bpo-45663: Fix is_dataclass() for dataclasses which are subclasses of types.GenericAlias (GH-29294)

(cherry picked from commit 446be166861b2f08f87f74018113dd98ca5fca02)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index ad981d1..fa5adfc 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -7,6 +7,7 @@ from dataclasses import *
 import pickle
 import inspect
 import builtins
+import types
 import unittest
 from unittest.mock import Mock
 from typing import ClassVar, Any, List, Union, Tuple, Dict, Generic, TypeVar, Optional, Protocol
@@ -1348,6 +1349,17 @@ class TestCase(unittest.TestCase):
                 with self.assertRaisesRegex(TypeError, 'should be called on dataclass instances'):
                     replace(obj, x=0)
 
+    def test_is_dataclass_genericalias(self):
+        @dataclass
+        class A(types.GenericAlias):
+            origin: type
+            args: type
+        self.assertTrue(is_dataclass(A))
+        a = A(list, int)
+        self.assertTrue(is_dataclass(type(a)))
+        self.assertTrue(is_dataclass(a))
+
+
     def test_helper_fields_with_class_instance(self):
         # Check that we can call fields() on either a class or instance,
         #  and get back the same thing.