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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](https://github.com/rust-lang/rfcs/blob/e17e19ac7ad1c8ccad55d4babfaee1aa107d1da5/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](https://github.com/rust-lang/rfcs/blob/e17e19ac7ad1c8ccad55d4babfaee1aa107d1da5/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
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matthiaskrgr authored Aug 6, 2024
2 parents 38e631e + d495b84 commit 16b251b
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Showing 16 changed files with 218 additions and 4 deletions.
1 change: 1 addition & 0 deletions compiler/rustc_span/src/symbol.rs
Original file line number Diff line number Diff line change
Expand Up @@ -276,6 +276,7 @@ symbols! {
Path,
PathBuf,
Pending,
PinCoerceUnsized,
Pointer,
Poll,
ProcMacro,
Expand Down
5 changes: 4 additions & 1 deletion library/alloc/src/boxed.rs
Original file line number Diff line number Diff line change
Expand Up @@ -200,7 +200,7 @@ use core::ops::{
AsyncFn, AsyncFnMut, AsyncFnOnce, CoerceUnsized, Coroutine, CoroutineState, Deref, DerefMut,
DerefPure, DispatchFromDyn, Receiver,
};
use core::pin::Pin;
use core::pin::{Pin, PinCoerceUnsized};
use core::ptr::{self, addr_of_mut, NonNull, Unique};
use core::task::{Context, Poll};
use core::{borrow, fmt, slice};
Expand Down Expand Up @@ -2726,3 +2726,6 @@ impl<T: core::error::Error> core::error::Error for Box<T> {
core::error::Error::provide(&**self, request);
}
}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for Box<T, A> {}
1 change: 1 addition & 0 deletions library/alloc/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -138,6 +138,7 @@
#![feature(maybe_uninit_uninit_array_transpose)]
#![feature(panic_internals)]
#![feature(pattern)]
#![feature(pin_coerce_unsized_trait)]
#![feature(ptr_internals)]
#![feature(ptr_metadata)]
#![feature(ptr_sub_ptr)]
Expand Down
10 changes: 10 additions & 0 deletions library/alloc/src/rc.rs
Original file line number Diff line number Diff line change
Expand Up @@ -256,6 +256,7 @@ use core::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, Rece
use core::panic::{RefUnwindSafe, UnwindSafe};
#[cfg(not(no_global_oom_handling))]
use core::pin::Pin;
use core::pin::PinCoerceUnsized;
use core::ptr::{self, drop_in_place, NonNull};
#[cfg(not(no_global_oom_handling))]
use core::slice::from_raw_parts_mut;
Expand Down Expand Up @@ -2177,6 +2178,12 @@ impl<T: ?Sized, A: Allocator> Deref for Rc<T, A> {
}
}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for Rc<T, A> {}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for Weak<T, A> {}

#[unstable(feature = "deref_pure_trait", issue = "87121")]
unsafe impl<T: ?Sized, A: Allocator> DerefPure for Rc<T, A> {}

Expand Down Expand Up @@ -3691,6 +3698,9 @@ impl<T: ?Sized, A: Allocator> Deref for UniqueRc<T, A> {
}
}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized> PinCoerceUnsized for UniqueRc<T> {}

#[unstable(feature = "unique_rc_arc", issue = "112566")]
impl<T: ?Sized, A: Allocator> DerefMut for UniqueRc<T, A> {
fn deref_mut(&mut self) -> &mut T {
Expand Down
8 changes: 7 additions & 1 deletion library/alloc/src/sync.rs
Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@ use core::marker::{PhantomData, Unsize};
use core::mem::{self, align_of_val_raw, ManuallyDrop};
use core::ops::{CoerceUnsized, Deref, DerefPure, DispatchFromDyn, Receiver};
use core::panic::{RefUnwindSafe, UnwindSafe};
use core::pin::Pin;
use core::pin::{Pin, PinCoerceUnsized};
use core::ptr::{self, NonNull};
#[cfg(not(no_global_oom_handling))]
use core::slice::from_raw_parts_mut;
Expand Down Expand Up @@ -2142,6 +2142,12 @@ impl<T: ?Sized, A: Allocator> Deref for Arc<T, A> {
}
}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for Arc<T, A> {}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for Weak<T, A> {}

