8 files changed, 223 insertions, 13 deletions
diff --git a/sources/pyside6/libpyside/pyside.cpp b/sources/pyside6/libpyside/pyside.cpp
index 42b7725cc..29a3d2884 100644
--- a/sources/pyside6/libpyside/pyside.cpp
+++ b/sources/pyside6/libpyside/pyside.cpp
@@ -299,7 +299,8 @@ static bool _setProperty(PyObject *qObj, PyObject *name, PyObject *value, bool *
     return true;
 }
 
-bool fillQtProperties(PyObject *qObj, const QMetaObject *metaObj, PyObject *kwds)
+bool fillQtProperties(PyObject *qObj, const QMetaObject *metaObj,
+                      PyObject *kwds, bool allowErrors)
 {
 
     PyObject *key, *value;
@@ -331,6 +332,10 @@ bool fillQtProperties(PyObject *qObj, const QMetaObject *metaObj, PyObject *kwds
                     return false;
             }
         }
+        if (allowErrors) {
+            PyErr_Clear();
+            continue;
+        }
         if (!accept) {
             PyErr_Format(PyExc_AttributeError, "'%s' is not a Qt property or a signal",
                          propName.constData());
diff --git a/sources/pyside6/libpyside/pysideqobject.h b/sources/pyside6/libpyside/pysideqobject.h
index 2bd9b74ca..07453bc12 100644
--- a/sources/pyside6/libpyside/pysideqobject.h
+++ b/sources/pyside6/libpyside/pysideqobject.h
@@ -22,7 +22,8 @@ namespace PySide
 /// \param metaObj QMetaObject of \p qObj.
 /// \param kwds key->value dictonary.
 /// \return True if everything goes well, false with a Python error set otherwise.
-PYSIDE_API bool fillQtProperties(PyObject *qObj, const QMetaObject *metaObj, PyObject *kwds);
+PYSIDE_API bool fillQtProperties(PyObject *qObj, const QMetaObject *metaObj,
+                                 PyObject *kwds, bool allowErrors);
 
 PYSIDE_API void initDynamicMetaObject(PyTypeObject *type, const QMetaObject *base,
                                       std::size_t cppObjSize);
diff --git a/sources/pyside6/tests/pysidetest/CMakeLists.txt b/sources/pyside6/tests/pysidetest/CMakeLists.txt
index 797b72c45..f64cea904 100644
--- a/sources/pyside6/tests/pysidetest/CMakeLists.txt
+++ b/sources/pyside6/tests/pysidetest/CMakeLists.txt
@@ -145,6 +145,7 @@ PYSIDE_TEST(iterable_test.py)
 PYSIDE_TEST(list_signal_test.py)
 PYSIDE_TEST(mixin_signal_slots_test.py)
 PYSIDE_TEST(modelview_test.py)
+PYSIDE_TEST(multiple_inheritance_test.py)
 PYSIDE_TEST(new_inherited_functions_test.py)
 PYSIDE_TEST(notify_id.py)
 PYSIDE_TEST(properties_test.py)
diff --git a/sources/pyside6/tests/pysidetest/multiple_inheritance_test.py b/sources/pyside6/tests/pysidetest/multiple_inheritance_test.py
new file mode 100644
index 000000000..6e48ac735
--- /dev/null
+++ b/sources/pyside6/tests/pysidetest/multiple_inheritance_test.py
@@ -0,0 +1,127 @@
+# Copyright (C) 2023 The Qt Company Ltd.
+# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+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.usesqapplication import UsesQApplication
+from PySide6 import QtCore, QtGui, QtWidgets
+
+
+def xprint(*args, **kw):
+    if "-v" in sys.argv:
+        print(*args, **kw)
+
+# This is the original testcase of PYSIDE-1564
+class Age(object):
+    def __init__(self, age=0, **kwds):
+        super().__init__(**kwds)
+
+        self.age = age
+
+class Person(QtCore.QObject, Age):
+    def __init__(self, name, **kwds):
+        super().__init__(**kwds)
+
+        self.name = name
+
+
+class OriginalMultipleInheritanceTest(unittest.TestCase):
+
+    def testIt(self):
+        xprint()
+        p = Person("Joe", age=38)
+        xprint(f"p.age = {p.age}")
+        # This would crash if MI does not work.
+
+# More tests follow:
+
+# mro ('C', 'A', 'QObject', 'Object', 'B', 'object')
+class A(QtCore.QObject):
+    def __init__(self, anna=77, **kw):
+        xprint(f'A: before init kw = {kw}')
+        super().__init__(**kw)
+        xprint('A: after init')
+
+class B:
+    def __init__(self, otto=6, age=7, **kw):
+        xprint(f'B: before init kw = {kw}')
+        if "killme" in kw:
+            raise AssertionError("asdf")
+        super().__init__(**kw)
+        self.age = age
+        xprint('B: after init')
+
+class C(A, B):
+    def __init__(self, **kw):
+        xprint(f'C: before init kw = {kw}')
+        super().__init__(**kw)
+        xprint('C: after init')
+
+# 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}')
+        super().__init__(**kw)
+        xprint('D: after init')
+
+class E:
+    def __init__(self, age=7, **kw):
+        xprint(f'E: before init kw = {kw}')
+        super().__init__(**kw)
+        self.age = age
+        xprint('E: after init')
+
+class F(D, E, QtWidgets.QLabel):
+    def __init__(self, **kw):
+        xprint(f'F: before init kw = {kw}')
+        super().__init__(**kw)
+        xprint('F: after init')
+
+# 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
+
+class H:
+    def __init__(self, age=7, **kw):
+        xprint(f'H: before init kw = {kw}')
+        super().__init__(**kw)
+        self.age = age
+        xprint('H: after init')
+
+class I(G, H, QtWidgets.QLabel):
+    pass
+
+
+class AdditionalMultipleInheritanceTest(UsesQApplication):
+
+    def testABC(self):
+        xprint()
+        res = C(otto=3, anna=5)
+        self.assertEqual(res.age, 7)
+        xprint()
+        with self.assertRaises(AssertionError):
+            res=C(killme=42)
+        xprint()
+
+    def testDEF(self):
+        xprint()
+        res = F(anna=5)
+        self.assertEqual(res.age, 7)
+        xprint()
+
+    def testGHI(self):
+        xprint()
+        res = I(age=7)
+        self.assertEqual(res.age, 7)
+        xprint()
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/sources/shiboken6/generator/shiboken/cppgenerator.cpp b/sources/shiboken6/generator/shiboken/cppgenerator.cpp
index 63fc65f19..8563aec8e 100644
--- a/sources/shiboken6/generator/shiboken/cppgenerator.cpp
+++ b/sources/shiboken6/generator/shiboken/cppgenerator.cpp
@@ -2297,11 +2297,12 @@ void CppGenerator::writeMethodWrapperPreamble(TextStream &s,const OverloadData &
         initPythonArguments = minArgs != maxArgs || maxArgs > 1;
     }
 
