Update for mypy 1.0.0

This commit fixes a new issue reported by mypy 1.0.0 and works around
a problem with type variables that was triggering a mypy internal error.

asyncssh/connection.py

@@ -179,7 +179,6 @@
 _ProtocolFactory = Union[_ClientFactory, _ServerFactory]
 
 _Conn = TypeVar('_Conn', 'SSHClientConnection', 'SSHServerConnection')
-_ConnectionFactory = Callable[[], _Conn]
 
 class _TunnelProtocol(Protocol):
     """Base protocol for connections to tunnel SSH over"""
@@ -269,7 +268,7 @@ async def create_server(self, session_factory: TCPListenerFactory,
 
 async def _open_proxy(
         loop: asyncio.AbstractEventLoop, command: Sequence[str],
-        conn_factory: _ConnectionFactory[_Conn]) -> _Conn:
+        conn_factory: Callable[[], _Conn]) -> _Conn:
     """Open a tunnel running a proxy command"""
 
     class _ProxyCommandTunnel(asyncio.SubprocessProtocol):
@@ -376,7 +375,7 @@ async def _open_tunnel(tunnel: object, passphrase: Optional[BytesOrStr]) -> \
 async def _connect(options: 'SSHConnectionOptions',
                    loop: asyncio.AbstractEventLoop, flags: int,
                    sock: Optional[socket.socket],
-                   conn_factory: _ConnectionFactory[_Conn], msg: str) -> _Conn:
+                   conn_factory: Callable[[], _Conn], msg: str) -> _Conn:
     """Make outbound TCP or SSH tunneled connection"""
 
     host = options.host
@@ -455,7 +454,7 @@ async def _listen(options: 'SSHConnectionOptions',
                   loop: asyncio.AbstractEventLoop, flags: int,
                   backlog: int, sock: Optional[socket.socket],
                   reuse_address: bool, reuse_port: bool,
-                  conn_factory: _ConnectionFactory[_Conn],
+                  conn_factory: Callable[[], _Conn],
                   msg: str) -> 'SSHAcceptor':
     """Make inbound TCP or SSH tunneled listener"""
 
@@ -4240,9 +4239,10 @@ async def open_connection(self, *args: object, **kwargs: object) -> \
 
     @async_context_manager
     async def create_server(
-            self, session_factory: TCPListenerFactory, listen_host: str,
-            listen_port: int, *, encoding: Optional[str] = None,
-            errors: str = 'strict', window: int = _DEFAULT_WINDOW,
+            self, session_factory: TCPListenerFactory[AnyStr],
+            listen_host: str, listen_port: int, *,
+            encoding: Optional[str] = None, errors: str = 'strict',
+            window: int = _DEFAULT_WINDOW,
             max_pktsize: int = _DEFAULT_MAX_PKTSIZE) -> SSHListener:
         """Create a remote SSH TCP listener