Subject: Re: [PATCH 1/3] add -p: avoid ambiguous signed/unsigned comparison

From: Junio C Hamano <[email-masked]>
Date: Tue, 30 Aug 2022 12:09:29 -0700

"Johannes Schindelin via GitGitGadget" <[email-masked]>
writes:

> From: Johannes Schindelin <[email-masked]>
>
> In the interactive `add` operation, users can choose to jump to specific
> hunks, and Git will present the hunk list in that case. To avoid showing
> too many lines at once, only a maximum of 21 hunks are shown, skipping
> the "mode change" pseudo hunk.

Wow.

While the whole "add -i" was what I started, I admit that everything
more recent than the support of the "edit" action in "add -p" is
foreign to me.  I didn't remember the existence of, and the
justification for, the 20-line limit.  It seems that this came from
3f6aff68 (Add subroutine to display one-line summary of hunks,
2008-12-04).

> The comparison performed to skip the "mode change" pseudo hunk (if any)
> compares a signed integer `i` to the unsigned value `mode_change` (which
> can be 0 or 1 because it is a 1-bit type).

OK, that warrants a casting to signed, surely.

> Note: This is a long-standing bug in the Visual C build of Git, but it
> has never been caught because t3701 is skipped when `NO_PERL` is set,
> which is the case in the `vs-test` jobs of Git's CI runs.

Good finding.

> Signed-off-by: Johannes Schindelin <[email-masked]>
> ---
>  add-patch.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/add-patch.c b/add-patch.c
> index 509ca04456b..3524555e2b0 100644
> --- a/add-patch.c
> +++ b/add-patch.c
> @@ -1547,7 +1547,7 @@ soft_increment:
>  			strbuf_remove(&s->answer, 0, 1);
>  			strbuf_trim(&s->answer);
>  			i = hunk_index - DISPLAY_HUNKS_LINES / 2;
> -			if (i < file_diff->mode_change)
> +			if (i < (int)file_diff->mode_change)
>  				i = file_diff->mode_change;
>  			while (s->answer.len == 0) {
>  				i = display_hunks(s, file_diff, i);