gh-117266: Fix crashes on user-created AST subclasses (GH-117276)

Fix crashes on user-created AST subclasses

1 files changed, 13 insertions, 2 deletions

diff --git a/Parser/asdl_c.py b/Parser/asdl_c.py
index 59cc391..c4df2c5 100755
--- a/Parser/asdl_c.py
+++ b/Parser/asdl_c.py
@@ -973,11 +973,22 @@ ast_type_init(PyObject *self, PyObject *args, PyObject *kw)
     Py_ssize_t size = PySet_Size(remaining_fields);
     PyObject *field_types = NULL, *remaining_list = NULL;
     if (size > 0) {
-        if (!PyObject_GetOptionalAttr((PyObject*)Py_TYPE(self), &_Py_ID(_field_types),
-                                      &field_types)) {
+        if (PyObject_GetOptionalAttr((PyObject*)Py_TYPE(self), &_Py_ID(_field_types),
+                                     &field_types) < 0) {
             res = -1;
             goto cleanup;
         }
+        if (field_types == NULL) {
+            if (PyErr_WarnFormat(
+                PyExc_DeprecationWarning, 1,
+                "%.400s provides _fields but not _field_types. "
+                "This will become an error in Python 3.15.",
+                Py_TYPE(self)->tp_name
+            ) < 0) {
+                res = -1;
+            }
+            goto cleanup;
+        }
         remaining_list = PySequence_List(remaining_fields);
         if (!remaining_list) {
             goto set_remaining_cleanup;