anchor.diff:          let
             extraOptions = concatMapStrings (arg: " -o ${arg}") backup.extraOptions;
             resticCmd = "${pkgs.restic}/bin/restic${extraOptions}";
  +          pruneCmd = if (builtins.length backup.pruneOpts > 0)
  +                     then [ ( resticCmd + " forget --prune " +
  +                              (concatStringsSep " " backup.pruneOpts) )
  +                            ( resticCmd + " check" ) ]
  +                     else [];
           in nameValuePair "restic-backups-${name}" ({
             environment = {
               RESTIC_PASSWORD_FILE = backup.passwordFile;
  
positive.code:             Create the repository if it doesn't exist.
            '';
          };
        };
      }));
      default = {};
  
negative.code:           restartIfChanged = false;
            serviceConfig = {
              Type = "oneshot";
              ExecStart = [ "${resticCmd} backup ${concatStringsSep " " backup.extraBackupArgs} ${concatStringsSep " " backup.paths}" ] ++ pruneCmd;
              User = backup.user;
            } // optionalAttrs (backup.s3CredentialsFile != null) {
              EnvironmentFile = backup.s3CredentialsFile;
  