rebase -r: some merge related fixes

This is a collection of merge related fixes for rebase -r

* Make merge -c behave like reword.
* When fast-forwarding a merge don't leave .git/MERGE_MSG around (reported by Gábor)
* Make merge -c work when with --strategy

Phillip Wood (4):
rebase -r: make 'merge -c' behave like reword rebase -i: Add another reword test
rebase -r: don't write .git/MERGE_MSG when fast-forwarding rebase -r: fix merge -c with a merge strategy

 sequencer.c                   | 106 ++++++++++++++++++----------------
 t/lib-rebase.sh               |  56 ++++++++++++++++++
 t/t3404-rebase-interactive.sh |  13 +++++
 t/t3430-rebase-merges.sh      |  38 +++++++++---
 4 files changed, 155 insertions(+), 58 deletions(-)

base-commit: 66262451ec94d30ac4b80eb3123549cf7a788afd
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1015%2Fphillipwood%2Fwip%2Fsequencer-merge-c-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1015/phillipwood/wip/sequencer-merge-c-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1015
--
gitgitgadget

From: Phillip Wood <[email protected]>

When fast-forwarding we do not create a new commit so .git/MERGE_MSG is not removed and can end up seeding the message of a commit made after the rebase has finished. Avoid writing .git/MERGE_MSG when we are fast-forwarding by writing the file after the fast-forward checks.

Note that the way this change is implemented means we no longer write the author script when fast-forwarding either. I believe this is safe for the reasons below but it is a departure from what we do when fast-forwarding a non-merge commit. If we reword the merge then 'git commit --amend' will keep the authorship of the commit we're rewording as it ignores GIT_AUTHOR_* unless --reset-author is passed. It will also export the correct GIT_AUTHOR_* variables to any hooks and we already test the authorship of the reworded commit. If we are not rewording then we no longer call spilt_ident() which means we are no longer checking the commit author header looks sane. However this is what we already do when fast-forwarding non-merge commits in skip_unnecessary_picks() so I don't think we're breaking any promises by not checking the author here.

Reported-by SZEDER Gábor <[email protected]>

Signed-off-by Phillip Wood <[email protected]>

---
 sequencer.c     | 81 +++++++++++++++++++++++++------------------------
 t/lib-rebase.sh | 10 ++++--
 2 files changed, 49 insertions(+), 42 deletions(-)

sequencer.c +41 -40

index cc8a361cceb..c2cba5ed4b1 100644
@@ -983,7 +983,8 @@ static int run_git_commit(const char *defmsg,
 
 	cmd.git_cmd = 1;
 
-	if (is_rebase_i(opts) && read_env_script(&cmd.env_array)) {
+	if (is_rebase_i(opts) && !(!defmsg && (flags & AMEND_MSG)) &&
+	    read_env_script(&cmd.env_array)) {
 		const char *gpg_opt = gpg_sign_opt_quoted(opts);
 
 		return error(_(staged_changes_advice),

@@ -3815,6 +3816,45 @@ static int do_merge(struct repository *r,
 		goto leave_merge;
 	}
 
+	/*
+	 * If HEAD is not identical to the first parent of the original merge
+	 * commit, we cannot fast-forward.
+	 */
+	can_fast_forward = opts->allow_ff && commit && commit->parents &&
+		oideq(&commit->parents->item->object.oid,
+		      &head_commit->object.oid);
+
+	/*
+	 * If any merge head is different from the original one, we cannot
+	 * fast-forward.
+	 */
+	if (can_fast_forward) {
+		struct commit_list *p = commit->parents->next;
+
+		for (j = to_merge; j && p; j = j->next, p = p->next)
+			if (!oideq(&j->item->object.oid,
+				   &p->item->object.oid)) {
+				can_fast_forward = 0;
+				break;
+			}
+		/*
+		 * If the number of merge heads differs from the original merge
+		 * commit, we cannot fast-forward.
+		 */
+		if (j || p)
+			can_fast_forward = 0;
+	}
+
+	if (can_fast_forward) {
+		rollback_lock_file(&lock);
+		ret = fast_forward_to(r, &commit->object.oid,
+				      &head_commit->object.oid, 0, opts);
+		if (flags & TODO_EDIT_MERGE_MSG)
+			goto fast_forward_edit;
+
+		goto leave_merge;
+	}
+
 	if (commit) {
 		const char *encoding = get_commit_output_encoding();
 		const char *message = logmsg_reencode(commit, NULL, encoding);

