Replace autoloader accessors with Rails.autoloaders.{main,once}

Rails.autoloader and Rails.once_autoloader was just tentative API good
enough for a first patch. Rails.autoloader is singular and does not
convey in its name that there is another autoloader. That might be
confusing, for example if you set a logger and miss traces. On the other
hand, the name `once_autoloader` is very close to being horrible.

Rails.autoloaders.main and Rails.autoloaders.once read better for my
taste, and have a nice symmetry. Also, both "main" and "once" are four
letters long, short and same length.

They are tagged as "rails.main" and "rails.once", respectively.

References #35235.

5 files changed, 65 insertions, 41 deletions

diff --git a/railties/lib/rails.rb b/railties/lib/rails.rb
index bca2cf34e1..1f533a8c04 100644
--- a/railties/lib/rails.rb
+++ b/railties/lib/rails.rb
@@ -13,6 +13,7 @@ require "active_support/core_ext/object/blank"
 
 require "rails/application"
 require "rails/version"
+require "rails/autoloaders"
 
 require "active_support/railtie"
 require "action_dispatch/railtie"
@@ -111,24 +112,8 @@ module Rails
       application && Pathname.new(application.paths["public"].first)
     end
 
-    def autoloader
-      if configuration.autoloader == :zeitwerk
-        @autoloader ||= Zeitwerk::Loader.new
-      end
-    end
-
-    def once_autoloader
-      if configuration.autoloader == :zeitwerk
-        @once_autoloader ||= Zeitwerk::Loader.new
-      end
-    end
-
     def autoloaders
-      if configuration.autoloader == :zeitwerk
-        [autoloader, once_autoloader]
-      else
-        []
-      end
+      Autoloaders
     end
   end
 end
diff --git a/railties/lib/rails/autoloaders.rb b/railties/lib/rails/autoloaders.rb
new file mode 100644
index 0000000000..4b71f90c6b
--- /dev/null
+++ b/railties/lib/rails/autoloaders.rb
@@ -0,0 +1,30 @@
+module Rails
+  module Autoloaders # :nodoc:
+    class << self
+      include Enumerable
+
+      def main
+        if zeitwerk_enabled?
+          @main ||= Zeitwerk::Loader.new.tap { |loader| loader.tag = "rails.main" }
+        end
+      end
+
+      def once
+        if zeitwerk_enabled?
+          @once ||= Zeitwerk::Loader.new.tap { |loader| loader.tag = "rails.once" }
+        end
+      end
+
+      def each
+        if zeitwerk_enabled?
+          yield main
+          yield once
+        end
+      end
+
+      def zeitwerk_enabled?
+        Rails.configuration.autoloader == :zeitwerk
+      end
+    end
+  end
+end
diff --git a/railties/lib/rails/engine.rb b/railties/lib/rails/engine.rb
index 2485158a7b..76be6a8ac7 100644
--- a/railties/lib/rails/engine.rb
+++ b/railties/lib/rails/engine.rb
@@ -472,7 +472,7 @@ module Rails
     # Eager load the application by loading all ruby
     # files inside eager_load paths.
     def eager_load!
-      if Rails.autoloader
+      if Rails.autoloaders.zeitwerk_enabled?
         eager_load_with_zeitwerk!
       else
         eager_load_with_dependencies!
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index f3161ad2a8..73773602a3 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -1157,23 +1157,30 @@ module ApplicationTests
       end
     end
 
-    test "autoloader & autoloader=" do
+    test "autoloaders" do
       app "development"
 
       config = Rails.application.config
-      assert_instance_of Zeitwerk::Loader, Rails.autoloader
-      assert_instance_of Zeitwerk::Loader, Rails.once_autoloader
-      assert_equal [Rails.autoloader, Rails.once_autoloader], Rails.autoloaders
+      assert Rails.autoloaders.zeitwerk_enabled?
+      assert_instance_of Zeitwerk::Loader, Rails.autoloaders.main
+      assert_equal "rails.main", Rails.autoloaders.main.tag
+      assert_instance_of Zeitwerk::Loader, Rails.autoloaders.once
+      assert_equal "rails.once", Rails.autoloaders.once.tag
+      assert_equal [Rails.autoloaders.main, Rails.autoloaders.once], Rails.autoloaders.to_a
 
