anchor.diff:      directories = { basedirlist = "."; };
       libs = {
         system_freetype = true;
  +      system_qhull = true;
       } // lib.optionalAttrs stdenv.isDarwin {
         # LTO not working in darwin stdenv, see #19312
         enable_lto = false;
  
positive.code:     ++ lib.optional stdenv.isDarwin [ Cocoa ];
  
    propagatedBuildInputs =
      [ cycler dateutil numpy pyparsing tornado freetype kiwisolver
        certifi libpng mock pytz pillow ]
      ++ lib.optionals enableGtk3 [ cairo pycairo gtk3 gobject-introspection pygobject3 ]
      ++ lib.optionals enableTk [ tcl tk tkinter libX11 ]
      ++ lib.optionals enableQt [ pyqt5 ];
  
negative.code: { lib, stdenv, fetchPypi, writeText, python, buildPythonPackage, isPy3k, pycairo, backports_functools_lru_cache
  , which, cycler, dateutil, nose, numpy, pyparsing, sphinx, tornado, kiwisolver
  , freetype, qhull, libpng, pkg-config, mock, pytz, pygobject3, gobject-introspection
  , certifi, pillow
  , enableGhostscript ? true, ghostscript ? null, gtk3
  , enableGtk3 ? false, cairo
  