let
  overlay = self: super: {
    freecad-flatmesh = super.freecad.overrideAttrs (oldAttrs: {
      cmakeFlags = [ "-DBUILD_FLAT_MESH:BOOL=ON" ];
    });
  };
in

{ pkgs ? import <nixpkgs> { overlays = [ overlay ]; } }:
  pkgs.mkShell {
    # nativeBuildInputs is usually what you want -- tools you need to run
    nativeBuildInputs = [ pkgs.godot-server pkgs.freecad-flatmesh ];
}