anchor.diff:    nativeBuildInputs = [ autoreconfHook gettext ];
   
     preAutoreconf = ''
  -    # duff is currently badly packaged, requiring us to do extra work here that
  -    # should be done upstream. If that is ever fixed, this entire phase can be
  -    # removed along with all buildInputs.
  -
       # gettexttize rightly refuses to run non-interactively:
       cp ${gettext}/bin/gettextize .
       substituteInPlace gettextize \
  
positive.code:   enableParallelBuilding = true;
  
    meta = with stdenv.lib; {
      description = "Quickly find duplicate files";
      homepage = http://duff.dreda.org/;
      license = licenses.zlib;
      longDescription = ''
        Duff is a Unix command-line utility for quickly finding duplicates in
        a given set of files.
      '';
      maintainers = with maintainers; [ nckx ];
      platforms = with platforms; all;
    };
  }
  
negative.code: { stdenv, fetchFromGitHub, autoreconfHook, gettext }:
  
  # The last release (0.5.2) is more than 2 years old and lacks features like -D,
  # limiting its usefulness. Upstream appears comatose if not dead.
  let version = "2014-07-03"; in
  stdenv.mkDerivation {
    name = "duff-${version}";
  
    src = fetchFromGitHub {
      sha256 = "1k2dx38pjzc5d624vw1cs5ipj9fprsm5vqv55agksc29m63lswnx";
      rev = "f26d4837768b062a3f98fa075c791d9c8a0bb75c";
      repo = "duff";
      owner = "elmindreda";
    };
  