Add some more checking -- don't want non-gc values to sneak in again

src/runtime/capi.cpp

@@ -289,6 +289,9 @@ extern "C" void _PyErr_BadInternalCall(const char* filename, int lineno) {
 }
 
 extern "C" PyObject* PyObject_Init(PyObject* op, PyTypeObject* tp) {
+    assert(gc::isValidGCObject(op));
+    assert(gc::isValidGCObject(tp));
+
     RELEASE_ASSERT(op, "");
     RELEASE_ASSERT(tp, "");
     Py_TYPE(op) = tp;
@@ -296,6 +299,9 @@ extern "C" PyObject* PyObject_Init(PyObject* op, PyTypeObject* tp) {
 }
 
 extern "C" PyVarObject* PyObject_InitVar(PyVarObject* op, PyTypeObject* tp, Py_ssize_t size) {
+    assert(gc::isValidGCObject(op));
+    assert(gc::isValidGCObject(tp));
+
     RELEASE_ASSERT(op, "");
     RELEASE_ASSERT(tp, "");
     Py_TYPE(op) = tp;

src/runtime/types.cpp

@@ -303,6 +303,8 @@ extern "C" Box* createUserClass(std::string* name, Box* _base, Box* _attr_dict)
     ASSERT(_attr_dict->cls == dict_cls, "%s", getTypeName(_attr_dict)->c_str());
     BoxedDict* attr_dict = static_cast<BoxedDict*>(_attr_dict);
 
+    RELEASE_ASSERT(attr_dict->d.count(boxStrConstant("__metaclass__")) == 0, "metaclasses not supported yet");
+
     BoxedClass* made;
 
     if (base->instancesHaveAttrs()) {