You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: config.rb
    path of file: ./repos/Sinatra-Partial/examples/app_with_underscores_and_erb_and_subdirs
    
    the code of the file until where you have to start completion: # encoding: utf
    
  def self.app
    Rack::Builder.app do
      run App
    end
  end # self.app

end