t0040-parse-options: test parse_options() with various 'parse_opt_flags'

In 't0040-parse-options.sh' we thoroughly test the parsing of all
types and forms of options, but in all those tests parse_options() is
always invoked with a 0 flags parameter.

Add a few tests to demonstrate how various 'enum parse_opt_flags'
values are supposed to influence option parsing.

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

t/helper/test-parse-options.c

@@ -192,3 +192,69 @@ int cmd__parse_options(int argc, const char **argv)
 
 	return ret;
 }
+
+static void print_args(int argc, const char **argv)
+{
+	for (int i = 0; i < argc; i++)
+		printf("arg %02d: %s\n", i, argv[i]);
+}
+
+static int parse_options_flags__cmd(int argc, const char **argv,
+				    enum parse_opt_flags test_flags)
+{
+	const char *usage[] = {
+		"<...> cmd [options]",
+		NULL
+	};
+	int opt = 0;
+	const struct option options[] = {
+		OPT_INTEGER('o', "opt", &opt, "an integer option"),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, NULL, options, usage, test_flags);
+
+	printf("opt: %d\n", opt);
+	print_args(argc, argv);
+
+	return 0;
+}
+
+static enum parse_opt_flags test_flags = 0;
+static const struct option test_flag_options[] = {
+	OPT_GROUP("flag-options:"),
+	OPT_BIT(0, "keep-dashdash", &test_flags,
+		"pass PARSE_OPT_KEEP_DASHDASH to parse_options()",
+		PARSE_OPT_KEEP_DASHDASH),
+	OPT_BIT(0, "stop-at-non-option", &test_flags,
+		"pass PARSE_OPT_STOP_AT_NON_OPTION to parse_options()",
+		PARSE_OPT_STOP_AT_NON_OPTION),
+	OPT_BIT(0, "keep-argv0", &test_flags,
+		"pass PARSE_OPT_KEEP_ARGV0 to parse_options()",
+		PARSE_OPT_KEEP_ARGV0),
+	OPT_BIT(0, "keep-unknown", &test_flags,
+		"pass PARSE_OPT_KEEP_UNKNOWN to parse_options()",
+		PARSE_OPT_KEEP_UNKNOWN),
+	OPT_BIT(0, "no-internal-help", &test_flags,
+		"pass PARSE_OPT_NO_INTERNAL_HELP to parse_options()",
+		PARSE_OPT_NO_INTERNAL_HELP),
+	OPT_END()
+};
+
+int cmd__parse_options_flags(int argc, const char **argv)
+{
+	const char *usage[] = {
+		"test-tool parse-options-flags [flag-options] cmd [options]",
+		NULL
+	};
+
+	argc = parse_options(argc, argv, NULL, test_flag_options, usage,
+			     PARSE_OPT_STOP_AT_NON_OPTION);
+
+	if (argc == 0 || strcmp(argv[0], "cmd")) {
+		error("'cmd' is mandatory");
+		usage_with_options(usage, test_flag_options);
+	}
+
+	return parse_options_flags__cmd(argc, argv, test_flags);
+}