rebase -i: reword empty commit after fast-forward

From: Phillip Wood <[email protected]>

When rebase rewords a commit it picks the commit and then runs "git commit --amend" to reword it. When the commit is picked the sequencer tries to reuse existing commits by fast-forwarding if the parents are unchanged. Rewording an empty commit that has been fast-forwarded fails because "git commit --amend" is called without "--allow-empty". This happens because when a commit is fast-forwarded the logic that checks whether we should pass "--allow-empty" is skipped. Fix this by always passing "--allow-empty" when rewording a commit. This is safe because we are amending a commit that has already been picked so if it had become empty when it was picked we'd have already returned an error.

As "git commit" will happily create empty merge commits without "--allow-empty" we do not need to pass that flag when rewording merge commits.

---
rebase -i: reword empty commit after fast-forward

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1860%2Fphillipwood%2Frebase-reword-empty-commit-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1860/phillipwood/rebase-reword-empty-commit-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1860

 sequencer.c                   |  5 ++---
 t/t3404-rebase-interactive.sh | 14 ++++++++++++++
 t/t3430-rebase-merges.sh      | 20 ++++++++++++++++++++
 3 files changed, 36 insertions(+), 3 deletions(-)

index 407ee4e90fe..763bef1c898 100644
@@ -2510,9 +2510,8 @@ static int do_pick_commit(struct repository *r,
 		*check_todo = !!(flags & EDIT_MSG);
 		if (!res && reword) {
 fast_forward_edit:
-			res = run_git_commit(NULL, opts, EDIT_MSG |
-					     VERIFY_MSG | AMEND_MSG |
-					     (flags & ALLOW_EMPTY));
+			flags = EDIT_MSG | VERIFY_MSG | AMEND_MSG | ALLOW_EMPTY;
+			res = run_git_commit(NULL, opts, flags);
 			*check_todo = 1;
 		}
 	}

index ecfc02062cd..2aee9789a2f 100755
@@ -791,6 +791,20 @@ test_expect_success 'reword' '
 	grep "C changed" actual
 '
 
+test_expect_success 'reword fast-forwarded empty commit' '
+	git commit --allow-empty -m "empty commit" --only &&
+	(
+		set_fake_editor &&
+		FAKE_COMMIT_AMEND=edited FAKE_LINES="reword 1" \
+			git rebase -i HEAD^
+	) &&
+	test_commit_message HEAD <<-\EOF
+	empty commit
+
+	edited
+	EOF
+'
+
 test_expect_success 'no uncommitted changes when rewording and the todo list is reloaded' '
 	git checkout E &&
 	test_when_finished "git checkout @{-1}" &&

index 2593711fecd..b84d68c4b96 100755
@@ -610,4 +610,24 @@ test_expect_success 'truncate label names' '
 	grep "label 0123456789-$" out
 '
 
+test_expect_success 'reword fast-forwarded empty merge commit' '
+	oid="$(git commit-tree -m "D1" -p A D^{tree})" &&
+	oid="$(git commit-tree -m "empty merge" -p D -p $oid D^{tree})" &&
+
+	write_script sequence-editor.sh <<-\EOF &&
+	sed /^merge/s/-C/-c/ "$1" >"$1.tmp"
+	mv "$1.tmp" "$1"
+	EOF
+
+	(
+		test_set_sequence_editor "$(pwd)/sequence-editor.sh" &&
+		GIT_EDITOR="echo edited >>" git rebase -i -r D $oid
+	) &&
+	test_commit_message HEAD <<-\EOF
+	empty merge
+
+	edited
+	EOF
+'
+
 test_done

base-commit: 58b5801aa94ad5031978f8e42c1be1230b3d352f

gitgitgadget

From: Phillip Wood <[email protected]>

When rebase rewords a commit it picks the commit and then runs "git commit --amend" to reword it. When the commit is picked the sequencer tries to reuse existing commits by fast-forwarding if the parents are unchanged. Rewording an empty commit that has been fast-forwarded fails because "git commit --amend" is called without "--allow-empty". This happens because when a commit is fast-forwarded the logic that checks whether we should pass "--allow-empty" is skipped. Fix this by always passing "--allow-empty" when rewording a commit. This is safe because we are amending a commit that has already been picked so if it had become empty when it was picked we'd have already returned an error.

