[PATCH v4 6/6] ref-filter.c: parse trailers arguments with %(contents) atom

[Taylor Blau <me@ttaylorr.com>]

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`). 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>
---
 ref-filter.c            |  6 ++++--
 t/t6300-for-each-ref.sh | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/ref-filter.c b/ref-filter.c
index 43ed10a5e..2c03c2bf5 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -212,8 +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, "trailers", &arg)) {
+		skip_prefix(arg, ":", &arg);
+		trailers_atom_parser(atom, *arg ? NULL : arg);
+	}
 	else if (skip_prefix(arg, "lines=", &arg)) {
 		atom->u.contents.option = C_LINES;
 		if (strtoul_ui(arg, 10, &atom->u.contents.nlines))
diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index e4ce9c550..ab95fe427 100755
--- a/t/t6300-for-each-ref.sh
+++ b/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' '
 	cat >expect <<-EOF &&
 	fatal: unknown %(trailers) argument: unsupported
@@ -663,6 +692,14 @@ test_expect_success '%(trailers) rejects unknown trailers arguments' '
   test_cmp expect actual
 '
 
+test_expect_success '%(contents:trailers) rejects unknown trailers arguments' '
+	cat >expect <<-EOF &&
+	fatal: unknown %(trailers) argument: unsupported
+	EOF
+  test_must_fail git for-each-ref --format="%(contents:trailers:unsupported)" 2>actual &&
+  test_cmp 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 &&
-- 
2.14.1.145.gb3622a4ee