From 57c7cbb1623c0e8befc58988a34bbb9896fd226a Mon Sep 17 00:00:00 2001
From: Xavier Noria <fxn@hashref.com>
Date: Sun, 7 Apr 2019 12:30:34 +0200
Subject: depend on Zeitwerk 2

---
 Gemfile.lock                                               |  4 ++--
 activesupport/CHANGELOG.md                                 |  6 ++++++
 activesupport/activesupport.gemspec                        |  2 +-
 .../active_support/dependencies/zeitwerk_integration.rb    |  7 ++++---
 railties/lib/rails/application/finisher.rb                 |  2 +-
 railties/test/application/zeitwerk_integration_test.rb     | 14 ++++++++++++++
 6 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/Gemfile.lock b/Gemfile.lock
index 92dcee9542..b1f9991adc 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -71,7 +71,7 @@ PATH
       i18n (>= 0.7, < 2)
       minitest (~> 5.1)
       tzinfo (~> 1.1)
-      zeitwerk (~> 1.4, >= 1.4.3)
+      zeitwerk (~> 2.0)
     rails (6.0.0.beta3)
       actioncable (= 6.0.0.beta3)
       actionmailbox (= 6.0.0.beta3)
@@ -526,7 +526,7 @@ GEM
     websocket-extensions (0.1.3)
     xpath (3.2.0)
       nokogiri (~> 1.8)
-    zeitwerk (1.4.3)
+    zeitwerk (2.0.0)
 
 PLATFORMS
   java
diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index db9c7e96f3..cf72673dbb 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Depends on Zeitwerk 2, which stores less metadata if reloading is disabled
+    and hence uses less memory when `config.cache_classes` is `true`, a standard
+    setup in production.
+
+    *Xavier Noria*
+
 *   In `:zeitwerk` mode, eager load directories in engines and applications only
     if present in their respective `config.eager_load_paths`.
 
diff --git a/activesupport/activesupport.gemspec b/activesupport/activesupport.gemspec
index bf0fe0f76d..e719fc6176 100644
--- a/activesupport/activesupport.gemspec
+++ b/activesupport/activesupport.gemspec
@@ -34,5 +34,5 @@ Gem::Specification.new do |s|
   s.add_dependency "tzinfo",          "~> 1.1"
   s.add_dependency "minitest",        "~> 5.1"
   s.add_dependency "concurrent-ruby", "~> 1.0", ">= 1.0.2"
-  s.add_dependency "zeitwerk",        "~> 1.4", ">= 1.4.3"
+  s.add_dependency "zeitwerk",        "~> 2.0"
 end
diff --git a/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb b/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb
index a43d03cf09..faf9edef27 100644
--- a/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb
+++ b/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb
@@ -51,15 +51,15 @@ module ActiveSupport
       end
 
       class << self
-        def take_over
-          setup_autoloaders
+        def take_over(enable_reloading:)
+          setup_autoloaders(enable_reloading)
           freeze_paths
           decorate_dependencies
         end
 
         private
 
-          def setup_autoloaders
+          def setup_autoloaders(enable_reloading)
             Dependencies.autoload_paths.each do |autoload_path|
               # Zeitwerk only accepts existing directories in `push_dir` to
               # prevent misconfigurations.
@@ -72,6 +72,7 @@ module ActiveSupport
               autoloader.do_not_eager_load(autoload_path) unless eager_load?(autoload_path)
             end
 
+            Rails.autoloaders.main.enable_reloading if enable_reloading
             Rails.autoloaders.each(&:setup)
           end
 
diff --git a/railties/lib/rails/application/finisher.rb b/railties/lib/rails/application/finisher.rb
index 8d2c13d2a8..1cf44a480c 100644
--- a/railties/lib/rails/application/finisher.rb
+++ b/railties/lib/rails/application/finisher.rb
@@ -24,7 +24,7 @@ module Rails
       initializer :let_zeitwerk_take_over do
         if config.autoloader == :zeitwerk
           require "active_support/dependencies/zeitwerk_integration"
-          ActiveSupport::Dependencies::ZeitwerkIntegration.take_over
+          ActiveSupport::Dependencies::ZeitwerkIntegration.take_over(enable_reloading: !config.cache_classes)
         end
       end
 
diff --git a/railties/test/application/zeitwerk_integration_test.rb b/railties/test/application/zeitwerk_integration_test.rb
index dc6db429a9..a9da060347 100644
--- a/railties/test/application/zeitwerk_integration_test.rb
+++ b/railties/test/application/zeitwerk_integration_test.rb
@@ -131,6 +131,20 @@ class ZeitwerkIntegrationTest < ActiveSupport::TestCase
     assert $zeitwerk_integration_test_post
   end
 
+  test "reloading is enabled if config.cache_classes is false" do
+    boot
+
+    assert     Rails.autoloaders.main.reloading_enabled?
+    assert_not Rails.autoloaders.once.reloading_enabled?
+  end
+
+  test "reloading is disabled if config.cache_classes is true" do
+    boot("production")
+
+    assert_not Rails.autoloaders.main.reloading_enabled?
+    assert_not Rails.autoloaders.once.reloading_enabled?
+  end
+
   test "eager loading loads code in engines" do
     $test_blog_engine_eager_loaded = false
 
-- 
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