@@ -3864,45 +3904,6 @@ static int do_merge(struct repository *r,
 		}
 	}
 
-	/*
-	 * If HEAD is not identical to the first parent of the original merge
-	 * commit, we cannot fast-forward.
-	 */
-	can_fast_forward = opts->allow_ff && commit && commit->parents &&
-		oideq(&commit->parents->item->object.oid,
-		      &head_commit->object.oid);
-
-	/*
-	 * If any merge head is different from the original one, we cannot
-	 * fast-forward.
-	 */
-	if (can_fast_forward) {
-		struct commit_list *p = commit->parents->next;
-
-		for (j = to_merge; j && p; j = j->next, p = p->next)
-			if (!oideq(&j->item->object.oid,
-				   &p->item->object.oid)) {
-				can_fast_forward = 0;
-				break;
-			}
-		/*
-		 * If the number of merge heads differs from the original merge
-		 * commit, we cannot fast-forward.
-		 */
-		if (j || p)
-			can_fast_forward = 0;
-	}
-
-	if (can_fast_forward) {
-		rollback_lock_file(&lock);
-		ret = fast_forward_to(r, &commit->object.oid,
-				      &head_commit->object.oid, 0, opts);
-		if (flags & TODO_EDIT_MERGE_MSG)
-			goto fast_forward_edit;
-
-		goto leave_merge;
-	}
-
 	if (strategy || to_merge->next) {
 		/* Octopus merge */
 		struct child_process cmd = CHILD_PROCESS_INIT;

t/lib-rebase.sh +8 -2

index 99d9e7efd2d..ec6b9b107da 100644
@@ -173,10 +173,16 @@ set_reword_editor () {
 
 	write_script reword-editor.sh <<-EOF &&
 	# Save the oid of the first reworded commit so we can check rebase
-	# fast-forwards to it
+	# fast-forwards to it. Also check that we do not write .git/MERGE_MSG
+	# when fast-forwarding
 	if ! test -s reword-oid
 	then
-		git rev-parse HEAD >reword-oid
+		git rev-parse HEAD >reword-oid &&
+		if test -f .git/MERGE_MSG
+		then
+			echo 1>&2 "error: .git/MERGE_MSG exists"
+			exit 1
+		fi
 	fi &&
 	# There should be no uncommited changes
 	git diff --exit-code HEAD &&

Signature · 1 line

gitgitgadget

Hi Phillip,

Quoted 7 lines · Phillip Wood via GitGitGadget

This is a collection of merge related fixes for rebase -r

* Make merge -c behave like reword.
* When fast-forwarding a merge don't leave .git/MERGE_MSG around (reported by Gábor)
* Make merge -c work when with --strategy

Quoted 5 lines

Phillip Wood (4):
rebase -r: make 'merge -c' behave like reword rebase -i: Add another reword test
rebase -r: don't write .git/MERGE_MSG when fast-forwarding rebase -r: fix merge -c with a merge strategy

I reviewed all four patches (the first one took the most time, obviously) and it was quite the pleasant read. I am in favor of integrating them as-are.

Thank you,
Dscho

Quoted 15 lines

  sequencer.c                   | 106 ++++++++++++++++++----------------
  t/lib-rebase.sh               |  56 ++++++++++++++++++
  t/t3404-rebase-interactive.sh |  13 +++++
  t/t3430-rebase-merges.sh      |  38 +++++++++---
  4 files changed, 155 insertions(+), 58 deletions(-)

base-commit: 66262451ec94d30ac4b80eb3123549cf7a788afd
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1015%2Fphillipwood%2Fwip%2Fsequencer-merge-c-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1015/phillipwood/wip/sequencer-merge-c-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1015
--
gitgitgadget

Quoted 8 lines · Phillip Wood via GitGitGadget

From: Phillip Wood <[email protected]>

When fast-forwarding we do not create a new commit so .git/MERGE_MSG is not removed and can end up seeding the message of a commit made after the rebase has finished. Avoid writing .git/MERGE_MSG when we are fast-forwarding by writing the file after the fast-forward checks.

