Re: [PATCH v4 00/12] rebase: update branches in multi-part topic

[Phillip Wood <phillip.wood123@gmail.com>]

On 12/07/2022 14:06, Derrick Stolee via GitGitGadget wrote:

I haven't looked at the first two patches but I think I read everything 
else that has changed in V4. It all looks good to me. I've left some 
comments on the later patches but I don't think there are any 
showstoppers and this version could be merged into next.

Thanks for working on this

Phillip

> This series is based on ds/branch-checked-out.
> 
> This is a feature I've wanted for quite a while. When working on the sparse
> index topic, I created a long RFC that actually broke into three topics for
> full review upstream. These topics were sequential, so any feedback on an
> earlier one required updates to the later ones. I would work on the full
> feature and use interactive rebase to update the full list of commits.
> However, I would need to update the branches pointing to those sub-topics.
> 
> This series adds a new --update-refs option to 'git rebase' (along with a
> rebase.updateRefs config option) that adds 'update-ref' commands into the
> TODO list. This is powered by the commit decoration machinery.
> 
> As an example, here is my in-progress bundle URI RFC split into subtopics as
> they appear during the TODO list of a git rebase -i --update-refs:
> 
> pick 2d966282ff3 docs: document bundle URI standard
> pick 31396e9171a remote-curl: add 'get' capability
> pick 54c6ab70f67 bundle-uri: create basic file-copy logic
> pick 96cb2e35af1 bundle-uri: add support for http(s):// and file://
> pick 6adaf842684 fetch: add --bundle-uri option
> pick 6c5840ed77e fetch: add 'refs/bundle/' to log.excludeDecoration
> update-ref refs/heads/bundle-redo/fetch
> 
> pick 1e3f6546632 clone: add --bundle-uri option
> pick 9e4a6fe9b68 clone: --bundle-uri cannot be combined with --depth
> update-ref refs/heads/bundle-redo/clone
> 
> pick 5451cb6599c bundle-uri: create bundle_list struct and helpers
> pick 3029c3aca15 bundle-uri: create base key-value pair parsing
> pick a8b2de79ce8 bundle-uri: create "key=value" line parsing
> pick 92625a47673 bundle-uri: unit test "key=value" parsing
> pick a8616af4dc2 bundle-uri: limit recursion depth for bundle lists
> pick 9d6809a8d53 bundle-uri: parse bundle list in config format
> pick 287a732b54c bundle-uri: fetch a list of bundles
> update-ref refs/heads/bundle-redo/list
> 
> pick b09f8226185 protocol v2: add server-side "bundle-uri" skeleton
> pick 520204dcd1c bundle-uri client: add minimal NOOP client
> pick 62e8b457b48 bundle-uri client: add "git ls-remote-bundle-uri"
> pick 00eae925043 bundle-uri: serve URI advertisement from bundle.* config
> pick 4277440a250 bundle-uri client: add boolean transfer.bundleURI setting
> pick caf4599a81d bundle-uri: allow relative URLs in bundle lists
> pick df255000b7e bundle-uri: download bundles from an advertised list
> pick d71beabf199 clone: unbundle the advertised bundles
> pick c9578391976 t5601: basic bundle URI tests
> # Ref refs/heads/bundle-redo/rfc-3 checked out at '/home/stolee/_git/git-bundles'
> 
> update-ref refs/heads/bundle-redo/advertise
> 
> 
> Here is an outline of the series:
> 
>   * Patch 1 updates some tests for branch_checked_out() to use 'git bisect'
>     and 'git rebase' as black-boxes instead of manually editing files inside
>     $GIT_DIR. (Thanks, Junio!)
>   * Patch 2 updates some tests for branch_checked_out() for the 'apply'
>     backend.
>   * Patch 3 updates branch_checked_out() to parse the
>     rebase-merge/update-refs file to block concurrent ref updates and
>     checkouts on branches selected by --update-refs.
>   * Patch 4 updates the todo list documentation to remove some unnecessary
>     dots in the 'merge' command. This makes it consistent with the 'fixup'
>     command before we document the 'update-ref' command.
>   * Patch 5 updates the definition of todo_command_info to use enum values as
>     array indices.
>   * Patches 6-8 implement the --update-refs logic itself.
>   * Patch 9 specifically updates the update-refs file every time the user
>     edits the todo-list (Thanks Phillip!)
>   * Patch 10 adds the rebase.updateRefs config option similar to
>     rebase.autoSquash.
>   * Patch 11 ignores the HEAD ref when creating the todo list instead of
>     making a comment (Thanks Elijah!)
