anchor.diff:          VISUAL=${merger passwdFile} ${pkgs.shadow}/sbin/vipw &>/dev/null
           ${pkgs.shadow}/sbin/grpconv
           ${pkgs.shadow}/sbin/pwconv
  +        ${concatStrings (mapAttrsToList groupadd nonGidGroups)}
  +        ${concatStrings (mapAttrsToList useradd nonUidUsers)}
           ${concatStrings (mapAttrsToList mkhome mkhomeUsers)}
           ${concatStrings (mapAttrsToList setpw setpwUsers)}
         '';
  
positive.code: 
        name = mkOption {
          type = types.str;
          description = "The name of the user account. If undefined, the name of the attribute set will be used.";
        };
  
        description = mkOption {
  
negative.code:       then builtins.trace "Duplicate ${idAttr} ${id}" { dup = true; acc = null; }
        else { dup = false; acc = newAcc; }
      ) { dup = false; acc = {}; } (builtins.attrNames set)).dup;
  
    uidsAreUnique = idsAreUnique (filterAttrs (n: u: u.uid != null) cfg.extraUsers) "uid";
    gidsAreUnique = idsAreUnique (filterAttrs (n: g: g.gid != null) cfg.extraGroups) "gid";
  
  in {
  
    ###### interface
  
  