From 821d6c694cd305b7792b96d6ebc1c15ca235cf3e Mon Sep 17 00:00:00 2001
From: Xavier Noria <fxn@hashref.com>
Date: Mon, 11 Feb 2019 12:44:25 -0800
Subject: Zeitwerk integration

---
 railties/lib/rails.rb                              |  20 +++
 railties/lib/rails/application/configuration.rb    |  13 +-
 railties/lib/rails/application/finisher.rb         |   8 +
 railties/lib/rails/engine.rb                       |  26 +++-
 .../generators/rails/app/templates/Gemfile.tt      |   6 +-
 railties/test/application/configuration_test.rb    |  21 +++
 railties/test/application/mailer_previews_test.rb  |   3 +
 .../test/application/multiple_applications_test.rb |  24 ---
 railties/test/application/rake_test.rb             |   4 +-
 .../test/application/zeitwerk_integration_test.rb  | 164 +++++++++++++++++++++
 railties/test/generators/app_generator_test.rb     |   9 ++
 railties/test/isolation/abstract_unit.rb           |  10 +-
 railties/test/railties/engine_test.rb              |  32 ++--
 13 files changed, 289 insertions(+), 51 deletions(-)
 create mode 100644 railties/test/application/zeitwerk_integration_test.rb

(limited to 'railties')

diff --git a/railties/lib/rails.rb b/railties/lib/rails.rb
index 092105d502..bca2cf34e1 100644
--- a/railties/lib/rails.rb
+++ b/railties/lib/rails.rb
@@ -110,5 +110,25 @@ module Rails
     def public_path
       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
+    end
   end
 end
diff --git a/railties/lib/rails/application/configuration.rb b/railties/lib/rails/application/configuration.rb
index b7838f7e32..16fbc99e7a 100644
--- a/railties/lib/rails/application/configuration.rb
+++ b/railties/lib/rails/application/configuration.rb
@@ -20,7 +20,7 @@ module Rails
                     :read_encrypted_secrets, :log_level, :content_security_policy_report_only,
                     :content_security_policy_nonce_generator, :require_master_key, :credentials
 
-      attr_reader :encoding, :api_only, :loaded_config_version
+      attr_reader :encoding, :api_only, :loaded_config_version, :autoloader
 
       def initialize(*)
         super
@@ -64,6 +64,7 @@ module Rails
         @credentials                             = ActiveSupport::OrderedOptions.new
         @credentials.content_path                = default_credentials_content_path
         @credentials.key_path                    = default_credentials_key_path
+        @autoloader                              = :classic
       end
 
       def load_defaults(target_version)
@@ -117,6 +118,8 @@ module Rails
         when "6.0"
           load_defaults "5.2"
 
+          self.autoloader = :zeitwerk if RUBY_ENGINE == "ruby"
+
           if respond_to?(:action_view)
             action_view.default_enforce_utf8 = false
           end
@@ -267,6 +270,14 @@ module Rails
         end
       end
 
+      def autoloader=(autoloader)
+        if %i(classic zeitwerk).include?(autoloader)
+          @autoloader = autoloader
+        else
+          raise ArgumentError, "config.autoloader may be :classic or :zeitwerk, got #{autoloader.inspect} instead"
+        end
+      end
+
       class Custom #:nodoc:
         def initialize
           @configurations = Hash.new
diff --git a/railties/lib/rails/application/finisher.rb b/railties/lib/rails/application/finisher.rb
index 04aaf6dd9a..39e8ef6631 100644
--- a/railties/lib/rails/application/finisher.rb
+++ b/railties/lib/rails/application/finisher.rb
@@ -21,6 +21,13 @@ module Rails
         end
       end
 
