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Use ManuallyDrop instead of mem::forget #2765

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Oct 18, 2023
Merged

Use ManuallyDrop instead of mem::forget #2765

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13 changes: 6 additions & 7 deletions tracing/src/instrument.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@ use crate::span::Span;
use core::{
future::Future,
marker::Sized,
mem::{self, ManuallyDrop},
mem::ManuallyDrop,
pin::Pin,
task::{Context, Poll},
};
Expand Down Expand Up @@ -392,12 +392,11 @@ impl<T> Instrumented<T> {
///
/// Note that this drops the span.
pub fn into_inner(self) -> T {
// To manually destructure `Instrumented` without `Drop`, we save
// pointers to the fields and use `mem::forget` to leave those pointers
// valid.
let span: *const Span = &self.span;
let inner: *const ManuallyDrop<T> = &self.inner;
mem::forget(self);
// To manually destructure `Instrumented` without `Drop`, we
// move it into a ManuallyDrop and use pointers to its fields
let this = ManuallyDrop::new(self);
let span: *const Span = &this.span;
let inner: *const ManuallyDrop<T> = &this.inner;
// SAFETY: Those pointers are valid for reads, because `Drop` didn't
// run, and properly aligned, because `Instrumented` isn't
// `#[repr(packed)]`.
Expand Down
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