parse-opt: optionally show "--no-" option string

It is usually better to have positive options, to avoid confusing double
negations.  However, sometimes it is desirable to show the negative option
in the help.

Introduce the flag PARSE_OPT_NEGHELP to do that.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

parse-options.c

@@ -511,7 +511,7 @@ static int usage_with_options_internal(const char * const *usagestr,
 			continue;
 
 		pos = fprintf(stderr, "    ");
-		if (opts->short_name) {
+		if (opts->short_name && !(opts->flags & PARSE_OPT_NEGHELP)) {
 			if (opts->flags & PARSE_OPT_NODASH)
 				pos += fprintf(stderr, "%c", opts->short_name);
 			else
@@ -520,7 +520,9 @@ static int usage_with_options_internal(const char * const *usagestr,
 		if (opts->long_name && opts->short_name)
 			pos += fprintf(stderr, ", ");
 		if (opts->long_name)
-			pos += fprintf(stderr, "--%s", opts->long_name);
+			pos += fprintf(stderr, "--%s%s",
+				(opts->flags & PARSE_OPT_NEGHELP) ?  "no-" : "",
+				opts->long_name);
 		if (opts->type == OPTION_NUMBER)
 			pos += fprintf(stderr, "-NUM");
 

parse-options.h

@@ -36,6 +36,7 @@ enum parse_opt_option_flags {
 	PARSE_OPT_LASTARG_DEFAULT = 16,
 	PARSE_OPT_NODASH = 32,
 	PARSE_OPT_LITERAL_ARGHELP = 64,
+	PARSE_OPT_NEGHELP = 128,
 };
 
 struct option;
@@ -80,6 +81,9 @@ typedef int parse_opt_cb(const struct option *, const char *arg, int unset);
  *   PARSE_OPT_LITERAL_ARGHELP: says that argh shouldn't be enclosed in brackets
  *				(i.e. '<argh>') in the help message.
  *				Useful for options with multiple parameters.
+ *   PARSE_OPT_NEGHELP: says that the long option should always be shown with
+ *				the --no prefix in the usage message. Sometimes
+ *				useful for users of OPTION_NEGBIT.
  *
  * `callback`::
  *   pointer to the callback to use for OPTION_CALLBACK.