Fix stubtest failures for asyncio on windows (#4092)

stdlib/3/asyncio/windows_events.pyi

@@ -1,9 +1,18 @@
 import socket
 import sys
-from typing import IO, Any, Callable, ClassVar, List, NoReturn, Optional, Tuple
+from typing import IO, Any, Callable, ClassVar, List, NoReturn, Optional, Tuple, Type
 
 from . import events, futures, proactor_events, selector_events, streams, windows_utils
 
+__all__ = [
+    "SelectorEventLoop",
+    "ProactorEventLoop",
+    "IocpProactor",
+    "DefaultEventLoopPolicy",
+    "WindowsSelectorEventLoopPolicy",
+    "WindowsProactorEventLoopPolicy",
+]
+
 NULL: int
 INFINITE: int
 ERROR_CONNECTION_REFUSED: int
@@ -42,24 +51,24 @@ class IocpProactor:
     def sendfile(self, sock: socket.socket, file: IO[bytes], offset: int, count: int) -> futures.Future[Any]: ...
     def accept_pipe(self, pipe: socket.socket) -> futures.Future[Any]: ...
     async def connect_pipe(self, address: bytes) -> windows_utils.PipeHandle: ...
-    def wait_for_handle(self, handle: windows_utils.PipeHandle, timeout: int = ...) -> bool: ...
+    def wait_for_handle(self, handle: windows_utils.PipeHandle, timeout: Optional[int] = ...) -> bool: ...
     def close(self) -> None: ...
 
 SelectorEventLoop = _WindowsSelectorEventLoop
 
 if sys.version_info >= (3, 7):
     class WindowsSelectorEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
-        _loop_factory: ClassVar[events.AbstractEventLoop]
+        _loop_factory: ClassVar[Type[SelectorEventLoop]]
         def get_child_watcher(self) -> NoReturn: ...
         def set_child_watcher(self, watcher: Any) -> NoReturn: ...
     class WindowsProactorEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
-        _loop_factory: ClassVar[events.AbstractEventLoop]
+        _loop_factory: ClassVar[Type[ProactorEventLoop]]
         def get_child_watcher(self) -> NoReturn: ...
         def set_child_watcher(self, watcher: Any) -> NoReturn: ...
     DefaultEventLoopPolicy = WindowsSelectorEventLoopPolicy
 else:
     class _WindowsDefaultEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
-        _loop_factory: ClassVar[events.AbstractEventLoop]
+        _loop_factory: ClassVar[Type[SelectorEventLoop]]
         def get_child_watcher(self) -> NoReturn: ...
         def set_child_watcher(self, watcher: Any) -> NoReturn: ...
     DefaultEventLoopPolicy = _WindowsDefaultEventLoopPolicy

stdlib/3/asyncio/windows_utils.pyi

@@ -1,7 +1,13 @@
 
-from typing import Tuple, Callable, Optional
+import sys
+from typing import Tuple, Callable, Optional, Type, Protocol
 from types import TracebackType
 
+
+class _WarnFunction(Protocol):
+    def __call__(self, message: str, category: Type[Warning], source: PipeHandle): ...
+
+
 BUFSIZE: int
 PIPE: int
 STDOUT: int
@@ -12,7 +18,10 @@ class PipeHandle:
 
     def __init__(self, handle: int) -> None: ...
     def __repr__(self) -> str: ...
-    def __del__(self) -> None: ...
+    if sys.version_info >= (3, 8):
+        def __del__(self, _warn: _WarnFunction = ...) -> None: ...
+    else:
+        def __del__(self) -> None: ...
     def __enter__(self) -> PipeHandle: ...
     def __exit__(self, t: Optional[type], v: Optional[BaseException], tb: Optional[TracebackType]) -> None: ...
     @property