Re: [PATCH 1/3] rebase -r: do create merge commit after empty resolution

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

Hi Philippe

On 28/03/2025 17:03, Philippe Blain via GitGitGadget wrote:
> From: Philippe Blain <levraiphilippeblain@gmail.com>
> 
> When a user runs 'git rebase --continue' to conclude a conflicted merge
> during a 'git rebase -r' invocation, we do not create a merge commit if
> the resolution was empty (i.e. if the index and HEAD are identical). We
> simply continue the rebase as if no 'merge' instruction had been given.
> This is confusing since all commits from the side branch are absent from
> the rebased history. What's more, if that 'merge' is the last
> instruction in the todo list, we fail to remove the merge state, such
> that running 'git status' shows we are still merging after the rebase
> has concluded.
> 
> This happens because in 'sequencer.c::commit_staged_changes', we exit
> early before calling 'run_git_commit' if 'is_clean' is true, i.e. if
> nothing is staged. Fix this by also checking for the presence of
> MERGE_HEAD before exiting early, such that we do call 'run_git_commit'
> when MERGE_HEAD is present. This also ensures that we unlink
> git_path_merge_head later in 'commit_staged_changes' to clear the merge
> state.
> 
> Make sure to also remove MERGE_HEAD when a merge command fails to start.
> We already remove MERGE_MSG since e032abd5a0 (rebase: fix rewritten list
> for failed pick, 2023-09-06). Removing MERGE_HEAD ensures that in this
> situation, upon 'git rebase --continue' we still exit early in
> 'commit_staged_changes', without calling 'run_git_commit'. This is
> already covered by t5407.11, which fails without this change because we
> enter 'run_git_commit' and then fail to find 'rebase_path_message'.

Thanks for fixing this.

> Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
> ---
>   sequencer.c                |  3 ++-
>   t/t3418-rebase-continue.sh | 24 ++++++++++++++++++++++++
>   2 files changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/sequencer.c b/sequencer.c
> index ad0ab75c8d4..2baaf716a3c 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -4349,6 +4349,7 @@ static int do_merge(struct repository *r,
>   		error(_("could not even attempt to merge '%.*s'"),
>   		      merge_arg_len, arg);
>   		unlink(git_path_merge_msg(r));
> +		unlink(git_path_merge_head(r));


I think we want to clean up git_path_merge_mode() as well. Perhaps we 
should call remove_merge_branch_state() instead of deleting the 
individual files ourselves here.

> +test_expect_success '--continue creates merge commit after empty resolution' '
> +	git reset --hard main &&
> +	git checkout -b rebase_i_merge &&
> +	test_commit unrelated &&
> +	git checkout -b rebase_i_merge_side &&
> +	test_commit side2 main.txt &&
> +	git checkout rebase_i_merge &&
> +	test_commit side1 main.txt &&
> +	PICK=$(git rev-parse --short rebase_i_merge) &&
> +	test_must_fail git merge rebase_i_merge_side &&
> +	echo side1 >main.txt &&
> +	git add main.txt &&
> +	test_tick &&
> +	git commit --no-edit &&
> +	FAKE_LINES="1 2 3 5 6 7 8 9 10 11" &&
> +	export FAKE_LINES &&
> +	test_must_fail git rebase -ir main &&
> +	echo side1 >main.txt &&
> +	git add main.txt &&
> +	git rebase --continue &&
> +	git log --merges >out &&
> +	test_grep "Merge branch '\''rebase_i_merge_side'\''" out
> +'

I wonder if t3430 would be a better home for this as it already has the 
setup necessary to create a failing merge. It would be good to add a 
test to check that "git rebase --skip" does not create an empty merge as 
well.

Thanks

Phillip

>   test_expect_success '--skip after failed fixup cleans commit message' '
>   	test_when_finished "test_might_fail git rebase --abort" &&
>   	git checkout -b with-conflicting-fixup &&