>   * Patch 12 adds messaging to the end of the rebase stating which refs were
>     updated (Thanks Elijah!)
> 
> 
> Updates in v4
> =============
> 
> This version took longer than I'd hoped (I had less time to work on it than
> anticipated) but it also has some major updates. These major updates are
> direct responses to the significant review this series has received. Thank
> you!
> 
>   * The update-refs file now stores "ref/before/after" triples (still
>     separated by lines). This allows us to store the "before" OID of a ref in
>     addition to the "after" that we will write to that ref at the end of the
>     rebase. This allows us to do a "force-with-lease" update. The
>     branch_checked_out() updates should prevent Git from updating those refs
>     while under the rebase, but older versions and third-party tools don't
>     have that protection.
>   * The update-refs file is updated with every update to the todo-list file.
>     This allows for some advanced changes to the file, including removing,
>     adding, and duplicating 'update-ref' commands.
>   * The message at the end of the rebase process now lists which refs were
>     updated with the update-ref steps. This includes any ref updates that
>     fail.
>   * The branch_checked_out() tests now use 'git bisect' and 'git rebase' as
>     black-boxes instead of testing their internals directly.
> 
> Here are the more minor updates:
> 
>   * Dropped an unnecessary stat() call.
>   * Updated commit messages to include extra details, based on confusion in
>     last round.
>   * The HEAD branch no longer appears as a comment line in the initial todo
>     list.
>   * The update-refs file is now written using a lockfile.
>   * Tests now use test_cmp_rev.
>   * A memory leak ('path' variable) is resolved.
> 
> 
> Updates in v3
> =============
> 
>   * The branch_checked_out() API was extracted to its own topic and is now
>     the ds/branch-checked-out branch. This series is now based on that one.
>   * The for_each_decoration() API was removed, since it became trivial once
>     it did not take a commit directly.
>   * The branch_checked_out() tests did not verify the rebase-apply data (for
>     the apply backend), so that is fixed.
>   * Instead of using the 'label' command and a final 'update-refs' command in
>     the todo list, use a new 'update-ref ' command. This command updates the
>     rebase-merge/update-refs file with the OID of HEAD at these steps. At the
>     very end of the rebase sequence, those refs are updated to the stored OID
>     values (assuming that they were not removed by the user, in which case we
>     notice that the OID is the null OID and we do nothing).
>   * New tests are added.
>   * The todo-list comment documentation has some new formatting updates, but
>     also includes a description of 'update-refs' in this version.
> 
> 
> Updates in v2
> =============
> 
> As recommended by the excellent feedback, I have removed the 'exec' commands
> in favor of the 'label' commands and a new 'update-refs' command at the very
> end. This way, there is only one step that updates all of the refs at the
> end instead of updating refs during the rebase. If a user runs 'git rebase
> --abort' in the middle, then their refs are still where they need to be.
> 
> Based on some of the discussion, it seemed like one way to do this would be
> to have an 'update-ref ' command that would take the place of these 'label'
> commands. However, this would require two things that make it a bit awkward:
> 
>   1. We would need to replicate the storage of those positions during the
>      rebase. 'label' already does this pretty well. I've added the
>      "for-update-refs/" label to help here.
>   2. If we want to close out all of the refs as the rebase is finishing, then
>      that "step" becomes invisible to the user (and a bit more complicated to
>      insert). Thus, the 'update-refs' step performs this action. If the user
>      wants to do things after that step, then they can do so by editing the
>      TODO list.
> 
> Other updates:
> 
>   * The 'keep_decorations' parameter was renamed to 'update_refs'.
>   * I added tests for --rebase-merges=rebase-cousins to show how these labels
>     interact with other labels and merge commands.
>   * I changed the order of the insertion of these update-refs labels to be
>     before the fixups are rearranged. This fixes a bug where the tip commit
>     is a fixup! so its decorations are never inspected (and they would be in
>     the wrong place even if they were). The fixup! commands are properly
>     inserted between a pick and its following label command. Tests
>     demonstrate this is correct.
>   * Numerous style choices are updated based on feedback.
> 
> Thank you for all of the detailed review and ideas in this space. I
> appreciate any more ideas that can make this feature as effective as it can
> be.
