remote: force completing --mirror= instead of --mirror

"git remote --mirror" is a special case. Technically it is possible to
specify --mirror without any argument. But we will get a "dangerous,
deprecated!" warning in that case.

This new parse-opt flag allows --git-completion-helper to always
complete --mirror=, ignoring the dangerous use case.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/remote.c b/builtin/remote.c
index d95bf90..fce9e5c 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -168,7 +168,7 @@ static int add(int argc, const char **argv)
 		OPT_STRING('m', "master", &master, N_("branch"), N_("master branch")),
 		{ OPTION_CALLBACK, 0, "mirror", &mirror, N_("push|fetch"),
 			N_("set up remote as a mirror to push to or fetch from"),
-			PARSE_OPT_OPTARG, parse_mirror_opt },
+			PARSE_OPT_OPTARG | PARSE_OPT_COMP_ARG, parse_mirror_opt },
 		OPT_END()
 	};