#[unstable(feature = "deref_pure_trait", issue = "87121")]
unsafe impl<T: ?Sized, A: Allocator> DerefPure for Arc<T, A> {}

Expand Down
14 changes: 14 additions & 0 deletions library/alloc/tests/arc.rs
Original file line number Diff line number Diff line change
Expand Up @@ -227,3 +227,17 @@ fn make_mut_unsized() {
assert_eq!(*data, [11, 21, 31]);
assert_eq!(*other_data, [110, 20, 30]);
}

#[allow(unused)]
mod pin_coerce_unsized {
use alloc::sync::Arc;
use core::pin::Pin;

pub trait MyTrait {}
impl MyTrait for String {}

// Pin coercion should work for Arc
pub fn pin_arc(arg: Pin<Arc<String>>) -> Pin<Arc<dyn MyTrait>> {
arg
}
}
37 changes: 37 additions & 0 deletions library/alloc/tests/boxed.rs
Original file line number Diff line number Diff line change
Expand Up @@ -179,3 +179,40 @@ unsafe impl Allocator for ConstAllocator {
self
}
}

#[allow(unused)]
mod pin_coerce_unsized {
use alloc::boxed::Box;
use core::pin::Pin;

trait MyTrait {
fn action(&self) -> &str;
}
impl MyTrait for String {
fn action(&self) -> &str {
&*self
}
}
struct MyStruct;
impl MyTrait for MyStruct {
fn action(&self) -> &str {
"MyStruct"
}
}

// Pin coercion should work for Box
fn pin_box<T: MyTrait + 'static>(arg: Pin<Box<T>>) -> Pin<Box<dyn MyTrait>> {
arg
}

#[test]
fn pin_coerce_unsized_box() {
let my_string = "my string";
let a_string = Box::pin(String::from(my_string));
let pin_box_str = pin_box(a_string);
assert_eq!(pin_box_str.as_ref().action(), my_string);
let a_struct = Box::pin(MyStruct);
let pin_box_struct = pin_box(a_struct);
assert_eq!(pin_box_struct.as_ref().action(), "MyStruct");
}
}
1 change: 1 addition & 0 deletions library/alloc/tests/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@
#![feature(drain_keep_rest)]
#![feature(local_waker)]
#![feature(vec_pop_if)]
#![feature(unique_rc_arc)]
#![allow(internal_features)]
#![deny(fuzzy_provenance_casts)]
#![deny(unsafe_op_in_unsafe_fn)]
Expand Down
17 changes: 17 additions & 0 deletions library/alloc/tests/rc.rs
Original file line number Diff line number Diff line change
Expand Up @@ -205,3 +205,20 @@ fn weak_may_dangle() {
// `val` dropped here while still borrowed
// borrow might be used here, when `val` is dropped and runs the `Drop` code for type `std::rc::Weak`
}

#[allow(unused)]
mod pin_coerce_unsized {
use alloc::rc::{Rc, UniqueRc};
use core::pin::Pin;

pub trait MyTrait {}
impl MyTrait for String {}

// Pin coercion should work for Rc
pub fn pin_rc(arg: Pin<Rc<String>>) -> Pin<Rc<dyn MyTrait>> {
arg
}
pub fn pin_unique_rc(arg: Pin<UniqueRc<String>>) -> Pin<UniqueRc<dyn MyTrait>> {
arg
}
}
19 changes: 19 additions & 0 deletions library/core/src/cell.rs
Original file line number Diff line number Diff line change
Expand Up @@ -255,6 +255,7 @@ use crate::fmt::{self, Debug, Display};
use crate::marker::{PhantomData, Unsize};
use crate::mem;
use crate::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn};
use crate::pin::PinCoerceUnsized;
use crate::ptr::{self, NonNull};

