anchor.diff:  
       environment.etc =
         (mapAttrs' (name: cfg: nameValuePair "tarsnap/${name}.conf"
  -        { text = configFile cfg;
  +        { text = configFile name cfg;
           }) cfg.archives) //
         (mapAttrs' (name: cfg: nameValuePair "tarsnap/${name}.dirs"
           { text = concatStringsSep " " cfg.directories;
  
positive.code:           will refuse to run until you manually rebuild the cache with
            <command>tarsnap --fsck</command>.
  
            Set to <literal>null</literal> to disable caching.
          '';
        };
  
negative.code: let
    cfg = config.services.tarsnap;
  
    configFile = name: cfg: ''
      cachedir ${config.services.tarsnap.cachedir}/${name}
      keyfile  ${config.services.tarsnap.keyfile}
      ${optionalString cfg.nodump "nodump"}
      ${optionalString cfg.printStats "print-stats"}
  