rails 3.1 asset pipeline: ignore assets from a gem

Rails 4.X

It didn't work on Rails 4.X, a possible (dirty) workaround is:

require 'sprockets/railtie'

Bundler.require(:default, Rails.env)

module Sprockets
  module Paths
    SKIP_GEMS = ["rails-assets-jquery", "rails-assets-bootstrap"]

    def append_path_with_rails_assets(path)
      append_path_without_rails_assets(path) unless SKIP_GEMS.any? { |gem| path.to_s.start_with?(Gem.loaded_specs[gem].full_gem_path) }
    end

    alias_method_chain :append_path, :rails_assets
  end
end

Update for Rails 5.X

alias_method_chain is deprecated since Rails 5.X. Here is an updated version using prepend, and overriding the Sprockets::Environment module instead of Sprockets::Paths.

module SprocketsPathsOverride
  SKIP_GEMS = ["rails-assets-jquery", "rails-assets-bootstrap"]

  def append_path(path)
    should_skip = SKIP_GEMS.any? do |gem|
      path.to_s.start_with?(Gem.loaded_specs[gem].full_gem_path)
    end
    super(path) unless should_skip
  end
end

Sprockets::Environment.prepend(SprocketsPathsOverride)

I guess there is a smart way to achieve your goal using sprockets. Maybe some require_directory instead of require_tree.

But the most direct thing would be to remove theses assets from your assets paths. To achieve this, add this at the very end of your application.rb file (doesn't work in an initializer):

class Engine < Rails::Engine
   initializer "remove assets directories from pipeline" do |app|
     app.config.assets.paths = app.config.assets.paths - app.config.assets.paths.grep(/nice_regexp_here_to_match_the_dir_where_the_unwanted_files_live/)
   end
end

---

Just tried a hack: put the code in an initializer but require it at the end of your application.rb:

require "config/initializers/your_file'

I prefer very specific code to be visible this way.