grimm-nixos-laptop/overlays/factorio.nix

{ lib, prev, ... }:
let
  loginFile = ./factorioLogin.nix;
in
{
  factorio = prev.factorio.override (
    {
      versionsJson = ./versions.json;
    }
    // lib.optionalAttrs (builtins.pathExists loginFile) (import loginFile)
  );
}