ref-filter.c: parse trailers arguments with %(contents) atom

The %(contents) atom takes a contents "field" as its argument. Since
"trailers" is one of those fields, extend contents_atom_parser to parse
"trailers"'s arguments when used through "%(contents)", like:

  %(contents:trailers:unfold,only)

A caveat: trailers_atom_parser expects NULL when no arguments are given
(see: `parse_ref_filter_atom`). This is because string_list_split (given
a maxsplit of -1) returns a 1-ary string_list* containing the given
string if the delimiter could not be found using `strchr`.

To simulate this behavior without teaching trailers_atom_parser to
accept strings with length zero, conditionally pass NULL to
trailers_atom_parser if the arguments portion of the argument to
%(contents) is empty.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/ref-filter.c b/ref-filter.c
index 43ed10a..85625fe 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -212,9 +212,10 @@ static void contents_atom_parser(const struct ref_format *format, struct used_at
 		atom->u.contents.option = C_SIG;
 	else if (!strcmp(arg, "subject"))
 		atom->u.contents.option = C_SUB;
-	else if (!strcmp(arg, "trailers"))
-		atom->u.contents.option = C_TRAILERS;
-	else if (skip_prefix(arg, "lines=", &arg)) {
+	else if (skip_prefix(arg, "trailers", &arg)) {
+		skip_prefix(arg, ":", &arg);
+		trailers_atom_parser(format, atom, *arg ? arg : NULL);
+	} else if (skip_prefix(arg, "lines=", &arg)) {
 		atom->u.contents.option = C_LINES;
 		if (strtoul_ui(arg, 10, &atom->u.contents.nlines))
 			die(_("positive value expected contents:lines=%s"), arg);