As "git commit" will happily create empty merge commits without "--allow-empty" we do not need to pass that flag when rewording merge commits.

---
rebase -i: reword empty commit after fast-forward

Thanks to Junio for his comments on V1. I've added a comment explaining why we use a fixed set of commits flags as he suggested.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1860%2Fphillipwood%2Frebase-reword-empty-commit-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1860/phillipwood/rebase-reword-empty-commit-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1860

Range-diff vs v1:

1: 06de47a91d8 ! 1: 826edd3ba48 rebase -i: reword empty commit after fast-forward

     @@ sequencer.c: static int do_pick_commit(struct repository *r,
      -			res = run_git_commit(NULL, opts, EDIT_MSG |
      -					     VERIFY_MSG | AMEND_MSG |
      -					     (flags & ALLOW_EMPTY));
     ++			/*
     ++			 * To reword we amend the commit we just
     ++			 * picked or fast-forwarded. As the commit has
     ++			 * already been picked we want to use the same
     ++			 * set of commit flags regardless of how we
     ++			 * got here.
     ++			 */
      +			flags = EDIT_MSG | VERIFY_MSG | AMEND_MSG | ALLOW_EMPTY;
      +			res = run_git_commit(NULL, opts, flags);
       			*check_todo = 1;

 sequencer.c                   | 12 +++++++++---
 t/t3404-rebase-interactive.sh | 14 ++++++++++++++
 t/t3430-rebase-merges.sh      | 20 ++++++++++++++++++++
 3 files changed, 43 insertions(+), 3 deletions(-)

index 407ee4e90fe..ad0ab75c8d4 100644
@@ -2510,9 +2510,15 @@ static int do_pick_commit(struct repository *r,
 		*check_todo = !!(flags & EDIT_MSG);
 		if (!res && reword) {
 fast_forward_edit:
-			res = run_git_commit(NULL, opts, EDIT_MSG |
-					     VERIFY_MSG | AMEND_MSG |
-					     (flags & ALLOW_EMPTY));
+			/*
+			 * To reword we amend the commit we just
+			 * picked or fast-forwarded. As the commit has
+			 * already been picked we want to use the same
+			 * set of commit flags regardless of how we
+			 * got here.
+			 */
+			flags = EDIT_MSG | VERIFY_MSG | AMEND_MSG | ALLOW_EMPTY;
+			res = run_git_commit(NULL, opts, flags);
 			*check_todo = 1;
 		}
 	}

index ecfc02062cd..2aee9789a2f 100755
@@ -791,6 +791,20 @@ test_expect_success 'reword' '
 	grep "C changed" actual
 '
 
+test_expect_success 'reword fast-forwarded empty commit' '
+	git commit --allow-empty -m "empty commit" --only &&
+	(
+		set_fake_editor &&
+		FAKE_COMMIT_AMEND=edited FAKE_LINES="reword 1" \
+			git rebase -i HEAD^
+	) &&
+	test_commit_message HEAD <<-\EOF
+	empty commit
+
+	edited
+	EOF
+'
+
 test_expect_success 'no uncommitted changes when rewording and the todo list is reloaded' '
 	git checkout E &&
 	test_when_finished "git checkout @{-1}" &&

index 2593711fecd..b84d68c4b96 100755
@@ -610,4 +610,24 @@ test_expect_success 'truncate label names' '
 	grep "label 0123456789-$" out
 '
 
+test_expect_success 'reword fast-forwarded empty merge commit' '
+	oid="$(git commit-tree -m "D1" -p A D^{tree})" &&
+	oid="$(git commit-tree -m "empty merge" -p D -p $oid D^{tree})" &&
+
+	write_script sequence-editor.sh <<-\EOF &&
+	sed /^merge/s/-C/-c/ "$1" >"$1.tmp"
+	mv "$1.tmp" "$1"
+	EOF
+
+	(
+		test_set_sequence_editor "$(pwd)/sequence-editor.sh" &&
+		GIT_EDITOR="echo edited >>" git rebase -i -r D $oid
+	) &&
+	test_commit_message HEAD <<-\EOF
+	empty merge
+
+	edited
+	EOF
+'
+
 test_done

base-commit: 58b5801aa94ad5031978f8e42c1be1230b3d352f

gitgitgadget

Thanks, will queue. Let's mark it for 'next'.