rails--rails/actionpack/lib/abstract_controller/url_for.rb

module AbstractController
  # Includes +url_for+ into the host class (e.g. an abstract controller or mailer). The class
  # has to provide a +RouteSet+ by implementing the <tt>_routes</tt> methods. Otherwise, an
  # exception will be raised.
  #
  # Note that this module is completely decoupled from HTTP - the only requirement is a valid
  # <tt>_routes</tt> implementation.
  module UrlFor
    extend ActiveSupport::Concern
    include ActionDispatch::Routing::UrlFor

    def _routes
      raise "In order to use #url_for, you must include routing helpers explicitly. " \
            "For instance, `include Rails.application.routes.url_helpers`."
    end

    module ClassMethods
      def _routes
        nil
      end

      def action_methods
        @action_methods ||= begin
          if _routes
            super - _routes.named_routes.helper_names
          else
            super
          end
        end
      end
    end
  end
end