> 
> Thanks, -Stolee
> 
> Derrick Stolee (12):
>    t2407: test bisect and rebase as black-boxes
>    t2407: test branches currently using apply backend
>    branch: consider refs under 'update-refs'
>    rebase-interactive: update 'merge' description
>    sequencer: define array with enum values
>    sequencer: add update-ref command
>    rebase: add --update-refs option
>    rebase: update refs from 'update-ref' commands
>    sequencer: rewrite update-refs as user edits todo list
>    rebase: add rebase.updateRefs config option
>    sequencer: ignore HEAD ref under --update-refs
>    sequencer: notify user of --update-refs activity
> 
>   Documentation/config/rebase.txt |   3 +
>   Documentation/git-rebase.txt    |  11 +
>   branch.c                        |  13 +
>   builtin/rebase.c                |  10 +
>   rebase-interactive.c            |  15 +-
>   sequencer.c                     | 469 +++++++++++++++++++++++++++++++-
>   sequencer.h                     |  23 ++
>   t/lib-rebase.sh                 |  15 +
>   t/t2407-worktree-heads.sh       | 103 +++++--
>   t/t3404-rebase-interactive.sh   | 269 ++++++++++++++++++
>   10 files changed, 887 insertions(+), 44 deletions(-)
> 
> 
> base-commit: 9bef0b1e6ec371e786c2fba3edcc06ad040a536c
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1247%2Fderrickstolee%2Frebase-keep-decorations-v4
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1247/derrickstolee/rebase-keep-decorations-v4
> Pull-Request: https://github.com/gitgitgadget/git/pull/1247
> 
> Range-diff vs v3:
> 
>    -:  ----------- >  1:  9e53a27017a t2407: test bisect and rebase as black-boxes
>    1:  fbaedc7f1f0 !  2:  540a3be256f t2407: test branches currently using apply backend
>       @@ Commit message
>            Signed-off-by: Derrick Stolee <derrickstolee@github.com>
>        
>         ## t/t2407-worktree-heads.sh ##
>       -@@ t/t2407-worktree-heads.sh: test_expect_success 'refuse to overwrite: worktree in bisect' '
>       - 	grep "cannot force update the branch '\''fake-2'\'' checked out at.*wt-4" err
>       +@@ t/t2407-worktree-heads.sh: test_expect_success !SANITIZE_LEAK 'refuse to overwrite: worktree in bisect' '
>       + 	grep "cannot force update the branch '\''wt-4'\'' checked out at.*wt-4" err
>         '
>         
>       --test_expect_success 'refuse to overwrite: worktree in rebase' '
>       -+test_expect_success 'refuse to overwrite: worktree in rebase (apply)' '
>       -+	test_when_finished rm -rf .git/worktrees/wt-*/rebase-apply &&
>       +-test_expect_success !SANITIZE_LEAK 'refuse to overwrite: worktree in rebase' '
>       ++test_expect_success !SANITIZE_LEAK 'refuse to overwrite: worktree in rebase (apply)' '
>       ++	test_when_finished git -C wt-2 rebase --abort &&
>        +
>       -+	mkdir -p .git/worktrees/wt-3/rebase-apply &&
>       -+	echo refs/heads/fake-1 >.git/worktrees/wt-3/rebase-apply/head-name &&
>       -+	echo refs/heads/fake-2 >.git/worktrees/wt-3/rebase-apply/onto &&
>       ++	# This will fail part-way through due to a conflict.
>       ++	test_must_fail git -C wt-2 rebase --apply conflict-2 &&
>        +
>       -+	test_must_fail git branch -f fake-1 HEAD 2>err &&
>       -+	grep "cannot force update the branch '\''fake-1'\'' checked out at.*wt-3" err
>       ++	test_must_fail git branch -f wt-2 HEAD 2>err &&
>       ++	grep "cannot force update the branch '\''wt-2'\'' checked out at.*wt-2" err
>        +'
>        +
>       -+test_expect_success 'refuse to overwrite: worktree in rebase (merge)' '
>       - 	test_when_finished rm -rf .git/worktrees/wt-*/rebase-merge &&
>       ++test_expect_success !SANITIZE_LEAK 'refuse to overwrite: worktree in rebase (merge)' '
>       + 	test_when_finished git -C wt-2 rebase --abort &&
>         
>       - 	mkdir -p .git/worktrees/wt-3/rebase-merge &&
>       + 	# This will fail part-way through due to a conflict.
>    2:  2bc647b6fcd !  3:  bf301a054e3 branch: consider refs under 'update-refs'
>       @@ Commit message
>            branch_checked_out().
>        
>            The data store is a plaintext file inside the 'rebase-merge' directory
>       -    for that worktree. The file alternates refnames and OIDs. The OIDs will
>       -    be used to store the to-be-written values as the rebase progresses, but
>       -    can be ignored at the moment.
