[PATCH v3] submodule: warn on valueless active config

[tilak-raaz <raaztilak07@gmail.com>]

The config parser previously threw a hard error if 'submodule.active'
was provided without a value, causing commands to abort.

Swap repo_config_get_string_multi() to repo_config_get_value_multi()
to parse valueless keys safely. Use the standard config_error_nonbool()
helper to emit a warning to the user rather than crashing.

This resolves a NEEDSWORK comment in submodule.c.

Signed-off-by: tilak-raaz <raaztilak07@gmail.com>
---
Junio, thank you for the review and guidance on the terminology and tense.
Regarding causing the command to fail on a malformed config: I investigated returning an error code here, but is_tree_submodule_active() is evaluated as a boolean predicate by its callers (for example, if (!is_tree_submodule_active(...))). Since -1 is truthy in C, returning -1 would cause callers to treat the broken submodule as active.
To avoid changing the existing caller semantics or introducing process termination from this helper, I kept the continue behavior so the malformed entry is skipped after being reported with config_error_nonbool(), while valid entries continue to be processed.
Please let me know if you would prefer a different error-propagation approach.
Changes in v3:
-Updated the commit message to use present tense.
-Updated the commit message to use "valueless true".
-Fixed the whitespace and indentation in the t7400 test script.

 submodule.c                | 12 ++++++------
 t/t7400-submodule-basic.sh | 11 +++++++++++
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/submodule.c b/submodule.c
index 5c92575888..07d1fc63e9 100644
--- a/submodule.c
+++ b/submodule.c
@@ -231,11 +231,7 @@ int option_parse_recurse_submodules_worktree_updater(const struct option *opt,
 /*
  * Determine if a submodule has been initialized at a given 'path'
  */
-/*
- * NEEDSWORK: Emit a warning if submodule.active exists, but is valueless,
- * ie, the config looks like: "[submodule] active\n".
- * Since that is an invalid pathspec, we should inform the user.
- */
+
 int is_tree_submodule_active(struct repository *repo,
 			     const struct object_id *treeish_name,
 			     const char *path)
@@ -261,12 +257,16 @@ int is_tree_submodule_active(struct repository *repo,
 	free(key);
 
 	/* submodule.active is set */
-	if (!repo_config_get_string_multi(repo, "submodule.active", &sl)) {
+	if (!repo_config_get_value_multi(repo, "submodule.active", &sl)) {
 		struct pathspec ps;
 		struct strvec args = STRVEC_INIT;
 		const struct string_list_item *item;
 
 		for_each_string_list_item(item, sl) {
+			 if (!item->string) {
+				config_error_nonbool("submodule.active");
+				continue;
+			}
 			strvec_push(&args, item->string);
 		}
 
diff --git a/t/t7400-submodule-basic.sh b/t/t7400-submodule-basic.sh
index eefdecb0bd..62b2537174 100755
--- a/t/t7400-submodule-basic.sh
+++ b/t/t7400-submodule-basic.sh
@@ -1549,4 +1549,15 @@ test_expect_success 'submodule add fails when name is reused' '
 	)
 '
 
+
+test_expect_success 'warn on valueless submodule.active' '
+	test_when_finished "rm -rf empty-active" &&
+	git init empty-active &&
+	test_commit -C empty-active initial &&
+	git -c protocol.file.allow=always -C empty-active submodule add ../empty-active sub &&
+	git -C empty-active config --unset submodule.sub.active &&
+	printf "[submodule]\n\tactive\n" >>empty-active/.git/config &&
+	git -C empty-active submodule status 2>err &&
+	grep "missing value for .submodule.active." err
+'
 test_done
-- 
2.50.1 (Apple Git-155)