[PATCHv3 0/2] Fix spurious conflicts with pull --rebase

[PATCHv3 0/2] Fix spurious conflicts with pull --rebase

[Elijah Newren]

This patch series fixes spurious conflict issues with git pull
--rebase for the case where the upstream repository is *not* rebased.
(There is no change in the case where the upstream repository is
rebased.)

In c85c79279d and d44e71261f, the call to git-rebase was modified in
an effort to reduce the number of commits being reapplied, by trying
to avoid commits that upstream already had or has.  It was
specifically designed with an upstream that is rebased in mind.
Unfortunately, it had two side effects for the non-rebased upstream
case: (1) it prevented detecting if "local" patches are already
upstream, and (2) it could in some cases cause more patches known to
be upstream to be reapplied rather than less.  This series fixes both
of these issues for the non-rebased upstream case.  See the commit
message of the second patch for details.

It's worth noting that issue (1) above also affects the case where the
upstream repository has been rebased, which this patch series does not
address.  As far as I can tell, fixing it would require changes
(including new syntax) to format-patch to allow it to be told what
'upstream' is, and some changes to git-pull.sh/git-rebase.sh to pass
it this information.

Changes since the last series:
  * Address issues in t5520-pull.sh raised by Ævar Arnfjörð Bjarmason

Elijah Newren (2):
  t5520-pull: Add testcases showing spurious conflicts from git pull
    --rebase
  pull --rebase: Avoid spurious conflicts and reapplying unnecessary
    patches

 git-pull.sh     |   34 +++++++++++++++++++----------
 t/t5520-pull.sh |   63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 85 insertions(+), 12 deletions(-)

-- 
1.7.2.1

[PATCHv3 1/2] t5520-pull: Add testcases showing spurious conflicts from git pull --rebase

[Elijah Newren]

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 t/t5520-pull.sh |   63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 63 insertions(+), 0 deletions(-)

diff --git a/t/t5520-pull.sh b/t/t5520-pull.sh
index 319e389..9099e55 100755
--- a/t/t5520-pull.sh
+++ b/t/t5520-pull.sh
@@ -4,6 +4,11 @@ test_description='pulling into void'
 
 . ./test-lib.sh
 
+modify () {
+	sed -e "$1" < "$2" > "$2".x &&
+	mv "$2".x "$2"
+}
+
 D=`pwd`
 
 test_expect_success setup '
@@ -160,4 +165,62 @@ test_expect_success 'pull --rebase works on branch yet to be born' '
 	test_cmp expect actual
 '
 
+test_expect_success 'setup for detecting upstreamed changes' '
+	mkdir src &&
+	(cd src &&
+	 git init &&
+	 for i in $(seq 1 10); do echo $i; done > stuff &&
+	 git add stuff &&
+	 git commit -m "Initial revision"
+	) &&
+	git clone src dst &&
+	(cd src &&
+	 modify s/5/43/ stuff &&
+	 git commit -a -m "5->43" &&
+	 modify s/6/42/ stuff &&
+	 git commit -a -m "Make it bigger" &&
+	 correct=$(git rev-parse HEAD)
+	) &&
+	(cd dst &&
+	 modify s/5/43/ stuff &&
+	 git commit -a -m "Independent discovery of 5->43"
+	)
+'
+
+test_expect_failure 'git pull --rebase detects upstreamed changes' '
+	(cd dst &&
+	 git pull --rebase &&
+	 test -z "$(git ls-files -u)"
+	)
+'
+
+test_expect_success 'setup for avoiding reapplying old patches' '
+	(cd dst &&
+	 git rebase --abort;
+	 git reset --hard origin/master
+	) &&
+	git clone --bare src src-replace.git &&
+	rm -rf src &&
+	mv src-replace.git src &&
+	(cd dst &&
+	 modify s/2/22/ stuff &&
+	 git commit -a -m "Change 2" &&
+	 modify s/3/33/ stuff &&
+	 git commit -a -m "Change 3" &&
+	 modify s/4/44/ stuff &&
+	 git commit -a -m "Change 4" &&
+	 git push &&
+
+	 modify s/44/55/ stuff &&
+	 git commit --amend -a -m "Modified Change 4"
+	)
+'
+
+test_expect_failure 'git pull --rebase does not reapply old patches' '
+	(cd dst &&
+	 git pull --rebase;
+	 test 1 = $(find .git/rebase-apply -name "000*" | wc -l)
+	)
+'
+
 test_done
-- 
1.7.2.1

Re: [PATCHv3 1/2] t5520-pull: Add testcases showing spurious conflicts from git pull --rebase

[Elijah Newren]

