repeated panics when using ServiceExt::oneshot

[hdevalence]

Using ServiceExt::oneshot (tower 0.3.1) I get repeated panics with the message "We immediately transition to ::Called".

It looks like this comes from the service impl:

impl<S, Req> Future for Oneshot<S, Req>
where
    S: Service<Req>,
{
    type Output = Result<S::Response, S::Error>;

    #[project]
    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let mut this = self.project();
        loop {
            #[project]
            match this.state.as_mut().project() {
                State::NotReady(nr) => {
                    let (mut svc, req) = nr.take().expect("We immediately transition to ::Called");
                    let _ = ready!(svc.poll_ready(cx))?;
                    this.state.set(State::Called(svc.call(req)));
                }
                State::Called(fut) => {
                    let res = ready!(fut.poll(cx))?;
                    this.state.set(State::Done);
                    return Poll::Ready(Ok(res));
                }
                State::Done => panic!("polled after complete"),
            }
        }
    }
}

I'm not sure I follow the reasoning here: svc is taken from the nr: Option<_>, but if svc.poll_ready returns Poll::Pending, poll will return early (via ready) without putting svc back. So I don't see how it immediately transitions to ::Called.

[hawkw]

I believe this is the same bug that was fixed in #447. Maybe that was not backported to 0.3?

[LucioFranco]

@hdevalence I think you all updated to 0.4, is this still an issue or can we close this?

[hawkw]

This is fixed in 0.4.