merge revision(s) f3c77bd480834f2835fe6fef5c0475336248dbde: [Backport #18489]

	Fix the placeholder subclass entry skipping [Bug #18489]

	---
	 class.c                  | 3 +--
	 test/ruby/test_module.rb | 9 +++++++++
	 2 files changed, 10 insertions(+), 2 deletions(-)

1 files changed, 9 insertions, 0 deletions

diff --git a/test/ruby/test_module.rb b/test/ruby/test_module.rb
index b84a090fce..fa890c0e40 100644
--- a/test/ruby/test_module.rb
+++ b/test/ruby/test_module.rb
@@ -475,6 +475,15 @@ class TestModule < Test::Unit::TestCase
     assert_not_include(mod.ancestor_list, BasicObject)
   end
 
+  def test_module_collected_extended_object
+    m1 = labeled_module("m1")
+    m2 = labeled_module("m2")
+    Object.new.extend(m1)
+    GC.start
+    m1.include(m2)
+    assert_equal([m1, m2], m1.ancestors)
+  end
+
   def test_dup
     OtherSetup.call