>       +    for that worktree. The file lists refnames followed by two OIDs, each on
>       +    separate lines. The OIDs will be used to store the original values of
>       +    the refs and the to-be-written values as the rebase progresses, but can
>       +    be ignored at the moment.
>        
>            Create a new sequencer_get_update_refs_state() method that parses this
>            file and populates a struct string_list with the ref-OID pairs. We can
>       @@ Commit message
>            method.
>        
>            We can test that this works without having Git write this file by
>       -    artificially creating one in our test script.
>       +    artificially creating one in our test script, at least until 'git rebase
>       +    --update-refs' is implemented and we can use it directly.
>        
>            Signed-off-by: Derrick Stolee <derrickstolee@github.com>
>        
>       @@ branch.c: static void prepare_checked_out_branches(void)
>         	free_worktrees(worktrees);
>        
>         ## sequencer.c ##
>       +@@ sequencer.c: static GIT_PATH_FUNC(rebase_path_squash_onto, "rebase-merge/squash-onto")
>       +  */
>       + static GIT_PATH_FUNC(rebase_path_refs_to_delete, "rebase-merge/refs-to-delete")
>       +
>       ++/*
>       ++ * The update-refs file stores a list of refs that will be updated at the end
>       ++ * of the rebase sequence. The 'update-ref <ref>' commands in the todo file
>       ++ * update the OIDs for the refs in this file, but the refs are not updated
>       ++ * until the end of the rebase sequence.
>       ++ *
>       ++ * rebase_path_update_refs() returns the path to this file for a given
>       ++ * worktree directory. For the current worktree, pass the_repository->gitdir.
>       ++ */
>       ++static char *rebase_path_update_refs(const char *wt_dir)
>       ++{
>       ++	return xstrfmt("%s/rebase-merge/update-refs", wt_dir);
>       ++}
>       ++
>       + /*
>       +  * The following files are written by git-rebase just after parsing the
>       +  * command-line.
>       +@@ sequencer.c: static GIT_PATH_FUNC(rebase_path_no_reschedule_failed_exec, "rebase-merge/no-res
>       + static GIT_PATH_FUNC(rebase_path_drop_redundant_commits, "rebase-merge/drop_redundant_commits")
>       + static GIT_PATH_FUNC(rebase_path_keep_redundant_commits, "rebase-merge/keep_redundant_commits")
>       +
>       ++/**
>       ++ * A 'struct update_refs_record' represents a value in the update-refs
>       ++ * list. We use a string_list to map refs to these (before, after) pairs.
>       ++ */
>       ++struct update_ref_record {
>       ++	struct object_id before;
>       ++	struct object_id after;
>       ++};
>       ++
>       + static int git_sequencer_config(const char *k, const char *v, void *cb)
>       + {
>       + 	struct replay_opts *opts = cb;
>        @@ sequencer.c: int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)
>         
>         	return 0;
>       @@ sequencer.c: int sequencer_determine_whence(struct repository *r, enum commit_wh
>        +				    struct string_list *refs)
>        +{
>        +	int result = 0;
>       -+	struct stat st;
>        +	FILE *fp = NULL;
>        +	struct strbuf ref = STRBUF_INIT;
>        +	struct strbuf hash = STRBUF_INIT;
>       -+	char *path = xstrfmt("%s/rebase-merge/update-refs", wt_dir);
>       ++	struct update_ref_record *rec = NULL;
>        +
>       -+	if (stat(path, &st))
>       -+		goto cleanup;
>       ++	char *path = rebase_path_update_refs(wt_dir);
>        +
>        +	fp = fopen(path, "r");
>        +	if (!fp)
>        +		goto cleanup;
>        +
>        +	while (strbuf_getline(&ref, fp) != EOF) {
>       -+		struct object_id oid;
>        +		struct string_list_item *item;
>        +
>       ++		CALLOC_ARRAY(rec, 1);
>       ++
>        +		if (strbuf_getline(&hash, fp) == EOF ||
>       -+		    get_oid_hex(hash.buf, &oid)) {
>       ++		    get_oid_hex(hash.buf, &rec->before)) {
>        +			warning(_("update-refs file at '%s' is invalid"),
>        +				  path);
>        +			result = -1;
>        +			goto cleanup;
>        +		}
>        +
>       -+		item = string_list_append(refs, ref.buf);
>       -+		item->util = oiddup(&oid);
>       ++		if (strbuf_getline(&hash, fp) == EOF ||
>       ++		    get_oid_hex(hash.buf, &rec->after)) {
