Type checking against asyncssh using mypy 1.0.0 fails.

[jonathanslenders]

See: python/mypy#14631

I'm opening an issue here as well, to discuss it from the asyncssh side.

So, basically: mypy -c 'import asyncssh' fails.

The code in question which I think is problematic is this:
https://github.com/ronf/asyncssh/blob/develop/asyncssh/connection.py#L181

[jonathanslenders]

It looks like not using a _ConnectionFactory prevents mypy from crashing. This is a fix:

diff --git a/asyncssh/connection.py b/asyncssh/connection.py
index 898652b..fc91eb6 100644
--- a/asyncssh/connection.py
+++ b/asyncssh/connection.py
@@ -179,7 +179,7 @@ _ServerFactory = Callable[[], SSHServer]
 _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 +269,7 @@ _DEFAULT_MAX_LINE_LENGTH = 1024     # 1024 characters

 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 +376,7 @@ 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 +455,7 @@ 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"""

jonathan@ubuntu ~/git/asyncssh [develop]

[ronf]

Thanks for the report! It looks like there's a fix for this already proposed at python/mypy#14642, so this change may not be needed in asyncssh, but let me know if you're still running into issues after that.

[jonathanslenders]

Closing this. There is a mypy fix that got merged!