Implement multiple inheritance correctly, 2nd. amendment

When a Python class does _not_ implement __init__,
then we might get the default of object.__init__, which
must be skipped like the object class alone.

Change-Id: I0416c97854e8d1c9edf0b9ac44d3df58223fef84
Fixes: PYSIDE-2654
Task-number: PYSIDE-2294
Pick-to: 6.5
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
(cherry picked from commit 7b709cf594d9c308b57eacd784845beff9c72c2f)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit a5a2e97aaaf7b5c2ea7d9547cc0fdfbc9b09c97a)

2 files changed, 41 insertions, 5 deletions

diff --git a/sources/pyside6/tests/pysidetest/multiple_inheritance_test.py b/sources/pyside6/tests/pysidetest/multiple_inheritance_test.py
index fe8e14f9f..49550ba55 100644
--- a/sources/pyside6/tests/pysidetest/multiple_inheritance_test.py
+++ b/sources/pyside6/tests/pysidetest/multiple_inheritance_test.py
@@ -12,7 +12,7 @@ init_test_paths(False)
 
 from helper.usesqapplication import UsesQApplication
 from PySide6 import QtCore, QtGui, QtWidgets
-from PySide6.QtWidgets import QMainWindow, QLabel
+from PySide6.QtWidgets import QMainWindow, QLabel, QWidget
 
 
 def xprint(*args, **kw):
@@ -71,7 +71,8 @@ class C(A, B):
         xprint('C: after init')
 
 
-# mro ('F', 'D', 'QCursor', 'E', 'QLabel', 'QFrame', 'QWidget', 'QObject', 'QPaintDevice', 'Object', 'object')
+# mro ('F', 'D', 'QCursor', 'E', 'QLabel', 'QFrame', 'QWidget', 'QObject',
+#      'QPaintDevice', 'Object', 'object')
 class D(QtGui.QCursor):
     def __init__(self, anna=77, **kw):
         xprint(f'D: before init kw = {kw}')
@@ -94,7 +95,8 @@ class F(D, E, QtWidgets.QLabel):
         xprint('F: after init')
 
 
-# mro ('I', 'G', 'QTextDocument', 'H', 'QLabel', 'QFrame', 'QWidget', 'QObject', 'QPaintDevice', 'Object', 'object')
+# mro ('I', 'G', 'QTextDocument', 'H', 'QLabel', 'QFrame', 'QWidget', 'QObject',
+#      'QPaintDevice', 'Object', 'object')
 # Similar, but this time we want to reach `H` without support from `super`.
 class G(QtGui.QTextDocument):
     pass
@@ -108,7 +110,7 @@ class H:
         xprint('H: after init')
 
 
-class I(G, H, QtWidgets.QLabel):
+class II(G, H, QtWidgets.QLabel):
     pass
 
 
@@ -145,7 +147,7 @@ class AdditionalMultipleInheritanceTest(UsesQApplication):
 
     def testGHI(self):
         xprint()
-        res = I(age=7)
+        res = II(age=7)
         self.assertEqual(res.age, 7)
         xprint()
 
@@ -155,5 +157,33 @@ class AdditionalMultipleInheritanceTest(UsesQApplication):
         MainWindow()
 
 
+# PYSIDE-2654: Additional missing init test.
+#              This must work if no __init__ is defined (Ui_Form)
+class Ui_Form(object):
+    pass
+
+
+class Mixin:
+    def __init__(self, **kwargs) -> None:
+        super().__init__(**kwargs)
+
+
+class Card(Mixin, QWidget):
+    def __init__(self, parent=None) -> None:
+        super().__init__(parent=parent)
+
+
+class Demo(Card, Ui_Form):
+    def __init__(self) -> None:
+        super().__init__()
+
+
+class MissingInitFunctionTest(UsesQApplication):
+    def testMissing(self):
+        Demo()
+        # Tests if this works. Would crash without the extra
+        # check for object.__init__
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/sources/shiboken6/libshiboken/bindingmanager.cpp b/sources/shiboken6/libshiboken/bindingmanager.cpp
index a9b87f7f4..a0acc4e4b 100644
--- a/sources/shiboken6/libshiboken/bindingmanager.cpp
+++ b/sources/shiboken6/libshiboken/bindingmanager.cpp
@@ -408,6 +408,8 @@ bool callInheritedInit(PyObject *self, PyObject *args, PyObject *kwds,
     using Shiboken::AutoDecRef;
 
     static PyObject *const _init = String::createStaticString("__init__");
+    static PyObject *objectInit =
+        PyObject_GetAttr(reinterpret_cast<PyObject *>(&PyBaseObject_Type), _init);
 
     // A native C++ self cannot have multiple inheritance.
     if (!Object::isUserType(self))
@@ -441,6 +443,10 @@ bool callInheritedInit(PyObject *self, PyObject *args, PyObject *kwds,
     if (subType == &PyBaseObject_Type)
         return false;
     AutoDecRef func(PyObject_GetAttr(obSubType, _init));
+    // PYSIDE-2654: If this has no implementation then we get object.__init__
+    //              but that is the same case like above.
+    if (func == objectInit)
+        return false;
     // PYSIDE-2294: We need to explicitly ignore positional args in a mixin class.
     SBK_UNUSED(args);
     AutoDecRef newArgs(PyTuple_New(1));