Re: [PATCH v3 5/7] rebase: fix rewritten list for failed pick

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Phillip,

On Tue, 1 Aug 2023, Phillip Wood via GitGitGadget wrote:

> From: Phillip Wood <phillip.wood@dunelm.org.uk>
>
> git rebase keeps a list that maps the OID of each commit before it was
> rebased to the OID of the equivalent commit after the rebase.  This list
> is used to drive the "post-rewrite" hook that is called at the end of a
> successful rebase. When a rebase stops for the user to resolve merge
> conflicts the OID of the commit being picked is written to
> ".git/rebase-merge/stopped-sha". Then when the rebase is continued that
> OID is added to the list of rewritten commits. Unfortunately if a commit
> cannot be picked because it would overwrite an untracked file we still
> write the "stopped-sha1" file. This means that when the rebase is
> continued the commit is added into the list of rewritten commits even
> though it has not been picked yet.
>
> Fix this by not calling error_with_patch() for failed commands. The pick
> has failed so there is nothing to commit and therefore we do not want to
> set up the state files for committing staged changes when the rebase
> continues. This change means we no-longer write a patch for the failed
> command or display the error message printed by error_with_patch(). As
> the command has failed the patch isn't really useful and in any case the
> user can inspect the commit associated with the failed command by
> inspecting REBASE_HEAD. Unless the user has disabled it we already print
> an advice message that is more helpful than the message from
> error_with_patch() which the user will still see. Even if the advice is
> disabled the user will see the messages from the merge machinery
> detailing the problem.
>
> To simplify writing REBASE_HEAD in this case pick_one_commit() is
> modified to avoid duplicating the code that adds the failed command
> back into the todo list.

This motivates the change well, and answered all but one of the questions
I had about it, being:

> diff --git a/sequencer.c b/sequencer.c
> index 62277e7bcc1..e25abfd2fb4 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> [...]
> @@ -4658,12 +4659,8 @@ static int pick_one_commit(struct repository *r,
>  			     check_todo);
>  	if (is_rebase_i(opts) && res < 0) {
>  		/* Reschedule */
> -		advise(_(rescheduled_advice),
> -		       get_item_line_length(todo_list, todo_list->current),
> -		       get_item_line(todo_list, todo_list->current));
> -		todo_list->current--;

Why is it okay to remove this decrement?

Here is why: The code that calls `save_todo()` in the `if (reschedule)`
block of the loop of `pick_commits()` _duplicates_ the logic that is
removed here, including the advice and the decrementing of `current`.

I had to instrument the code before and after this patch to figure this
out, as I had missed the fact that the now-remaining code also decremented
the `current` attribute.

So: All is good with this patch. If you'd like to amend the commit message
accordingly, I would not be opposed, but I could now live equally as
easily without it.

> -		if (save_todo(todo_list, opts))
> -			return -1;
> +		*reschedule = 1;
> +		return -1;
>  	}
>  	if (item->command == TODO_EDIT) {
>  		struct commit *commit = item->commit;

I'd like to point out how delighted I am about this careful test case:

> diff --git a/t/t3430-rebase-merges.sh b/t/t3430-rebase-merges.sh
> index 96ae0edf1e1..4938ebb1c17 100755
> --- a/t/t3430-rebase-merges.sh
> +++ b/t/t3430-rebase-merges.sh
> @@ -165,12 +165,12 @@ test_expect_success 'failed `merge -C` writes patch (may be rescheduled, too)' '
>  	test_config sequence.editor \""$PWD"/replace-editor.sh\" &&
>  	test_tick &&
>  	test_must_fail git rebase -ir HEAD &&
> +	test_cmp_rev REBASE_HEAD H^0 &&
>  	grep "^merge -C .* G$" .git/rebase-merge/done &&
>  	grep "^merge -C .* G$" .git/rebase-merge/git-rebase-todo &&
> -	test_path_is_file .git/rebase-merge/patch &&
> +	test_path_is_missing .git/rebase-merge/patch &&
>
>  	: fail because of merge conflict &&
> -	rm G.t .git/rebase-merge/patch &&
>  	git reset --hard conflicting-G &&
>  	test_must_fail git rebase --continue &&
>  	! grep "^merge -C .* G$" .git/rebase-merge/git-rebase-todo &&
> diff --git a/t/t5407-post-rewrite-hook.sh b/t/t5407-post-rewrite-hook.sh
> index 5f3ff051ca2..ad7f8c6f002 100755
> --- a/t/t5407-post-rewrite-hook.sh
> +++ b/t/t5407-post-rewrite-hook.sh
> @@ -17,6 +17,12 @@ test_expect_success 'setup' '
>  	git checkout A^0 &&
>  	test_commit E bar E &&
>  	test_commit F foo F &&
> +	git checkout B &&
> +	git merge E &&
> +	git tag merge-E &&
> +	test_commit G G &&
> +	test_commit H H &&
> +	test_commit I I &&
>  	git checkout main &&
>
>  	test_hook --setup post-rewrite <<-EOF
> @@ -173,6 +179,48 @@ test_fail_interactive_rebase () {
>  	)
>  }
>
> +test_expect_success 'git rebase with failed pick' '
> +	clear_hook_input &&
> +	cat >todo <<-\EOF &&
> +	exec >bar
> +	merge -C merge-E E
> +	exec >G
> +	pick G
> +	exec >H 2>I
> +	pick H
> +	fixup I
> +	EOF
> +
> +	(
> +		set_replace_editor todo &&
> +		test_must_fail git rebase -i D D 2>err
> +	) &&
> +	grep "would be overwritten" err &&
> +	rm bar &&
> +
> +	test_must_fail git rebase --continue 2>err &&
> +	grep "would be overwritten" err &&
> +	rm G &&
> +
> +	test_must_fail git rebase --continue 2>err &&
> +	grep "would be overwritten" err &&
> +	rm H &&
> +
> +	test_must_fail git rebase --continue 2>err &&
> +	grep "would be overwritten" err &&
> +	rm I &&
> +
> +	git rebase --continue &&
> +	echo rebase >expected.args &&
> +	cat >expected.data <<-EOF &&
> +	$(git rev-parse merge-E) $(git rev-parse HEAD~2)
> +	$(git rev-parse G) $(git rev-parse HEAD~1)
> +	$(git rev-parse H) $(git rev-parse HEAD)
> +	$(git rev-parse I) $(git rev-parse HEAD)
> +	EOF
> +	verify_hook_input
> +'
> +
>  test_expect_success 'git rebase -i (unchanged)' '
>  	git reset --hard D &&
>  	clear_hook_input &&

Here is my ACK.

Thank you,
Johannes