On Sun, Aug 8, 2010 at 2:55 PM, Elijah Newren <newren@gmail.com> wrote:
>
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>  t/t5520-pull.sh |   63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 63 insertions(+), 0 deletions(-)
>
> diff --git a/t/t5520-pull.sh b/t/t5520-pull.sh
> index 319e389..9099e55 100755
> --- a/t/t5520-pull.sh
> +++ b/t/t5520-pull.sh
> @@ -4,6 +4,11 @@ test_description='pulling into void'
>
>  . ./test-lib.sh
>
> +modify () {
> +       sed -e "$1" < "$2" > "$2".x &&
> +       mv "$2".x "$2"
> +}
> +
>  D=`pwd`
>
>  test_expect_success setup '
> @@ -160,4 +165,62 @@ test_expect_success 'pull --rebase works on branch yet to be born' '
>        test_cmp expect actual
>  '
>
> +test_expect_success 'setup for detecting upstreamed changes' '
> +       mkdir src &&
> +       (cd src &&
> +        git init &&
> +        for i in $(seq 1 10); do echo $i; done > stuff &&
> +        git add stuff &&
> +        git commit -m "Initial revision"
> +       ) &&
> +       git clone src dst &&
> +       (cd src &&
> +        modify s/5/43/ stuff &&
> +        git commit -a -m "5->43" &&
> +        modify s/6/42/ stuff &&
> +        git commit -a -m "Make it bigger" &&
> +        correct=$(git rev-parse HEAD)
> +       ) &&
> +       (cd dst &&
> +        modify s/5/43/ stuff &&
> +        git commit -a -m "Independent discovery of 5->43"
> +       )
> +'
> +
> +test_expect_failure 'git pull --rebase detects upstreamed changes' '
> +       (cd dst &&
> +        git pull --rebase &&
> +        test -z "$(git ls-files -u)"
> +       )
> +'
> +
> +test_expect_success 'setup for avoiding reapplying old patches' '
> +       (cd dst &&
> +        git rebase --abort;
> +        git reset --hard origin/master
> +       ) &&
> +       git clone --bare src src-replace.git &&
> +       rm -rf src &&
> +       mv src-replace.git src &&
> +       (cd dst &&
> +        modify s/2/22/ stuff &&
> +        git commit -a -m "Change 2" &&
> +        modify s/3/33/ stuff &&
> +        git commit -a -m "Change 3" &&
> +        modify s/4/44/ stuff &&
> +        git commit -a -m "Change 4" &&
> +        git push &&
> +
> +        modify s/44/55/ stuff &&
> +        git commit --amend -a -m "Modified Change 4"
> +       )
> +'
> +
> +test_expect_failure 'git pull --rebase does not reapply old patches' '
> +       (cd dst &&
> +        git pull --rebase;
> +        test 1 = $(find .git/rebase-apply -name "000*" | wc -l)
> +       )
> +'
> +
>  test_done
> --

Interdiff addressing Hannes' comments (given on previous series):

diff -u b/t/t5520-pull.sh b/t/t5520-pull.sh
--- b/t/t5520-pull.sh
+++ b/t/t5520-pull.sh
@@ -169,7 +169,7 @@
 	mkdir src &&
 	(cd src &&
 	 git init &&
-	 for i in $(seq 1 10); do echo $i; done > stuff &&
+	 printf "1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n" > stuff &&
 	 git add stuff &&
 	 git commit -m "Initial revision"
 	) &&
@@ -178,8 +178,7 @@
 	 modify s/5/43/ stuff &&
 	 git commit -a -m "5->43" &&
 	 modify s/6/42/ stuff &&
-	 git commit -a -m "Make it bigger" &&
-	 correct=$(git rev-parse HEAD)
+	 git commit -a -m "Make it bigger"
 	) &&
 	(cd dst &&
 	 modify s/5/43/ stuff &&
@@ -196,7 +195,7 @@

 test_expect_success 'setup for avoiding reapplying old patches' '
 	(cd dst &&
-	 git rebase --abort;
+	 test_might_fail git rebase --abort &&
 	 git reset --hard origin/master
 	) &&
 	git clone --bare src src-replace.git &&
@@ -218,7 +217,7 @@

 test_expect_failure 'git pull --rebase does not reapply old patches' '
 	(cd dst &&
-	 git pull --rebase;
+	 test_must_fail git pull --rebase &&
 	 test 1 = $(find .git/rebase-apply -name "000*" | wc -l)
 	)
 '

Re: [PATCHv3 1/2] t5520-pull: Add testcases showing spurious conflicts from git pull --rebase

[Junio C Hamano]

Elijah Newren <newren@gmail.com> writes:

> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>  t/t5520-pull.sh |   63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 63 insertions(+), 0 deletions(-)
>
> diff --git a/t/t5520-pull.sh b/t/t5520-pull.sh
> index 319e389..9099e55 100755
> --- a/t/t5520-pull.sh
> +++ b/t/t5520-pull.sh
> @@ -4,6 +4,11 @@ test_description='pulling into void'
>  
>  . ./test-lib.sh
>  
> +modify () {
> +	sed -e "$1" < "$2" > "$2".x &&
> +	mv "$2".x "$2"
> +}

Just a style thing but I'd prefer to see the above written like this:

        modify () {
                sed -e "$1" <"$2" >"$2.x" &&
                mv "$2.x" "$2"
        }

> +test_expect_success 'setup for avoiding reapplying old patches' '
> +	(cd dst &&
> +	 git rebase --abort;

This may be hypothetical but this discards error condition from failing to
ch into dst (for whatever reason).  Don't we expect "git rebase --abort"
to exit with a non-zero status?  Same comment for the last one in the
patch below.

> +test_expect_failure 'git pull --rebase does not reapply old patches' '
> +	(cd dst &&
> +	 git pull --rebase;
> +	 test 1 = $(find .git/rebase-apply -name "000*" | wc -l)
> +	)
> +'
> +
>  test_done

Thanks.

Re: [PATCHv3 1/2] t5520-pull: Add testcases showing spurious conflicts from git pull --rebase

[Elijah Newren]

On Mon, Aug 9, 2010 at 1:09 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Elijah Newren <newren@gmail.com> writes:
<snip>
>> +modify () {
>> +     sed -e "$1" < "$2" > "$2".x &&
>> +     mv "$2".x "$2"
>> +}
>
> Just a style thing but I'd prefer to see the above written like this:
>
>        modify () {
>                sed -e "$1" <"$2" >"$2.x" &&
>                mv "$2.x" "$2"
>        }

I copied this function verbatim from t/t4127-apply-same-fn.sh.  Would
you like me to fix that one too?

>> +test_expect_success 'setup for avoiding reapplying old patches' '
>> +     (cd dst &&
>> +      git rebase --abort;
>
> This may be hypothetical but this discards error condition from failing to
> ch into dst (for whatever reason).  Don't we expect "git rebase --abort"
> to exit with a non-zero status?  Same comment for the last one in the
> patch below.

Yes, Hannes pointed out the same issue.  Does the follow-up interdiff
I posted in response to my patch address this in a way you'd like?

Re: [PATCHv3 1/2] t5520-pull: Add testcases showing spurious conflicts from git pull --rebase

[Ævar Arnfjörð Bjarmason]

On Mon, Aug 9, 2010 at 19:22, Elijah Newren <newren@gmail.com> wrote:
> On Mon, Aug 9, 2010 at 1:09 PM, Junio C Hamano <gitster@pobox.com> wrote:
>> Elijah Newren <newren@gmail.com> writes:
> <snip>
>>> +modify () {
>>> +     sed -e "$1" < "$2" > "$2".x &&
>>> +     mv "$2".x "$2"
>>> +}
>>
>> Just a style thing but I'd prefer to see the above written like this:
>>
>>        modify () {
>>                sed -e "$1" <"$2" >"$2.x" &&
>>                mv "$2.x" "$2"
>>        }
>
> I copied this function verbatim from t/t4127-apply-same-fn.sh.  Would
> you like me to fix that one too?

Rather than copy-paste this around we should just turn it into a
utility function.

It'd be very useful (if you're up to it) to just use sed in this
patch, then submit another patch to include the modify() function in
the test-lib.sh (and document it in t/README).

These could also use a modify():

    cd t && grep -A1 sed  *sh | grep -B1 mv | less

[PATCHv3 2/2] pull --rebase: Avoid spurious conflicts and reapplying unnecessary patches

[Elijah Newren]

Prior to c85c79279df2c8a583d95449d1029baba41f8660, pull --rebase would run
  git rebase $merge_head
which resulted in a call to
  git format-patch ... --ignore-if-in-upstream $merge_head..$cur_branch

This resulted in patches from $merge_head..$cur_branch being applied, as
long as they did not already exist in $cur_branch..$merge_head.
Unfortunately, when upstream is rebased, $merge_head..$cur_branch also
refers to "old" commits that have already been rebased upstream, meaning
that many patches that were already fixed upstream would be reapplied.
This could result in many spurious conflicts, as well as reintroduce
patches that were intentionally dropped upstream.

