anchor.diff:  
     configureFlags = [
       "--with-sasl"
  -    "--disable-smartcard"
  +    "--enable-smartcard"
       "--enable-client"
       "--enable-lz4"
     ];
  
positive.code: 
    buildInputs = [ pixman celt alsaLib openssl libjpeg zlib
                    libXrandr libXfixes libXrender libXext libXinerama
                    python pyparsing glib cyrus_sasl lz4 ];
  
    nativeBuildInputs = [ pkgconfig spice-protocol ];
  
  
negative.code: { stdenv, fetchurl, pkgconfig, pixman, celt, alsaLib
  , openssl, libXrandr, libXfixes, libXext, libXrender, libXinerama
  , libjpeg, zlib, spice-protocol, python, pyparsing, glib, cyrus_sasl
  , libcacard, lz4 }:
  
  with stdenv.lib;
  
  