Merge branch 'sb/atomic-push'

"git push" has been taught a "--atomic" option that makes push to
update more than one ref an "all-or-none" affair.

* sb/atomic-push:
  Document receive.advertiseatomic
  t5543-atomic-push.sh: add basic tests for atomic pushes
  push.c: add an --atomic argument
  send-pack.c: add --atomic command line argument
  send-pack: rename ref_update_to_be_sent to check_to_send_update
  receive-pack.c: negotiate atomic push support
  receive-pack.c: add execute_commands_atomic function
  receive-pack.c: move transaction handling in a central place
  receive-pack.c: move iterating over all commands outside execute_commands
  receive-pack.c: die instead of error in case of possible future bug
  receive-pack.c: shorten the execute_commands loop over all commands

send-pack.c

@@ -193,10 +193,13 @@ static void advertise_shallow_grafts_buf(struct strbuf *sb)
 	for_each_commit_graft(advertise_shallow_grafts_cb, sb);
 }
 
-static int ref_update_to_be_sent(const struct ref *ref, const struct send_pack_args *args)
+#define CHECK_REF_NO_PUSH -1
+#define CHECK_REF_STATUS_REJECTED -2
+#define CHECK_REF_UPTODATE -3
+static int check_to_send_update(const struct ref *ref, const struct send_pack_args *args)
 {
 	if (!ref->peer_ref && !args->send_mirror)
-		return 0;
+		return CHECK_REF_NO_PUSH;
 
 	/* Check for statuses set by set_ref_status_for_push() */
 	switch (ref->status) {
@@ -206,10 +209,11 @@ static int ref_update_to_be_sent(const struct ref *ref, const struct send_pack_a
 	case REF_STATUS_REJECT_NEEDS_FORCE:
 	case REF_STATUS_REJECT_STALE:
 	case REF_STATUS_REJECT_NODELETE:
+		return CHECK_REF_STATUS_REJECTED;
 	case REF_STATUS_UPTODATE:
-		return 0;
+		return CHECK_REF_UPTODATE;
 	default:
-		return 1;
+		return 0;
 	}
 }
 
@@ -253,7 +257,7 @@ static int generate_push_cert(struct strbuf *req_buf,
 	strbuf_addstr(&cert, "\n");
 
 	for (ref = remote_refs; ref; ref = ref->next) {
-		if (!ref_update_to_be_sent(ref, args))
+		if (check_to_send_update(ref, args) < 0)
 			continue;
 		update_seen = 1;
 		strbuf_addf(&cert, "%s %s %s\n",
@@ -281,6 +285,29 @@ free_return:
 	return update_seen;
 }
 
+
+static int atomic_push_failure(struct send_pack_args *args,
+			       struct ref *remote_refs,
+			       struct ref *failing_ref)
+{
+	struct ref *ref;
+	/* Mark other refs as failed */
+	for (ref = remote_refs; ref; ref = ref->next) {
+		if (!ref->peer_ref && !args->send_mirror)
+			continue;
+
+		switch (ref->status) {
+		case REF_STATUS_EXPECTING_REPORT:
+			ref->status = REF_STATUS_ATOMIC_PUSH_FAILED;
+			continue;
+		default:
+			break; /* do nothing */
+		}
+	}
+	return error("atomic push failed for ref %s. status: %d\n",
+		     failing_ref->name, failing_ref->status);
+}
+
 int send_pack(struct send_pack_args *args,
 	      int fd[], struct child_process *conn,
 	      struct ref *remote_refs,
@@ -297,6 +324,8 @@ int send_pack(struct send_pack_args *args,
 	int use_sideband = 0;
 	int quiet_supported = 0;
 	int agent_supported = 0;
+	int use_atomic = 0;
+	int atomic_supported = 0;
 	unsigned cmds_sent = 0;
 	int ret;
 	struct async demux;
@@ -317,6 +346,8 @@ int send_pack(struct send_pack_args *args,
 		agent_supported = 1;
 	if (server_supports("no-thin"))
 		args->use_thin_pack = 0;
+	if (server_supports("atomic"))
+		atomic_supported = 1;
 	if (args->push_cert) {
 		int len;
 
@@ -331,6 +362,10 @@ int send_pack(struct send_pack_args *args,
 			"Perhaps you should specify a branch such as 'master'.\n");
 		return 0;
 	}
+	if (args->atomic && !atomic_supported)
+		die(_("server does not support --atomic push"));
+
+	use_atomic = atomic_supported && args->atomic;
 
 	if (status_report)
 		strbuf_addstr(&cap_buf, " report-status");
@@ -338,6 +373,8 @@ int send_pack(struct send_pack_args *args,
 		strbuf_addstr(&cap_buf, " side-band-64k");
 	if (quiet_supported && (args->quiet || !args->progress))
 		strbuf_addstr(&cap_buf, " quiet");
+	if (use_atomic)
+		strbuf_addstr(&cap_buf, " atomic");
 	if (agent_supported)
 		strbuf_addf(&cap_buf, " agent=%s", git_user_agent_sanitized());
 
@@ -362,9 +399,21 @@ int send_pack(struct send_pack_args *args,
 	 * the pack data.
 	 */
 	for (ref = remote_refs; ref; ref = ref->next) {
-		if (!ref_update_to_be_sent(ref, args))
+		switch (check_to_send_update(ref, args)) {
+		case 0: /* no error */
+			break;
+		case CHECK_REF_STATUS_REJECTED:
+			/*
+			 * When we know the server would reject a ref update if
+			 * we were to send it and we're trying to send the refs
+			 * atomically, abort the whole operation.
+			 */
+			if (use_atomic)
+				return atomic_push_failure(args, remote_refs, ref);
+			/* Fallthrough for non atomic case. */
+		default:
 			continue;
-
+		}
 		if (!ref->deletion)
 			need_pack_data = 1;
 
@@ -383,7 +432,7 @@ int send_pack(struct send_pack_args *args,
 		if (args->dry_run || args->push_cert)
 			continue;
 
-		if (!ref_update_to_be_sent(ref, args))
+		if (check_to_send_update(ref, args) < 0)
 			continue;
 
 		old_hex = sha1_to_hex(ref->old_sha1);