Zeitwerk integration

4 files changed, 44 insertions, 9 deletions

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]