Proof-of-concept for a more aggressive GIT_UNUSED()

This adds a `-Wunused-result`-proof `GIT_UNUSED()`, just to demonstrate
that it works. With this, sortedcache.h is now completely
`GIT_WARN_UNUSED_RESULT`-annotated!

src/cc-compat.h

@@ -43,7 +43,15 @@
 #	define GIT_ALIGN(x,size) x
 #endif
 
-#define GIT_UNUSED(x) ((void)(x))
+#if defined(__GNUC__)
+# define GIT_UNUSED(x)                                                                              \
+	do {                                                                                       \
+		typeof(x) _unused __attribute__((unused));                                         \
+		_unused = (x);                                                                     \
+	} while (0)
+#else
+# define GIT_UNUSED(x) ((void)(x))
+#endif
 
 /* Define the printf format specifier to use for size_t output */
 #if defined(_MSC_VER) || defined(__MINGW32__)

src/odb.c

@@ -573,7 +573,7 @@ int git_odb__add_default_backends(
 	git_odb *db, const char *objects_dir,
 	bool as_alternates, int alternate_depth)
 {
-	size_t i;
+	size_t i = 0;
 	struct stat st;
 	ino_t inode;
 	git_odb_backend *loose, *packed;
@@ -582,7 +582,7 @@ int git_odb__add_default_backends(
 	 * a cross-platform workaround for this */
 #ifdef GIT_WIN32
 	GIT_UNUSED(i);
-	GIT_UNUSED(st);
+	GIT_UNUSED(&st);
 
 	inode = 0;
 #else

src/refdb_fs.c

@@ -122,7 +122,7 @@ static int packed_reload(refdb_fs_backend *backend)
 	 */
 	if (error <= 0) {
 		if (error == GIT_ENOTFOUND) {
-			git_sortedcache_clear(backend->refcache, true);
+			GIT_UNUSED(git_sortedcache_clear(backend->refcache, true));
 			git_error_clear();
 			error = 0;
 		}
@@ -131,7 +131,7 @@ static int packed_reload(refdb_fs_backend *backend)
 
 	/* At this point, refresh the packed refs from the loaded buffer. */
 
-	git_sortedcache_clear(backend->refcache, false);
+	GIT_UNUSED(git_sortedcache_clear(backend->refcache, false));
 
 	scan = (char *)packedrefs.ptr;
 	eof  = scan + packedrefs.size;
@@ -219,7 +219,7 @@ static int packed_reload(refdb_fs_backend *backend)
 parse_failed:
 	git_error_set(GIT_ERROR_REFERENCE, "corrupted packed references file");
 
-	git_sortedcache_clear(backend->refcache, false);
+	GIT_UNUSED(git_sortedcache_clear(backend->refcache, false));
 	git_sortedcache_wunlock(backend->refcache);
 	git_buf_dispose(&packedrefs);
 

src/sortedcache.h

@@ -133,7 +133,8 @@ void git_sortedcache_updated(git_sortedcache *sc);
  * If `wlock` is true, grabs write lock and releases when done, otherwise
  * you should already be holding a write lock when you call this.
  */
-int git_sortedcache_clear(git_sortedcache *sc, bool wlock);
+GIT_WARN_UNUSED_RESULT int git_sortedcache_clear(
+	git_sortedcache *sc, bool wlock);
 
 /* Find and/or insert item, returning pointer to item data.
  * You should already be holding the write lock when you call this.

tests/core/sha1.c

@@ -52,7 +52,7 @@ void test_core_sha1__detect_collision_attack(void)
 	git_oid oid, expected;
 
 #ifdef GIT_SHA1_COLLISIONDETECT
-	GIT_UNUSED(expected);
+	GIT_UNUSED(&expected);
 	cl_git_fail(sha1_file(&oid, FIXTURE_DIR "/shattered-1.pdf"));
 	cl_assert_equal_s("SHA1 collision attack detected", git_error_last()->message);
 #else

tests/core/sortedcache.c

@@ -54,7 +54,7 @@ void test_core_sortedcache__name_only(void)
 	cl_assert_equal_i(
 		GIT_ENOTFOUND, git_sortedcache_lookup_index(&pos, sc, "abc"));
 
-	git_sortedcache_clear(sc, true);
+	cl_git_pass(git_sortedcache_clear(sc, true));
 
 	cl_assert_equal_sz(0, git_sortedcache_entrycount(sc));
 	cl_assert(git_sortedcache_entry(sc, 0) == NULL);
@@ -154,7 +154,7 @@ void test_core_sortedcache__in_memory(void)
 
 	cl_assert_equal_i(0, free_count);
 
-	git_sortedcache_clear(sc, true);
+	cl_git_pass(git_sortedcache_clear(sc, true));
 
 	cl_assert_equal_i(5, free_count);
 
@@ -247,7 +247,7 @@ static void sortedcache_test_reload(git_sortedcache *sc)
 
 	cl_assert(git_sortedcache_lockandload(sc, &buf) > 0);
 
-	git_sortedcache_clear(sc, false); /* clear once we already have lock */
+	cl_git_pass(git_sortedcache_clear(sc, false)); /* clear once we already have lock */
 
 	for (scan = buf.ptr; *scan; scan = after + 1) {
 		int val = strtol(scan, &after, 0);

tests/index/addall.c

@@ -318,11 +318,9 @@ void test_index_addall__files_in_folders(void)
 
 void test_index_addall__hidden_files(void)
 {
+#ifdef GIT_WIN32
 	git_index *index;
 
-	GIT_UNUSED(index);
-
-#ifdef GIT_WIN32
 	addall_create_test_repo(true);
 
 	cl_git_pass(git_repository_index(&index, g_repo));

tests/index/bypath.c

@@ -49,13 +49,10 @@ void test_index_bypath__add_submodule_unregistered(void)
 
 void test_index_bypath__add_hidden(void)
 {
+#ifdef GIT_WIN32
 	const git_index_entry *entry;
 	bool hidden;
 
-	GIT_UNUSED(entry);
-	GIT_UNUSED(hidden);
-
-#ifdef GIT_WIN32
 	cl_git_mkfile("submod2/hidden_file", "you can't see me");
 
 	cl_git_pass(git_win32__hidden(&hidden, "submod2/hidden_file"));