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Rollup merge of #125048 - dingxiangfei2009:stable-deref, r=amanieu

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PinCoerceUnsized trait into core

cc ``@Darksonn`` ``@wedsonaf`` ``@ojeda``

This is a PR to introduce a `PinCoerceUnsized` trait in order to make trait impls generated by the proc-macro `#[derive(SmartPointer)]`, proposed by [RFC](e17e19ac7a/text/3621-derive-smart-pointer.md (pincoerceunsized-1)), sound. There you may find explanation, justification and discussion about the alternatives.

Note that we do not seek stabilization of this `PinCoerceUnsized` trait in the near future. The stabilisation of this trait does not block the eventual stabilization process of the `#[derive(SmartPointer)]` macro. Ideally, use of `DerefPure` is more preferrable except this will actually constitute a breaking change. `PinCoerceUnsized` emerges as a solution to the said soundness hole while avoiding the breaking change. More details on the `DerefPure` option have been described in this [section](e17e19ac7a/text/3621-derive-smart-pointer.md (derefpure)) of the RFC linked above.

Earlier discussion can be found in this [Zulip stream](https://rust-lang.zulipchat.com/#narrow/stream/136281-t-opsem/topic/Pin.20and.20soundness.20of.20unsizing.20coercions) and [rust-for-linux thread](https://rust-lang.zulipchat.com/#narrow/stream/425075-rust-for-linux/topic/.23.5Bderive.28SmartPointer.29.5D.20and.20pin.20unsoundness.20rfc.233621).

try-job: dist-various-2
This commit is contained in:
Matthias Krüger 2024-08-07 00:34:11 +02:00 • committed by GitHub
commit 16b251be10
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16 changed files with 218 additions and 4 deletions
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1
library/std/src/lib.rs
View file

@ -339,6 +339,7 @@
#![feature(maybe_uninit_write_slice)]
#![feature(panic_can_unwind)]
#![feature(panic_internals)]
#![feature(pin_coerce_unsized_trait)]
#![feature(pointer_is_aligned_to)]
#![feature(portable_simd)]
#![feature(prelude_2024)]

4
library/std/src/sys/pal/sgx/abi/usercalls/alloc.rs
View file

@ -8,6 +8,7 @@ use crate::cell::UnsafeCell;
use crate::convert::TryInto;
use crate::mem::{self, ManuallyDrop};
use crate::ops::{CoerceUnsized, Deref, DerefMut, Index, IndexMut};
use crate::pin::PinCoerceUnsized;
use crate::ptr::{self, NonNull};
use crate::slice::SliceIndex;
use crate::{cmp, intrinsics, slice};
@ -751,6 +752,9 @@ where
#[unstable(feature = "sgx_platform", issue = "56975")]
impl<T: CoerceUnsized<U>, U> CoerceUnsized<UserRef<U>> for UserRef<T> {}
#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized> PinCoerceUnsized for UserRef<T> {}
#[unstable(feature = "sgx_platform", issue = "56975")]
impl<T, I> Index<I> for UserRef<[T]>
where