default.nix

# in rails project

with (import <nixpkgs> {});

let
  rubyenv = bundlerEnv {
    name = "cart-env";
    # Setup for ruby gems using bundix generated gemset.nix
    inherit ruby_2_6;
    gemfile = ./Gemfile;
    lockfile = ./Gemfile.lock;
    gemset = ./gemset.nix;
    # Bundler groups available in this environment
    groups = ["default" "development" "test" "toolbox"];
  };
in {
  inherit rubyenv;
  wrapper = writeScript "wrapper" ''
    #!/bin/sh
    exec ${rubyenv}/bin/bundle exec foreman start -p 5001
  '';
  cart = stdenv.mkDerivation {
  name = "cart";
  version = "0.0.1";

  buildInputs = [
    git

    # Ruby deps
    ruby_2_6.devEnv
    bundler
    bundix

    # Rails deps
    clang
    libxml2
    libxslt
    nodejs
    openssl
    postgresql_10
    readline
    zlib
  ];

  shellHook = ''
    export LIBXML2_DIR=${pkgs.libxml2}
    export LIBXSLT_DIR=${pkgs.libxslt}
  '';
  };
}

services.nix

# home-manager config

{
  systemd.user.services.cart = {
    Unit = {
      Description = "Cart";
    };
    Service = {
      WorkingDirectory = "/home/jon/dev/cart";
      ExecStart = "${(import ./default.nix).wrapper}";
    };
  };
}