parse-options: show negatability of options in short help

Add a "[no-]" prefix to options without the flag PARSE_OPT_NONEG to
document the fact that you can negate them.

This looks a bit strange for options that already start with "no-", e.g.
for the option --no-name of git show-branch:

    --[no-]no-name        suppress naming strings

You can actually use --no-no-name as an alias of --name, so the short
help is not wrong.  If we strip off any of the "no-"s, we lose either
the ability to see if the remaining one belongs to the documented
variant or to see if it can be negated.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/parse-options.c b/parse-options.c
index 87c9fae634..b750bf91cd 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -1137,8 +1137,14 @@ static enum parse_opt_result usage_with_options_internal(struct parse_opt_ctx_t
 		}
 		if (opts->long_name && opts->short_name)
 			pos += fprintf(outfile, ", ");
-		if (opts->long_name)
-			pos += fprintf(outfile, "--%s", opts->long_name);
+		if (opts->long_name) {
+			const char *long_name = opts->long_name;
+			if (opts->flags & PARSE_OPT_NONEG)
+				pos += fprintf(outfile, "--%s", long_name);
+			else
+				pos += fprintf(outfile, "--[no-]%s", long_name);
+		}
+
 		if (opts->type == OPTION_NUMBER)
 			pos += utf8_fprintf(outfile, _("-NUM"));