shiboken6: Fix an impossible reference to type_new

[ChangeLog][shiboken6] It is now possible to derive classes from
enum types like `QtCore.Key` in earlier Python versions.

In SbkEnumTypeTpNew the reference to `PyType_Type.tp_new` was
made through `PyType_GetSlot` in a Limited API compatible way.

Unfortunately, `PyType_GetSlot` works for non-heaptypes in
Python 3.10, only, and `PyType_Type is not a heaptype.

This was found while creating a minimum example to prove that
the PyPy implementation of type_new is not correct.

Task-number: PYSIDE-535
Change-Id: Ibe300f4670d9db6d29fbdeb1d147e1a074ec23c6
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

2 files changed, 7 insertions, 1 deletions

diff --git a/sources/pyside6/tests/QtCore/qenum_test.py b/sources/pyside6/tests/QtCore/qenum_test.py
index 0d524505a..76caa9a37 100644
--- a/sources/pyside6/tests/QtCore/qenum_test.py
+++ b/sources/pyside6/tests/QtCore/qenum_test.py
@@ -77,6 +77,12 @@ class TestEnum(unittest.TestCase):
         with self.assertRaises(TypeError):
             a = k * 2.0
 
+    def testInherit(self):
+        class A(Qt.Key):
+            pass
+
+        self.assertEqual(A.Key_1, Qt.Key.Key_1)
+
     @unittest.skipUnless(getattr(sys, "getobjects", None), "requires --with-trace-refs")
     @unittest.skipUnless(getattr(sys, "gettotalrefcount", None), "requires --with-pydebug")
     def testEnumNew_NoLeak(self):
diff --git a/sources/shiboken6/libshiboken/sbkenum.cpp b/sources/shiboken6/libshiboken/sbkenum.cpp
index a6f65c7ab..b97cff209 100644
--- a/sources/shiboken6/libshiboken/sbkenum.cpp
+++ b/sources/shiboken6/libshiboken/sbkenum.cpp
@@ -310,7 +310,7 @@ void SbkEnumTypeDealloc(PyObject *pyObj)
 
 PyObject *SbkEnumTypeTpNew(PyTypeObject *metatype, PyObject *args, PyObject *kwds)
 {
-    auto type_new = reinterpret_cast<newfunc>(PyType_GetSlot(&PyType_Type, Py_tp_new));
+    auto type_new = reinterpret_cast<newfunc>(PyType_Type.tp_new);
     auto newType = reinterpret_cast<SbkEnumType *>(type_new(metatype, args, kwds));
     if (!newType)
         return nullptr;