>       ++			warning(_("update-refs file at '%s' is invalid"),
>       ++				  path);
>       ++			result = -1;
>       ++			goto cleanup;
>       ++		}
>       ++
>       ++		item = string_list_insert(refs, ref.buf);
>       ++		item->util = rec;
>       ++		rec = NULL;
>        +	}
>        +
>        +cleanup:
>        +	if (fp)
>        +		fclose(fp);
>        +	free(path);
>       ++	free(rec);
>        +	strbuf_release(&ref);
>        +	strbuf_release(&hash);
>        +	return result;
>       @@ sequencer.h: void sequencer_post_commit_cleanup(struct repository *r, int verbos
>         #endif /* SEQUENCER_H */
>        
>         ## t/t2407-worktree-heads.sh ##
>       -@@ t/t2407-worktree-heads.sh: TEST_PASSES_SANITIZE_LEAK=true
>       +@@ t/t2407-worktree-heads.sh: test_expect_success !SANITIZE_LEAK 'refuse to overwrite: worktree in rebase (mer
>       + 	grep "cannot force update the branch '\''wt-2'\'' checked out at.*wt-2" err
>       + '
>         
>       - test_expect_success 'setup' '
>       - 	test_commit init &&
>       --	git branch -f fake-1 &&
>       --	git branch -f fake-2 &&
>       ++test_expect_success 'refuse to overwrite: worktree in rebase with --update-refs' '
>       ++	test_when_finished rm -rf .git/worktrees/wt-3/rebase-merge &&
>       ++
>       ++	mkdir -p .git/worktrees/wt-3/rebase-merge &&
>       ++	touch .git/worktrees/wt-3/rebase-merge/interactive &&
>        +
>       -+	for i in 1 2 3 4
>       -+	do
>       -+		git branch -f fake-$i || return 1
>       -+	done &&
>       -
>       - 	for i in 1 2 3 4
>       - 	do
>       -@@ t/t2407-worktree-heads.sh: test_expect_success 'refuse to overwrite: worktree in rebase (merge)' '
>       - 	echo refs/heads/fake-1 >.git/worktrees/wt-3/rebase-merge/head-name &&
>       - 	echo refs/heads/fake-2 >.git/worktrees/wt-3/rebase-merge/onto &&
>       -
>       --	test_must_fail git branch -f fake-1 HEAD 2>err &&
>       --	grep "cannot force update the branch '\''fake-1'\'' checked out at.*wt-3" err
>        +	cat >.git/worktrees/wt-3/rebase-merge/update-refs <<-EOF &&
>        +	refs/heads/fake-3
>        +	$(git rev-parse HEAD~1)
>       ++	$(git rev-parse HEAD)
>        +	refs/heads/fake-4
>        +	$(git rev-parse HEAD)
>       ++	$(git rev-parse HEAD)
>        +	EOF
>        +
>       -+	for i in 1 3 4
>       ++	for i in 3 4
>        +	do
>        +		test_must_fail git branch -f fake-$i HEAD 2>err &&
>        +		grep "cannot force update the branch '\''fake-$i'\'' checked out at.*wt-3" err ||
>        +			return 1
>        +	done
>       - '
>       -
>       ++'
>       ++
>         test_expect_success !SANITIZE_LEAK 'refuse to fetch over ref: checked out' '
>       + 	test_must_fail git fetch server +refs/heads/wt-3:refs/heads/wt-3 2>err &&
>       + 	grep "refusing to fetch into branch '\''refs/heads/wt-3'\''" err &&
>    3:  669f4abd59e !  4:  dec95681d2b rebase-interactive: update 'merge' description
>       @@ Commit message
>            The 'merge' command description for the todo list documentation in an
>            interactive rebase has multiple lines. The lines other than the first
>            one start with dots ('.') while the similar multi-line documentation for
>       -    'fixup' does not.
>       +    'fixup' does not. This description only appears in the comment text of
>       +    the todo file during an interactive rebase.
>        
>            The 'merge' command was documented when interactive rebase was first
>            ported to C in 145e05ac44b (rebase -i: rewrite append_todo_help() in C,
>    4:  6528a50343f =  5:  b2c09600918 sequencer: define array with enum values
>    5:  e95ad41d355 =  6:  fa7ecb718cf sequencer: add update-ref command
>    6:  918b398d6a2 !  7:  3ec2cc922f9 rebase: add --update-refs option
>       @@ Commit message
>            'update-ref' commands. Tests are added to ensure that these todo
>            commands are added in the correct locations.
>        
>       -    A future change will update the behavior to actually update the refs
>       -    at the end of the rebase sequence.
>       +    This change does _not_ include the actual behavior of tracking the
>       +    updated refs and writing the new ref values at the end of the rebase
>       +    process. That is deferred to a later change.
