anchor.diff:  { lib, stdenv, fetchFromGitHub, cmake, pkg-config
   , cairo, curl, fcgi, freetype, fribidi, gdal, geos, giflib, harfbuzz
   , libjpeg, libpng, librsvg, libxml2, postgresql, proj, protobufc, zlib
  -, withPython ? true, swig, python2
  +, withPython ? true, swig, python3
   }:
   
   stdenv.mkDerivation rec {
  
positive.code:   nativeBuildInputs = [
      cmake
      pkg-config
    ] ++ lib.optional withPython swig;
  
    buildInputs = [
      cairo
  
negative.code:     proj
      protobufc
      zlib
    ] ++ lib.optional withPython python3;
  
    cmakeFlags = [
      "-DWITH_KML=ON"
  