[PATCH v3 01/15] rebase -i: handle NULL value for rebase.missingCommitsCheck

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

From: Thomas Bachem <mail@thomasbachem.com>

A rebase.missingCommitsCheck without a value, as in

  [rebase]
  missingCommitsCheck

or "git -c rebase.missingCommitsCheck", makes "git rebase -i"
segfault as it writes the todo list: get_missing_commit_check_level()
passes the NULL value to strcasecmp().

The setting takes "ignore", "warn" or "error". An unrecognized value,
perhaps one meant for a newer version of Git, gets a warning and is
treated as "ignore". Treat a missing value the same way.

Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Assisted-by: Claude Fable 5.1
Assisted-by: Claude Opus 5.5
Signed-off-by: Thomas Bachem <mail@thomasbachem.com>
---
 rebase-interactive.c          | 10 ++++++++--
 t/t3404-rebase-interactive.sh | 12 ++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/rebase-interactive.c b/rebase-interactive.c
index 809f76a87b..9eb70b09b3 100644
--- a/rebase-interactive.c
+++ b/rebase-interactive.c
@@ -30,8 +30,14 @@ static enum missing_commit_check_level get_missing_commit_check_level(void)
 {
 	const char *value;
 
-	if (repo_config_get_value(the_repository, "rebase.missingcommitscheck", &value) ||
-			!strcasecmp("ignore", value))
+	if (repo_config_get_value(the_repository, "rebase.missingcommitscheck", &value))
+		return MISSING_COMMIT_CHECK_IGNORE;
+	if (!value) {
+		warning(_("missing value for option "
+			  "rebase.missingCommitsCheck. Ignoring."));
+		return MISSING_COMMIT_CHECK_IGNORE;
+	}
+	if (!strcasecmp("ignore", value))
 		return MISSING_COMMIT_CHECK_IGNORE;
 	if (!strcasecmp("warn", value))
 		return MISSING_COMMIT_CHECK_WARN;
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index b3ee96f560..16fdf6b6e3 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1562,6 +1562,18 @@ test_expect_success 'rebase -i respects rebase.missingCommitsCheck = error' '
 	test B = $(git cat-file commit HEAD^ | sed -ne \$p)
 '
 
+test_expect_success 'rebase -i warns about and ignores rebase.missingCommitsCheck without a value' '
+	rebase_setup_and_clean missing-commit &&
+	(
+		set_fake_editor &&
+		FAKE_LINES=1 \
+			git -c rebase.missingCommitsCheck rebase -i HEAD~3 2>actual
+	) &&
+	test_commit_message HEAD -m C &&
+	test_grep "missing value for option rebase.missingCommitsCheck" actual &&
+	test_grep ! "commits may have been dropped" actual
+'
+
 test_expect_success 'rebase --edit-todo respects rebase.missingCommitsCheck = ignore' '
 	test_config rebase.missingCommitsCheck ignore &&
 	rebase_setup_and_clean missing-commit &&
-- 
gitgitgadget