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Fix issue with field retagging in scopeguard #359

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merged 2 commits into from
Sep 9, 2022
Merged

Fix issue with field retagging in scopeguard #359

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f4c9597
Use `ManuallyDrop<T>` instead of `mem::forget` in scopeguard
Noratrieb Sep 6, 2022
1f751c6
Enable `-Zmiri-retag-fields` in CI
Noratrieb Sep 6, 2022
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2 changes: 1 addition & 1 deletion ci/miri.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -9,4 +9,4 @@ rustup toolchain install nightly --component miri
rustup override set nightly
cargo miri setup

cargo miri test
MIRIFLAGS='-Zmiri-retag-fields' cargo miri test
14 changes: 6 additions & 8 deletions src/scopeguard.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
// Extracted from the scopeguard crate
use core::{
mem,
mem::ManuallyDrop,
ops::{Deref, DerefMut},
ptr,
};
Expand Down Expand Up @@ -28,15 +28,13 @@ where
#[inline]
pub fn into_inner(guard: Self) -> T {
// Cannot move out of Drop-implementing types, so
// ptr::read the value and forget the guard.
// ptr::read the value out of a ManuallyDrop<Self>
// Don't use mem::forget as that might invalidate value
let guard = ManuallyDrop::new(guard);
unsafe {
let value = ptr::read(&guard.value);
// read the closure so that it is dropped, and assign it to a local
// variable to ensure that it is only dropped after the guard has
// been forgotten. (In case the Drop impl of the closure, or that
// of any consumed captured variable, panics).
let _dropfn = ptr::read(&guard.dropfn);
mem::forget(guard);
// read the closure so that it is dropped
let _ = ptr::read(&guard.dropfn);
value
}
}
Expand Down