+      initializer :let_zeitwerk_take_over do
+        if config.autoloader == :zeitwerk
+          require "active_support/dependencies/zeitwerk_integration"
+          ActiveSupport::Dependencies::ZeitwerkIntegration.take_over
+        end
+      end
+
       initializer :add_builtin_route do |app|
         if Rails.env.development?
           app.routes.prepend do
@@ -66,6 +73,7 @@ module Rails
       initializer :eager_load! do
         if config.eager_load
           ActiveSupport.run_load_hooks(:before_eager_load, self)
+          Zeitwerk::Loader.eager_load_all if defined?(Zeitwerk)
           config.eager_load_namespaces.each(&:eager_load!)
         end
       end
diff --git a/railties/lib/rails/engine.rb b/railties/lib/rails/engine.rb
index d6c329b581..2485158a7b 100644
--- a/railties/lib/rails/engine.rb
+++ b/railties/lib/rails/engine.rb
@@ -472,12 +472,10 @@ module Rails
     # Eager load the application by loading all ruby
     # files inside eager_load paths.
     def eager_load!
-      config.eager_load_paths.each do |load_path|
-        # Starts after load_path plus a slash, ends before ".rb".
-        relname_range = (load_path.to_s.length + 1)...-3
-        Dir.glob("#{load_path}/**/*.rb").sort.each do |file|
-          require_dependency file[relname_range]
-        end
+      if Rails.autoloader
+        eager_load_with_zeitwerk!
+      else
+        eager_load_with_dependencies!
       end
     end
 
@@ -653,6 +651,22 @@ module Rails
 
     private
 
+      def eager_load_with_zeitwerk!
+        (config.eager_load_paths - Zeitwerk::Loader.all_dirs).each do |path|
+          Dir.glob("#{path}/**/*.rb").sort.each { |file| require file }
+        end
+      end
+
+      def eager_load_with_dependencies!
+        config.eager_load_paths.each do |load_path|
+          # Starts after load_path plus a slash, ends before ".rb".
+          relname_range = (load_path.to_s.length + 1)...-3
+          Dir.glob("#{load_path}/**/*.rb").sort.each do |file|
+            require_dependency file[relname_range]
+          end
+        end
+      end
+
       def load_config_initializer(initializer) # :doc:
         ActiveSupport::Notifications.instrument("load_config_initializer.railties", initializer: initializer) do
           load(initializer)
diff --git a/railties/lib/rails/generators/rails/app/templates/Gemfile.tt b/railties/lib/rails/generators/rails/app/templates/Gemfile.tt
index d39b5d311f..a1f1224a45 100644
--- a/railties/lib/rails/generators/rails/app/templates/Gemfile.tt
+++ b/railties/lib/rails/generators/rails/app/templates/Gemfile.tt
@@ -28,7 +28,7 @@ ruby <%= "'#{RUBY_VERSION}'" -%>
 
 <% if depend_on_bootsnap? -%>
 # Reduces boot times through caching; required in config/boot.rb
-gem 'bootsnap', '>= 1.1.0', require: false
+gem 'bootsnap', '>= 1.4.0', require: false
 
 <%- end -%>
 <%- if options.api? -%>
@@ -36,7 +36,9 @@ gem 'bootsnap', '>= 1.1.0', require: false
 # gem 'rack-cors'
 
 <%- end -%>
-<% if RUBY_ENGINE == 'ruby' -%>
+<% if RUBY_ENGINE == "ruby" -%>
+gem "zeitwerk", ">= 1.0.0"
+
 group :development, :test do
   # Call 'byebug' anywhere in the code to stop execution and get a debugger console
   gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 9ea4d6dc5f..960f708bdf 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -1157,6 +1157,27 @@ module ApplicationTests
       end
     end
 
