anchor.diff:          };
   
           masterPort = mkOption {
  -          type = types.int;
  +          type = types.port;
             default = 3306;
             description = "Port number on which the MySQL master server runs.";
           };
  
positive.code:           Group account under which MySQL runs.
  
            <note><para>
            If left as the default value this user will automatically be created
            on system activation, otherwise you are responsible for
            ensuring the user exists before the MySQL service starts.
            </para></note>
  
negative.code: 
    ###### implementation
  
    config = mkIf cfg.enable {
  
      services.mysql.dataDir =
        mkDefault (if versionAtLeast config.system.stateVersion "17.09" then "/var/lib/mysql"
  