anchor.diff:    propagatedBuildInputs = old.propagatedBuildInputs
       ++ [
         # Update rust to latest stable
  -      rustChannels.stable.rust
  -      rustChannels.stable.cargo
  +      rustChannel.rust
  +      rustChannel.cargo
       ];
   })
  
positive.code: { releng_pkgs }:
  
  let
    inherit (releng_pkgs.pkgs) rustChannels bash autoconf213 clang_4 llvm_4 llvmPackages_4;
    inherit (releng_pkgs.pkgs.devEnv) gecko;
  
  in gecko.overrideDerivation (old: {
    # Dummy src, cannot be null
  
negative.code:     echo "export CLANG_MOZCONFIG=$mozconfig" >> $geckoenv
  
      # Use updated rust version
      echo "export PATH=${rustChannel.rust}/bin:${rustChannel.cargo}/bin:\$PATH" >> $geckoenv
    '';
    installPhase = ''
      geckoenv=$out/bin/gecko-env
  