fix #1019

irc/client_lookup_set.go

@@ -233,6 +233,11 @@ func (clients *ClientManager) SetNick(client *Client, session *Session, newNick
 		currentClient.SetNames("user", realname, true)
 		// successful reattach!
 		return newNick, nil
+	} else if currentClient == client && currentClient.Nick() == newNick {
+		// see #1019: normally no-op nick changes are caught earlier, by performNickChange,
+		// but they are not detected there when force-guest-format is enabled (because
+		// the proposed nickname is e.g. alice and the current nickname is Guest-alice)
+		return "", errNoop
 	}
 	// analogous checks for skeletons
 	skeletonHolder := clients.bySkeleton[newSkeleton]

irc/nickname.go

@@ -47,6 +47,8 @@ func performNickChange(server *Server, client *Client, target *Client, session *
 		rb.Add(nil, server.name, ERR_UNKNOWNERROR, currentNick, "NICK", client.t("You must use your account name as your nickname"))
 	} else if err == errNickMissing {
 		rb.Add(nil, server.name, ERR_NONICKNAMEGIVEN, currentNick, client.t("No nickname given"))
+	} else if err == errNoop {
+		// no message
 	} else if err != nil {
 		rb.Add(nil, server.name, ERR_UNKNOWNERROR, currentNick, "NICK", fmt.Sprintf(client.t("Could not set or change nickname: %s"), err.Error()))
 	}