gc.c: do not expose internal singleton class

* gc.c (internal_object_p): should not expose singleton classes
  without a metaclass.  based on patches by ko1 and shugo.
  [Bug #11740]
* class.c (rb_singleton_class_object_p): added.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53243 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 7 insertions, 0 deletions

diff --git a/test/ruby/test_objectspace.rb b/test/ruby/test_objectspace.rb
index b701e0fc91..ec561bc405 100644
--- a/test/ruby/test_objectspace.rb
+++ b/test/ruby/test_objectspace.rb
@@ -149,5 +149,12 @@ End
       }
       assert(exist, 'Bug #11360')
     End
+
+    klass = Class.new
+    instance = klass.new
+    sclass = instance.singleton_class
+    meta = klass.singleton_class
+    assert_kind_of(meta, sclass)
+    assert_include(ObjectSpace.each_object(meta).to_a, sclass)
   end
 end