Clean up unneeded code and docs

Since we switched to the Zeitwerk autoloader, these are no longer
necessary

.gitlab/ci/rails.gitlab-ci.yml

@@ -268,22 +268,6 @@ static-analysis as-if-foss:
     - .static-analysis:rules:as-if-foss
     - .as-if-foss
 
-zeitwerk-check:
-  extends:
-    - .rails-cache
-    - .default-before_script
-    - .rails:rules:ee-and-foss-unit
-  variables:
-    BUNDLE_WITHOUT: ""
-    SETUP_DB: "false"
-  needs: []
-  stage: test
-  script:
-    - sed -i -e "s/config\.autoloader = :classic/config\.autoloader = :zeitwerk/" config/application.rb
-    - RAILS_ENV=test bundle exec rake zeitwerk:check
-    - RAILS_ENV=development bundle exec rake zeitwerk:check
-    - RAILS_ENV=production bundle exec rake zeitwerk:check
-
 rspec migration pg12:
   extends:
     - .rspec-base-pg12

config/initializers/0_inject_enterprise_edition_module.rb

@@ -58,39 +58,7 @@ module InjectEnterpriseEditionModule
   end
 
   def const_get_maybe_false(mod, name)
-    # We're still heavily relying on Rails autoloading instead of zeitwerk,
-    # therefore this check: `mod.const_defined?(name, false)`
-    # Is not reliable, which may return false while it's defined.
-    # After we moved everything over to zeitwerk we can avoid rescuing
-    # NameError and just check if const_defined?
-    # mod && mod.const_defined?(name, false) && mod.const_get(name, false)
-    result = mod && mod.const_get(name, false)
-
-    if result.name == "#{mod}::#{name}"
-      result
-    else
-      # This may hit into a Rails issue that when we try to load
-      # `EE::API::Appearance`, Rails might load `::Appearance` the first time
-      # when `mod.const_get(name, false)` is called if `::Appearance` is not
-      # loaded yet. This can be demonstrated as the following:
-      #
-      #     EE.const_get('API::Appearance', false) # => Appearance
-      #     EE.const_get('API::Appearance', false) # => raise NameError
-      #
-      # Getting a `NameError` is what we're expecting here, because
-      # `EE::API::Appearance` doesn't exist.
-      #
-      # This is because Rails will attempt to load constants from all the
-      # parent namespaces, and if it finds one it'll load it and return it.
-      # However, the second time when it's called, since the top-level class
-      # is already loaded, then Rails will skip this process. This weird
-      # behaviour can be worked around by calling this the second time.
-      # The particular line is at:
-      # https://github.com/rails/rails/blob/v6.1.3.2/activesupport/lib/active_support/dependencies.rb#L569-L570
-      mod.const_get(name, false)
-    end
-  rescue NameError
-    false
+    mod && mod.const_defined?(name, false) && mod.const_get(name, false)
   end
 end
 

doc/development/gotchas.md

@@ -203,76 +203,6 @@ in an initializer.
 
 - Stack Overflow: [Why you should not write inline JavaScript](https://softwareengineering.stackexchange.com/questions/86589/why-should-i-avoid-inline-scripting)
 
-## Auto loading
-
-Rails auto-loading on `development` differs from the load policy in the `production` environment.
-In development mode, `config.eager_load` is set to `false`, which means classes
-are loaded as needed. With the classic Rails autoloader, it is known that this can lead to
-[Rails resolving the wrong class](https://guides.rubyonrails.org/v5.2/autoloading_and_reloading_constants.html#when-constants-aren-t-missed-relative-references)
-if the class name is ambiguous. This can be fixed by specifying the complete namespace to the class.
-
-### Error prone example
-
-```ruby
-# app/controllers/application_controller.rb
-class ApplicationController < ActionController::Base
-  ...
-end
-
-# app/controllers/projects/application_controller.rb
-class Projects::ApplicationController < ApplicationController
-  ...
-  private
-
-  def project
-    ...
-  end
-end
-
-# app/controllers/projects/submodule/some_controller.rb
-module Projects
-  module Submodule
-    class SomeController < ApplicationController
-      def index
-        @some_id = project.id
-      end
-    end
-  end
-end
-```
-
-In this case, if for any reason the top level `ApplicationController`
-is loaded but `Projects::ApplicationController` is not, `ApplicationController`
-would be resolved to `::ApplicationController` and then the `project` method is
-undefined, causing an error.
-
-#### Solution
-
-```ruby
-# app/controllers/projects/submodule/some_controller.rb
-module Projects
-  module Submodule
-    class SomeController < Projects::ApplicationController
-      def index
-        @some_id = project.id
-      end
-    end
-  end
-end
-```
-
-By specifying `Projects::`, we tell Rails exactly what class we are referring
-to and we would avoid the issue.
-
-NOTE:
-This problem disappears as soon as we upgrade to Rails 6 and use the Zeitwerk autoloader.
-
-### Further reading
-
-- Rails Guides: [Autoloading and Reloading Constants (Classic Mode)](https://guides.rubyonrails.org/autoloading_and_reloading_constants_classic_mode.html)
-- Ruby Constant lookup: [Everything you ever wanted to know about constant lookup in Ruby](https://cirw.in/blog/constant-lookup)
-- Rails 6 and Zeitwerk autoloader: [Understanding Zeitwerk in Rails 6](https://medium.com/cedarcode/understanding-zeitwerk-in-rails-6-f168a9f09a1f)
-
 ## Storing assets that do not require pre-compiling
 
 Assets that need to be served to the user are stored under the `app/assets` directory, which is later pre-compiled and placed in the `public/` directory.