An updated rails template for gem bundler

A few months ago I wrote a rails template for gem bundler. Since then, bundler has changed a lot, and my template no longer works. Here then is an updated version, based on this gist from Andre Arko. Using it, you should be able to get a rails 2.3.5 project working with bundler in less than 5 minutes.

The first step is to install the latest bundler. At the time of writing, this was 0.9.9.

gem install bundler

Now you should be able to run the template, either on a new project, or on an existing rails 2.3.5 project.

rails -m http://github.com/tomafro/dotfiles/raw/master/resources/rails/bundler.rb <project>

On a fresh project, that should be all you need to do. On an existing that used an older version of bundler, you’ll need to remove the old hooks in config/preinitializer.rb and config/environment.rb, and the gems folder.

Explaining the template, step by step

The first step creates the project Gemfile, with rails available in all environments, and ruby-debug included in development. If the project has other gems, they should be added here, rather than using rails own config.gem mechanism.

file 'Gemfile', %{
source 'http://rubygems.org'

gem 'rails', '#{Rails::VERSION::STRING}'

group :development do
  gem 'ruby-debug'
end
}.strip

The next step is get bundler to load correctly. This is done in two stages. First, in config\preinitializer.rb bundler needs to be setup. This adds all the bundled gems to the ruby load path, but doesn’t initialise them.

append_file '/config/preinitializer.rb', %{
begin
  # Require the preresolved locked set of gems.
  require File.expand_path('../../.bundle/environment', __FILE__)
rescue LoadError
  # Fallback on doing the resolve at runtime.
  require "rubygems"
  require "bundler"
  if Bundler::VERSION <= "0.9.5"
    raise RuntimeError, "Bundler incompatible.\n" +
      "Your bundler version is incompatible with Rails 2.3 and an unlocked bundle.\n" +
      "Run `gem install bundler` to upgrade or `bundle lock` to lock."
  else
    Bundler.setup
  end
end
}.strip

Second, the rails boot process is modified to start the bundler environment. This ‘requires’ all gems in the bundle, letting them run initialisation code.

gsub_file 'config/boot.rb', "Rails.boot!", %{

class Rails::Boot
 def run
   load_initializer
   extend_environment
   Rails::Initializer.run(:set_load_path)
 end

 def extend_environment
   Rails::Initializer.class_eval do
     old_load = instance_method(:load_environment)
     define_method(:load_environment) do
       Bundler.require :default, Rails.env
       old_load.bind(self).call
     end
   end
 end
end

Rails.boot!
}

All that’s left now is a little cleaning up. The .bundle folder should never be checked into the code repository as it holds machine-local configuration, so it’s added to .gitignore. Finally, bundle install is run to fetch the bundled gems.

append_file '/.gitignore', %{
/.bundle
}

run 'bundle install'

And that’s it. I hope you find it useful.