anchor.diff:  { stdenv, nix, perlPackages, buildEnv, releaseTools, fetchFromGitHub
   , makeWrapper, autoconf, automake, libtool, unzip, pkgconfig, sqlite, libpqxx
   , gitAndTools, mercurial, darcs, subversion, bazaar, openssl, bzip2, libxslt
  -, guile, perl, postgresql, nukeReferences, git, boehmgc
  +, guile, perl, postgresql, nukeReferences, git, boehmgc, nlohmann_json
   , docbook_xsl, openssh, gnused, coreutils, findutils, gzip, lzma, gnutar
   , rpm, dpkg, cdrkit, pixz, lib, fetchpatch, boost, autoreconfHook
   }:
  
positive.code:   };
  in releaseTools.nixBuild rec {
    name = "hydra-${version}";
    version = "2018-08-07";
  
    inherit stdenv;
  
    src = fetchFromGitHub {
      owner = "NixOS";
      repo = "hydra";
      rev = "4dca8fe14d3f782bdf927f37efce722acefffff3";
      sha256 = "1yas4psmvfp7lhcp81ia2sy93b78j9hiw9a6n3q2m1a616hwpm25";
    };
  
    buildInputs =
  
negative.code:         CatalystViewDownload
          CatalystViewJSON
          CatalystViewTT
          CatalystXScriptServerStarman
          CatalystXRoleApplicator
          CryptRandPasswd
          DBDPg
          DBDSQLite
  