Quoted 13 lines

Note that the way this change is implemented means we no longer write the author script when fast-forwarding either. I believe this is safe for the reasons below but it is a departure from what we do when fast-forwarding a non-merge commit. If we reword the merge then 'git commit --amend' will keep the authorship of the commit we're rewording as it ignores GIT_AUTHOR_* unless --reset-author is passed. It will also export the correct GIT_AUTHOR_* variables to any hooks and we already test the authorship of the reworded commit. If we are not rewording then we no longer call spilt_ident() which means we are no longer checking the commit author header looks sane. However this is what we already do when fast-forwarding non-merge commits in skip_unnecessary_picks() so I don't think we're breaking any promises by not checking the author here.

Thanks you for fixing this bug.

FWIW (not that much, I'm afraid), I think your reasoning about the harmlessness of the behavior change concerning the author script makes sense.

My only nit is that the movement of a ~40 lines block of code makes out the bulk of the patch; perhaps it would be worth mentioning it explicitly in the commit message, so future readers of this commit won't look for changes in those hunks.

Quoted 139 lines

Reported-by SZEDER Gábor <[email protected]>

Signed-off-by Phillip Wood <[email protected]>

---
  sequencer.c     | 81 +++++++++++++++++++++++++------------------------
  t/lib-rebase.sh | 10 ++++--
  2 files changed, 49 insertions(+), 42 deletions(-)

sequencer.c +41 -40

index cc8a361cceb..c2cba5ed4b1 100644
@@ -983,7 +983,8 @@ static int run_git_commit(const char *defmsg,
 
  	cmd.git_cmd = 1;
 
-	if (is_rebase_i(opts) && read_env_script(&cmd.env_array)) {
+	if (is_rebase_i(opts) && !(!defmsg && (flags & AMEND_MSG)) &&
+	    read_env_script(&cmd.env_array)) {
  		const char *gpg_opt = gpg_sign_opt_quoted(opts);
 
  		return error(_(staged_changes_advice),

@@ -3815,6 +3816,45 @@ static int do_merge(struct repository *r,
  		goto leave_merge;
  	}
 
+	/*
+	 * If HEAD is not identical to the first parent of the original merge
+	 * commit, we cannot fast-forward.
+	 */
+	can_fast_forward = opts->allow_ff && commit && commit->parents &&
+		oideq(&commit->parents->item->object.oid,
+		      &head_commit->object.oid);
+
+	/*
+	 * If any merge head is different from the original one, we cannot
+	 * fast-forward.
+	 */
+	if (can_fast_forward) {
+		struct commit_list *p = commit->parents->next;
+
+		for (j = to_merge; j && p; j = j->next, p = p->next)
+			if (!oideq(&j->item->object.oid,
+				   &p->item->object.oid)) {
+				can_fast_forward = 0;
+				break;
+			}
+		/*
+		 * If the number of merge heads differs from the original merge
+		 * commit, we cannot fast-forward.
+		 */
+		if (j || p)
+			can_fast_forward = 0;
+	}
+
+	if (can_fast_forward) {
+		rollback_lock_file(&lock);
+		ret = fast_forward_to(r, &commit->object.oid,
+				      &head_commit->object.oid, 0, opts);
+		if (flags & TODO_EDIT_MERGE_MSG)
+			goto fast_forward_edit;
+
+		goto leave_merge;
+	}
+
  	if (commit) {
  		const char *encoding = get_commit_output_encoding();
  		const char *message = logmsg_reencode(commit, NULL, encoding);

