parse-options: sanity check PARSE_OPT_NOARG flag

Some option types cannot use an argument --- boolean options that
would set a bit or flag or increment a counter, for example.  If
configured in the flag word to accept an argument anyway, the result
is an argument that is advertised in "program -h" output only to be
rejected by parse-options::get_value.

Luckily all current users of these option types use PARSE_OPT_NOARG
and do not use PARSE_OPT_OPTARG.  Add a check to ensure that that
remains true.  The check is run once for each invocation of
parse_option_start().

Improved-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

parse-options.c

@@ -330,6 +330,19 @@ static void parse_options_check(const struct option *opts)
 		     opts->long_name))
 			err |= optbug(opts, "uses feature "
 					"not supported for dashless options");
+		switch (opts->type) {
+		case OPTION_BOOLEAN:
+		case OPTION_BIT:
+		case OPTION_NEGBIT:
+		case OPTION_SET_INT:
+		case OPTION_SET_PTR:
+		case OPTION_NUMBER:
+			if ((opts->flags & PARSE_OPT_OPTARG) ||
+			    !(opts->flags & PARSE_OPT_NOARG))
+				err |= optbug(opts, "should not accept an argument");
+		default:
+			; /* ok. (usually accepts an argument) */
+		}
 	}
 	if (err)
 		exit(128);