--- ../contextlib.pyi	2021-07-16 08:26:16.409945194 +0100
+++ contextlib2/__init__.pyi	2021-07-16 08:32:00.363150171 +0100
@@ -1,3 +1,6 @@
+# Type hints copied from the typeshed project under the Apache License 2.0
+# https://github.com/python/typeshed/blob/64c85cdd449ccaff90b546676220c9ecfa6e697f/LICENSE
+
 import sys
 from _typeshed import Self
 from types import TracebackType
@@ -17,8 +20,14 @@
 )
 from typing_extensions import ParamSpec, Protocol
 
+# contextlib2 API adaptation notes:
+# * the various 'if True:' guards replace sys.version checks in the original
+#   typeshed file (those APIs are available on all supported versions)
+# * deliberately omitted APIs are listed in `dev/mypy.allowlist`
+#   (e.g. deprecated experimental APIs that never graduated to the stdlib)
+
 AbstractContextManager = ContextManager
-if sys.version_info >= (3, 7):
+if True:
     AbstractAsyncContextManager = AsyncContextManager
 
 _T = TypeVar("_T")
@@ -36,7 +45,7 @@
 # type ignore to deal with incomplete ParamSpec support in mypy
 def contextmanager(func: Callable[_P, Iterator[_T]]) -> Callable[_P, _GeneratorContextManager[_T]]: ...  # type: ignore
 
-if sys.version_info >= (3, 7):
+if True:
     def asynccontextmanager(func: Callable[_P, AsyncIterator[_T]]) -> Callable[_P, AsyncContextManager[_T]]: ...  # type: ignore
 
 class _SupportsClose(Protocol):
@@ -47,7 +56,7 @@
 class closing(ContextManager[_SupportsCloseT]):
     def __init__(self, thing: _SupportsCloseT) -> None: ...
 
-if sys.version_info >= (3, 10):
+if True:
     class _SupportsAclose(Protocol):
         def aclose(self) -> Awaitable[object]: ...
     _SupportsAcloseT = TypeVar("_SupportsAcloseT", bound=_SupportsAclose)
@@ -87,7 +96,7 @@
         __traceback: Optional[TracebackType],
     ) -> bool: ...
 
-if sys.version_info >= (3, 7):
+if True:
     _ExitCoroFunc = Callable[[Optional[Type[BaseException]], Optional[BaseException], Optional[TracebackType]], Awaitable[bool]]
     _CallbackCoroFunc = Callable[..., Awaitable[Any]]
     _ACM_EF = TypeVar("_ACM_EF", AsyncContextManager[Any], _ExitCoroFunc)
@@ -109,7 +118,8 @@
             __traceback: Optional[TracebackType],
         ) -> Awaitable[bool]: ...
 
-if sys.version_info >= (3, 10):
+
+if True:
     class nullcontext(AbstractContextManager[_T], AbstractAsyncContextManager[_T]):
         enter_result: _T
         @overload
@@ -120,13 +130,3 @@
         def __exit__(self, *exctype: Any) -> None: ...
         async def __aenter__(self) -> _T: ...
         async def __aexit__(self, *exctype: Any) -> None: ...
-
-elif sys.version_info >= (3, 7):
-    class nullcontext(AbstractContextManager[_T]):
-        enter_result: _T
-        @overload
-        def __init__(self: nullcontext[None], enter_result: None = ...) -> None: ...
-        @overload
-        def __init__(self: nullcontext[_T], enter_result: _T) -> None: ...
-        def __enter__(self) -> _T: ...
-        def __exit__(self, *exctype: Any) -> None: ...