objspace_dump.c: tag singleton classes and reference the superclass

ext/objspace/objspace_dump.c

@@ -419,14 +419,37 @@ dump_object(VALUE obj, struct dump_config *dc)
             dump_append(dc, ", \"embedded\":true");
         break;
 
+      case T_ICLASS:
+        if (rb_class_get_superclass(obj)) {
+            dump_append(dc, ", \"superclass\":");
+            dump_append_ref(dc, rb_class_get_superclass(obj));
+        }
+        break;
+
       case T_CLASS:
       case T_MODULE:
+        if (rb_class_get_superclass(obj)) {
+            dump_append(dc, ", \"superclass\":");
+            dump_append_ref(dc, rb_class_get_superclass(obj));
+        }
+
         if (dc->cur_obj_klass) {
             VALUE mod_name = rb_mod_name(obj);
             if (!NIL_P(mod_name)) {
                 dump_append(dc, ", \"name\":\"");
                 dump_append(dc, RSTRING_PTR(mod_name));
                 dump_append(dc, "\"");
+            } else {
+                VALUE real_mod_name = rb_mod_name(rb_class_real(obj));
+                if (RTEST(real_mod_name)) {
+                    dump_append(dc, ", \"real_class_name\":\"");
+                    dump_append(dc, RSTRING_PTR(real_mod_name));
+                    dump_append(dc, "\"");
+                }
+            }
+
+            if (FL_TEST(obj, FL_SINGLETON)) {
+                dump_append(dc, ", \"singleton\":true");
             }
         }
         break;

test/objspace/test_objspace.rb

@@ -299,6 +299,21 @@ class TestObjSpace < Test::Unit::TestCase
     assert_equal('{"type":"SYMBOL", "value":"foo"}', ObjectSpace.dump(:foo))
   end
 
+  def test_dump_singleton_class
+    assert_include(ObjectSpace.dump(Object), '"name":"Object"')
+    assert_include(ObjectSpace.dump(Kernel), '"name":"Kernel"')
+    assert_include(ObjectSpace.dump(Object.new.singleton_class), '"real_class_name":"Object"')
+
+    singleton = Object.new.singleton_class
+    singleton_dump = ObjectSpace.dump(singleton)
+    assert_include(singleton_dump, '"singleton":true')
+    if defined?(JSON)
+      assert_equal(Object, singleton.superclass)
+      superclass_address = JSON.parse(ObjectSpace.dump(Object)).fetch('address')
+      assert_equal(superclass_address, JSON.parse(singleton_dump).fetch('superclass'))
+    end
+  end
+
   def test_dump_special_floats
     assert_match(/"value":"NaN"/, ObjectSpace.dump(Float::NAN))
     assert_match(/"value":"Inf"/, ObjectSpace.dump(Float::INFINITY))