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(-)

3 files changed, 11 insertions, 3 deletions

diff --git a/class.c b/class.c
index 5d3d46d1e6..65a989f9d7 100644
--- a/class.c
+++ b/class.c
@@ -1053,8 +1053,7 @@ rb_include_module(VALUE klass, VALUE module)
     if (RB_TYPE_P(klass, T_MODULE)) {
         rb_subclass_entry_t *iclass = RCLASS_SUBCLASSES(klass);
         // skip the placeholder subclass entry at the head of the list
-        if (iclass && iclass->next) {
-            RUBY_ASSERT(!iclass->klass);
+        if (iclass && !iclass->klass) {
             iclass = iclass->next;
         }
 
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
 
diff --git a/version.h b/version.h
index 7af99cc04a..06df6ce639 100644
--- a/version.h
+++ b/version.h
@@ -11,7 +11,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 0
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 8
+#define RUBY_PATCHLEVEL 9
 
 #define RUBY_RELEASE_YEAR 2022
 #define RUBY_RELEASE_MONTH 1