3 files changed, 126 insertions, 10 deletions
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index b8e167b488..a2e3e781c0 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -1704,6 +1704,61 @@ module ApplicationTests
       end
     end
 
+    test "autoloading during initialization gets deprecation message and clearing if config.cache_classes is false" do
+      app_file "lib/c.rb", <<~EOS
+        class C
+          extend ActiveSupport::DescendantsTracker
+        end
+
+        class X < C
+        end
+      EOS
+
+      app_file "app/models/d.rb", <<~EOS
+        require "c"
+
+        class D < C
+        end
+      EOS
+
+      app_file "config/initializers/autoload.rb", "D"
+
+      app "development"
+
+      # TODO: Test deprecation message, assert_depcrecated { app "development" }
+      # does not collect it.
+
+      assert_equal [X], C.descendants
+      assert_empty ActiveSupport::Dependencies.autoloaded_constants
+    end
+
+    test "autoloading during initialization triggers nothing if config.cache_classes is true" do
+      app_file "lib/c.rb", <<~EOS
+        class C
+          extend ActiveSupport::DescendantsTracker
+        end
+
+        class X < C
+        end
+      EOS
+
+      app_file "app/models/d.rb", <<~EOS
+        require "c"
+
+        class D < C
+        end
+      EOS
+
+      app_file "config/initializers/autoload.rb", "D"
+
+      app "production"
+
+      # TODO: Test no deprecation message is issued.
+
+      assert_equal [X, D], C.descendants
+    end
+
+
     test "raises with proper error message if no database configuration found" do
       FileUtils.rm("#{app_path}/config/database.yml")
       err = assert_raises RuntimeError do
diff --git a/railties/test/application/rake/routes_test.rb b/railties/test/application/rake/routes_test.rb
index 9879d1f047..dffdae7bde 100644
--- a/railties/test/application/rake/routes_test.rb
+++ b/railties/test/application/rake/routes_test.rb
@@ -20,7 +20,6 @@ module ApplicationTests
         assert_equal <<~MESSAGE, run_rake_routes
                                          Prefix Verb   URI Pattern                                                                              Controller#Action
                                            cart GET    /cart(.:format)                                                                          cart#show
-                    rails_amazon_inbound_emails POST   /rails/action_mailbox/amazon/inbound_emails(.:format)                                    action_mailbox/ingresses/amazon/inbound_emails#create
                   rails_mandrill_inbound_emails POST   /rails/action_mailbox/mandrill/inbound_emails(.:format)                                  action_mailbox/ingresses/mandrill/inbound_emails#create
                   rails_postmark_inbound_emails POST   /rails/action_mailbox/postmark/inbound_emails(.:format)                                  action_mailbox/ingresses/postmark/inbound_emails#create
                      rails_relay_inbound_emails POST   /rails/action_mailbox/relay/inbound_emails(.:format)                                     action_mailbox/ingresses/relay/inbound_emails#create
diff --git a/railties/test/application/zeitwerk_integration_test.rb b/railties/test/application/zeitwerk_integration_test.rb
index a9da060347..40d06ee999 100644
--- a/railties/test/application/zeitwerk_integration_test.rb
+++ b/railties/test/application/zeitwerk_integration_test.rb
@@ -98,24 +98,35 @@ class ZeitwerkIntegrationTest < ActiveSupport::TestCase
     assert_nil deps.safe_constantize("Admin")
   end
 
-  test "autoloaded_constants returns autoloaded constant paths" do
-    app_file "app/models/admin/user.rb", "class Admin::User; end"
+  test "to_unload? says if a constant would be unloaded (main)" do
+    app_file "app/models/user.rb", "class User; end"
     app_file "app/models/post.rb", "class Post; end"
     boot
 
