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use core::pin::Pin;
use futures_core::future::{FusedFuture, Future, TryFuture};
use futures_core::ready;
use futures_core::task::{Context, Poll};
use pin_project_lite::pin_project;
pin_project! {
#[project = TryFlattenErrProj]
#[derive(Debug)]
pub enum TryFlattenErr<Fut1, Fut2> {
First { #[pin] f: Fut1 },
Second { #[pin] f: Fut2 },
Empty,
}
}
impl<Fut1, Fut2> TryFlattenErr<Fut1, Fut2> {
pub(crate) fn new(future: Fut1) -> Self {
Self::First { f: future }
}
}
impl<Fut> FusedFuture for TryFlattenErr<Fut, Fut::Error>
where
Fut: TryFuture,
Fut::Error: TryFuture<Ok = Fut::Ok>,
{
fn is_terminated(&self) -> bool {
match self {
Self::Empty => true,
_ => false,
}
}
}
impl<Fut> Future for TryFlattenErr<Fut, Fut::Error>
where
Fut: TryFuture,
Fut::Error: TryFuture<Ok = Fut::Ok>,
{
type Output = Result<Fut::Ok, <Fut::Error as TryFuture>::Error>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
Poll::Ready(loop {
match self.as_mut().project() {
TryFlattenErrProj::First { f } => match ready!(f.try_poll(cx)) {
Err(f) => self.set(Self::Second { f }),
Ok(e) => {
self.set(Self::Empty);
break Ok(e);
}
},
TryFlattenErrProj::Second { f } => {
let output = ready!(f.try_poll(cx));
self.set(Self::Empty);
break output;
}
TryFlattenErrProj::Empty => panic!("TryFlattenErr polled after completion"),
}
})
}
}