>        
>            Signed-off-by: Derrick Stolee <derrickstolee@github.com>
>        
>       @@ sequencer.c: static int skip_unnecessary_picks(struct repository *r,
>        +			item->command = TODO_UPDATE_REF;
>        +			strbuf_addf(ctx->buf, "%s\n", decoration->name);
>        +
>       -+			sti = string_list_append(&ctx->refs_to_oids,
>       ++			sti = string_list_insert(&ctx->refs_to_oids,
>        +						 decoration->name);
>        +			sti->util = oiddup(the_hash_algo->null_oid);
>        +		}
>       @@ t/t2407-worktree-heads.sh: test_expect_success 'refuse to overwrite when in erro
>        +		grep "update-ref refs/heads/allow-update" todo
>        +	)
>        +'
>       ++
>       ++# This must be the last test in this file
>       ++test_expect_success '$EDITOR and friends are unchanged' '
>       ++	test_editor_unchanged
>       ++'
>        +
>         test_done
>        
>    7:  72e0481b643 !  8:  fb5f64c5201 rebase: update refs from 'update-ref' commands
>       @@ Commit message
>            interactive rebase.
>        
>            Teach Git to record the HEAD position when reaching these 'update-ref'
>       -    commands. The ref/OID pair is stored in the
>       +    commands. The ref/before/after triple is stored in the
>            $GIT_DIR/rebase-merge/update-refs file. A previous change parsed this
>            file to avoid having other processes updating the refs in that file
>            while the rebase is in progress.
>       @@ Commit message
>            Not only do we update the file when the sequencer reaches these
>            'update-ref' commands, we then update the refs themselves at the end of
>            the rebase sequence. If the rebase is aborted before this final step,
>       -    then the refs are not updated.
>       +    then the refs are not updated. The 'before' value is used to ensure that
>       +    we do not accidentally obliterate a ref that was updated concurrently
>       +    (say, by an older version of Git or a third-party tool).
>       +
>       +    Now that the 'git rebase --update-refs' command is implemented to write
>       +    to the update-refs file, we can remove the fake construction of the
>       +    update-refs file from a test in t2407-worktree-heads.sh.
>        
>            Signed-off-by: Derrick Stolee <derrickstolee@github.com>
>        
>       @@ sequencer.c
>         
>         #define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"
>         
>       -@@ sequencer.c: static GIT_PATH_FUNC(rebase_path_squash_onto, "rebase-merge/squash-onto")
>       -  */
>       - static GIT_PATH_FUNC(rebase_path_refs_to_delete, "rebase-merge/refs-to-delete")
>       +@@ sequencer.c: struct update_ref_record {
>       + 	struct object_id after;
>       + };
>         
>       -+/*
>       -+ * The update-refs file stores a list of refs that will be updated at the end
>       -+ * of the rebase sequence. The 'update-ref <ref>' commands in the todo file
>       -+ * update the OIDs for the refs in this file, but the refs are not updated
>       -+ * until the end of the rebase sequence.
>       -+ */
>       -+static GIT_PATH_FUNC(rebase_path_update_refs, "rebase-merge/update-refs")
>       -+
>       - /*
>       -  * The following files are written by git-rebase just after parsing the
>       -  * command-line.
