How to use gems not in a Gemfile when working with bundler?

Question

When using bundler with a project in general and Rails specifically, you have access only to gems defined in your Gemfile. While this makes sense, it can be limiting. Mostly

Answer 1

You can use something like this in your Gemfile:

gem 'foo' if ENV['ENABLE_FOO_GEM']

Then just set ENABLE_FOO_GEM in your environment.

export ENABLE_FOO_GEM=1

The gem will be disabled by default, but easily turned on (permanently) by anyone who wants to use it.