+    test "autoloader & autoloader=" 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
+
+      config.autoloader = :classic
+      assert_nil Rails.autoloader
+      assert_nil Rails.once_autoloader
+      assert_empty Rails.autoloaders
+
+      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_raises(ArgumentError) { config.autoloader = :unknown }
+    end
+
     test "config.action_view.cache_template_loading with cache_classes default" do
       add_to_config "config.cache_classes = true"
 
diff --git a/railties/test/application/mailer_previews_test.rb b/railties/test/application/mailer_previews_test.rb
index ba186bda44..fb84276b8a 100644
--- a/railties/test/application/mailer_previews_test.rb
+++ b/railties/test/application/mailer_previews_test.rb
@@ -85,6 +85,7 @@ module ApplicationTests
     end
 
     test "mailer previews are loaded from a custom preview_path" do
+      app_dir "lib/mailer_previews"
       add_to_config "config.action_mailer.preview_path = '#{app_path}/lib/mailer_previews'"
 
       mailer "notifier", <<-RUBY
@@ -254,6 +255,7 @@ module ApplicationTests
     end
 
     test "mailer previews are reloaded from a custom preview_path" do
+      app_dir "lib/mailer_previews"
       add_to_config "config.action_mailer.preview_path = '#{app_path}/lib/mailer_previews'"
 
       app("development")
@@ -818,6 +820,7 @@ module ApplicationTests
       def build_app
         super
         app_file "config/routes.rb", "Rails.application.routes.draw do; end"
+        app_dir "test/mailers/previews"
       end
 
       def mailer(name, contents)
diff --git a/railties/test/application/multiple_applications_test.rb b/railties/test/application/multiple_applications_test.rb
index 432344bccc..f0f1112f6b 100644
--- a/railties/test/application/multiple_applications_test.rb
+++ b/railties/test/application/multiple_applications_test.rb
@@ -100,30 +100,6 @@ module ApplicationTests
       assert_nothing_raised { AppTemplate::Application.new }
     end
 
-    def test_initializers_run_on_different_applications_go_to_the_same_class
-      application1 = AppTemplate::Application.new
-      run_count = 0
-
-      AppTemplate::Application.initializer :init0 do
-        run_count += 1
-      end
-
-      application1.initializer :init1 do
-        run_count += 1
-      end
-
-      AppTemplate::Application.new.initializer :init2 do
-        run_count += 1
-      end
-
-      assert_equal 0, run_count, "Without loading the initializers, the count should be 0"
-
-      # Set config.eager_load to false so that an eager_load warning doesn't pop up
-      AppTemplate::Application.create { config.eager_load = false }.initialize!
-
-      assert_equal 3, run_count, "There should have been three initializers that incremented the count"
-    end
-
     def test_consoles_run_on_different_applications_go_to_the_same_class
       run_count = 0
       AppTemplate::Application.console { run_count += 1 }
diff --git a/railties/test/application/rake_test.rb b/railties/test/application/rake_test.rb
index 44e3b0f66b..fe56e3d076 100644
--- a/railties/test/application/rake_test.rb
+++ b/railties/test/application/rake_test.rb
@@ -145,8 +145,8 @@ module ApplicationTests
       # loading a specific fixture
       rails "db:fixtures:load", "FIXTURES=products"
 
-      assert_equal 2, ::AppTemplate::Application::Product.count
-      assert_equal 0, ::AppTemplate::Application::User.count
+      assert_equal 2, Product.count
+      assert_equal 0, User.count
     end
 
