builtin/commit-graph.c: let parse-options parse subcommands

'git commit-graph' parses its subcommands with an if-else if
statement.  parse-options has just learned to parse subcommands, so
let's use that facility instead, with the benefits of shorter code,
handling missing or unknown subcommands, and listing subcommands for
Bash completion.

Note that the functions implementing each subcommand only accept the
'argc' and '**argv' parameters, so add a (unused) '*prefix' parameter
to make them match the type expected by parse-options, and thus avoid
casting function pointers.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit-graph.c

@@ -58,7 +58,7 @@ static struct option *add_common_options(struct option *to)
 	return parse_options_concat(common_opts, to);
 }
 
-static int graph_verify(int argc, const char **argv)
+static int graph_verify(int argc, const char **argv, const char *prefix)
 {
 	struct commit_graph *graph = NULL;
 	struct object_directory *odb = NULL;
@@ -190,7 +190,7 @@ static int git_commit_graph_write_config(const char *var, const char *value,
 	return 0;
 }
 
-static int graph_write(int argc, const char **argv)
+static int graph_write(int argc, const char **argv, const char *prefix)
 {
 	struct string_list pack_indexes = STRING_LIST_INIT_DUP;
 	struct strbuf buf = STRBUF_INIT;
@@ -307,26 +307,22 @@ static int graph_write(int argc, const char **argv)
 
 int cmd_commit_graph(int argc, const char **argv, const char *prefix)
 {
-	struct option *builtin_commit_graph_options = common_opts;
+	parse_opt_subcommand_fn *fn = NULL;
+	struct option builtin_commit_graph_options[] = {
+		OPT_SUBCOMMAND("verify", &fn, graph_verify),
+		OPT_SUBCOMMAND("write", &fn, graph_write),
+		OPT_END(),
+	};
+	struct option *options = parse_options_concat(builtin_commit_graph_options, common_opts);
 
 	git_config(git_default_config, NULL);
-	argc = parse_options(argc, argv, prefix,
-			     builtin_commit_graph_options,
-			     builtin_commit_graph_usage,
-			     PARSE_OPT_STOP_AT_NON_OPTION);
-	if (!argc)
-		goto usage;
 
 	read_replace_refs = 0;
 	save_commit_buffer = 0;
 
-	if (!strcmp(argv[0], "verify"))
-		return graph_verify(argc, argv);
-	else if (argc && !strcmp(argv[0], "write"))
-		return graph_write(argc, argv);
+	argc = parse_options(argc, argv, prefix, options,
+			     builtin_commit_graph_usage, 0);
+	FREE_AND_NULL(options);
 
-	error(_("unrecognized subcommand: %s"), argv[0]);
-usage:
-	usage_with_options(builtin_commit_graph_usage,
-			   builtin_commit_graph_options);
+	return fn(argc, argv, prefix);
 }

t/t5318-commit-graph.sh

@@ -12,12 +12,12 @@ test_expect_success 'usage' '
 
 test_expect_success 'usage shown without sub-command' '
 	test_expect_code 129 git commit-graph 2>err &&
-	! grep error: err
+	grep usage: err
 '
 
 test_expect_success 'usage shown with an error on unknown sub-command' '
 	cat >expect <<-\EOF &&
-	error: unrecognized subcommand: unknown
+	error: unknown subcommand: `unknown'\''
 	EOF
 	test_expect_code 129 git commit-graph unknown 2>stderr &&
 	grep error stderr >actual &&