>       ++static struct update_ref_record *init_update_ref_record(const char *ref)
>       ++{
>       ++	struct update_ref_record *rec = xmalloc(sizeof(*rec));
>       ++
>       ++	oidcpy(&rec->before, null_oid());
>       ++	oidcpy(&rec->after, null_oid());
>       ++
>       ++	/* This may fail, but that's fine, we will keep the null OID. */
>       ++	read_ref(ref, &rec->before);
>       ++
>       ++	return rec;
>       ++}
>       ++
>       + static int git_sequencer_config(const char *k, const char *v, void *cb)
>       + {
>       + 	struct replay_opts *opts = cb;
>        @@ sequencer.c: leave_merge:
>         	return ret;
>         }
>         
>        -static int do_update_ref(struct repository *r, const char *ref_name)
>        +static int write_update_refs_state(struct string_list *refs_to_oids)
>       -+{
>       + {
>        +	int result = 0;
>       ++	struct lock_file lock = LOCK_INIT;
>        +	FILE *fp = NULL;
>        +	struct string_list_item *item;
>       -+	char *path = xstrdup(rebase_path_update_refs());
>       ++	char *path;
>       ++
>       ++	if (!refs_to_oids->nr)
>       ++		return 0;
>       ++
>       ++	path = rebase_path_update_refs(the_repository->gitdir);
>        +
>        +	if (safe_create_leading_directories(path)) {
>        +		result = error(_("unable to create leading directories of %s"),
>       @@ sequencer.c: leave_merge:
>        +		goto cleanup;
>        +	}
>        +
>       -+	fp = fopen(path, "w");
>       ++	if (hold_lock_file_for_update(&lock, path, 0) < 0) {
>       ++		result = error(_("another 'rebase' process appears to be running; "
>       ++				 "'%s.lock' already exists"),
>       ++			       path);
>       ++		goto cleanup;
>       ++	}
>       ++
>       ++	fp = fdopen_lock_file(&lock, "w");
>        +	if (!fp) {
>        +		result = error_errno(_("could not open '%s' for writing"), path);
>       ++		rollback_lock_file(&lock);
>        +		goto cleanup;
>        +	}
>        +
>       -+	for_each_string_list_item(item, refs_to_oids)
>       -+		fprintf(fp, "%s\n%s\n", item->string, oid_to_hex(item->util));
>       ++	for_each_string_list_item(item, refs_to_oids) {
>       ++		struct update_ref_record *rec = item->util;
>       ++		fprintf(fp, "%s\n%s\n%s\n", item->string,
>       ++			oid_to_hex(&rec->before), oid_to_hex(&rec->after));
>       ++	}
>       ++
>       ++	result = commit_lock_file(&lock);
>        +
>        +cleanup:
>       -+	if (fp)
>       -+		fclose(fp);
>       ++	free(path);
>        +	return result;
>        +}
>        +
>        +static int do_update_ref(struct repository *r, const char *refname)
>       - {
>       ++{
>        +	struct string_list_item *item;
>        +	struct string_list list = STRING_LIST_INIT_DUP;
>       -+	int found = 0;
>        +
>        +	sequencer_get_update_refs_state(r->gitdir, &list);
>        +
>        +	for_each_string_list_item(item, &list) {
>        +		if (!strcmp(item->string, refname)) {
>       -+			struct object_id oid;
>       -+			free(item->util);
>       -+			found = 1;
>       -+
>       -+			if (!read_ref("HEAD", &oid)) {
>       -+				item->util = oiddup(&oid);
>       -+				break;
>       -+			}
>       ++			struct update_ref_record *rec = item->util;
>       ++			read_ref("HEAD", &rec->after);
>       ++			break;
>        +		}
>        +	}
>        +
>       -+	if (!found) {
>       -+		struct object_id oid;
>       -+		item = string_list_append(&list, refname);
>       -+
>       -+		if (!read_ref("HEAD", &oid))
>       -+			item->util = oiddup(&oid);
>       -+		else
>       -+			item->util = oiddup(the_hash_algo->null_oid);
>       -+	}
>       -+
>        +	write_update_refs_state(&list);
>        +	string_list_clear(&list, 1);
>         	return 0;
>       @@ sequencer.c: leave_merge:
>        +	sequencer_get_update_refs_state(r->gitdir, &refs_to_oids);
>        +
>        +	for_each_string_list_item(item, &refs_to_oids) {
>       -+		struct object_id *oid_to = item->util;
>       -+		struct object_id oid_from;
>       ++		struct update_ref_record *rec = item->util;
>        +
>       -+		if (oideq(oid_to, the_hash_algo->null_oid)) {
>       ++		if (oideq(&rec->after, the_hash_algo->null_oid)) {
>        +			/*
>        +			 * Ref was not updated. User may have deleted the
>        +			 * 'update-ref' step.
>       @@ sequencer.c: leave_merge:
>        +			continue;
>        +		}
>        +
>       -+		if (read_ref(item->string, &oid_from)) {
>       -+			/*
>       -+			 * The ref does not exist. The user probably
>       -+			 * inserted a new 'update-ref' step with a new
>       -+			 * branch name.
