Using host application helpers in mountable engine views

Question

Ruby on Rails

I have a mountable engine that mounts to the main application.
In the main application, directly in ApplicationHelperthere is a very simple helper edit_link(path): you give it a url, it returns the html code of the link.
The engine has a couple of controllers with views (interfaces) in which I want to use this helper.
By default, Rails doesn't let me do this: I've tried using both simple edit_link(path)and main_app.edit_link(path)(this works with routes, but not with helpers).
Then I decided to do this:
app/helpers/my_engine/application_helper.rb

module MyEngine
  module ApplicationHelper
    include ActionView::Helpers::ApplicationHelper
  end
end

It worked, though. When I restarted the dev server, the first request to the engine interface caught an exception:

uninitialized constant ActionView::Helpers::ApplicationHelper

I made a request to the main application controller and returned to the engine interface - it works again. Restarted the server again and made the first request to the engine interface - it works. And I can’t catch uninitialized constantthe exception anymore.
I would like to understand what it was and whether it is possible to include helpers of the main application in the views of the mountable engine using this method.

Answer 1

In general, it seems to work like this:
lib/my_engine/engine.rb (this is inside the engine)

module MyEngine
  class Engine < ::Rails::Engine
    isolate_namespace MyEngine
    config.to_prepare do
      ApplicationController.helper(ActionView::Helpers::ApplicationHelper)
    end
  end
end

PS He includekilled accordingly.