[Bug #19901]

fix leak in module clone

Co-authored-by: Peter Zhu <peter@peterzhu.ca>

class.c

@@ -471,6 +471,7 @@ copy_tables(VALUE clone, VALUE orig)
         rb_id_table_foreach(rb_cvc_tbl, cvc_table_copy, &ctx);
         RCLASS_CVC_TBL(clone) = rb_cvc_tbl_dup;
     }
+    rb_id_table_free(RCLASS_M_TBL(clone));
     RCLASS_M_TBL(clone) = 0;
     if (!RB_TYPE_P(clone, T_ICLASS)) {
         st_data_t id;

test/ruby/test_module.rb

@@ -3321,6 +3321,18 @@ class TestModule < Test::Unit::TestCase
     CODE
   end
 
+  def test_module_clone_memory_leak
+    # [Bug #19901]
+    assert_no_memory_leak([], <<~PREP, <<~CODE, rss: true)
+      code = proc do
+        Module.new.clone
+      end
+      1_000.times(&code)
+    PREP
+      1_000_000.times(&code)
+    CODE
+  end
+
   private
 
   def assert_top_method_is_private(method)