Fix Memory Leak Caused By Wrong Limited API Default

When a type has nullptr as tp_dealloc, there apply different defaults.

Static types had object_dealloc as default, while new heaptypes
created with type_new have subtype_dealloc as default.

A problem was now that PyType_FromSpec also has
subtype_dealloc as default. But that is wrong, because a type that
was written with the static type approach is already written with
object_dealloc in mind and takes somehow care about further issues
with that type.

When we now convert this type and suddenly use subtype_dealloc
instead of object_dealloc, things get pretty wrong.

Finding that out was pretty hard and took quite long to understand.

The fix was then very easy and is the best proof:
Replacing our former (wrong) solution of supplying an
SbkDummyDealloc with a function object_dealloc works perfectly,
and the leakage completely vanished.

The documentation now is also corrected.

Task-number: PYSIDE-832
Change-Id: Ifc20c28172eb5663cd5e60dac52e0a43acfb626c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 5 insertions, 7 deletions

diff --git a/sources/shiboken2/libshiboken/basewrapper.h b/sources/shiboken2/libshiboken/basewrapper.h
index 06b17a151..134a3bc51 100644
--- a/sources/shiboken2/libshiboken/basewrapper.h
+++ b/sources/shiboken2/libshiboken/basewrapper.h
@@ -109,17 +109,15 @@ LIBSHIBOKEN_API PyObject* SbkObjectTpNew(PyTypeObject* subtype, PyObject*, PyObj
 LIBSHIBOKEN_API PyObject* SbkQAppTpNew(PyTypeObject *subtype, PyObject *args, PyObject *kwds);
 
 /**
- *  PYSIDE-595: Use a null deallocator instead of nullptr.
+ *  PYSIDE-832: Use object_dealloc instead of nullptr.
  *
  *  When moving to heaptypes, we were struck by a special default behavior of
  *  PyType_FromSpecWithBases that inserts subtype_dealloc when tp_dealloc is
- *  nullptr. To prevent inserting this, we use a null deallocator that is there
- *  as a placeholder.
- *
- *  The same holds for a null tp_new. We use one that raises the right error.
+ *  nullptr. But the default before conversion to heaptypes was to assign
+ *  object_dealloc. This seems to be a bug in the Limited API.
  */
-LIBSHIBOKEN_API void SbkDummyDealloc(PyObject*);
-LIBSHIBOKEN_API PyObject *SbkDummyNew(PyTypeObject *type, PyObject*, PyObject*);
+LIBSHIBOKEN_API void object_dealloc(PyObject *);
+LIBSHIBOKEN_API PyObject *SbkDummyNew(PyTypeObject *type, PyObject *, PyObject *);
 
 } // extern "C"