Improves compatibility of require_dependency in zeitwerk mode [Closes #36774]

Applications are not supposed to use require_dependency in their own
code if running in zeitwerk mode, and require_dependency was initially
aliased to require with that use case in mind.

However, there are situations in which you cannot control the mode and
need to be compatible with both. There, you might need require_dependency
in case you are being executed in classic mode. Think about engines that
want to support both modes in their parent applications, for example.

Furthermore, Rails itself loads helpers using require_dependency.

Therefore, we need better compatibility.

activesupport/CHANGELOG.md

+*   Let `require_dependency` in `zeitwerk` mode look the autoload paths up for
+    better backwards compatibility.
+
+    *Xavier Noria*
+
+*   Let `require_dependency` in `zeitwerk` mode support arguments that respond
+    to `to_path` for better backwards compatibility.
+
+    *Xavier Noria*
+
 *   Make ActiveSupport::Logger Fiber-safe. Fixes #36752.
 
     Use `Fiber.current.__id__` in `ActiveSupport::Logger#local_level=` in order

activesupport/lib/active_support/dependencies/zeitwerk_integration.rb

@@ -42,6 +42,17 @@ def unhook!
         end
       end
 
+      module RequireDependency
+        def require_dependency(filename)
+          filename = filename.to_path if filename.respond_to?(:to_path)
+          if abspath = ActiveSupport::Dependencies.search_for_file(filename)
+            require abspath
+          else
+            require filename
+          end
+        end
+      end
+
       module Inflector
         def self.camelize(basename, _abspath)
           basename.camelize
@@ -91,7 +102,7 @@ def freeze_paths
           def decorate_dependencies
             Dependencies.unhook!
             Dependencies.singleton_class.prepend(Decorations)
-            Object.class_eval { alias_method :require_dependency, :require }
+            Object.prepend(RequireDependency)
           end
       end
     end

railties/test/application/zeitwerk_integration_test.rb

@@ -150,6 +150,35 @@ def self.name
     assert_empty deps.autoloaded_constants
   end
 
+  [true, false].each do |add_aps_to_lp|
+    test "require_dependency looks autoload paths up (#{add_aps_to_lp})" do
+      add_to_config "config.add_autoload_paths_to_load_path = #{add_aps_to_lp}"
+      app_file "app/models/user.rb", "class User; end"
+      boot
+
+      assert require_dependency("user")
+    end
+
+    test "require_dependency handles absolute paths correctly (#{add_aps_to_lp})" do
+      add_to_config "config.add_autoload_paths_to_load_path = #{add_aps_to_lp}"
+      app_file "app/models/user.rb", "class User; end"
+      boot
+
+      assert require_dependency("#{app_path}/app/models/user.rb")
+    end
+
+    test "require_dependency supports arguments that repond to to_path (#{add_aps_to_lp})" do
+      add_to_config "config.add_autoload_paths_to_load_path = #{add_aps_to_lp}"
+      app_file "app/models/user.rb", "class User; end"
+      boot
+
+      user = Object.new
+      def user.to_path; "user"; end
+
+      assert require_dependency(user)
+    end
+  end
+
   test "eager loading loads the application code" do
     $zeitwerk_integration_test_user = false
     $zeitwerk_integration_test_post = false