git: add hidden --list-builtins option

It can be useful in the test suite to be able to iterate
over the list of builtins. We could do this with some
Makefile magic. But since the authoritative list is in the
commands array inside git.c, and since this could also be
handy for debugging, let's add a hidden command-line option
to dump that list.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git.c

@@ -26,6 +26,8 @@ static const char *env_names[] = {
 static char *orig_env[4];
 static int save_restore_env_balance;
 
+static void list_builtins(void);
+
 static void save_env_before_alias(void)
 {
 	int i;
@@ -232,6 +234,9 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			}
 			(*argv)++;
 			(*argc)--;
+		} else if (!strcmp(cmd, "--list-builtins")) {
+			list_builtins();
+			exit(0);
 		} else {
 			fprintf(stderr, "Unknown option: %s\n", cmd);
 			usage(git_usage_string);
@@ -529,6 +534,13 @@ int is_builtin(const char *s)
 	return !!get_builtin(s);
 }
 
+static void list_builtins(void)
+{
+	int i;
+	for (i = 0; i < ARRAY_SIZE(commands); i++)
+		printf("%s\n", commands[i].cmd);
+}
+
 #ifdef STRIP_EXTENSION
 static void strip_extension(const char **argv)
 {