you
+can combine them. With `--no-edit`, the oldest commit's message is preserved
+instead, except that an `amend!` commit targeting it replaces its message.
 +
 The selected commits must form a connected graph with a single tip and must
 not include a root commit. Every parent of a commit after the oldest one must
@@ -148,6 +149,13 @@ of markers for one target is combined into a single commit. With `--no-edit`,
 the last `amend!` message is used if there is one; a `squash!` or `amend!` is
 otherwise refused if folding it would discard its message.
 +
+The editor template mirrors `git rebase -i --autosquash`: each `fixup!`,
+`squash!`, or `amend!` is grouped under the commit it targets rather than
+shown in commit order. A `fixup!` message is dropped (commented out in full),
+a `squash!` keeps its body with only the marker subject commented, and an
+`amend!` replaces its target's message, unless a `squash!` folded into that
+target first, in which case it keeps its body like a `squash!`.
++
 A local branch descended from a selected commit but not from the range tip
 cannot be rewritten as a descendant of the result, so with the default
 `--update-refs=branches` the command refuses. Rerun with `--update-refs=head`
@@ -163,6 +171,12 @@ OPTIONS
 	objects will be written into the repository, so applying these printed
 	ref updates is generally safe.
 
+`--edit`::
+`--no-edit`::
+	For `squash`, open an editor to combine the messages of the folded commits.
+	This is the default; use `--no-edit` to keep the selected message without
+	opening an editor.
+
 `--reedit-message`::
 	Open an editor to modify the target commit's message.
 
diff --git a/builtin/history.c b/builtin/history.c
index 8176f6794e..2d88bc4352 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -1266,6 +1266,10 @@ static int squash_check_subject(struct repository *repo,
 	return ret;
 }
 
+static int build_squash_message(struct repository *repo,
+				const struct strbuf *todo_buf,
+				struct strbuf *out);
+
 static int setup_squash_revisions(struct repository *repo,
 				  int argc, const char **argv,
 				  struct rev_info *revs)
@@ -1319,6 +1323,7 @@ static int setup_squash_revisions(struct repository *repo,
  */
 static int resolve_squash_range(struct repository *repo,
 				bool update_branches,
+				bool edit_message,
 				int argc, const char **argv,
 				struct commit **oldest_out,
 				struct commit **tip_out,
@@ -1327,11 +1332,13 @@ static int resolve_squash_range(struct repository *repo,
 	struct rev_info revs;
 	struct subject_data subject_data = SUBJECT_DATA_INIT;
 	struct commit *commit, *oldest = NULL, *tip = NULL;
+	struct strbuf todo_buf = STRBUF_INIT;
 	int ret, tip_count = 0;
 	bool walk_started = false;
 	struct ref_filter filter = REF_FILTER_INIT;
 	struct ref_array refs = { 0 };
 
+	subject_data.edit_message = edit_message;
 	ret = setup_squash_revisions(repo, argc, argv, &revs);
 	if (ret < 0)
 		goto out;
@@ -1344,6 +1351,10 @@ static int resolve_squash_range(struct repository *repo,
 	while ((commit = get_revision(&revs))) {
 		struct commit_list *p;
 
+		if (edit_message)
+			strbuf_addf(&todo_buf, "pick %s\n",
+				    oid_to_hex(&commit->object.oid));
+
 		if (!commit->parents) {
 			ret = error(_("cannot squash down to root commit"));
 			goto out;
@@ -1457,6 +1468,13 @@ static int resolve_squash_range(struct repository *repo,
 		string_list_clear(&sorting_options, 0);
 		goto out;
 	}
+	if (edit_message) {
+		strbuf_reset(&subject_data.squash_message);
+		ret = build_squash_message(repo, &todo_buf,
+					   &subject_data.squash_message);
+		if (ret < 0)
+			goto out;
+	}
 
