```ruby
module Bootstrap
  module Rails
    class Engine < ::Rails::Engine
      initializer 'bootstrap-sass.assets.precompile' do |app|
        %w(stylesheets javascripts fonts images).each do |sub|
          app.config.assets.paths << root.join('assets', sub).to_s
        end
        app.config.assets.precompile << %r(bootstrap/glyphicons-halflings-regular\.(?:eot|svg|ttf|woff2?)$)
      end
    end
  end
end
```

Add support for `sprockets-rails` 3 and `sprockets` 4.
user
```ruby
module Bootstrap
  module Rails
    class Engine < ::Rails::Engine
      initializer 'bootstrap-sass.assets.precompile' do |app|
        %w(stylesheets javascripts fonts images).each do |sub|
          app.config.assets.paths << root.join('assets', sub).to_s
        end

        # sprockets-rails 3 tracks down the calls to `font_path` and `image_path`
        # and automatically precompiles the referenced assets.
        unless Sprockets::Rails::VERSION.starts_with?('3')
          app.config.assets.precompile << %r(bootstrap/glyphicons-halflings-regular\.(?:eot|svg|ttf|woff2?)$)
        end
      end
    end
  end
end
```
assistant