Import typing_extensions.TypeAlias only on python < 3.11 (#447)

* Import typing_extensions.TypeAlias only on python < 3.11

* Tweak history

---------

Co-authored-by: Tin Tvrtkovic <tinchester@gmail.com>

HISTORY.md

@@ -1,5 +1,10 @@
 # History
 
+## 23.2.1 (UNRELEASED)
+
+- Fix unnecessary `typing_extensions` import on Python 3.11.
+  ([#446](https://github.com/python-attrs/cattrs/issues/446) [#447](https://github.com/python-attrs/cattrs/pull/447))
+
 ## 23.2.0 (2023-11-17)
 
 - **Potentially breaking**: skip _attrs_ fields marked as `init=False` by default. This change is potentially breaking for unstructuring.

src/cattrs/_compat.py

@@ -20,7 +20,13 @@
 from attrs import fields as attrs_fields
 from attrs import resolve_types
 
-__all__ = ["ExceptionGroup", "ExtensionsTypedDict", "TypedDict", "is_typeddict"]
+__all__ = [
+    "ExceptionGroup",
+    "ExtensionsTypedDict",
+    "TypedDict",
+    "TypeAlias",
+    "is_typeddict",
+]
 
 try:
     from typing_extensions import TypedDict as ExtensionsTypedDict
@@ -39,6 +45,12 @@
     assert sys.version_info >= (3, 10)
     from typing import is_typeddict as _is_typeddict
 
+try:
+    from typing_extensions import TypeAlias
+except ImportError:
+    assert sys.version_info >= (3, 11)
+    from typing import TypeAlias
+
 
 def is_typeddict(cls):
     """Thin wrapper around typing(_extensions).is_typeddict"""

src/cattrs/dispatch.py

@@ -2,7 +2,8 @@
 from typing import Any, Callable, Dict, Generic, List, Optional, Tuple, TypeVar, Union
 
 from attrs import Factory, define, field
-from typing_extensions import TypeAlias
+
+from cattrs._compat import TypeAlias
 
 T = TypeVar("T")