Singleton raises TypeError on #new

src/class.c

@@ -1047,6 +1047,9 @@ mrb_instance_new(mrb_state *mrb, mrb_value cv)
   mrb_value *argv;
   int argc;
 
+  if (c->tt == MRB_TT_SCLASS)
+    mrb_raise(mrb, E_TYPE_ERROR, "can't create instance of singleton class");
+
   if (ttype == 0) ttype = MRB_TT_OBJECT;
   o = (struct RObject*)mrb_obj_alloc(mrb, ttype, c);
   obj = mrb_obj_value(o);

test/t/class.rb

@@ -30,13 +30,9 @@ assert('Class#initialize_copy', '15.2.3.3.2') do
 end
 
 assert('Class#new', '15.2.3.3.3') do
-  # at the moment no exception on singleton class
-  #e1 = nil
-  #begin
-  #  class1 = e1.singleton_class.new
-  #rescue => e1
-  #  e2 = e1
-  #end
+  assert_raise(TypeError, 'Singleton should raise TypeError') do
+    "a".singleton_class.new
+  end
 
   class TestClass
     def initialize args, &block