       config.autoloader = :classic
-      assert_nil Rails.autoloader
-      assert_nil Rails.once_autoloader
-      assert_empty Rails.autoloaders
+      assert_not Rails.autoloaders.zeitwerk_enabled?
+      assert_nil Rails.autoloaders.main
+      assert_nil Rails.autoloaders.once
+      assert_equal 0, Rails.autoloaders.count
 
       config.autoloader = :zeitwerk
-      assert_instance_of Zeitwerk::Loader, Rails.autoloader
-      assert_instance_of Zeitwerk::Loader, Rails.once_autoloader
-      assert_equal [Rails.autoloader, Rails.once_autoloader], Rails.autoloaders
+      assert Rails.autoloaders.zeitwerk_enabled?
+      assert_instance_of Zeitwerk::Loader, Rails.autoloaders.main
+      assert_equal "rails.main", Rails.autoloaders.main.tag
+      assert_instance_of Zeitwerk::Loader, Rails.autoloaders.once
+      assert_equal "rails.once", Rails.autoloaders.once.tag
+      assert_equal [Rails.autoloaders.main, Rails.autoloaders.once], Rails.autoloaders.to_a
 
       assert_raises(ArgumentError) { config.autoloader = :unknown }
     end
diff --git a/railties/test/application/zeitwerk_integration_test.rb b/railties/test/application/zeitwerk_integration_test.rb
index 628a85acd8..16ffbe56bb 100644
--- a/railties/test/application/zeitwerk_integration_test.rb
+++ b/railties/test/application/zeitwerk_integration_test.rb
@@ -30,9 +30,10 @@ class ZeitwerkIntegrationTest < ActiveSupport::TestCase
     boot
 
     assert decorated?
-    assert_instance_of Zeitwerk::Loader, Rails.autoloader
-    assert_instance_of Zeitwerk::Loader, Rails.once_autoloader
-    assert_equal [Rails.autoloader, Rails.once_autoloader], Rails.autoloaders
+    assert Rails.autoloaders.zeitwerk_enabled?
+    assert_instance_of Zeitwerk::Loader, Rails.autoloaders.main
+    assert_instance_of Zeitwerk::Loader, Rails.autoloaders.once
+    assert_equal [Rails.autoloaders.main, Rails.autoloaders.once], Rails.autoloaders.to_a
   end
 
   test "ActiveSupport::Dependencies is not decorated in classic mode" do
@@ -40,9 +41,10 @@ class ZeitwerkIntegrationTest < ActiveSupport::TestCase
     boot
 
     assert_not decorated?
-    assert_nil Rails.autoloader
-    assert_nil Rails.once_autoloader
-    assert_empty Rails.autoloaders
+    assert_not Rails.autoloaders.zeitwerk_enabled?
+    assert_nil Rails.autoloaders.main
+    assert_nil Rails.autoloaders.once
+    assert_equal 0, Rails.autoloaders.count
   end
 
   test "constantize returns the value stored in the constant" do
@@ -136,8 +138,8 @@ class ZeitwerkIntegrationTest < ActiveSupport::TestCase
     )
     boot
 
-    assert_not_includes Rails.autoloader.dirs, "#{app_path}/extras"
-    assert_includes Rails.once_autoloader.dirs, "#{app_path}/extras"
+    assert_not_includes Rails.autoloaders.main.dirs, "#{app_path}/extras"
+    assert_includes Rails.autoloaders.once.dirs, "#{app_path}/extras"
   end
 
   test "clear reloads the main autoloader, and does not reload the once one" do
@@ -145,13 +147,13 @@ class ZeitwerkIntegrationTest < ActiveSupport::TestCase
 
     $zeitwerk_integration_reload_test = []
 
-    autoloader = Rails.autoloader
-    def autoloader.reload
-      $zeitwerk_integration_reload_test << :autoloader
+    main_autoloader = Rails.autoloaders.main
+    def main_autoloader.reload
+      $zeitwerk_integration_reload_test << :main_autoloader
       super
     end
 
-    once_autoloader = Rails.once_autoloader
+    once_autoloader = Rails.autoloaders.once
     def once_autoloader.reload
       $zeitwerk_integration_reload_test << :once_autoloader
       super
@@ -159,6 +161,6 @@ class ZeitwerkIntegrationTest < ActiveSupport::TestCase
 
     ActiveSupport::Dependencies.clear
 
-    assert_equal %i(autoloader), $zeitwerk_integration_reload_test
+    assert_equal %i(main_autoloader), $zeitwerk_integration_reload_test
   end
 end