-    if (needsArgumentErrorHandling(overloadData)) {
-        s << R"(Shiboken::AutoDecRef errInfo{};
-static const char fullName[] = ")" << fullPythonFunctionName(rfunc, true)
-            << "\";\nSBK_UNUSED(fullName)\n";
-    }
+    if (needsArgumentErrorHandling(overloadData))
+        s << "Shiboken::AutoDecRef errInfo{};\n";
+
+    s << "static const char fullName[] = \"" << fullPythonFunctionName(rfunc, true)
+        << "\";\nSBK_UNUSED(fullName)\n";
+
     if (maxArgs > 0) {
         s << "int overloadId = -1;\n"
             << PYTHON_TO_CPPCONVERSION_STRUCT << ' ' << PYTHON_TO_CPP_VAR;
@@ -2389,6 +2390,12 @@ void CppGenerator::writeConstructorWrapper(TextStream &s, const OverloadData &ov
     if (overloadData.maxArgs() > 0)
         writeOverloadedFunctionDecisor(s, overloadData, errorReturn);
 
+    // Handles Python Multiple Inheritance
+    QString pre = needsMetaObject ? u"bool usesPyMI = "_s : u""_s;
+    s << "\n// PyMI support\n"
+        << pre << "Shiboken::callInheritedInit(self, args, kwds, fullName);\n"
+        << "if (PyErr_Occurred())\n" << indent << errorReturn << outdent << "\n";
+
     writeFunctionCalls(s, overloadData, classContext, errorReturn);
     s << '\n';
 
@@ -2423,7 +2430,7 @@ void CppGenerator::writeConstructorWrapper(TextStream &s, const OverloadData &ov
             << "PySide::Signal::updateSourceObject(self);\n"
             << "metaObject = cptr->metaObject(); // <- init python qt properties\n"
             << "if (!errInfo.isNull() && PyDict_Check(errInfo.object())) {\n" << indent
-                << "if (!PySide::fillQtProperties(self, metaObject, errInfo))\n" << indent
+                << "if (!PySide::fillQtProperties(self, metaObject, errInfo, usesPyMI))\n" << indent
                     << "return " << returnErrorWrongArguments(overloadData, errorReturn) << ";\n"
                     << outdent << outdent
             << "};\n";
diff --git a/sources/shiboken6/libshiboken/bindingmanager.cpp b/sources/shiboken6/libshiboken/bindingmanager.cpp
index 01e073020..ed8b6743a 100644
--- a/sources/shiboken6/libshiboken/bindingmanager.cpp
+++ b/sources/shiboken6/libshiboken/bindingmanager.cpp
@@ -379,5 +379,66 @@ void BindingManager::visitAllPyObjects(ObjectVisitor visitor, void *data)
     }
 }
 