So the algorithm was changed in c85c79279df2c8a583d95449d1029baba41f8660
and d44e71261f91d3cc81293e0976bb40daa8abb583.  Defining $old_remote_ref to
be the most recent entry in the reflog for @{upstream} that is an ancestor
of $cur_branch, pull --rebase was changed to run
  git rebase --onto $merge_head $old_remote_ref
which results in a call to
  git format-patch ... --ignore-if-in-upstream $old_remote_ref..$cur_branch

The whole point of this change was to reduce the number of commits being
reapplied, by avoiding commits that upstream already has or had.

In the rebased upstream case, this change achieved that purpose.  It is
worth noting, though, that since $old_remote_ref is always an ancestor of
$cur_branch (by its definition), format-patch will not know what upstream
is and thus will not be able to determine if any patches are already
upstream; they will all be reapplied.

In the non-rebased upstream case, this new form is usually the same as the
original code but in some cases $old_remote_ref can be an ancestor of
   $(git merge-base $merge_head $cur_branch)
meaning that instead of avoiding reapplying commits that upstream already
has, it actually includes more such commits.  Combined with the fact that
format-patch can no longer detect commits that are already upstream (since
it is no longer told what upstream is), results in lots of confusion for
users (e.g. "git is giving me lots of conflicts in stuff I didn't even
change since my last push.")

Fix the non-rebased upstream case by ignoring $old_remote_ref whenever it
is contained in $(git merge-base $merge_head $cur_branch).  This should
have no affect on the rebased upstream case.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
Note that 24 lines of the patch are simply due to moving 12 lines; I
considered leaving those 12 lines where they were, but it'd split the
code that handles the setting of oldremoteref, which I thought should
be together.  I couldn't place the new code earlier, because it
depends on the definition of $merge_head.  I'd be happy to reshuffle
differently if anyone has any strong preferences.

 git-pull.sh     |   34 ++++++++++++++++++++++------------
 t/t5520-pull.sh |    4 ++--
 2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/git-pull.sh b/git-pull.sh
index a09a44e..54da07b 100755
--- a/git-pull.sh
+++ b/git-pull.sh
@@ -206,18 +206,6 @@ test true = "$rebase" && {
 		git diff-index --ignore-submodules --cached --quiet HEAD -- ||
 		die "refusing to pull with rebase: your working tree is not up-to-date"
 	fi
-	oldremoteref= &&
-	. git-parse-remote &&
-	remoteref="$(get_remote_merge_branch "$@" 2>/dev/null)" &&
-	oldremoteref="$(git rev-parse -q --verify "$remoteref")" &&
-	for reflog in $(git rev-list -g $remoteref 2>/dev/null)
-	do
-		if test "$reflog" = "$(git merge-base $reflog $curr_branch)"
-		then
-			oldremoteref="$reflog"
-			break
-		fi
-	done
 }
 orig_head=$(git rev-parse -q --verify HEAD)
 git fetch $verbosity $progress $dry_run --update-head-ok "$@" || exit 1
@@ -273,6 +261,28 @@ then
 	exit
 fi
 
+if test true = "$rebase"
+then
+	oldremoteref= &&
+	. git-parse-remote &&
+	remoteref="$(get_remote_merge_branch "$@" 2>/dev/null)" &&
+	oldremoteref="$(git rev-parse -q --verify "$remoteref")" &&
+	for reflog in $(git rev-list -g $remoteref 2>/dev/null)
+	do
+		if test "$reflog" = "$(git merge-base $reflog $curr_branch)"
+		then
+			oldremoteref="$reflog"
+			break
+		fi
+	done
+
+	o=$(git show-branch --merge-base $curr_branch $merge_head $oldremoteref)
+	if test "$oldremoteref" = "$o"
+	then
+		unset oldremoteref
+	fi
+fi
+
 merge_name=$(git fmt-merge-msg $log_arg <"$GIT_DIR/FETCH_HEAD") || exit
 case "$rebase" in
 true)
diff --git a/t/t5520-pull.sh b/t/t5520-pull.sh
index 9099e55..0e5d097 100755
--- a/t/t5520-pull.sh
+++ b/t/t5520-pull.sh
@@ -187,7 +187,7 @@ test_expect_success 'setup for detecting upstreamed changes' '
 	)
 '
 
-test_expect_failure 'git pull --rebase detects upstreamed changes' '
+test_expect_success 'git pull --rebase detects upstreamed changes' '
 	(cd dst &&
 	 git pull --rebase &&
 	 test -z "$(git ls-files -u)"
@@ -216,7 +216,7 @@ test_expect_success 'setup for avoiding reapplying old patches' '
 	)
 '
 
-test_expect_failure 'git pull --rebase does not reapply old patches' '
+test_expect_success 'git pull --rebase does not reapply old patches' '
 	(cd dst &&
 	 git pull --rebase;
 	 test 1 = $(find .git/rebase-apply -name "000*" | wc -l)
-- 
1.7.2.1