Exclude singleton classes from `subclasses` and `descendants`

This behavior changed in Ruby starting with 2.3.0, as a result of
https://bugs.ruby-lang.org/issues/11360. This results in a change in
behavior of these methods which is likely undesirable.

Fixes #27238

1 files changed, 10 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/class_test.rb b/activesupport/test/core_ext/class_test.rb
index a9c44907cc..a7905196ae 100644
--- a/activesupport/test/core_ext/class_test.rb
+++ b/activesupport/test/core_ext/class_test.rb
@@ -25,4 +25,14 @@ class ClassTest < ActiveSupport::TestCase
     assert_equal [Baz], Bar.subclasses
     assert_equal [], Baz.subclasses
   end
+
+  def test_descendants_excludes_singleton_classes
+    klass = Parent.new.singleton_class
+    refute Parent.descendants.include?(klass), "descendants should not include singleton classes"
+  end
+
+  def test_subclasses_excludes_singleton_classes
+    klass = Parent.new.singleton_class
+    refute Parent.subclasses.include?(klass), "subclasses should not include singleton classes"
+  end
 end