Customized rendering pipeline gives an error on certain Blacklight 8.x versions with zeitwerk 2.6.18

[sandbergja]

Description

If you have customized the rendering pipeline, as described in this wiki page, starting the rails app fails with uninitialized constant Blacklight::Rendering (NameError).

This works fine on Blacklight 8.3 and earlier. As long as your application is using zeitwerk 2.6.18 or higher, it works fine on Blacklight 8.6.1 as well.

Steps to recreate

1. Check out the release-8.x branch of the Blacklight git repo
2. Follow the step-by-step instructions to set up a local development copy of blacklight.
3. cd into the .internal_test_app directory.
4. Create a file config/initializers/blacklight.rb with the following content:

   Blacklight::Rendering::Pipeline.operations = [Blacklight::Rendering::HelperMethod,
                                             Blacklight::Rendering::LinkToFacet,
                                             Blacklight::Rendering::Microdata,
                                             CustomJoin]
   

5. Then create a file app/processors/custom_join.rb with the following content:

   # Joins values using configured value or linebreak
   class CustomJoin < Blacklight::Rendering::AbstractStep
     include ActionView::Helpers::TextHelper
   
     def render
       joiner = config.join_with || '<br>'.html_safe
       next_step(safe_join(values, joiner))
     end
   end
   

6. Then try to start the application bundle exec rails s.
7. Note that you get uninitialized constant Blacklight::Rendering (NameError).