show-ref: accept HEAD with --verify

Previously, when --verify was specified, show-ref would use a separate
code path which did not handle HEAD and treated it as an invalid
ref. Thus, "git show-ref --verify HEAD" (where "--verify" is used
because the user is not interested in seeing refs/remotes/origin/HEAD)
did not work as expected.

Instead of insisting that the input begins with "refs/", allow "HEAD"
as well in the codepath that handles "--verify", so that all valid
full refnames including HEAD are passed to the same output machinery.

Signed-off-by: Vladimir Panteleev <git@thecybershadow.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/show-ref.c

@@ -202,7 +202,7 @@ int cmd_show_ref(int argc, const char **argv, const char *prefix)
 		while (*pattern) {
 			struct object_id oid;
 
-			if (starts_with(*pattern, "refs/") &&
+			if ((starts_with(*pattern, "refs/") || !strcmp(*pattern, "HEAD")) &&
 			    !read_ref(*pattern, oid.hash)) {
 				if (!quiet)
 					show_one(*pattern, &oid);

t/t1403-show-ref.sh

@@ -164,4 +164,15 @@ test_expect_success 'show-ref --heads, --tags, --head, pattern' '
 	test_cmp expect actual
 '
 
+test_expect_success 'show-ref --verify HEAD' '
+	echo $(git rev-parse HEAD) HEAD >expect &&
+	git show-ref --verify HEAD >actual &&
+	test_cmp expect actual &&
+
+	>expect &&
+
+	git show-ref --verify -q HEAD >actual &&
+	test_cmp expect actual
+'
+
 test_done