diff-parseopt: convert --ignore-submodules

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -5013,6 +5013,19 @@ static int diff_opt_follow(const struct option *opt,
 	return 0;
 }
 
+static int diff_opt_ignore_submodules(const struct option *opt,
+				      const char *arg, int unset)
+{
+	struct diff_options *options = opt->value;
+
+	BUG_ON_OPT_NEG(unset);
+	if (!arg)
+		arg = "all";
+	options->flags.override_submodule_config = 1;
+	handle_ignore_submodules_arg(options, arg);
+	return 0;
+}
+
 static enum parse_opt_result diff_opt_output(struct parse_opt_ctx_t *ctx,
 					     const struct option *opt,
 					     const char *arg, int unset)
@@ -5321,6 +5334,10 @@ static void prep_parse_options(struct diff_options *options)
 		OPT_CALLBACK_F(0, "textconv", options, NULL,
 			       N_("run external text conversion filters when comparing binary files"),
 			       PARSE_OPT_NOARG, diff_opt_textconv),
+		OPT_CALLBACK_F(0, "ignore-submodules", options, N_("<when>"),
+			       N_("ignore changes to submodules in the diff generation"),
+			       PARSE_OPT_NONEG | PARSE_OPT_OPTARG,
+			       diff_opt_ignore_submodules),
 		{ OPTION_CALLBACK, 0, "output", options, N_("<file>"),
 		  N_("Output to a specific file"),
 		  PARSE_OPT_NONEG, NULL, 0, diff_opt_output },
@@ -5370,9 +5387,6 @@ int diff_opt_parse(struct diff_options *options,
 		if (cm & COLOR_MOVED_WS_ERROR)
 			return -1;
 		options->color_moved_ws_handling = cm;
-	} else if (skip_to_optional_arg_default(arg, "--ignore-submodules", &arg, "all")) {
-		options->flags.override_submodule_config = 1;
-		handle_ignore_submodules_arg(options, arg);
 	} else if (skip_to_optional_arg_default(arg, "--submodule", &arg, "log"))
 		return parse_submodule_opt(options, arg);
 	else if (skip_prefix(arg, "--ws-error-highlight=", &arg))