py/objtype: Eliminate __set_name__ hazard.

AJMansfield · AJMansfield · commit a893a8b8b72e · 2025-02-25T11:24:26.000-05:00
Signed-off-by: Anson Mansfield &lt;amansfield@mantaro.com&gt;
diff --git a/py/objtype.c b/py/objtype.c
@@ -974,6 +974,38 @@ static bool check_for_special_accessors(mp_obj_t key, mp_obj_t value) {
 }
 #endif
 
+#if MICROPY_PY_DESCRIPTORS
+static void run_set_name_hooks(mp_obj_t locals_dict, mp_obj_t owner) {
+    // copy the dict so we can iterate safely even while __set_name__ potentially modifies the original
+    mp_obj_dict_t *locals_dict_copy = MP_OBJ_TO_PTR(mp_obj_dict_copy(locals_dict));
+    mp_map_t *locals_map = mp_obj_dict_get_map(locals_dict_copy);
+
+    // make sure we don't leak this copy's memory
+    nlr_buf_t nlr;
+    bool ok = (nlr_push(&nlr) == 0);
+    if (ok) {
+        // use the copy to call __set_name__ on each
+        for (size_t i = 0; i < locals_map->alloc; i++) {
+            if (mp_map_slot_is_filled(locals_map, i)) {
+                mp_map_elem_t *elem = &(locals_map->table[i]);
+                mp_obj_t set_name_method[4];
+                mp_load_method_maybe(elem->value, MP_QSTR___set_name__, set_name_method);
+                if (set_name_method[1] != MP_OBJ_NULL) {
+                    set_name_method[2] = owner;
+                    set_name_method[3] = elem->key;
+                    mp_call_method_n_kw(2, 0, set_name_method);
+                }
+            }
+        }
+        nlr_pop();
+    }
+    m_del_obj(locals_dict_copy->base.type, locals_dict_copy);
+    if (!ok) {
+        nlr_raise(nlr.ret_val); // TODO cpython raises a RuntimeError from this instead
+    }
+}
+#endif
+
 static void type_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
     (void)kind;
     mp_obj_type_t *self = MP_OBJ_TO_PTR(self_in);
@@ -1242,20 +1274,7 @@ mp_obj_t mp_obj_new_type(qstr name, mp_obj_t bases_tuple, mp_obj_t locals_dict)
     }
 
     #if MICROPY_PY_DESCRIPTORS
-    // call __set_name__ on all entries (especially descriptors)
-    for (size_t i = 0; i < locals_map->alloc; i++) {
-        if (mp_map_slot_is_filled(locals_map, i)) {
-            elem = &(locals_map->table[i]);
-
-            mp_obj_t set_name_method[4];
-            mp_load_method_maybe(elem->value, MP_QSTR___set_name__, set_name_method);
-            if (set_name_method[1] != MP_OBJ_NULL) {
-                set_name_method[2] = MP_OBJ_FROM_PTR(o);
-                set_name_method[3] = elem->key;
-                mp_call_method_n_kw(2, 0, set_name_method);
-            }
-        }
-    }
+    run_set_name_hooks(locals_dict, MP_OBJ_FROM_PTR(o));
     #endif
 
     return MP_OBJ_FROM_PTR(o);
