default.nix

with (import <nixpkgs> {});
with (import /home/maarten/code/nixos/yarn2nix { inherit pkgs; });
let
  gems = bundlerEnv {
    name = "project-name";
    inherit ruby;
    gemdir = ./.;
  };
in stdenv.mkDerivation {
  name = "project-name";
  buildInputs = [gems ruby];
}

shell.nix

{ pkgs ? import <nixpkgs> { } }:

with pkgs;

let
  jdk = openjdk;
  node = nodejs-14_x;
  ruby = ruby_3_0;
  android-nixpkgs = callPackage (import (builtins.fetchGit {
    url = "https://github.com/tadfisher/android-nixpkgs.git";
  })) {
    channel = "stable";
  };
  android-sdk = android-nixpkgs.sdk (sdkPkgs: with sdkPkgs; [
    cmdline-tools-latest
    build-tools-30-0-2
    platform-tools
    tools
    platforms-android-30
    build-tools-29-0-2
  ]);
  in
  stdenv.mkDerivation {
    name="react-native";
    buildInputs = [
      android-sdk
      coreutils
      node
      ruby
      yarn2nix
      bundix
    ];
  }