anchor.diff:  #, libxshmfence
   , libxt
   , libxtst
  +, nettle
   , opengl-dummy
   , openssl
   #, pixman
  -, presentproto
  -, randrproto
  -, recordproto
  -, renderproto
  -, resourceproto
  -, scrnsaverproto
   , systemd_lib
   , tslib
  -, videoproto
   , wayland
   , wayland-protocols
  -, windowswmproto
   #, xcb-util
   #, xcbutilwm
   #, xcbutilimage
   #, xcbutilkeysyms
   #, xcbutilrenderutil
  -, xcmiscproto
  -, xextproto
  -, xf86bigfontproto
  -, xf86dgaproto
  -, xf86driproto
  -, xf86vidmodeproto
  -, xineramaproto
   , xorg
  -, xproto
  +, xorgproto
   , xtrans
  +
  +, channel
   }:
   
  +assert opengl-dummy.glx;
  +
  +let
  +  inherit (stdenv)
  +    targetSystem;
  +
  +  inherit (lib)
  +    boolTf
  +    elem
  +    optionals
  +    optionalString
  +    platforms
  +    versionAtLeast;
  +
  +  sources = {
  +    "1.19" = {
  +      version = "1.19.6";
  +      sha256 = "a732502f1db000cf36a376cd0c010ffdbf32ecdd7f1fa08ba7f5bdf9601cc197";
  +    };
  +    "1.20" = {
  +      version = "1.19.99.901";
  +      sha256 = "3654e69e19426d9738381abbe0c325082be42971535eb791fb3604f60499a36e";
  +    };
  +  };
  +  source = sources."${channel}";
  +in
   stdenv.mkDerivation rec {
  -  name = "xorg-server-1.19.6";
  +  name = "xorg-server-${source.version}";
   
     src = fetchurl {
       url = "mirror://xorg/individual/xserver/${name}.tar.bz2";
       hashOutput = false;
  -    sha256 = "a732502f1db000cf36a376cd0c010ffdbf32ecdd7f1fa08ba7f5bdf9601cc197";
  +    inherit (source) sha256;
     };
   
     nativeBuildInputs = [
  
positive.code:     flex
      makeWrapper
      util-macros
    ];
  
    buildInputs = [
      audit_lib
      bigreqsproto
      compositeproto
      damageproto
      dbus
      dmxproto
      dri2proto
      dri3proto
      fixesproto
      fontsproto
      glproto
      inputproto
      kbproto
      libdmx
      libdrm
      libepoxy
      xorg.libpciaccess
      libselinux
      libunwind
      libx11
      libxau
  
negative.code: , flex
  , lib
  , makeWrapper
  , meson
  , ninja
  , util-macros
  
  , audit_lib
  , dbus
  , libbsd
  , libdmx
  , libdrm
  , libepoxy
  #, libpciaccess
  , libselinux
  , libtirpc
  , libunwind
  , libx11
  , libxau
  