Fix crash retrieving a QGraphicsProxyObject from QVariant

Remove the default-superclass specification QGraphicsItem for
QGraphicsObject since it causes the type discovery to directly cast
from QGraphicsObject* to QGraphicsItem*. This crashes
since QGraphicsObject inherits from QObject as first base class.

The intention of the class attribute was to ensure that any
QGraphicsObject class is stored as a QGraphicsItem. To preserve this,
hardcode it in QVariant_resolveMetaType().

Pick-to: 6.9
Fixes: PYSIDE-3069
Task-number: PYSIDE-86
Task-number: PYSIDE-1887
Change-Id: I3704988f105b118b1e4ef8d078b68c01ba89386c
Reviewed-by: Cristian Maureira-Fredes <[email protected]>

Author: FriedemannKleint

sources/pyside6/PySide6/QtCore/glue/core_snippets.cpp

@@ -45,7 +45,14 @@ QMetaType QVariant_resolveMetaType(PyTypeObject *type)
     // that has added any python fields or slots to its object layout.
     // See https://mail.python.org/pipermail/python-list/2009-January/520733.html
     if (type->tp_bases) {
-        for (Py_ssize_t i = 0, size = PyTuple_Size(type->tp_bases); i < size; ++i) {
+        const auto size = PyTuple_Size(type->tp_bases);
+        Py_ssize_t i = 0;
+        // PYSIDE-1887, PYSIDE-86: Skip QObject base class of QGraphicsObject;
+        // it needs to use always QGraphicsItem as a QVariant type for
+        // QGraphicsItem::itemChange() to work.
+        if (qstrcmp(typeName, "QGraphicsObject*") == 0)
+            ++i;
+        for ( ; i < size; ++i) {
             auto baseType = reinterpret_cast<PyTypeObject *>(PyTuple_GetItem(type->tp_bases, i));
             const QMetaType derived = QVariant_resolveMetaType(baseType);
             if (derived.isValid())

sources/pyside6/PySide6/QtWidgets/typesystem_widgets_common.xml

@@ -3358,7 +3358,7 @@
       <enum-type name="PixmapPadMode"/>
   </object-type>
 
-  <object-type name="QGraphicsObject" default-superclass="QGraphicsItem"/>
+  <object-type name="QGraphicsObject"/>
   <object-type name="QGraphicsOpacityEffect"/>
   <object-type name="QGraphicsRotation"/>
   <object-type name="QGraphicsScale"/>

sources/pyside6/tests/QtWidgets/CMakeLists.txt

@@ -84,6 +84,7 @@ PYSIDE_TEST(qapp_issue_585.py)
 PYSIDE_TEST(qapp_test.py)
 PYSIDE_TEST(qapplication_test.py)
 PYSIDE_TEST(qapplication_exit_segfault_test.py)
+PYSIDE_TEST(pyside3069.py)
 PYSIDE_TEST(qdialog_test.py)
 PYSIDE_TEST(qdynamic_signal.py)
 # TODO: This passes, but requires manual button clicking (at least on mac)

sources/pyside6/tests/QtWidgets/pyside3069.py

@@ -0,0 +1,51 @@
+# Copyright (C) 2025 The Qt Company Ltd.
+# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+from __future__ import annotations
+
+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  # noqa: E402
+init_test_paths(False)
+
+from PySide6.QtCore import Qt  # noqa: E402
+from PySide6.QtWidgets import QApplication, QComboBox, QGraphicsScene, QGraphicsView  # noqa: E402
+
+from helper.usesqapplication import UsesQApplication  # noqa: E402
+
+
+class BugTest(UsesQApplication):
+    """PYSIDE-3069: Test that the conversion of an element of a list
+       QGraphicsItem* to QGraphicsProxyWidget* (inheriting QObject/QGraphicsItem)
+       works correctly without crash.
+
+       For this, we need a QGraphicsProxyWidget for which no wrapper exists,
+       created in C++. So, we populate a combo, add it to the scene and show its
+       popup, which creates a top level that is automatically wrapped by
+       another QGraphicsProxyWidget. This, we print from the list of items().
+
+       See also PYSIDE-86, PYSIDE-1887."""
+    def test(self):
+        qApp.setEffectEnabled(Qt.UI_AnimateCombo, False)  # noqa: F821
+        cb = QComboBox()
+        cb.addItem("i1")
+        cb.addItem("i2")
+        scene = QGraphicsScene()
+        scene.addWidget(cb)
+        view = QGraphicsView(scene)
+        view.show()
+        cb.showPopup()
+        while not view.windowHandle().isExposed():
+            QApplication.processEvents()
+        items = scene.items()
+        self.assertEqual(len(items), 2)  # Combo and its popup, created in C++
+        for i in items:
+            print(i)
+        view.close()
+
+
+if __name__ == "__main__":
+    unittest.main()

sources/pyside6/tests/QtWidgets/qgraphicsobjectreimpl_test.py

@@ -50,6 +50,7 @@ def testReimplementationTypes(self):
         #   and then the QVariant was not associated with
         #   a QGraphicsItem but a QObjectItem because the base
         #   class was a QObject.
+        #   See also PYSIDE-1887, PYSIDE-3069
         gobjA = GObjA()
         gobjA.setParentItem(w)
         self.assertIs(type(w), type(gobjA.parentItem()))