Local gems in your Gemfile

All the Ruby devs know Bundler, which is the de-facto solution to manage the dependencies of a project.

When you are working on a team, chances are that every dev has his own set of tools or preferences, or that because of an unexpected situation or a specific necessity someone needs to add a gem which won’t be used by anyone else.

At the office we all use MySQL as our development database, but I needed to switch to PostgreSQL and I didn’t want to force the rest of the team to install the pg gem just because of this.

Gerard Caulfield has come up with a clever method to make this possible, Gemfile.local. Basically, the idea is to have a file that wraps the contents of the Gemfile and adds the gems you want on top of it.

# Include the regular Gemfile
eval File.read('Gemfile')

# Add any gems and groups that you don't want to keep local
gem 'pg'

So now that you have defined your local Gemfile, how to load it by default starting a Rails application?

According to the bundle-config program documentation, you can specify an alternative Gemfile for a directory by typing bundle config Gemfile.local. Unfortunately this doesn’t seem to work and the solution involves setting the BUNDLE_GEMFILE environment variable.

Now, how you do this depends entirely on you. I use a feature of zsh which allows me to set a function that will run before the execution of any shell command.

set_bundle_gemfile () {
  if [[ -f Gemfile.local ]]; then
    export BUNDLE_GEMFILE=Gemfile.local
  else
    unset BUNDLE_GEMFILE
  fi
}

preexec_functions+=(set_bundle_gemfile)

With that, if the file Gemfile.local exists in the current directory it will be automatically used by bundler.

Only one thing remains: to prevent polluting other teammates’ folders, we should avoid adding the Gemfile.local and Gemfile.local.lock files to the repository by mistake. If you use git, add them to the global .gitignore file.

echo "Gemfile.local*" >> ~/.gitignore