Only load example group modules when they're used

Currently the example group modules for all spec types are always
loaded, regardless of which type of spec is being run. Some of those
modules force parts of the user's application to load; for example,
RSpec::Rails::HelperExampleGroup includes ActionView::TestCase::Behavior
and loading ActionView::TestCase loads all of the application's helpers.

By autoloading these modules and including them lazily the first time
the corresponding spec type is defined, we can avoid loading parts of
the user's application unnecessarily.

Co-authored-by: Iliana Hadzhiatanasova <me@iliana.dev>

lib/rspec/rails.rb

@@ -1,6 +1,24 @@
 require 'rspec/core'
 require 'rails/version'
 
+module RSpec
+  module Rails
+    autoload :RailsExampleGroup, 'rspec/rails/example/rails_example_group'
+    autoload :ControllerExampleGroup, 'rspec/rails/example/controller_example_group'
+    autoload :HelperExampleGroup, 'rspec/rails/example/helper_example_group'
+    autoload :ModelExampleGroup, 'rspec/rails/example/model_example_group'
+    autoload :RequestExampleGroup, 'rspec/rails/example/request_example_group'
+    autoload :RoutingExampleGroup, 'rspec/rails/example/routing_example_group'
+    autoload :ViewExampleGroup, 'rspec/rails/example/view_example_group'
+    autoload :FeatureExampleGroup, 'rspec/rails/example/feature_example_group'
+    autoload :SystemExampleGroup, 'rspec/rails/example/system_example_group'
+    autoload :MailerExampleGroup, 'rspec/rails/example/mailer_example_group'
+    autoload :JobExampleGroup, 'rspec/rails/example/job_example_group'
+    autoload :ChannelExampleGroup, 'rspec/rails/example/channel_example_group'
+    autoload :MailboxExampleGroup, 'rspec/rails/example/mailbox_example_group'
+  end
+end
+
 # Load any of our adapters and extensions early in the process
 require 'rspec/rails/adapters'
 require 'rspec/rails/extensions'
@@ -11,7 +29,6 @@
 require 'rspec/rails/fixture_support'
 require 'rspec/rails/file_fixture_support'
 require 'rspec/rails/fixture_file_upload_support'
-require 'rspec/rails/example'
 require 'rspec/rails/vendor/capybara'
 require 'rspec/rails/configuration'
 require 'rspec/rails/active_record'

lib/rspec/rails/configuration.rb

@@ -45,15 +45,40 @@ class Configuration
     #
     # @api private
     def self.add_test_type_configurations(config)
-      config.include RSpec::Rails::ControllerExampleGroup, type: :controller
-      config.include RSpec::Rails::HelperExampleGroup,     type: :helper
-      config.include RSpec::Rails::ModelExampleGroup,      type: :model
-      config.include RSpec::Rails::RequestExampleGroup,    type: :request
-      config.include RSpec::Rails::RoutingExampleGroup,    type: :routing
-      config.include RSpec::Rails::ViewExampleGroup,       type: :view
-      config.include RSpec::Rails::FeatureExampleGroup,    type: :feature
+      config.define_derived_metadata(type: :controller) do
+        config.include RSpec::Rails::ControllerExampleGroup, type: :controller
+      end
+
+      config.define_derived_metadata(type: :helper) do
+        config.include RSpec::Rails::HelperExampleGroup, type: :helper
+      end
+
+      config.define_derived_metadata(type: :model) do
+        config.include RSpec::Rails::ModelExampleGroup, type: :model
+      end
+
+      config.define_derived_metadata(type: :request) do
+        config.include RSpec::Rails::RequestExampleGroup, type: :request
+      end
+
+      config.define_derived_metadata(type: :routing) do
+        require "action_controller/test_case"
+        config.include RSpec::Rails::RoutingExampleGroup, type: :routing
+      end
+
+      config.define_derived_metadata(type: :view) do
+        config.include RSpec::Rails::ViewExampleGroup, type: :view
+      end
+
+      config.define_derived_metadata(type: :feature) do
+        config.include RSpec::Rails::FeatureExampleGroup, type: :feature
+      end
+
       config.include RSpec::Rails::Matchers
-      config.include RSpec::Rails::SystemExampleGroup, type: :system
+
+      config.define_derived_metadata(type: :system) do
+        config.include RSpec::Rails::SystemExampleGroup, type: :system
+      end
     end
 
     # @private
@@ -192,27 +217,38 @@ def fixture_path=(path)
 
       if defined?(::Rails::Controller::Testing)
         [:controller, :view, :request].each do |type|
-          config.include ::Rails::Controller::Testing::TestProcess, type: type
-          config.include ::Rails::Controller::Testing::TemplateAssertions, type: type
-          config.include ::Rails::Controller::Testing::Integration, type: type
+          config.define_derived_metadata(type: type) do
+            config.include ::Rails::Controller::Testing::TestProcess, type: type
+            config.include ::Rails::Controller::Testing::TemplateAssertions, type: type
+            config.include ::Rails::Controller::Testing::Integration, type: type
+          end
         end
       end
 
       if RSpec::Rails::FeatureCheck.has_action_mailer?
-        config.include RSpec::Rails::MailerExampleGroup, type: :mailer
+        config.define_derived_metadata(type: :mailer) do
+          config.include RSpec::Rails::MailerExampleGroup, type: :mailer
+        end
+
         config.after { ActionMailer::Base.deliveries.clear }
       end
 
       if RSpec::Rails::FeatureCheck.has_active_job?
-        config.include RSpec::Rails::JobExampleGroup, type: :job
+        config.define_derived_metadata(type: :job) do
+          config.include RSpec::Rails::JobExampleGroup, type: :job
+        end
       end
 
       if RSpec::Rails::FeatureCheck.has_action_cable_testing?
-        config.include RSpec::Rails::ChannelExampleGroup, type: :channel
+        config.define_derived_metadata(type: :channel) do
+          config.include RSpec::Rails::ChannelExampleGroup, type: :channel
+        end
       end
 
       if RSpec::Rails::FeatureCheck.has_action_mailbox?
-        config.include RSpec::Rails::MailboxExampleGroup, type: :mailbox
+        config.define_derived_metadata(type: :mailbox) do
+          config.include RSpec::Rails::MailboxExampleGroup, type: :mailbox
+        end
       end
     end
 

lib/rspec/rails/example.rb

@@ -1,13 +1,3 @@
-require 'rspec/rails/example/rails_example_group'
-require 'rspec/rails/example/controller_example_group'
-require 'rspec/rails/example/request_example_group'
-require 'rspec/rails/example/helper_example_group'
-require 'rspec/rails/example/view_example_group'
-require 'rspec/rails/example/mailer_example_group'
-require 'rspec/rails/example/routing_example_group'
-require 'rspec/rails/example/model_example_group'
-require 'rspec/rails/example/job_example_group'
-require 'rspec/rails/example/feature_example_group'
-require 'rspec/rails/example/system_example_group'
-require 'rspec/rails/example/channel_example_group'
-require 'rspec/rails/example/mailbox_example_group'
+RSpec.warn_deprecation <<~WARNING
+  Requiring rspec/rails/example.rb no longer has any effect, and it will be removed in RSpec Rails 7.
+WARNING