From 688f8134573ab938df7873cb01917448edea4b70 Mon Sep 17 00:00:00 2001
From: Elliott Beach <elliott2.71828@gmail.com>
Date: Mon, 8 Jan 2018 08:02:30 -0600
Subject: [PATCH] fix subclassing ExitStack (#1810)

---
 stdlib/2and3/contextlib.pyi | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/stdlib/2and3/contextlib.pyi b/stdlib/2and3/contextlib.pyi
index 480546fb9..21f640a17 100644
--- a/stdlib/2and3/contextlib.pyi
+++ b/stdlib/2and3/contextlib.pyi
@@ -53,6 +53,8 @@ if sys.version_info >= (3,):
     class ContextDecorator:
         def __call__(self, func: Callable[..., None]) -> Callable[..., ContextManager[None]]: ...
 
+    _U = TypeVar('_U', bound='ExitStack')
+
     class ExitStack(ContextManager[ExitStack]):
         def __init__(self) -> None: ...
         def enter_context(self, cm: ContextManager[_T]) -> _T: ...
@@ -61,3 +63,4 @@ if sys.version_info >= (3,):
                      *args: Any, **kwds: Any) -> Callable[..., None]: ...
         def pop_all(self) -> ExitStack: ...
         def close(self) -> None: ...
+        def __enter__(self: _U) -> _U: ...