anchor.diff:    src = fetchurl {
       url = "mirror://gnome/sources/clutter-gst/${channel}/${name}.tar.xz";
       hashOutput = false;
  -    sha256 = "d8618a6d9accec0f2a8574c5e1220051f8505fb82b20336c26bdbd482aa6cb3a";
  +    sha256 = "fe69bd6c659d24ab30da3f091eb91cd1970026d431179b0724f13791e8ad9f9d";
     };
   
     buildInputs = [
  
positive.code:     optionals;
  
    channel = "3.0";
    version = "${channel}.26";
  in
  stdenv.mkDerivation rec {
    name = "clutter-gst-${version}";
  
negative.code:         outputHash
          outputHashAlgo
          urls;
        fullOpts = {
          sha256Url = map (n: (lib.replaceStrings ["tar.xz"] ["sha256sum"] n)) src.urls;
        };
        failEarly = true;
      };
    };
  