Test for object.__getstate__ (new in Py3.11) in auto-pickling code (GH-4732)

The presence of this generic special method should not prevent Cython from making a class pickleable.

Fixes https://github.com/cython/cython/issues/4730

Cython/Utility/ExtensionTypes.c

@@ -204,18 +204,31 @@ static int __Pyx_setup_reduce_is_named(PyObject* meth, PyObject* name) {
 static int __Pyx_setup_reduce(PyObject* type_obj) {
     int ret = 0;
     PyObject *object_reduce = NULL;
+    PyObject *object_getstate = NULL;
     PyObject *object_reduce_ex = NULL;
     PyObject *reduce = NULL;
     PyObject *reduce_ex = NULL;
     PyObject *reduce_cython = NULL;
     PyObject *setstate = NULL;
     PyObject *setstate_cython = NULL;
+    PyObject *getstate = NULL;
 
 #if CYTHON_USE_PYTYPE_LOOKUP
-    if (_PyType_Lookup((PyTypeObject*)type_obj, PYIDENT("__getstate__"))) goto __PYX_GOOD;
+    getstate = _PyType_Lookup((PyTypeObject*)type_obj, PYIDENT("__getstate__"));
 #else
-    if (PyObject_HasAttr(type_obj, PYIDENT("__getstate__"))) goto __PYX_GOOD;
+    getstate = __Pyx_PyObject_GetAttrStr(type_obj, PYIDENT("__getstate__"));
 #endif
+    if (getstate) {
+        // Python 3.11 introduces object.__getstate__. Because it's version-specific failure to find it should not be an error
+#if CYTHON_USE_PYTYPE_LOOKUP
+        object_getstate = _PyType_Lookup(&PyBaseObject_Type, PYIDENT("__getstate__"));
+#else
+        object_getstate = __Pyx_PyObject_GetAttrStrNoError((PyObject*)&PyBaseObject_Type, PYIDENT("__getstate__"));
+#endif
+        if (object_getstate != getstate) {
+            goto __PYX_GOOD;
+        }
+    }
 
 #if CYTHON_USE_PYTYPE_LOOKUP
     object_reduce_ex = _PyType_Lookup(&PyBaseObject_Type, PYIDENT("__reduce_ex__")); if (!object_reduce_ex) goto __PYX_BAD;
@@ -270,6 +283,8 @@ __PYX_GOOD:
 #if !CYTHON_USE_PYTYPE_LOOKUP
     Py_XDECREF(object_reduce);
     Py_XDECREF(object_reduce_ex);
+    Py_XDECREF(object_getstate);
+    Py_XDECREF(getstate);
 #endif
     Py_XDECREF(reduce);
     Py_XDECREF(reduce_ex);