If your Gemfile references other files, such as .ruby-verison, .tools-version or
vendored gems, bundlerEnv will run into issues as it copies the Gemfile and
Gemfile.lock to a separate directory in the store. When evaluating the Gemfile
you'll run into errors as the other files are not present. To fix we need to use
the extraConfigPaths option for bundlerEnv. In shell.nix you'll find a small
setup to show you how its done.
nix-shell -A default
rackup # the puddingAdditionally, bundler started supporting a keyword argument to the ruby method
named file: in version 2.4.19. So if your Gemfile has ruby file: .ruby-verison
you'll need to ensure that the bundler is 2.4.19 or higher. This might involve
updating the bundler version used by bundlerEnv. I've also included it in the
example.