Backport of Rails 3.1.x Sprockets integration to Rails 3.0.x

Most code has been extracted from the Rails 3-1-stable branch. Modified to suit our needs.

Usage

In your Gemfile:

gem "sprockets_rails3_backport"

...plus whatever supplementary gems you want for the asset pipeline:

gem 'coffee-script', '2.2.0'
gem 'therubyracer', '0.9.9'
gem 'uglifier', '>= 1.0.3'

In your routes.rb:

MyApp::Application.routes.draw do
  if (app = Rails.application).config.assets.compile
    mount app.assets => app.config.assets.prefix
  end
  
  # ...
end

Here are the various config.assets options and their defaults:

config.assets.paths                    = []
config.assets.precompile               = [ Proc.new{ |path| !['.js', '.css'].include?(File.extname(path)) },
                                           /(?:\/|\\|\A)application\.(css|js)$/ ]
config.assets.prefix                   = "/assets"
config.assets.version                  = ''
config.assets.debug                    = false
config.assets.compile                  = true
config.assets.digest                   = false
config.assets.manifest                 = nil
config.assets.cache_store              = [ :file_store, "#{root}/tmp/cache/assets/" ]
config.assets.js_compressor            = nil
config.assets.css_compressor           = nil
config.assets.initialize_on_precompile = true

Differences from Rails 3.1

This gem was made for Shopify's use, and I've made changes to some behaviour that either didn't work in Rails 3.0, or didn't make sense for Shopify:

• image_path (and therefore image_tag) do not use the asset pipeline.
• Rails 3.0 does not have support for initializer groups, so rake assets:precompile cannot do the trick of partially loading the environment.
• precompilation does not output gzipped versions of assets.
• javascript_path and stylesheet_path helpers have been fixed to append the appropriate file extension if there's none provided.
• computing digests in the view helpers no longer throws an error if the digest is not found and config.assets.compile is off.
• config.assets.enabled is not used.