This file at actionpack/lib/sprockets/railtie.rb defines the Sprockets::Railtie, defining another Railtie for Rails. This Railtie is responsible for detecting if the application at-hand is using CoffeeScript, and if so will set config.app_generators.javascript_engine on the application to be :coffee.
Next, this defines an initializer called sprockets.set_configs which sets up ActionController::Base to either use or not use sprockets depending on the configuration option config.assets.enabled.
Finally, this file defines an after_initialize hook for the application which is the real meat of this Railtie. If assets are disabled (with the config.assets.enabled config option set to false) then this after_initialize hook will do nothing.
If assets are enabled then, this initializer first makes a call to an asset_environment protected method near the bottom of this file which requires the sprockets gem, creates a new Sprockets::Environment object, and then co