anchor.diff:  
   mkDerivation rec {
     name = "quaternion-git-${version}";
  -  version = "2017-04-15";
  +  version = "2017-06-29";
   
     # quaternion and tensor share the same libqmatrixclient library as a git submodule
     #
  
positive.code:   postInstall = ''
      substituteInPlace $out/share/applications/quaternion.desktop \
        --replace 'Exec=quaternion' "Exec=$out/bin/quaternion"
  
      rm $out/share/icons/hicolor/icon-theme.cache
    '';
  
    meta = with lib; {
      homepage = https://matrix.org/docs/projects/client/quaternion.html;
      description = "Cross-platform desktop IM client for the Matrix protocol";
      license = licenses.gpl3;
      maintainers = with maintainers; [ peterhoeg ];
      inherit (qtbase.meta) platforms;
      inherit version;
  
negative.code:   # derivation.
  
    src = fetchgit {
      url             = "https://github.com/QMatrixClient/Quaternion.git";
      rev             = "1febc0178fd3d02b7426f58981b54924ad60c84d";
      sha256          = "1whjhlphdhk7kgw2zqc0wj3k2i9gkp79qq2bnrh4mbcp3qmcqngr";
      fetchSubmodules = true;
    };
  
  