sequencer.c: use ref transactions for all ref updates

Change to use ref transactions for all updates to refs.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Reviewed-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sequencer.c

@@ -272,23 +272,33 @@ static int error_dirty_index(struct replay_opts *opts)
 static int fast_forward_to(const unsigned char *to, const unsigned char *from,
 			int unborn, struct replay_opts *opts)
 {
-	struct ref_lock *ref_lock;
+	struct ref_transaction *transaction;
 	struct strbuf sb = STRBUF_INIT;
-	int ret;
+	struct strbuf err = STRBUF_INIT;
 
 	read_cache();
 	if (checkout_fast_forward(from, to, 1))
 		exit(1); /* the callee should have complained already */
-	ref_lock = lock_any_ref_for_update("HEAD", unborn ? null_sha1 : from,
-					   0, NULL);
-	if (!ref_lock)
-		return error(_("Failed to lock HEAD during fast_forward_to"));
 
 	strbuf_addf(&sb, "%s: fast-forward", action_name(opts));
-	ret = write_ref_sha1(ref_lock, to, sb.buf);
+
+	transaction = ref_transaction_begin(&err);
+	if (!transaction ||
+	    ref_transaction_update(transaction, "HEAD",
+				   to, unborn ? null_sha1 : from,
+				   0, 1, &err) ||
+	    ref_transaction_commit(transaction, sb.buf, &err)) {
+		ref_transaction_free(transaction);
+		error("%s", err.buf);
+		strbuf_release(&sb);
+		strbuf_release(&err);
+		return -1;
+	}
 
 	strbuf_release(&sb);
-	return ret;
+	strbuf_release(&err);
+	ref_transaction_free(transaction);
+	return 0;
 }
 
 static int do_recursive_merge(struct commit *base, struct commit *next,