anchor.diff:          this option is true, the initial password for a user will be set
           according to <literal>users.extraUsers</literal>, but existing passwords
           will not be changed.
  +      '';
  +    };
  +
  +    users.enforceIdUniqueness = mkOption {
  +      type = types.bool;
  +      default = true;
  +      description = ''
  +        Whether to require that no two users/groups share the same uid/gid.
         '';
       };
   
  
positive.code:     mv -f $1.tmp $1
    '';
  
  in
  
  {
  
negative.code:     # for backwards compatibility
      system.activationScripts.groups = stringAfter [ "users" ] "";
  
      assertions = [ { assertion = !cfg.enforceIdUniqueness || (uidsAreUnique && gidsAreUnique); message = "uids and gids must be unique!"; } ];
  
    };
  
  }
  