-    assert Admin::User
-    assert_equal ["Admin", "Admin::User"], deps.autoloaded_constants
+    assert Post
+    assert deps.to_unload?("Post")
+    assert_not deps.to_unload?("User")
+  end
+
+  test "to_unload? says if a constant would be unloaded (once)" do
+    add_to_config 'config.autoload_once_paths << "#{Rails.root}/extras"'
+    app_file "extras/foo.rb", "class Foo; end"
+    app_file "extras/bar.rb", "class Bar; end"
+    boot
+
+    assert Foo
+    assert_not deps.to_unload?("Foo")
+    assert_not deps.to_unload?("Bar")
   end
 
-  test "autoloaded? says if a constant has been autoloaded" do
+  test "to_unload? says if a constant would be unloaded (reloading disabled)" do
     app_file "app/models/user.rb", "class User; end"
     app_file "app/models/post.rb", "class Post; end"
-    boot
+    boot("production")
 
     assert Post
-    assert deps.autoloaded?("Post")
-    assert deps.autoloaded?(Post)
-    assert_not deps.autoloaded?("User")
+    assert_not deps.to_unload?("Post")
+    assert_not deps.to_unload?("User")
   end
 
   test "eager loading loads the application code" do
@@ -145,6 +156,15 @@ class ZeitwerkIntegrationTest < ActiveSupport::TestCase
     assert_not Rails.autoloaders.once.reloading_enabled?
   end
 
+  test "reloading raises if config.cache_classes is true" do
+    boot("production")
+
+    e = assert_raises(StandardError) do
+      deps.clear
+    end
+    assert_equal "reloading is disabled because config.cache_classes is true", e.message
+  end
+
   test "eager loading loads code in engines" do
     $test_blog_engine_eager_loaded = false
 
@@ -315,4 +335,46 @@ class ZeitwerkIntegrationTest < ActiveSupport::TestCase
       assert_nil autoloader.logger
     end
   end
+
+  # This is here because to guarantee classic mode works as always, Zeitwerk
+  # integration does not touch anything in classic. The descendants tracker is a
+  # very small one-liner exception. We leave its main test suite untouched, and
+  # add some minimal safety net here.
+  #
+  # When time passes, things are going to be reorganized (famous last words).
+  test "descendants tracker" do
+    class ::ZeitwerkDTIntegrationTestRoot
+      extend ActiveSupport::DescendantsTracker
+    end
+    class ::ZeitwerkDTIntegrationTestChild < ::ZeitwerkDTIntegrationTestRoot; end
+    class ::ZeitwerkDTIntegrationTestGrandchild < ::ZeitwerkDTIntegrationTestChild; end
+
+    begin
+      app_file "app/models/user.rb", "class User < ZeitwerkDTIntegrationTestRoot; end"
+      app_file "app/models/post.rb", "class Post < ZeitwerkDTIntegrationTestRoot; end"
+      app_file "app/models/tutorial.rb", "class Tutorial < Post; end"
+      boot
+
+      assert User
+      assert Tutorial
+
+      direct_descendants = [ZeitwerkDTIntegrationTestChild, User, Post].to_set
+      assert_equal direct_descendants, ZeitwerkDTIntegrationTestRoot.direct_descendants.to_set
+
+      descendants = direct_descendants.merge([ZeitwerkDTIntegrationTestGrandchild, Tutorial])
+      assert_equal descendants, ZeitwerkDTIntegrationTestRoot.descendants.to_set
+
+      ActiveSupport::DescendantsTracker.clear
+
+      direct_descendants = [ZeitwerkDTIntegrationTestChild].to_set
+      assert_equal direct_descendants, ZeitwerkDTIntegrationTestRoot.direct_descendants.to_set
+
+      descendants = direct_descendants.merge([ZeitwerkDTIntegrationTestGrandchild])
+      assert_equal descendants, ZeitwerkDTIntegrationTestRoot.descendants.to_set
+    ensure
+      Object.send(:remove_const, :ZeitwerkDTIntegrationTestRoot)
+      Object.send(:remove_const, :ZeitwerkDTIntegrationTestChild)
+      Object.send(:remove_const, :ZeitwerkDTIntegrationTestGrandchild)
+    end
+  end
 end