py3.10-prep: reset the type cache after feature switching

[ChangeLog][PySide6] Feature switching needs to reset the
internal type cache. This was an omittion that becomes
relevant in Python 3.10 .

When using feature switching in Python 3.10, there were
funny effects where switched and un-switched versions appeared
to co-exist.

It turned out that we were hit by function caching that
is now implemented for the LOAD_ATTR opcode.

It was not known that caching would happen at all for
PySide classes because we don't use Py_TPFLAGS_VALID_VERSION_TAG.
But actually, this flag is used internally by Python to do some
optimizations, and we just have to notify the interpreter of
type changes by PyType_Modified().

Task-number: PYSIDE-1436
Change-Id: Ie8a73f62bd6e9b8156b8ea23626fabd44700158b
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>
(cherry picked from commit 3a2b7c6f88bba04d8b7ddb571163d23c15c36a4f)
Reviewed-by: Christian Tismer <tismer@stackless.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/sources/pyside2/libpyside/feature_select.cpp b/sources/pyside2/libpyside/feature_select.cpp
index 6a21d168d..3da7dde38 100644
--- a/sources/pyside2/libpyside/feature_select.cpp
+++ b/sources/pyside2/libpyside/feature_select.cpp
@@ -405,6 +405,8 @@ static inline PyObject *SelectFeatureSet(PyTypeObject *type)
             if (!SelectFeatureSetSubtype(sub_type, select_id))
                 break;
         }
+        // PYSIDE-1436: Clear all caches for the type and subtypes.
+        PyType_Modified(type);
     }
     return type->tp_dict;
 }