1use futures_core::future::{FusedFuture, Future};
2use futures_core::task::{Context, Poll};
3use pin_project::pin_project;
4use std::pin::Pin;
5
6/// Combinator that guarantees one [`Poll::Pending`] before polling its inner
7/// future.
8///
9/// This is created by the
10/// [`FutureTestExt::pending_once`](super::FutureTestExt::pending_once)
11/// method.
12#[pin_project]
13#[derive(Debug, Clone)]
14#[must_use = "futures do nothing unless you `.await` or poll them"]
15pub struct PendingOnce<Fut> {
16 #[pin]
17 future: Fut,
18 polled_before: bool,
19}
20
21impl<Fut: Future> PendingOnce<Fut> {
22 pub(super) fn new(future: Fut) -> Self {
23 Self { future, polled_before: false }
24 }
25}
26
27impl<Fut: Future> Future for PendingOnce<Fut> {
28 type Output = Fut::Output;
29
30 fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
31 let this = self.project();
32 if *this.polled_before {
33 this.future.poll(cx)
34 } else {
35 *this.polled_before = true;
36 cx.waker().wake_by_ref();
37 Poll::Pending
38 }
39 }
40}
41
42impl<Fut: FusedFuture> FusedFuture for PendingOnce<Fut> {
43 fn is_terminated(&self) -> bool {
44 self.polled_before && self.future.is_terminated()
45 }
46}
47