anchor.diff:  
     ###### implementation
   
  -  config = mkIf config.services.mysql.enable {
  +  config = mkIf cfg.enable {
   
       services.mysql.dataDir =
         mkDefault (if versionAtLeast config.system.stateVersion "17.09" then "/var/lib/mysql"
  
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:         };
  
          masterPort = mkOption {
            type = types.port;
            default = 3306;
            description = "Port number on which the MySQL master server runs.";
          };
  