@@ -3864,45 +3904,6 @@ static int do_merge(struct repository *r,
  		}
  	}
 
-	/*
-	 * If HEAD is not identical to the first parent of the original merge
-	 * commit, we cannot fast-forward.
-	 */
-	can_fast_forward = opts->allow_ff && commit && commit->parents &&
-		oideq(&commit->parents->item->object.oid,
-		      &head_commit->object.oid);
-
-	/*
-	 * If any merge head is different from the original one, we cannot
-	 * fast-forward.
-	 */
-	if (can_fast_forward) {
-		struct commit_list *p = commit->parents->next;
-
-		for (j = to_merge; j && p; j = j->next, p = p->next)
-			if (!oideq(&j->item->object.oid,
-				   &p->item->object.oid)) {
-				can_fast_forward = 0;
-				break;
-			}
-		/*
-		 * If the number of merge heads differs from the original merge
-		 * commit, we cannot fast-forward.
-		 */
-		if (j || p)
-			can_fast_forward = 0;
-	}
-
-	if (can_fast_forward) {
-		rollback_lock_file(&lock);
-		ret = fast_forward_to(r, &commit->object.oid,
-				      &head_commit->object.oid, 0, opts);
-		if (flags & TODO_EDIT_MERGE_MSG)
-			goto fast_forward_edit;
-
-		goto leave_merge;
-	}
-
  	if (strategy || to_merge->next) {
  		/* Octopus merge */
  		struct child_process cmd = CHILD_PROCESS_INIT;

t/lib-rebase.sh +8 -2

index 99d9e7efd2d..ec6b9b107da 100644
@@ -173,10 +173,16 @@ set_reword_editor () {
 
  	write_script reword-editor.sh <<-EOF &&
  	# Save the oid of the first reworded commit so we can check rebase
-	# fast-forwards to it
+	# fast-forwards to it. Also check that we do not write .git/MERGE_MSG
+	# when fast-forwarding
  	if ! test -s reword-oid
  	then
-		git rev-parse HEAD >reword-oid
+		git rev-parse HEAD >reword-oid &&
+		if test -f .git/MERGE_MSG
+		then
+			echo 1>&2 "error: .git/MERGE_MSG exists"
+			exit 1
+		fi
  	fi &&
  	# There should be no uncommited changes
  	git diff --exit-code HEAD &&

Signature · 1 line

gitgitgadget

Thanks for the feedback on V1. I have added a sentence to the commit message of the third patch to make it clear that the fast-forward code is just moved, not changed

Cover letter from V1: This is a collection of merge related fixes for rebase -r

* Make merge -c behave like reword.
* When fast-forwarding a merge don't leave .git/MERGE_MSG around (reported by Gábor)
* Make merge -c work when with --strategy

Phillip Wood (4):
rebase -r: make 'merge -c' behave like reword rebase -i: Add another reword test
rebase -r: don't write .git/MERGE_MSG when fast-forwarding rebase -r: fix merge -c with a merge strategy

 sequencer.c                   | 106 ++++++++++++++++++----------------
 t/lib-rebase.sh               |  56 ++++++++++++++++++
 t/t3404-rebase-interactive.sh |  13 +++++
 t/t3430-rebase-merges.sh      |  38 +++++++++---
 4 files changed, 155 insertions(+), 58 deletions(-)

base-commit: 66262451ec94d30ac4b80eb3123549cf7a788afd
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1015%2Fphillipwood%2Fwip%2Fsequencer-merge-c-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1015/phillipwood/wip/sequencer-merge-c-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1015

Range-diff vs v1:

 1:  b514dbdf928 = 1:  b514dbdf928 rebase -r: make 'merge -c' behave like reword
 2:  511cf9204ad = 2:  511cf9204ad rebase -i: Add another reword test
 3:  01d5ed4cba0 ! 3:  080e580e11c rebase -r: don't write .git/MERGE_MSG when fast-forwarding

@@ Commit message
is not removed and can end up seeding the message of a commit made after the rebase has finished. Avoid writing .git/MERGE_MSG when we are fast-forwarding by writing the file after the fast-forward
- checks.
+ checks. Note that there are no changes to the fast-forward code, it is
+ simply moved.

Note that the way this change is implemented means we no longer write the author script when fast-forwarding either. I believe this is safe
4: f2a2e3531a1 = 4: b6981ea5439 rebase -r: fix merge -c with a merge strategy

--
gitgitgadget