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poll_fn and Unpin: fix pinning #102737

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merged 1 commit into from
Oct 29, 2022
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poll_fn and Unpin: fix pinning #102737

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11 changes: 7 additions & 4 deletions library/core/src/future/poll_fn.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,9 @@ use crate::task::{Context, Poll};

/// Creates a future that wraps a function returning [`Poll`].
///
/// Polling the future delegates to the wrapped function.
/// Polling the future delegates to the wrapped function. If the returned future is pinned, then the
/// captured environment of the wrapped function is also pinned in-place, so as long as the closure
/// does not move out of its captures it can soundly create pinned references to them.
///
/// # Examples
///
Expand Down Expand Up @@ -41,7 +43,7 @@ pub struct PollFn<F> {
}

#[stable(feature = "future_poll_fn", since = "1.64.0")]
impl<F> Unpin for PollFn<F> {}
impl<F: Unpin> Unpin for PollFn<F> {}

#[stable(feature = "future_poll_fn", since = "1.64.0")]
impl<F> fmt::Debug for PollFn<F> {
Expand All @@ -57,7 +59,8 @@ where
{
type Output = T;

fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
(&mut self.f)(cx)
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
// SAFETY: We are not moving out of the pinned field.
(unsafe { &mut self.get_unchecked_mut().f })(cx)
}
}