let
  moz_overlay =
    import (builtins.fetchTarball
      "https://github.com/mozilla/nixpkgs-mozilla/archive/master.tar.gz");
  nixpkgs = import <nixpkgs> {overlays = [moz_overlay];};
in
  with nixpkgs;
    stdenv.mkDerivation {
      name = "moz_overlay_shell";
      buildInputs = [
        # to use the latest nightly:
        nixpkgs.latest.rustChannels.nightly.rust
      ];
      shellHook = ''
        exec zsh
      '';
    }