builtin/merge: fix leaking struct cmdnames in get_strategy()

In "builtin/merge.c" we use the helper infrastructure to figure out what
merge strategies there are. We never free contents of the `cmdnames`
structures though and thus leak their memory.

Fix this by exposing the already existing `clean_cmdnames()` function to
release their memory. As this name isn't quite idiomatic, rename it to
`cmdnames_release()` while at it.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/merge.c

@@ -164,7 +164,7 @@ static struct strategy *get_strategy(const char *name)
 {
 	int i;
 	struct strategy *ret;
-	static struct cmdnames main_cmds, other_cmds;
+	static struct cmdnames main_cmds = {0}, other_cmds = {0};
 	static int loaded;
 	char *default_strategy = getenv("GIT_TEST_MERGE_ALGORITHM");
 
@@ -182,10 +182,9 @@ static struct strategy *get_strategy(const char *name)
 			return &all_strategy[i];
 
 	if (!loaded) {
-		struct cmdnames not_strategies;
+		struct cmdnames not_strategies = {0};
 		loaded = 1;
 
-		memset(&not_strategies, 0, sizeof(struct cmdnames));
 		load_command_list("git-merge-", &main_cmds, &other_cmds);
 		for (i = 0; i < main_cmds.cnt; i++) {
 			int j, found = 0;
@@ -197,6 +196,8 @@ static struct strategy *get_strategy(const char *name)
 				add_cmdname(&not_strategies, ent->name, ent->len);
 		}
 		exclude_cmds(&main_cmds, &not_strategies);
+
+		cmdnames_release(&not_strategies);
 	}
 	if (!is_in_cmdlist(&main_cmds, name) && !is_in_cmdlist(&other_cmds, name)) {
 		fprintf(stderr, _("Could not find merge strategy '%s'.\n"), name);
@@ -216,6 +217,9 @@ static struct strategy *get_strategy(const char *name)
 	CALLOC_ARRAY(ret, 1);
 	ret->name = xstrdup(name);
 	ret->attr = NO_TRIVIAL;
+
+	cmdnames_release(&main_cmds);
+	cmdnames_release(&other_cmds);
 	return ret;
 }
 

help.c

@@ -157,7 +157,7 @@ void add_cmdname(struct cmdnames *cmds, const char *name, int len)
 	cmds->names[cmds->cnt++] = ent;
 }
 
-static void clean_cmdnames(struct cmdnames *cmds)
+void cmdnames_release(struct cmdnames *cmds)
 {
 	int i;
 	for (i = 0; i < cmds->cnt; ++i)
@@ -359,8 +359,8 @@ void list_all_main_cmds(struct string_list *list)
 	for (i = 0; i < main_cmds.cnt; i++)
 		string_list_append(list, main_cmds.names[i]->name);
 
-	clean_cmdnames(&main_cmds);
-	clean_cmdnames(&other_cmds);
+	cmdnames_release(&main_cmds);
+	cmdnames_release(&other_cmds);
 }
 
 void list_all_other_cmds(struct string_list *list)
@@ -375,8 +375,8 @@ void list_all_other_cmds(struct string_list *list)
 	for (i = 0; i < other_cmds.cnt; i++)
 		string_list_append(list, other_cmds.names[i]->name);
 
-	clean_cmdnames(&main_cmds);
-	clean_cmdnames(&other_cmds);
+	cmdnames_release(&main_cmds);
+	cmdnames_release(&other_cmds);
 }
 
 void list_cmds_by_category(struct string_list *list,
@@ -689,7 +689,7 @@ const char *help_unknown_cmd(const char *cmd)
 	if (autocorrect && n == 1 && SIMILAR_ENOUGH(best_similarity)) {
 		const char *assumed = main_cmds.names[0]->name;
 		main_cmds.names[0] = NULL;
-		clean_cmdnames(&main_cmds);
+		cmdnames_release(&main_cmds);
 		fprintf_ln(stderr,
 			   _("WARNING: You called a Git command named '%s', "
 			     "which does not exist."),

help.h

@@ -13,6 +13,8 @@ struct cmdnames {
 	} **names;
 };
 
+void cmdnames_release(struct cmdnames *cmds);
+
 static inline void mput_char(char c, unsigned int num)
 {
 	while (num--)

t/t7606-merge-custom.sh

@@ -14,6 +14,7 @@ Testing a custom strategy.
 * (tag: c0) c0
 "
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success 'set up custom strategy' '