 	*oldest_out = oldest;
 	*tip_out = tip;
@@ -1464,6 +1482,7 @@ static int resolve_squash_range(struct repository *repo,
 	ret = 0;
 
 out:
+	strbuf_release(&todo_buf);
 	clear_object_flags(repo, SQUASH_SEEN | SQUASH_TIP |
 			   SQUASH_AMEND_TARGET);
 	if (walk_started)
@@ -1475,6 +1494,76 @@ out:
 	return ret;
 }
 
+static bool amend_replaces_target(struct todo_list *todo, int target)
+{
+	for (int i = target + 1; i < todo->nr &&
+				 todo->items[i].command != TODO_PICK; i++) {
+		if (todo->items[i].command == TODO_SQUASH)
+			return false;
+		if (todo->items[i].flags & TODO_REPLACE_FIXUP_MSG)
+			return true;
+	}
+	return false;
+}
+
+static int build_squash_message(struct repository *repo,
+				const struct strbuf *todo_buf,
+				struct strbuf *out)
+{
+	struct todo_list todo = TODO_LIST_INIT;
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	int nr_commits, ret;
+
+	if (todo_list_parse_insn_buffer(repo, &opts, todo_buf->buf, &todo) < 0 ||
+	    todo_list_rearrange_squash(&todo) < 0) {
+		ret = error(_("could not prepare the squash message"));
+		goto out;
+	}
+
+	nr_commits = todo.nr;
+	for (int i = 0; i < nr_commits; i++) {
+		struct todo_item *item = &todo.items[i];
+		const char *message, *body;
+		size_t commented_len;
+		bool skip, squashing;
+
+		squashing = item->command == TODO_SQUASH ||
+			    (item->flags & TODO_REPLACE_FIXUP_MSG);
+		if (item->command == TODO_PICK)
+			skip = amend_replaces_target(&todo, i);
+		else
+			skip = !squashing;
+
+		message = repo_logmsg_reencode(repo, item->commit, NULL, NULL);
+		find_commit_subject(message, &body);
+
+		if (skip)
+			commented_len = strlen(body);
+		else if (squashing)
+			commented_len = squash_subject_comment_len(body, 1);
+		else
+			commented_len = 0;
+
+		if (!i)
+			add_squash_combination_header(out, nr_commits);
+		strbuf_addch(out, '\n');
+		add_squash_message_header(out, i + 1, skip);
+		strbuf_addstr(out, "\n\n");
+		strbuf_add_commented_lines(out, body, commented_len, comment_line_str);
+		strbuf_addstr(out, body + commented_len);
+		strbuf_complete_line(out);
+
+		repo_unuse_commit_buffer(repo, item->commit, message);
+	}
+
+	ret = 0;
+
+out:
+	todo_list_release(&todo);
+	replay_opts_release(&opts);
+	return ret;
+}
+
 static int cmd_history_squash(int argc,
 			      const char **argv,
 			      const char *prefix,
@@ -1519,14 +1608,11 @@ static int cmd_history_squash(int argc,
 	strbuf_join_argv(&reflog_msg, argc - 1, argv + 1, ' ');
 
 	ret = resolve_squash_range(repo, action == REF_ACTION_BRANCHES,
+				   edit,
 				   argc, argv, &oldest, &tip,
 				   &message_template);
 	if (ret < 0)
 		goto out;
-	if (edit) {
-		ret = error(_("message editing is not supported yet; use '--no-edit'"));
-		goto out;
-	}
 
 	ret = setup_revwalk(repo, action, tip, &revs);
 	if (ret < 0)
@@ -1538,7 +1624,8 @@ static int cmd_history_squash(int argc,
 
 	ret = commit_tree_ext(repo, "squash", oldest, message_template,
 			      oldest->parents, base_tree_oid, tip_tree_oid,
-			      &rewritten, 0);
+			      &rewritten,
+			      edit ? COMMIT_TREE_EDIT_MESSAGE : 0);
 	if (ret < 0) {
 		ret = error(_("failed writing squashed commit"));
 		goto out;
diff --git a/t/t3455-history-squash.sh b/t/t3455-history-squash.sh
index fb06637aaf..d21e9d9fc4 100755
--- a/t/t3455-history-squash.sh
+++ b/t/t3455-history-squash.sh
@@ -381,6 +381,203 @@ test_expect_success 'squashing fixups into a merge' '
 	sed 1,2d msg | test_commit_message HEAD
 '
 
