Add missing dunder attributes for TypeAliasType instances

src/test_typing_extensions.py

@@ -7247,6 +7247,30 @@ def test_getitem(self):
         self.assertEqual(get_args(fully_subscripted), (Iterable[float],))
         self.assertIs(get_origin(fully_subscripted), ListOrSetT)
 
+    def test_alias_attributes(self):
+        T = TypeVar('T')
+        T2 = TypeVar('T2')
+        ListOrSetT = TypeAliasType("ListOrSetT", Union[List[T], Set[T]], type_params=(T,))
+        subscripted = ListOrSetT[int]
+        still_generic = ListOrSetT[Iterable[T2]]
+        fully_subscripted = still_generic[float]
+
+        self.assertEqual(subscripted.__module__, ListOrSetT.__module__)
+        self.assertEqual(subscripted.__name__, "ListOrSetT")
+        self.assertEqual(subscripted.__value__, Union[List[T], Set[T]])
+        self.assertEqual(subscripted.__type_params__, (T,))
+        self.assertEqual(still_generic.__module__, ListOrSetT.__module__)
+        self.assertEqual(still_generic.__name__, "ListOrSetT")
+        self.assertEqual(still_generic.__value__, Union[List[T], Set[T]])
+        self.assertEqual(still_generic.__type_params__, (T,))
+        with self.subTest(variable=fully_subscripted):
+            if not TYPING_3_10_0:  # needs to align with GenericAlias usage in __getitem__ else 3.12+
+                self.skipTest("Cannot further proxy attributes with _GenericAlias")
+            self.assertEqual(fully_subscripted.__module__, ListOrSetT.__module__)
+            self.assertEqual(fully_subscripted.__name__, "ListOrSetT")
+            self.assertEqual(fully_subscripted.__value__, Union[List[T], Set[T]])
+            self.assertEqual(fully_subscripted.__type_params__, (T,))
+
     def test_pickle(self):
         global Alias
         Alias = TypeAliasType("Alias", int)

src/typing_extensions.py

@@ -3533,7 +3533,14 @@ def __getitem__(self, parameters):
                 )
                 for item in parameters
             ]
-            return typing._GenericAlias(self, tuple(parameters))
+            if sys.version_info >= (3, 10):
+                return typing.GenericAlias(self, tuple(parameters))
+            alias = typing._GenericAlias(self, tuple(parameters))
+            alias.__value__ = self.__value__
+            alias.__type_params__ = self.__type_params__
+            if sys.version_info <= (3, 11):
+                alias.__name__ = self.__name__
+            return alias
 
         def __reduce__(self):
             return self.__name__