anchor.diff:  {stdenv, fetchurl, libusb}:
   
  -stdenv.mkDerivation rec {
  +with stdenv; mkDerivation rec {
     name = "libftdi-0.20";
   
     src = fetchurl {
  
positive.code:   meta = {
      description = "A library to talk to FTDI chips using libusb";
      homepage = https://www.intra2net.com/en/developer/libftdi/;
      license = stdenv.lib.licenses.lgpl21;
      platforms = stdenv.lib.platforms.linux;
    };
  }
  
negative.code: 
    # Hack to avoid TMPDIR in RPATHs.
    preFixup = ''rm -rf "$(pwd)" '';
    configureFlags = lib.optional (!isDarwin) [ "--with-async-mode" ];
  
    # allow async mode. from ubuntu. see:
    #   https://bazaar.launchpad.net/~ubuntu-branches/ubuntu/trusty/libftdi/trusty/view/head:/debian/patches/04_async_mode.diff
  