fixes eager loading edge case in :zeitwerk mode

3 files changed, 27 insertions, 7 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index f30249cb3f..de933ec122 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,12 @@
+*   In `:zeitwerk` mode, eager load directories in engines and applications only
+    if present in their respective `config.eager_load_paths`.
+
+    A common use case for this is adding `lib` to `config.autoload_paths`, but
+    not to `config.eager_load_paths`. In that configuration, for example, files
+    in the `lib` directory should not be eager loaded.
+
+    *Xavier Noria*
+
 *   Fix bug in Range comparisons when comparing to an excluded-end Range
 
     Before:
diff --git a/activesupport/lib/active_support/dependencies.rb b/activesupport/lib/active_support/dependencies.rb
index d5d00b5e6e..82f07c085e 100644
--- a/activesupport/lib/active_support/dependencies.rb
+++ b/activesupport/lib/active_support/dependencies.rb
@@ -70,6 +70,11 @@ module ActiveSupport #:nodoc:
     # only once. All directories in this set must also be present in +autoload_paths+.
     mattr_accessor :autoload_once_paths, default: []
 
+    # This is a private set that collects all eager load paths during bootstrap.
+    # Useful for Zeitwerk integration. Its public interface is the config.* path
+    # accessors of each engine.
+    mattr_accessor :_eager_load_paths, default: Set.new
+
     # An array of qualified constant names that have been loaded. Adding a name
     # to this array will cause it to be unloaded the next time Dependencies are
     # cleared.
diff --git a/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb b/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb
index c6fdade006..a43d03cf09 100644
--- a/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb
+++ b/activesupport/lib/active_support/dependencies/zeitwerk_integration.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require "set"
 require "active_support/core_ext/string/inflections"
 
 module ActiveSupport
@@ -52,7 +53,7 @@ module ActiveSupport
       class << self
         def take_over
           setup_autoloaders
-          freeze_autoload_paths
+          freeze_paths
           decorate_dependencies
         end
 
@@ -64,11 +65,11 @@ module ActiveSupport
               # prevent misconfigurations.
               next unless File.directory?(autoload_path)
 
-              if autoload_once?(autoload_path)
-                Rails.autoloaders.once.push_dir(autoload_path)
-              else
-                Rails.autoloaders.main.push_dir(autoload_path)
-              end
+              autoloader = \
+                autoload_once?(autoload_path) ? Rails.autoloaders.once : Rails.autoloaders.main
+
+              autoloader.push_dir(autoload_path)
+              autoloader.do_not_eager_load(autoload_path) unless eager_load?(autoload_path)
             end
 
             Rails.autoloaders.each(&:setup)
@@ -78,9 +79,14 @@ module ActiveSupport
             Dependencies.autoload_once_paths.include?(autoload_path)
           end
 
-          def freeze_autoload_paths
+          def eager_load?(autoload_path)
+            Dependencies._eager_load_paths.member?(autoload_path)
+          end
+
+          def freeze_paths
             Dependencies.autoload_paths.freeze
             Dependencies.autoload_once_paths.freeze
+            Dependencies._eager_load_paths.freeze
           end
 
           def decorate_dependencies