--- /home/ncoghlan/devel/contextlib2/../cpython/Lib/contextlib.py	2024-05-23 11:57:09.210023505 +1000
+++ /home/ncoghlan/devel/contextlib2/contextlib2/__init__.py	2024-05-23 17:05:06.549142813 +1000
@@ -5,7 +5,46 @@
 import _collections_abc
 from collections import deque
 from functools import wraps
-from types import MethodType, GenericAlias
+from types import MethodType
+
+# Python 3.8 compatibility: GenericAlias may not be defined
+try:
+    from types import GenericAlias
+except ImportError:
+    # If the real GenericAlias type doesn't exist, __class_getitem__ won't be used,
+    # so the fallback placeholder doesn't need to provide any meaningful behaviour
+    # (typecheckers may still be unhappy, but for that problem the answer is
+    # "use a newer Python version with better typechecking support")
+    class GenericAlias:
+        pass
+
+# Python 3.10 and earlier compatibility: BaseExceptionGroup may not be defined
+try:
+    BaseExceptionGroup
+except NameError:
+    # If the real BaseExceptionGroup type doesn't exist, it will never actually
+    # be raised. This means the fallback placeholder doesn't need to provide
+    # any meaningful behaviour, it just needs to be compatible with 'issubclass'
+    class BaseExceptionGroup(BaseException):
+        pass
+
+# Python 3.9 and earlier compatibility: anext may not be defined
+try:
+    anext
+except NameError:
+    def anext(obj, /):
+        return obj.__anext__()
+
+# Python 3.11+ behaviour consistency: replace AttributeError with TypeError
+if sys.version_info >= (3, 11):
+    # enter_context() and enter_async_context() follow the change in the
+    # exception type raised by with statements and async with statements
+    _CL2_ERROR_TO_CONVERT = AttributeError
+else:
+    # On older versions, raise AttributeError without any changes
+    class _CL2_ERROR_TO_CONVERT(Exception):
+        pass
+
 
 __all__ = ["asynccontextmanager", "contextmanager", "closing", "nullcontext",
            "AbstractContextManager", "AbstractAsyncContextManager",
@@ -62,6 +101,24 @@
 class ContextDecorator(object):
     "A base class or mixin that enables context managers to work as decorators."
 
+    def refresh_cm(self):
+        """Returns the context manager used to actually wrap the call to the
+        decorated function.
+
+        The default implementation just returns *self*.
+
+        Overriding this method allows otherwise one-shot context managers
+        like _GeneratorContextManager to support use as decorators via
+        implicit recreation.
+
+        DEPRECATED: refresh_cm was never added to the standard library's
+                    ContextDecorator API
+        """
+        import warnings # Only import if needed for the deprecation warning
+        warnings.warn("refresh_cm was never added to the standard library",
+                      DeprecationWarning)
+        return self._recreate_cm()
+
     def _recreate_cm(self):
         """Return a recreated instance of self.
 
@@ -520,7 +577,7 @@
         try:
             _enter = cls.__enter__
             _exit = cls.__exit__
-        except AttributeError:
+        except _CL2_ERROR_TO_CONVERT:
             raise TypeError(f"'{cls.__module__}.{cls.__qualname__}' object does "
                             f"not support the context manager protocol") from None
         result = _enter(cm)
@@ -652,7 +709,7 @@
         try:
             _enter = cls.__aenter__
             _exit = cls.__aexit__
-        except AttributeError:
+        except _CL2_ERROR_TO_CONVERT:
             raise TypeError(f"'{cls.__module__}.{cls.__qualname__}' object does "
                             f"not support the asynchronous context manager protocol"
                            ) from None
@@ -798,3 +855,22 @@
 
     def __exit__(self, *excinfo):
         os.chdir(self._old_cwd.pop())
+
+# Preserve backwards compatibility
+class ContextStack(ExitStack):
+    """(DEPRECATED) Backwards compatibility alias for ExitStack"""
+
+    def __init__(self):
+        import warnings # Only import if needed for the deprecation warning
+        warnings.warn("ContextStack has been renamed to ExitStack",
+                      DeprecationWarning)
+        super(ContextStack, self).__init__()
+
+    def register_exit(self, callback):
+        return self.push(callback)
+
+    def register(self, callback, *args, **kwds):
+        return self.callback(callback, *args, **kwds)
+
+    def preserve(self):
+        return self.pop_all()