>       -+			 */
>       -+			oidcpy(&oid_from, the_hash_algo->null_oid);
>       -+		}
>       -+
>        +		res |= refs_update_ref(refs, "rewritten during rebase",
>       -+				item->string,
>       -+				oid_to, &oid_from,
>       -+				0, UPDATE_REFS_MSG_ON_ERR);
>       ++				       item->string,
>       ++				       &rec->after, &rec->before,
>       ++				       0, UPDATE_REFS_MSG_ON_ERR);
>        +	}
>        +
>        +	string_list_clear(&refs_to_oids, 1);
>       @@ sequencer.c: cleanup_head_ref:
>         	/*
>         	 * Sequence of picks finished successfully; cleanup by
>         	 * removing the .git/sequencer directory
>       +@@ sequencer.c: static int add_decorations_to_list(const struct commit *commit,
>       +
>       + 			sti = string_list_insert(&ctx->refs_to_oids,
>       + 						 decoration->name);
>       +-			sti->util = oiddup(the_hash_algo->null_oid);
>       ++			sti->util = init_update_ref_record(decoration->name);
>       + 		}
>       +
>       + 		item->offset_in_buf = base_offset;
>        @@ sequencer.c: static int todo_list_add_update_ref_commands(struct todo_list *todo_list)
>         		}
>         	}
>       @@ sequencer.c: static int todo_list_add_update_ref_commands(struct todo_list *todo
>         	free(todo_list->items);
>         	todo_list->items = ctx.items;
>        
>       + ## t/t2407-worktree-heads.sh ##
>       +@@ t/t2407-worktree-heads.sh: test_expect_success !SANITIZE_LEAK 'refuse to overwrite: worktree in rebase (mer
>       + 	grep "cannot force update the branch '\''wt-2'\'' checked out at.*wt-2" err
>       + '
>       +
>       +-test_expect_success 'refuse to overwrite: worktree in rebase with --update-refs' '
>       +-	test_when_finished rm -rf .git/worktrees/wt-3/rebase-merge &&
>       +-
>       +-	mkdir -p .git/worktrees/wt-3/rebase-merge &&
>       +-	touch .git/worktrees/wt-3/rebase-merge/interactive &&
>       ++test_expect_success !SANITIZE_LEAK 'refuse to overwrite: worktree in rebase with --update-refs' '
>       ++	test_when_finished git -C wt-3 rebase --abort &&
>       +
>       +-	cat >.git/worktrees/wt-3/rebase-merge/update-refs <<-EOF &&
>       +-	refs/heads/fake-3
>       +-	$(git rev-parse HEAD~1)
>       +-	$(git rev-parse HEAD)
>       +-	refs/heads/fake-4
>       +-	$(git rev-parse HEAD)
>       +-	$(git rev-parse HEAD)
>       +-	EOF
>       ++	git branch -f can-be-updated wt-3 &&
>       ++	test_must_fail git -C wt-3 rebase --update-refs conflict-3 &&
>       +
>       + 	for i in 3 4
>       + 	do
>       +-		test_must_fail git branch -f fake-$i HEAD 2>err &&
>       +-		grep "cannot force update the branch '\''fake-$i'\'' checked out at.*wt-3" err ||
>       ++		test_must_fail git branch -f can-be-updated HEAD 2>err &&
>       ++		grep "cannot force update the branch '\''can-be-updated'\'' checked out at.*wt-3" err ||
>       + 			return 1
>       + 	done
>       + '
>       +
>         ## t/t3404-rebase-interactive.sh ##
>        @@ t/t3404-rebase-interactive.sh: test_expect_success '--update-refs adds commands with --rebase-merges' '
>         	)
>         '
>         
>       -+compare_two_refs () {
>       -+	git rev-parse $1 >expect &&
>       -+	git rev-parse $2 >actual &&
>       -+	test_cmp expect actual
>       -+}
>       -+
>        +test_expect_success '--update-refs updates refs correctly' '
>        +	git checkout -B update-refs no-conflict-branch &&
>        +	git branch -f base HEAD~4 &&
>       @@ t/t3404-rebase-interactive.sh: test_expect_success '--update-refs adds commands
>        +
>        +	git rebase -i --autosquash --update-refs primary &&
>        +
>       -+	compare_two_refs HEAD~3 refs/heads/first &&
>       -+	compare_two_refs HEAD~3 refs/heads/second &&
>       -+	compare_two_refs HEAD~1 refs/heads/third &&
>       -+	compare_two_refs HEAD refs/heads/no-conflict-branch
>       ++	test_cmp_rev HEAD~3 refs/heads/first &&
>       ++	test_cmp_rev HEAD~3 refs/heads/second &&
>       ++	test_cmp_rev HEAD~1 refs/heads/third &&
>       ++	test_cmp_rev HEAD refs/heads/no-conflict-branch
>        +'
>        +
>         # This must be the last test in this file
>    -:  ----------- >  9:  29c7c76805a sequencer: rewrite update-refs as user edits todo list
>    8:  d2cfdbfc431 = 10:  c0022d07579 rebase: add rebase.updateRefs config option
>    -:  ----------- > 11:  d53b4ff2cee sequencer: ignore HEAD ref under --update-refs
>    -:  ----------- > 12:  d5cd4b49e46 sequencer: notify user of --update-refs activity
>