anchor.diff:  
     enableParallelBuilding = true;
   
  -  buildPhase = ''
  -    python3 ${waf} build
  -  '' + optionalString stdenv.isDarwin ''
  +  postBuild = optionalString stdenv.isDarwin ''
       python3 TOOLS/osxbundle.py -s build/mpv
     '';
   
  
positive.code: assert zimgSupport        -> available zimg;
  
  let
    # Purity: Waf is normally downloaded by bootstrap.py, but
    # for purity reasons this behavior should be avoided.
    wafVersion = "2.0.9";
    waf = fetchurl {
      urls = [ "https://waf.io/waf-${wafVersion}"
               "http://www.freehackers.org/~tnagy/release/waf-${wafVersion}" ];
      sha256 = "0j7sbn3w6bgslvwwh5v9527w3gi2sd08kskrgxamx693y0b0i3ia";
    };
    luaEnv = lua.withPackages (ps: with ps; [ luasocket ]);
  
  in stdenv.mkDerivation rec {
  
negative.code: { config, stdenv, fetchurl, fetchFromGitHub, makeWrapper
  , addOpenGLRunpath, docutils, perl, pkgconfig, python3, wafHook, which
  , ffmpeg_4, freefont_ttf, freetype, libass, libpthreadstubs, mujs
  , nv-codec-headers, lua, libuchardet, libiconv ? null, darwin
  
  