Use typing-extensions only on Python < 3.8

All necessary attributes are available in the built-in typing module
since Python 3.8.  Use typing-extensions only for older versions
of Python, and avoid the unnecessary dep in 3.8+.

Author: mgorny

git/compat.py renamed to git/compat/__init__.py

@@ -0,0 +1,13 @@
+# -*- coding: utf-8 -*-
+# config.py
+# Copyright (C) 2021 Michael Trier (mtrier@gmail.com) and contributors
+#
+# This module is part of GitPython and is released under
+# the BSD License: http://www.opensource.org/licenses/bsd-license.php
+
+import sys
+
+if sys.version_info[:2] >= (3, 8):
+    from typing import Final, Literal
+else:
+    from typing_extensions import Final, Literal

git/compat/typing.py

@@ -16,14 +16,13 @@
 import fnmatch
 from collections import OrderedDict
 
-from typing_extensions import Literal
-
 from git.compat import (
     defenc,
     force_text,
     with_metaclass,
     is_win,
 )
+from git.compat.typing import Literal
 from git.util import LockFile
 
 import os.path as osp

git/config.py

@@ -5,6 +5,7 @@
 # the BSD License: http://www.opensource.org/licenses/bsd-license.php
 
 import re
+import sys
 from git.cmd import handle_process_output
 from git.compat import defenc
 from git.util import finalize_process, hex_to_bin
@@ -16,7 +17,7 @@
 # typing ------------------------------------------------------------------
 
 from typing import Any, Iterator, List, Match, Optional, Tuple, Type, Union, TYPE_CHECKING
-from typing_extensions import Final, Literal
+from git.compat.typing import Final, Literal
 from git.types import TBD
 
 if TYPE_CHECKING:

git/diff.py

@@ -7,6 +7,7 @@
 import logging
 import os
 import re
+import sys
 import warnings
 
 from git.cmd import (
@@ -34,8 +35,8 @@
 
 # typing ------------------------------------------------------
 
+from git.compat.typing import Literal
 from git.types import TBD, PathLike
-from typing_extensions import Literal
 from typing import (Any, BinaryIO, Callable, Dict,
                     Iterator, List, Mapping, Optional,
                     TextIO, Tuple, Type, Union,

git/repo/base.py

@@ -1,2 +1,2 @@
 gitdb>=4.0.1,<5
-typing-extensions>=3.7.4.0
+typing-extensions>=3.7.4.0;python_version<"3.8"

requirements.txt

@@ -5,4 +5,4 @@ tox
 virtualenv
 nose
 gitdb>=4.0.1,<5
-typing-extensions>=3.7.4.0
+typing-extensions>=3.7.4.0;python_version<"3.8"