From a3e061def14b50b86d9366d45565a4ad2efb0b08 Mon Sep 17 00:00:00 2001
From: Xavier Noria <fxn@hashref.com>
Date: Sat, 30 Mar 2019 12:20:00 +0100
Subject: [PATCH] optimizes eager loading in :zeitwerk mode

During initialization, the eager load paths of engines are unshifted
into AS::Dependencies.autoload_paths. After that, the collection is
frozen. (See the initializers in railties/lib/rails/engine.rb.)

Hence, there is no eager load path that is not an autoload path too, and
so the array difference in the deleted code is always an empty array.

Just do nothing.
---
 railties/lib/rails/engine.rb                  | 31 ++++++-------------
 .../application/zeitwerk_integration_test.rb  | 14 +++++++++
 2 files changed, 23 insertions(+), 22 deletions(-)

diff --git a/railties/lib/rails/engine.rb b/railties/lib/rails/engine.rb
index 2b5afd51b8..9b3698aa5e 100644
--- a/railties/lib/rails/engine.rb
+++ b/railties/lib/rails/engine.rb
@@ -469,13 +469,16 @@ module Rails
       self
     end
 
-    # Eager load the application by loading all ruby
-    # files inside eager_load paths.
     def eager_load!
-      if Rails.autoloaders.zeitwerk_enabled?
-        eager_load_with_zeitwerk!
-      else
-        eager_load_with_dependencies!
+      # Already done by Zeitwerk::Loader.eager_load_all in the finisher.
+      return if Rails.autoloaders.zeitwerk_enabled?
+
+      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
 
@@ -654,22 +657,6 @@ 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/test/application/zeitwerk_integration_test.rb b/railties/test/application/zeitwerk_integration_test.rb
index e4a17e5a31..a4320bbdc3 100644
--- a/railties/test/application/zeitwerk_integration_test.rb
+++ b/railties/test/application/zeitwerk_integration_test.rb
@@ -124,12 +124,26 @@ class ZeitwerkIntegrationTest < ActiveSupport::TestCase
 
     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 code in engines" do
+    $test_blog_engine_eager_loaded = false
+
+    engine("blog") do |bukkit|
+      bukkit.write("lib/blog.rb", "class BlogEngine < Rails::Engine; end")
+      bukkit.write("app/models/post.rb", "Post = $test_blog_engine_eager_loaded = true")
+    end
+
+    boot("production")
+
+    assert $test_blog_engine_eager_loaded
+  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"