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 <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ttaylorr

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);

t/t6300-for-each-ref.sh

@@ -655,6 +655,35 @@ test_expect_success '%(trailers:only) and %(trailers:unfold) work together' '
 	test_cmp expect actual
 '
 
+test_expect_success '%(contents:trailers:unfold) unfolds trailers' '
+	git for-each-ref --format="%(contents:trailers:unfold)" refs/heads/master >actual &&
+	{
+		unfold <trailers
+		echo
+	} >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '%(contents:trailers:only) shows only "key: value" trailers' '
+	git for-each-ref --format="%(contents:trailers:only)" refs/heads/master >actual &&
+	{
+		grep -v patch.description <trailers &&
+		echo
+	} >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success '%(contents:trailers:only) and %(contents:trailers:unfold) work together' '
+	git for-each-ref --format="%(contents:trailers:only,unfold)" refs/heads/master >actual &&
+	git for-each-ref --format="%(contents:trailers:unfold,only)" refs/heads/master >reverse &&
+	test_cmp actual reverse &&
+	{
+		grep -v patch.description <trailers | unfold &&
+		echo
+	} >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success '%(trailers) rejects unknown trailers arguments' '
 	# error message cannot be checked under i18n
 	cat >expect <<-EOF &&
@@ -664,6 +693,15 @@ test_expect_success '%(trailers) rejects unknown trailers arguments' '
 	test_i18ncmp expect actual
 '
 
+test_expect_success '%(contents:trailers) rejects unknown trailers arguments' '
+	# error message cannot be checked under i18n
+	cat >expect <<-EOF &&
+	fatal: unknown %(trailers) argument: unsupported
+	EOF
+	test_must_fail git for-each-ref --format="%(contents:trailers:unsupported)" 2>actual &&
+	test_i18ncmp expect actual
+'
+
 test_expect_success 'basic atom: head contents:trailers' '
 	git for-each-ref --format="%(contents:trailers)" refs/heads/master >actual &&
 	sanitize_pgp <actual >actual.clean &&