[PATCH v3 03/15] add-patch: handle NULL value for color slots

["Thomas Bachem via GitGitGadget" <gitgitgadget@gmail.com>]

From: Thomas Bachem <mail@thomasbachem.com>

With color on, a color slot without a value, such as
color.interactive.prompt or color.diff.frag, makes "git add -p",
"git add -i" and the other interactive patch modes segfault:
init_color() passes the NULL value to color_parse().

Read the slot with repo_config_get_string_tmp(), which rejects a
missing value with config_error_nonbool(), as "git diff" already does
for color.diff.frag and the other diff colors.

Assisted-by: Claude Fable 5.1
Signed-off-by: Thomas Bachem <mail@thomasbachem.com>
---
 add-patch.c                |  2 +-
 t/t3701-add-interactive.sh | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/add-patch.c b/add-patch.c
index f27edcbe8d..ad581eb4ae 100644
--- a/add-patch.c
+++ b/add-patch.c
@@ -295,7 +295,7 @@ static void init_color(struct repository *r,
 
 	if (!want_color(use_color))
 		dst[0] = '\0';
-	else if (repo_config_get_value(r, key, &value) ||
+	else if (repo_config_get_string_tmp(r, key, &value) ||
 		 color_parse(value, dst))
 		strlcpy(dst, default_color, COLOR_MAXLEN);
 
diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
index 6e120a4001..33050ccc53 100755
--- a/t/t3701-add-interactive.sh
+++ b/t/t3701-add-interactive.sh
@@ -815,6 +815,18 @@ test_expect_success 'colors can be overridden' '
 	test_cmp expect actual
 '
 
+test_expect_success 'a color without a value is rejected' '
+	git reset --hard &&
+	test_when_finished "git rm -f color-test" &&
+	test_write_lines context old >color-test &&
+	git add color-test &&
+	test_write_lines context new >color-test &&
+
+	test_must_fail git -c color.interactive=always \
+		-c color.interactive.prompt add -p </dev/null 2>err &&
+	test_grep "missing value for .color.interactive.prompt." err
+'
+
 test_expect_success 'brackets appear without color' '
 	git reset --hard &&
 	test_when_finished "git rm -f bracket-test" &&
-- 
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