let
  nixpkgs-pin = builtins.fromJSON (builtins.readFile ./nixpkgs.json);
  nixpkgs-src = builtins.fetchTarball nixpkgs-pin;
  nixpkgs = import nixpkgs-src { };
in
{ pkgs ? nixpkgs }:
let
  # Get a version of Morph known to work with our version of NixOS.
  morph-src = pkgs.fetchFromGitHub {
    owner = "DBCDK";
    repo = "morph";
    rev = "3856a9c2f733192dee1600b8655715d760ba1803";
    hash = "sha256:0jhypvj45yjg4cn4rvb2j9091pl6z5j541vcfaln5sb3ds14fkwf";
  };
  morph = pkgs.callPackage (morph-src + "/nix-packaging") { };
in
pkgs.mkShell {
  NIX_PATH = "nixpkgs=${nixpkgs-pin.url}";
  buildInputs = [
    morph
  ];
}