Unreachable error with TypeVar

[Dreamsorcerer]

With:

from functools import wraps
from typing import Any, AsyncIterator, Awaitable, Callable, Coroutine, Optional, TypeVar, Union, overload

from aiohttp import web

_T = TypeVar("_T")
_RequestView = TypeVar("_RequestView", web.Request, web.View)

def atomic(coro: Callable[[_RequestView], Awaitable[_T]]):
    @wraps(coro)
    async def wrapper(request_or_view: _RequestView) -> _T:
        reveal_type(request_or_view)
        if isinstance(request_or_view, web.View):
            request = request_or_view.request
        else:
            request = request_or_view

I get an unreachable error on the last line. I suspect it is type checking twice with the TypeVar set to web.Request and then to web.View, which is resulting in an unreachable error. Rather odd that it doesn't produce a second unreachable error though...

[brianschubert]

Fixed in #18217, which should land with mypy v1.14