anchor.diff: -{ stdenv, fetchurl, pkgconfig
  +{ lib, stdenv, fetchurl, pkgconfig
   , libffi, docbook_xsl, doxygen, graphviz, libxslt, xmlto
   , expat ? null # Build wayland-scanner (currently cannot be disabled as of 1.7.0)
   }:
  
positive.code:     sha256 = "173w0pqzk2m7hjlg15bymrx7ynxgq1ciadg03hzybxwnvfi4gsmx";
    };
  
    configureFlags = [
      (mkEnable (expat != null) "scanner" null)
    ];
  
    nativeBuildInputs = [ pkgconfig ];
  
  
negative.code: # Require the optional to be enabled until upstream fixes or removes the configure flag
  assert expat != null;
  
  stdenv.mkDerivation rec {
    name = "wayland-${version}";
    version = "1.7.0";
  