     def test_loading_only_yml_fixtures
diff --git a/railties/test/application/zeitwerk_integration_test.rb b/railties/test/application/zeitwerk_integration_test.rb
new file mode 100644
index 0000000000..d44b7f7e4d
--- /dev/null
+++ b/railties/test/application/zeitwerk_integration_test.rb
@@ -0,0 +1,164 @@
+# frozen_string_literal: true
+
+require "isolation/abstract_unit"
+require "active_support/dependencies/zeitwerk_integration"
+
+class ZeitwerkIntegrationTest < ActiveSupport::TestCase
+  include ActiveSupport::Testing::Isolation
+
+  def setup
+    build_app
+  end
+
+  def boot(env = "development")
+    app(env)
+  end
+
+  def teardown
+    teardown_app
+  end
+
+  def deps
+    ActiveSupport::Dependencies
+  end
+
+  def decorated?
+    deps.singleton_class < deps::ZeitwerkIntegration::Decorations
+  end
+
+  test "ActiveSupport::Dependencies is decorated by default" do
+    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
+  end
+
+  test "ActiveSupport::Dependencies is not decorated in classic mode" do
+    add_to_config 'config.autoloader = :classic'
+    boot
+
+    assert_not decorated?
+    assert_nil Rails.autoloader
+    assert_nil Rails.once_autoloader
+    assert_empty Rails.autoloaders
+  end
+
+  test "constantize returns the value stored in the constant" do
+    app_file "app/models/admin/user.rb", "class Admin::User; end"
+    boot
+
+    assert_same Admin::User, deps.constantize("Admin::User")
+  end
+
+  test "constantize raises if the constant is unknown" do
+    boot
+
+    assert_raises(NameError) { deps.constantize("Admin") }
+  end
+
+  test "safe_constantize returns the value stored in the constant" do
+    app_file "app/models/admin/user.rb", "class Admin::User; end"
+    boot
+
+    assert_same Admin::User, deps.safe_constantize("Admin::User")
+  end
+
+  test "safe_constantize returns nil for unknown constants" do
+    boot
+
+    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"
+    app_file "app/models/post.rb", "class Post; end"
+    boot
+
+    assert Admin::User
+    assert_equal ["Admin", "Admin::User"], deps.autoloaded_constants
+  end
+
+  test "autoloaded? says if a constant has been autoloaded" do
+    app_file "app/models/user.rb", "class User; end"
+    app_file "app/models/post.rb", "class Post; end"
+    boot
+
+    assert Post
+    assert deps.autoloaded?("Post")
+    assert deps.autoloaded?(Post)
+    assert_not deps.autoloaded?("User")
+  end
+
+  test "eager loading loads the application code" do
+    $zeitwerk_integration_test_user = false
+    $zeitwerk_integration_test_post = false
+
+    app_file "app/models/user.rb", "class User; end; $zeitwerk_integration_test_user = true"
+    app_file "app/models/post.rb", "class Post; end; $zeitwerk_integration_test_post = true"
+    boot("production")
+
+    assert $zeitwerk_integration_test_user
+    assert $zeitwerk_integration_test_post
+  end
+
+  test "eager loading loads anything managed by Zeitwerk" do
+    $zeitwerk_integration_test_user  = false
+    app_file "app/models/user.rb", "class User; end; $zeitwerk_integration_test_user = true"
+
+    $zeitwerk_integration_test_extras = false
+    app_dir "extras"
+    app_file "extras/webhook_hacks.rb", "WebhookHacks = 1; $zeitwerk_integration_test_extras = true"
+
+    require "zeitwerk"
+    autoloader = Zeitwerk::Loader.new
+    autoloader.push_dir("#{app_path}/extras")
+    autoloader.setup
+
+    boot("production")
+
+    assert $zeitwerk_integration_test_user
+    assert $zeitwerk_integration_test_extras
+  end
+
+  test "autoload paths that are below Gem.path go to the once autoloader" do
+    app_dir "extras"
+    add_to_config 'config.autoload_paths << "#{Rails.root}/extras"'
+
+    # Mocks Gem.path to include the extras directory.
+    Gem.singleton_class.prepend(
+      Module.new do
+        def path
+          super + ["#{Rails.root}/extras"]
+        end
+      end
+    )
+    boot
+
+    refute_includes Rails.autoloader.dirs, "#{app_path}/extras"
+    assert_includes Rails.once_autoloader.dirs, "#{app_path}/extras"
+  end
+
+  test "clear reloads the main autoloader, and does not reload the once one" do
+    boot
+
+    $zeitwerk_integration_reload_test = []
+
+    autoloader = Rails.autoloader
+    def autoloader.reload
+      $zeitwerk_integration_reload_test << :autoloader
+      super
+    end
+
+    once_autoloader = Rails.once_autoloader
+    def once_autoloader.reload
+      $zeitwerk_integration_reload_test << :once_autoloader
+      super
+    end
+
+    ActiveSupport::Dependencies.clear
+
+    assert_equal %i(autoloader), $zeitwerk_integration_reload_test
+  end
+end
diff --git a/railties/test/generators/app_generator_test.rb b/railties/test/generators/app_generator_test.rb
index 1ee9e43e89..937b8eb427 100644
--- a/railties/test/generators/app_generator_test.rb
+++ b/railties/test/generators/app_generator_test.rb
@@ -660,6 +660,15 @@ class AppGeneratorTest < Rails::Generators::TestCase
     assert_gem "jbuilder"
   end
 
