transport-helper: add support to delete branches

For remote-helpers that use 'export' to push.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5801-remote-helpers.sh

@@ -102,6 +102,14 @@ test_expect_success 'push new branch with HEAD:new refspec' '
 	compare_refs local HEAD server refs/heads/new-refspec-2
 '
 
+test_expect_success 'push delete branch' '
+	(cd local &&
+	 git push origin :new-name
+	) &&
+	test_must_fail git --git-dir="server/.git" \
+	 rev-parse --verify refs/heads/new-name
+'
+
 test_expect_success 'forced push' '
 	(cd local &&
 	git checkout -b force-test &&

transport-helper.c

@@ -882,9 +882,6 @@ static int push_refs_with_export(struct transport *transport,
 		char *private;
 		unsigned char sha1[20];
 
-		if (ref->deletion)
-			die("remote-helpers do not support ref deletion");
-
 		private = apply_refspecs(data->refspecs, data->refspec_nr, ref->name);
 		if (private && !get_sha1(private, sha1)) {
 			strbuf_addf(&buf, "^%s", private);
@@ -896,6 +893,8 @@ static int push_refs_with_export(struct transport *transport,
 		if (ref->peer_ref) {
 			if (strcmp(ref->name, ref->peer_ref->name)) {
 				struct strbuf buf = STRBUF_INIT;
+
+				if (!ref->deletion) {
 					const char *name;
 					int flag;
 
@@ -905,11 +904,14 @@ static int push_refs_with_export(struct transport *transport,
 						name = ref->peer_ref->name;
 
 					strbuf_addf(&buf, "%s:%s", name, ref->name);
+				} else
+					strbuf_addf(&buf, ":%s", ref->name);
 
 				string_list_append(&revlist_args, "--refspec");
 				string_list_append(&revlist_args, buf.buf);
 				strbuf_release(&buf);
 			}
+			if (!ref->deletion)
 				string_list_append(&revlist_args, ref->peer_ref->name);
 		}
 	}