Stupid MSVC ruining my day.

Author: ZeroIntensity

Modules/_ctypes/_ctypes.c

@@ -3201,25 +3201,39 @@ static PyMethodDef PyCData_methods[] = {
     { NULL, NULL },
 };
 
-static PyType_Slot pycdata_slots[] = {
-    {Py_tp_dealloc, PyCData_dealloc},
-    {Py_tp_hash, PyObject_HashNotImplemented},
-    {Py_tp_doc, PyDoc_STR("XXX to be provided")},
-    {Py_tp_traverse, PyCData_traverse},
-    {Py_tp_clear, PyCData_clear},
-    {Py_tp_methods, PyCData_methods},
-    {Py_tp_members, PyCData_members},
-    {Py_bf_getbuffer, PyCData_NewGetBuffer},
-    {0, NULL},
-};
-
-static PyType_Spec pycdata_spec = {
-    .name = "_ctypes._CData",
-    .basicsize = sizeof(CDataObject),
-    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC |
-              Py_TPFLAGS_IMMUTABLETYPE | Py_TPFLAGS_DISALLOW_INSTANTIATION),
-    .slots = pycdata_slots,
-};
+/*
+ * CData objects are mutable, so they cannot be hashable. Setting tp_hash to
+ * PyObject_HashNotImplemented() makes type_ready() set __hash__ to None.
+ *
+ * Unfortunately, on Windows, PyObject_HashNotImplemented is imported from
+ * the Python DLL, and MSVC resolves the address of an imported function in
+ * a static initializer to a local thunk that can't be recognized. So, we
+ * initialize the slots at runtime to load the real address from the import table.
+ */
+static PyObject *
+PyCData_create_type(PyObject *mod)
+{
+    PyType_Slot slots[] = {
+        {Py_tp_dealloc, PyCData_dealloc},
+        {Py_tp_hash, PyObject_HashNotImplemented},
+        {Py_tp_doc, PyDoc_STR("XXX to be provided")},
+        {Py_tp_traverse, PyCData_traverse},
+        {Py_tp_clear, PyCData_clear},
+        {Py_tp_methods, PyCData_methods},
+        {Py_tp_members, PyCData_members},
+        {Py_bf_getbuffer, PyCData_NewGetBuffer},
+        {0, NULL},
+    };
+    PyType_Spec spec = {
+        .name = "_ctypes._CData",
+        .basicsize = sizeof(CDataObject),
+        .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
+                  Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_IMMUTABLETYPE |
+                  Py_TPFLAGS_DISALLOW_INSTANTIATION),
+        .slots = slots,
+    };
+    return PyType_FromMetaclass(NULL, mod, &spec, NULL);
+}
 
 static int
 PyCData_MallocBuffer(CDataObject *obj, StgInfo *info)
@@ -6239,7 +6253,10 @@ _ctypes_add_types(PyObject *mod)
     */
     CREATE_TYPE(st->PyCArg_Type, &carg_spec, NULL, NULL);
     CREATE_TYPE(st->PyCThunk_Type, &cthunk_spec, NULL, NULL);
-    CREATE_TYPE(st->PyCData_Type, &pycdata_spec, NULL, NULL);
+    st->PyCData_Type = (PyTypeObject *)PyCData_create_type(mod);
+    if (st->PyCData_Type == NULL) {
+        return -1;
+    }
 
     // Common Metaclass
     CREATE_TYPE(st->PyCType_Type, &pyctype_type_spec,