+  def test_inclusion_of_zeitwerk
+    run_generator
+    if RUBY_ENGINE == "ruby"
+      assert_gem "zeitwerk"
+    else
+      assert_no_gem "zeitwerk"
+    end
+  end
+
   def test_inclusion_of_a_debugger
     run_generator
     if defined?(JRUBY_VERSION) || RUBY_ENGINE == "rbx"
diff --git a/railties/test/isolation/abstract_unit.rb b/railties/test/isolation/abstract_unit.rb
index 0e8e0e86ee..47d42645c6 100644
--- a/railties/test/isolation/abstract_unit.rb
+++ b/railties/test/isolation/abstract_unit.rb
@@ -421,6 +421,10 @@ module TestHelpers
       file_name
     end
 
+    def app_dir(path)
+      FileUtils.mkdir_p("#{app_path}/#{path}")
+    end
+
     def remove_file(path)
       FileUtils.rm_rf "#{app_path}/#{path}"
     end
@@ -487,7 +491,11 @@ Module.new do
   # Fake 'Bundler.require' -- we run using the repo's Gemfile, not an
   # app-specific one: we don't want to require every gem that lists.
   contents = File.read("#{app_template_path}/config/application.rb")
-  contents.sub!(/^Bundler\.require.*/, "%w(turbolinks webpacker).each { |r| require r }")
+  if RUBY_ENGINE == "ruby"
+    contents.sub!(/^Bundler\.require.*/, "%w(turbolinks webpacker zeitwerk).each { |r| require r }")
+  else
+    contents.sub!(/^Bundler\.require.*/, "%w(turbolinks webpacker).each { |r| require r }")
+  end
   File.write("#{app_template_path}/config/application.rb", contents)
 
   require "rails"
diff --git a/railties/test/railties/engine_test.rb b/railties/test/railties/engine_test.rb
index 851407dede..69f6e34d58 100644
--- a/railties/test/railties/engine_test.rb
+++ b/railties/test/railties/engine_test.rb
@@ -704,25 +704,27 @@ YAML
       RUBY
 
       @plugin.write "app/controllers/bukkits/foo_controller.rb", <<-RUBY
-        class Bukkits::FooController < ActionController::Base
-          def index
-            render inline: "<%= help_the_engine %>"
-          end
+        module Bukkits
+          class FooController < ActionController::Base
+            def index
+              render inline: "<%= help_the_engine %>"
+            end
 
-          def show
-            render plain: foo_path
-          end
+            def show
+              render plain: foo_path
+            end
 
-          def from_app
-            render inline: "<%= (self.respond_to?(:bar_path) || self.respond_to?(:something)) %>"
-          end
+            def from_app
+              render inline: "<%= (self.respond_to?(:bar_path) || self.respond_to?(:something)) %>"
+            end
 
-          def routes_helpers_in_view
-            render inline: "<%= foo_path %>, <%= main_app.bar_path %>"
-          end
+            def routes_helpers_in_view
+              render inline: "<%= foo_path %>, <%= main_app.bar_path %>"
+            end
 
-          def polymorphic_path_without_namespace
-            render plain: polymorphic_path(Post.new)
+            def polymorphic_path_without_namespace
+              render plain: polymorphic_path(Post.new)
+            end
           end
         end
       RUBY
-- 
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