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use std::{future::Future, mem::replace};
use pin_project_lite::pin_project;
use tracing::Span;
pin_project! {
pub struct With<T, H>
where
T: Future,
{
#[pin]
future: T,
span: Span,
handle: Option<H>,
}
}
impl<T, H> With<T, H>
where
T: Future,
{
pub fn new(future: T, span: Span, handle: H) -> Self {
Self {
future,
span,
handle: Some(handle),
}
}
}
impl<T, H> Future for With<T, H>
where
T: Future,
{
type Output = (H, Span, T::Output);
fn poll(
self: std::pin::Pin<&mut Self>,
cx: &mut std::task::Context<'_>,
) -> std::task::Poll<Self::Output> {
let this = self.project();
let guard = this.span.enter();
match this.future.poll(cx) {
std::task::Poll::Ready(result) => {
drop(guard);
std::task::Poll::Ready((
this.handle.take().expect("polled after completion"),
replace(this.span, Span::none()),
result,
))
}
std::task::Poll::Pending => std::task::Poll::Pending,
}
}
}
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