transport-helper: add support to push symbolic refs

For example 'HEAD'.

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

t/t5801-remote-helpers.sh

@@ -94,6 +94,14 @@ test_expect_success 'push new branch with old:new refspec' '
 	compare_refs local HEAD server refs/heads/new-refspec
 '
 
+test_expect_success 'push new branch with HEAD:new refspec' '
+	(cd local &&
+	 git checkout new-name
+	 git push origin HEAD:new-refspec-2
+	) &&
+	compare_refs local HEAD server refs/heads/new-refspec-2
+'
+
 test_expect_success 'forced push' '
 	(cd local &&
 	git checkout -b force-test &&

transport-helper.c

@@ -896,7 +896,16 @@ 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;
-				strbuf_addf(&buf, "%s:%s", ref->peer_ref->name, ref->name);
+				const char *name;
+				int flag;
+
+				/* Follow symbolic refs (mainly for HEAD). */
+				name = resolve_ref_unsafe(ref->peer_ref->name, sha1, 1, &flag);
+				if (!name || !(flag & REF_ISSYMREF))
+					name = ref->peer_ref->name;
+
+				strbuf_addf(&buf, "%s:%s", name, ref->name);
+
 				string_list_append(&revlist_args, "--refspec");
 				string_list_append(&revlist_args, buf.buf);
 				strbuf_release(&buf);