anchor.diff:  { releng_pkgs }:
   
   let
  -  inherit (releng_pkgs.pkgs) rustChannels bash autoconf213 clang_4 llvm_4 llvmPackages_4;
  +  inherit (releng_pkgs.pkgs) rustChannelOf bash autoconf213 clang_4 llvm_4 llvmPackages_4;
     inherit (releng_pkgs.pkgs.devEnv) gecko;
  +
  +  # Rust 1.26.2
  +  rustChannel = rustChannelOf { date = "2018-06-05"; channel = "stable"; };
   
   in gecko.overrideDerivation (old: {
     # Dummy src, cannot be null
  
positive.code:   propagatedBuildInputs = old.propagatedBuildInputs
      ++ [
        # Update rust to latest stable
        rustChannels.stable.rust
        rustChannels.stable.cargo
      ];
  })
  
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
  