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

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>
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 add-patch.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)