Shiboken: Fix subtle bug caused by PyPy support and "bug_825"

When implementing PyPy support, all Shiboken types lost their
hidden extra fields, because they were replaced by shadow dicts.

This creates a problem with multiple inheritance.
In Python < 3.12, the decision which base type will create the
instance is driven simply by the size of the type. In

    class MetaC(MetaA, MetaB):
        pass

when MetaA is derived from type and MetaB is derived from
SbkObjectType, MetaA is not the type that should win.
Fixed by simply adding 1 to the default size of PyType_Type.

Caused by bug_825 corrected version.
The old test is retained as bug_825_old.py .

NOTE: This touches a Python 3.8 bug that was fixed in 3.9.12
and 3.10.4 - unfortunately CI Python is older in all cases.

Task-number: PYSIDE-2230
Change-Id: I6e82cafb83c8351bbbeafcc80e11d5e45568f73d
Pick-to: 6.5 6.2
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
(cherry picked from commit 9557565b48b2a72b7697443930234f9f92c17781)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

5 files changed, 104 insertions, 9 deletions

diff --git a/build_history/blacklist.txt b/build_history/blacklist.txt
index cb9b1c500..60cc3f955 100644
--- a/build_history/blacklist.txt
+++ b/build_history/blacklist.txt
@@ -43,7 +43,10 @@
     darwin ci
 [QtAsyncio::qasyncio_test_chain]
     win32
-
+[QtQml::bug_825]
+    py3.8       # bug in typeobject::type_mro_modified, fix in 3.9
+    py3.9       # fixed in 3.9.12
+    py3.10      # fixed in 3.10.4
 # PYSIDE-535: These errors are still present. Please try to remove one :)
 [sample::mixed_mi]
     pypy
diff --git a/sources/pyside6/tests/QtQml/CMakeLists.txt b/sources/pyside6/tests/QtQml/CMakeLists.txt
index c24beb35a..720f0ef99 100644
--- a/sources/pyside6/tests/QtQml/CMakeLists.txt
+++ b/sources/pyside6/tests/QtQml/CMakeLists.txt
@@ -6,6 +6,7 @@ PYSIDE_TEST(bug_456.py)
 PYSIDE_TEST(bug_557.py)
 PYSIDE_TEST(bug_726.py)
 PYSIDE_TEST(bug_814.py)
+PYSIDE_TEST(bug_825_old.py)
 PYSIDE_TEST(bug_825.py)
 PYSIDE_TEST(bug_847.py)
 PYSIDE_TEST(bug_915.py)
diff --git a/sources/pyside6/tests/QtQml/bug_825.py b/sources/pyside6/tests/QtQml/bug_825.py
index 9771d0634..1d9b82d16 100644
--- a/sources/pyside6/tests/QtQml/bug_825.py
+++ b/sources/pyside6/tests/QtQml/bug_825.py
@@ -1,6 +1,11 @@
 # Copyright (C) 2022 The Qt Company Ltd.
 # SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
 
+"""
+This is the corrected version for Python 3.
+Unfortunately, this touches a Python 3.8 error that was fixed late.
+"""
+
 import os
 import sys
 import unittest
@@ -25,9 +30,8 @@ class MetaA(type):
     pass
 
 
-class A(object):
-    __metaclass__ = MetaA
-
+class A(object, metaclass=MetaA):
+    pass
 
 MetaB = type(QQuickPaintedItem)
 B = QQuickPaintedItem
@@ -37,8 +41,8 @@ class MetaC(MetaA, MetaB):
     pass
 
 
-class C(A, B):
-    __metaclass__ = MetaC
+class C(A, B, metaclass=MetaC):
+    pass
 
 
 class Bug825 (C):
diff --git a/sources/pyside6/tests/QtQml/bug_825_old.py b/sources/pyside6/tests/QtQml/bug_825_old.py
new file mode 100644
index 000000000..c44fa75f4
--- /dev/null
+++ b/sources/pyside6/tests/QtQml/bug_825_old.py
@@ -0,0 +1,80 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+"""
+This is the now incorrect old version from Python 2.
+It happens to work in another way and will be retained.
+"""
+
+import os
+import sys
+import unittest
+
+from pathlib import Path
+sys.path.append(os.fspath(Path(__file__).resolve().parents[1]))
+from init_paths import init_test_paths
+init_test_paths(False)
+
+from helper.helper import quickview_errorstring
+
+from PySide6.QtCore import Qt, QUrl, QTimer
+from PySide6.QtGui import QGuiApplication, QPen
+from PySide6.QtWidgets import QGraphicsItem
+from PySide6.QtQml import qmlRegisterType
+from PySide6.QtQuick import QQuickView, QQuickItem, QQuickPaintedItem
+
+paintCalled = False
+
+
+class MetaA(type):
+    pass
+
+
+class A(object):
+    __metaclass__ = MetaA
+
+
+MetaB = type(QQuickPaintedItem)
+B = QQuickPaintedItem
+
+
+class MetaC(MetaA, MetaB):
+    pass
+
+
+class C(A, B):
+    __metaclass__ = MetaC
+
+
+class Bug825 (C):
+    def __init__(self, parent=None):
+        QQuickPaintedItem.__init__(self, parent)
+
+    def paint(self, painter):
+        global paintCalled
+        pen = QPen(Qt.black, 2)
+        painter.setPen(pen)
+        painter.drawPie(self.boundingRect(), 0, 128)
+        paintCalled = True
+
+
+class TestBug825 (unittest.TestCase):
+    def testIt(self):
+        global paintCalled
+        app = QGuiApplication([])
+        qmlRegisterType(Bug825, 'bugs', 1, 0, 'Bug825')
+        self.assertRaises(TypeError, qmlRegisterType, A, 'bugs', 1, 0, 'A')
+
+        view = QQuickView()
+        file = Path(__file__).resolve().parent / 'bug_825.qml'
+        self.assertTrue(file.is_file())
+        view.setSource(QUrl.fromLocalFile(file))
+        self.assertTrue(view.rootObject(), quickview_errorstring(view))
+        view.show()
+        QTimer.singleShot(250, view.close)
+        app.exec()
+        self.assertTrue(paintCalled)
+
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/sources/shiboken6/libshiboken/basewrapper.cpp b/sources/shiboken6/libshiboken/basewrapper.cpp
index d33f06431..828c54a89 100644
--- a/sources/shiboken6/libshiboken/basewrapper.cpp
+++ b/sources/shiboken6/libshiboken/basewrapper.cpp
@@ -139,11 +139,18 @@ static PyTypeObject *createObjectTypeType()
     };
 
     // PYSIDE-535: The tp_itemsize field is inherited and does not need to be set.
-    // In PyPy, it _must_ not be set, because it would have the meaning that a
-    // `__len__` field must be defined. Not doing so creates a hard-to-find crash.
+    //             In PyPy, it _must_ not be set, because it would have the meanin
+    //             that a `__len__` field must be defined. Not doing so creates
+    //             a hard-to-find crash.
+    //
+    // PYSIDE-2230: In Python < 3.12, the decision which base class should create
+    //              the instance is arbitrarily drawn by the size of the type.
+    //              Ignoring this creates a bug in the new version of bug_825 that
+    //              selects the wrong metatype.
+    //
     PyType_Spec SbkObjectType_Type_spec = {
         "1:Shiboken.ObjectType",
-        0,
+        static_cast<int>(PyType_Type.tp_basicsize) + 1,           // see above
         0, // sizeof(PyMemberDef), not for PyPy without a __len__ defined
         Py_TPFLAGS_DEFAULT|Py_TPFLAGS_BASETYPE,
         SbkObjectType_Type_slots,