+test_expect_success 'edits every message and aborts on an empty result' '
+	git reset --hard start &&
+	stage_file b &&
+	git commit -m "re-one subject" -m "re-one body line" &&
+	test_commit --no-tag re-two file c &&
+	test_commit re-three file d &&
+	head_before=$(git rev-parse HEAD) &&
+
+	write_script empty-editor <<-\EOF &&
+	>"$1"
+	EOF
+	test_set_editor "$(pwd)/empty-editor" &&
+	test_must_fail git history squash start.. 2>err &&
+	test_grep "Aborting commit due to empty commit message" err &&
+	test_cmp_rev "$head_before" HEAD &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited &&
+	echo combined >"$1"
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# This is the 1st commit message:
+
+	re-one subject
+
+	re-one body line
+
+	# This is the commit message #2:
+
+	re-two
+
+	# This is the commit message #3:
+
+	re-three
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_subjects -1 <<-\EOF
+	combined
+	EOF
+'
+
+test_expect_success 'handles fixup!, squash! and amend! like rebase' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "fixup! mark-base\n\nfixup body\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+	stage_file e &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	mark-base
+
+	# The commit message #2 will be skipped:
+
+	# fixup! mark-base
+	#
+	# fixup body
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# This is the commit message #4:
+
+	# amend! mark-base
+
+	amended message
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	mark-base
+
+	squash remark
+
+	amended message
+
+	EOF
+'
+
+test_expect_success 'groups fixups under their targets in the editor' '
+	git reset --hard start &&
+	test_commit --no-tag alpha file a1 &&
+	test_commit --no-tag beta file b1 &&
+	stage_file a2 &&
+	commit_with_message "fixup! alpha\n" &&
+	stage_file b2 &&
+	commit_with_message "fixup! beta\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 4 commits.
+	# This is the 1st commit message:
+
+	alpha
+
+	# The commit message #2 will be skipped:
+
+	# fixup! alpha
+
+	# This is the commit message #3:
+
+	beta
+
+	# The commit message #4 will be skipped:
+
+	# fixup! beta
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited
+'
+
+test_expect_success 'lets amend! replace its target message in the editor' '
+	git reset --hard start &&
+	test_commit --no-tag mark-base file b &&
+	stage_file c &&
+	commit_with_message "amend! mark-base\n\namended message\n" &&
+	stage_file d &&
+	commit_with_message "squash! mark-base\n\nsquash remark\n" &&
+
+	write_script editor <<-\EOF &&
+	cat "$1" >edited
+	EOF
+	test_set_editor "$(pwd)/editor" &&
+	git history squash start.. &&
+
+	cat >expect <<-EOF &&
+	# This is a combination of 3 commits.
+	# The 1st commit message will be skipped:
+
+	# mark-base
+
+	# This is the commit message #2:
+
+	# amend! mark-base
+
+	amended message
+
+	# This is the commit message #3:
+
+	# squash! mark-base
+
+	squash remark
+
+	# Please enter the commit message for the squash changes. Lines starting
+	# with ${SQ}#${SQ} will be ignored, and an empty message aborts the commit.
+	# Changes to be committed:
+	#	modified:   file
+	#
+	EOF
+	test_cmp expect edited &&
+	check_log_messages -1 <<-\EOF
+	amended message
+
+	squash remark
+
+	EOF
+'
+
 test_expect_success '--update-refs=head only moves HEAD' '
 	git reset --hard three &&
 	git branch -f other HEAD &&
-- 
gitgitgadget