+static bool isPythonType(PyTypeObject *type)
+{
+    // This is a type which should be called by multiple inheritance.
+    // It is either a pure Python type or a derived PySide type.
+    return !ObjectType::checkType(type) || ObjectType::isUserType(type);
+}
+
+bool callInheritedInit(PyObject *self, PyObject *args, PyObject *kwds,
+                                       const char *fullName)
+{
+    using Shiboken::AutoDecRef;
+
+    static PyObject *const _init = String::createStaticString("__init__");
+
+    // A native C++ self cannot have multiple inheritance.
+    if (!Object::isUserType(self))
+        return false;
+
+    auto *startType = Py_TYPE(self);
+    auto *mro = startType->tp_mro;
+    Py_ssize_t idx, n = PyTuple_GET_SIZE(mro);
+    auto classNameLen = std::strrchr(fullName, '.') - fullName;
+    /* No need to check the last one: it's gonna be skipped anyway.  */
+    for (idx = 0; idx + 1 < n; ++idx) {
+        auto *lookType = reinterpret_cast<PyTypeObject *>(PyTuple_GET_ITEM(mro, idx));
+        const char *lookName = lookType->tp_name;
+        auto lookLen = long(std::strlen(lookName));
+        if (std::strncmp(lookName, fullName, classNameLen) == 0 && lookLen == classNameLen)
+            break;
+    }
+    // We are now at the first non-Python class `QObject`.
+    // mro: ('C', 'A', 'QObject', 'Object', 'B', 'object')
+    // We want to catch class `B` and call its `__init__`.
+    for (idx += 1; idx + 1 < n; ++idx) {
+        auto *t = reinterpret_cast<PyTypeObject *>(PyTuple_GET_ITEM(mro, idx));
+        if (isPythonType(t))
+            break;
+    }
+    if (idx >= n)
+        return false;
+
+    auto *obSubType = PyTuple_GET_ITEM(mro, idx);
+    auto *subType = reinterpret_cast<PyTypeObject *>(obSubType);
+    if (subType == &PyBaseObject_Type)
+        return false;
+    const Py_ssize_t nargs = PyTuple_GET_SIZE(args);
+    AutoDecRef func(PyObject_GetAttr(obSubType, _init));
+    AutoDecRef newArgs(PyTuple_New(1 + nargs));
+    auto *newArgsOb = newArgs.object();
+    Py_INCREF(self);
+    PyTuple_SET_ITEM(newArgsOb, 0, self);
+    for (idx = 0; idx < nargs; ++idx) {
+        auto *ob = PyTuple_GET_ITEM(args, idx);
+        Py_INCREF(ob);
+        PyTuple_SET_ITEM(newArgsOb, 1 + idx, ob);
+    }
+    // Note: This can fail, so please always check the error status.
+    AutoDecRef result(PyObject_Call(func, newArgs, kwds));
+    return true;
+}
+
 } // namespace Shiboken
 
diff --git a/sources/shiboken6/libshiboken/bindingmanager.h b/sources/shiboken6/libshiboken/bindingmanager.h
index e299dad96..955c0a1f4 100644
--- a/sources/shiboken6/libshiboken/bindingmanager.h
+++ b/sources/shiboken6/libshiboken/bindingmanager.h
@@ -67,6 +67,9 @@ private:
     BindingManagerPrivate *m_d;
 };
 
+LIBSHIBOKEN_API bool callInheritedInit(PyObject *self, PyObject *args, PyObject *kwds,
+                                       const char *fullName);
+
 } // namespace Shiboken
 
 #endif // BINDINGMANAGER_H
diff --git a/sources/shiboken6/tests/samplebinding/multi_cpp_inheritance_test.py b/sources/shiboken6/tests/samplebinding/multi_cpp_inheritance_test.py
index e655b8051..6fd735379 100644
--- a/sources/shiboken6/tests/samplebinding/multi_cpp_inheritance_test.py
+++ b/sources/shiboken6/tests/samplebinding/multi_cpp_inheritance_test.py
@@ -74,11 +74,16 @@ class MultipleCppDerivedReverseTest(unittest.TestCase):
         self.assertEqual(s.objectName(), "Hi")
 
     def testComplexInstanciation(self):
-        c = ComplexUseCaseReverse("Hi")
-        c.setObjectName(c)
-        self.assertEqual(c.objectName(), "Hi")
-        c.setX(2);
-        self.assertEqual(c, Point(2, 0))
+        # PYSIDE-1564: This test can no longer work because of this MRO:
+        # ('ComplexUseCaseReverse', 'Point', 'SimpleUseCase2', 'SimpleUseCase',
+        #  'ObjectType', 'Str', 'Object', 'object')
+        # By multiple inheritance Point would be called first but has no argument.
+        with self.assertRaises(TypeError):
+            c = ComplexUseCaseReverse("Hi")
+        # c.setObjectName(c)
+        # self.assertEqual(c.objectName(), "Hi")
+        # c.setX(2);
+        # self.assertEqual(c, Point(2, 0))
 
 if __name__ == '__main__':
     unittest.main()