[PATCH v2 02/15] odb: handle NULL values for core.alternateRefs* config

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

From: Thomas Bachem <mail@thomasbachem.com>

A core.alternateRefsCommand or core.alternateRefsPrefixes without a
value makes "git fetch", "git receive-pack" and
"git rev-list --alternate-refs" segfault in a repository that borrows
objects from an alternate: fill_alternate_refs_command() passes the
NULL value to strvec_push() or strvec_split().

Both settings take a string. Read them with
repo_config_get_string_tmp(), which rejects a missing value with
config_error_nonbool(), as the previous commit does for
rebase.missingCommitsCheck.

Assisted-by: Claude Fable 5.1
Signed-off-by: Thomas Bachem <mail@thomasbachem.com>
---
 odb.c                     | 4 ++--
 t/t5618-alternate-refs.sh | 9 +++++++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/odb.c b/odb.c
index 865c404910..ea086be8b3 100644
--- a/odb.c
+++ b/odb.c
@@ -161,7 +161,7 @@ static void fill_alternate_refs_command(struct repository *repo,
 {
 	const char *value;
 
-	if (!repo_config_get_value(repo, "core.alternateRefsCommand", &value)) {
+	if (!repo_config_get_string_tmp(repo, "core.alternateRefsCommand", &value)) {
 		cmd->use_shell = 1;
 
 		strvec_push(&cmd->args, value);
@@ -173,7 +173,7 @@ static void fill_alternate_refs_command(struct repository *repo,
 		strvec_push(&cmd->args, "for-each-ref");
 		strvec_push(&cmd->args, "--format=%(objectname)");
 
-		if (!repo_config_get_value(repo, "core.alternateRefsPrefixes", &value)) {
+		if (!repo_config_get_string_tmp(repo, "core.alternateRefsPrefixes", &value)) {
 			strvec_push(&cmd->args, "--");
 			strvec_split(&cmd->args, value);
 		}
diff --git a/t/t5618-alternate-refs.sh b/t/t5618-alternate-refs.sh
index 68139a1b3e..422da6dde7 100755
--- a/t/t5618-alternate-refs.sh
+++ b/t/t5618-alternate-refs.sh
@@ -83,4 +83,13 @@ test_expect_success 'refs of a shallow alternate are ignored' '
 	test_cmp expect actual
 '
 
+test_expect_success 'alternateRefsCommand and alternateRefsPrefixes need a value' '
+	test_must_fail git -c core.alternateRefsCommand \
+		rev-list --alternate-refs 2>err &&
+	test_grep "missing value for .core.alternateRefsCommand." err &&
+	test_must_fail git -c core.alternateRefsPrefixes \
+		rev-list --alternate-refs 2>err &&
+	test_grep "missing value for .core.alternateRefsPrefixes." err
+'
+
 test_done
-- 
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