PyPySide: Fix a hard-to-find bug triggered by tp_itemsize

In a metatype (a type inheriting from PyType_Type), it
is common to set tp_itemsize to sizeof(PyMemberDef).
This is not necessary, since tp_itemsize is otherwise
inherited.

In PyPy, tp_itemsize also has the undocumented meaning
that the type must define a `__len__` field. Not doing
so results in a barely understandable error message, and
all types created in PySide crash, resulting in many
failing tests.

As a conclusion: The tp_itemsize field must stay zero in
our metatypes. This bug was very hard to find. Many thanks
for a hint from Ronan Lamy wo is an experienced PyPy
developer. He saw the problem almost immediately.

[ChangeLog][shiboken6] A hard-to-find incompatibility to
PyPy in meta type creation was fixed. Many thanks to
Ronan Lamy from the PyPy group.

Task-number: PYSIDE-535
Change-Id: I99520b96c80d22195948d96cfb41b7b85c6815fa
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 5 insertions, 1 deletions

diff --git a/sources/shiboken6/libshiboken/basewrapper.cpp b/sources/shiboken6/libshiboken/basewrapper.cpp
index 90cb16ef5..fa60455db 100644
--- a/sources/shiboken6/libshiboken/basewrapper.cpp
+++ b/sources/shiboken6/libshiboken/basewrapper.cpp
@@ -152,10 +152,14 @@ static PyType_Slot SbkObjectType_Type_slots[] = {
     {Py_tp_getset, reinterpret_cast<void *>(SbkObjectType_Type_getsetlist)},
     {0, nullptr}
 };
+
+// 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.
 static PyType_Spec SbkObjectType_Type_spec = {
     "1:Shiboken.ObjectType",
     0,
-    sizeof(PyMemberDef),
+    0, // sizeof(PyMemberDef), not for PyPy without a __len__ defined
     Py_TPFLAGS_DEFAULT|Py_TPFLAGS_BASETYPE,
     SbkObjectType_Type_slots,
 };