anchor.diff:  
     src =
       if channel == "head" then
  -      fetchgit {
  +      fetchFromGitHub {
           version = source.fetchzipversion;
  -        url = "git://git.xiph.org/opus.git";
  +        owner = "xiph";
  +        repo = "opus";
           inherit (source) rev sha256;
         }
       else
  
positive.code: { stdenv
  , autoreconfHook
  , fetchgit
  , fetchurl
  , lib
  
  
negative.code:     };
      "head" = {
        fetchzipversion = 3;
        version = "2017-10-08";
        rev = "43dfdc08ba57ce164e99e11226bcfad31db413e4";
        sha256 = "3ae356d19d0b6248615088ad36b3dad3c05114b787828c94eb17872bc2171fac";
      };
    };
    source = sources."${channel}";
  