Re: [PATCH v3 3/5] add -p: avoid ambiguous signed/unsigned comparison

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Tue, Oct 18 2022, Johannes Schindelin via GitGitGadget wrote:

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
>
> 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.
>
> 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).
>
> According to section 6.3.1.8 of the C99 standard (see e.g.
> https://www.open-std.org/jtc1/sc22/WG14/www/docs/n1256.pdf), what should
> happen is an automatic conversion of the "lesser" type to the "greater"
> type, but since the types differ in signedness, it is ill-defined what
> is the correct "usual arithmetic conversion".
>
> Which means that Visual C's behavior can (and does) differ from GCC's:
> When compiling Git using the latter, `add -p`'s `goto` command shows no
> hunks by default because it casts a negative start offset to a pretty
> large unsigned value, breaking the "goto hunk" test case in
> `t3701-add-interactive.sh`.
>
> Let's avoid that by converting the unsigned bit explicitly to a signed
> integer.
>
> 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.
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  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);

Junio pointed out in the last round that this really could use a
separate submission, and I tend to agree. It's really nothing to do with
cmake...