[PATCH 03/10] config API: mark *_multi() with RESULT_MUST_BE_USED

[Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>]

Use the RESULT_MUST_BE_USED attribute to assert that all users of
the *_multi() API use the return values, in the preceding commit
"for-each-repo" started using the return value meaningfully.

This requires changing versioncmp() so that we use the "ret" versions
of the return values, and don't implicitly rely on
"deprecated_prereleases" being set to NULL if the key didn't exist.

See 1e8697b5c4e (submodule--helper: check repo{_submodule,}_init()
return values, 2022-09-01) for the introduction of
RESULT_MUST_BE_USED.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
---
 config.h     |  6 ++++++
 versioncmp.c | 22 +++++++++++++---------
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/config.h b/config.h
index c88619b7dcf..a5710c5856e 100644
--- a/config.h
+++ b/config.h
@@ -470,6 +470,7 @@ int git_configset_add_parameters(struct config_set *cs);
  * The caller should not free or modify the returned pointer, as it is
  * owned by the cache.
  */
+RESULT_MUST_BE_USED
 int git_configset_get_value_multi(struct config_set *cs, const char *key,
 				  const struct string_list **dest);
 
@@ -478,6 +479,7 @@ int git_configset_get_value_multi(struct config_set *cs, const char *key,
  * value is < 0. Use it for keys known to pass git_config_parse_key(),
  * i.e. those hardcoded in the code, and never user-provided keys.
  */
+RESULT_MUST_BE_USED
 int git_configset_get_knownkey_value_multi(struct config_set *cs,
 					   const char *const key,
 					   const struct string_list **dest);
@@ -514,9 +516,11 @@ struct repository;
 void repo_config(struct repository *repo, config_fn_t fn, void *data);
 int repo_config_get_value(struct repository *repo,
 			  const char *key, const char **value);
+RESULT_MUST_BE_USED
 int repo_config_get_value_multi(struct repository *repo,
 				const char *key,
 				const struct string_list **dest);
+RESULT_MUST_BE_USED
 int repo_config_get_knownkey_value_multi(struct repository *repo,
 					 const char *const key,
 					 const struct string_list **dest);
@@ -571,6 +575,7 @@ int git_config_get_value(const char *key, const char **value);
  * The caller should not free or modify the returned pointer, as it is
  * owned by the cache.
  */
+RESULT_MUST_BE_USED
 int git_config_get_value_multi(const char *key,
 			       const struct string_list **dest);
 
@@ -579,6 +584,7 @@ int git_config_get_value_multi(const char *key,
  * git_configset_get_knownkey_value_multi() does for
  * git_configset_get_value_multi().
  */
+RESULT_MUST_BE_USED
 int git_config_get_knownkey_value_multi(const char *const key,
 					const struct string_list **dest);
 
diff --git a/versioncmp.c b/versioncmp.c
index 9064478dc4a..effe1a6a6be 100644
--- a/versioncmp.c
+++ b/versioncmp.c
@@ -160,19 +160,23 @@ int versioncmp(const char *s1, const char *s2)
 	}
 
 	if (!initialized) {
-		const struct string_list *deprecated_prereleases = NULL;
+		const struct string_list *deprecated_prereleases;
+		int prereleases_ret, deprecated_prereleases_ret;
 
 		initialized = 1;
-		git_config_get_knownkey_value_multi("versionsort.suffix",
-						 &prereleases);
-		git_config_get_value_multi("versionsort.prereleasesuffix",
-					   &deprecated_prereleases);
-
-		if (prereleases) {
-			if (deprecated_prereleases)
+		prereleases_ret =
+			git_config_get_knownkey_value_multi("versionsort.suffix",
+							    &prereleases);
+		deprecated_prereleases_ret =
+			git_config_get_knownkey_value_multi("versionsort.prereleasesuffix",
+							    &deprecated_prereleases);
+
+		if (!prereleases_ret) {
+			if (!deprecated_prereleases_ret)
 				warning("ignoring versionsort.prereleasesuffix because versionsort.suffix is set");
-		} else
+		} else if (!deprecated_prereleases_ret) {
 			prereleases = deprecated_prereleases;
+		}
 	}
 	if (prereleases && swap_prereleases(s1, s2, (const char *) p1 - s1 - 1,
 					    &diff))
-- 
2.38.0.1251.g3eefdfb5e7a