mod lazy;
Expand Down Expand Up @@ -2396,3 +2397,21 @@ fn assert_coerce_unsized(
let _: Cell<&dyn Send> = c;
let _: RefCell<&dyn Send> = d;
}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized> PinCoerceUnsized for UnsafeCell<T> {}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized> PinCoerceUnsized for SyncUnsafeCell<T> {}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized> PinCoerceUnsized for Cell<T> {}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized> PinCoerceUnsized for RefCell<T> {}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<'b, T: ?Sized> PinCoerceUnsized for Ref<'b, T> {}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<'b, T: ?Sized> PinCoerceUnsized for RefMut<'b, T> {}
50 changes: 48 additions & 2 deletions library/core/src/pin.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1715,10 +1715,56 @@ impl<Ptr: fmt::Pointer> fmt::Pointer for Pin<Ptr> {
// for other reasons, though, so we just need to take care not to allow such
// impls to land in std.
#[stable(feature = "pin", since = "1.33.0")]
impl<Ptr, U> CoerceUnsized<Pin<U>> for Pin<Ptr> where Ptr: CoerceUnsized<U> {}
impl<Ptr, U> CoerceUnsized<Pin<U>> for Pin<Ptr>
where
Ptr: CoerceUnsized<U> + PinCoerceUnsized,
U: PinCoerceUnsized,
{
}

#[stable(feature = "pin", since = "1.33.0")]
impl<Ptr, U> DispatchFromDyn<Pin<U>> for Pin<Ptr>
where
Ptr: DispatchFromDyn<U> + PinCoerceUnsized,
U: PinCoerceUnsized,
{
}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
/// Trait that indicates that this is a pointer or a wrapper for one, where
/// unsizing can be performed on the pointee when it is pinned.
///
/// # Safety
///
/// If this type implements `Deref`, then the concrete type returned by `deref`
/// and `deref_mut` must not change without a modification. The following
/// operations are not considered modifications:
///
/// * Moving the pointer.
/// * Performing unsizing coercions on the pointer.
/// * Performing dynamic dispatch with the pointer.
/// * Calling `deref` or `deref_mut` on the pointer.
///
/// The concrete type of a trait object is the type that the vtable corresponds
/// to. The concrete type of a slice is an array of the same element type and
/// the length specified in the metadata. The concrete type of a sized type
/// is the type itself.
pub unsafe trait PinCoerceUnsized {}

#[stable(feature = "pin", since = "1.33.0")]
unsafe impl<'a, T: ?Sized> PinCoerceUnsized for &'a T {}

#[stable(feature = "pin", since = "1.33.0")]
unsafe impl<'a, T: ?Sized> PinCoerceUnsized for &'a mut T {}

#[stable(feature = "pin", since = "1.33.0")]
unsafe impl<T: PinCoerceUnsized> PinCoerceUnsized for Pin<T> {}

#[stable(feature = "pin", since = "1.33.0")]
unsafe impl<T: ?Sized> PinCoerceUnsized for *const T {}

#[stable(feature = "pin", since = "1.33.0")]
impl<Ptr, U> DispatchFromDyn<Pin<U>> for Pin<Ptr> where Ptr: DispatchFromDyn<U> {}
unsafe impl<T: ?Sized> PinCoerceUnsized for *mut T {}

/// Constructs a <code>[Pin]<[&mut] T></code>, by pinning a `value: T` locally.
///
Expand Down
4 changes: 4 additions & 0 deletions library/core/src/ptr/non_null.rs
Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@ use crate::marker::Unsize;
use crate::mem::{MaybeUninit, SizedTypeProperties};
use crate::num::NonZero;
use crate::ops::{CoerceUnsized, DispatchFromDyn};
use crate::pin::PinCoerceUnsized;
use crate::ptr::Unique;
use crate::slice::{self, SliceIndex};
use crate::ub_checks::assert_unsafe_precondition;
Expand Down Expand Up @@ -1724,6 +1725,9 @@ impl<T: ?Sized, U: ?Sized> CoerceUnsized<NonNull<U>> for NonNull<T> where T: Uns
#[unstable(feature = "dispatch_from_dyn", issue = "none")]
impl<T: ?Sized, U: ?Sized> DispatchFromDyn<NonNull<U>> for NonNull<T> where T: Unsize<U> {}

#[stable(feature = "pin", since = "1.33.0")]
unsafe impl<T: ?Sized> PinCoerceUnsized for NonNull<T> {}

#[stable(feature = "nonnull", since = "1.25.0")]
impl<T: ?Sized> fmt::Debug for NonNull<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
Expand Down
4 changes: 4 additions & 0 deletions library/core/src/ptr/unique.rs
Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
use crate::fmt;
use crate::marker::{PhantomData, Unsize};
use crate::ops::{CoerceUnsized, DispatchFromDyn};
use crate::pin::PinCoerceUnsized;
use crate::ptr::NonNull;

/// A wrapper around a raw non-null `*mut T` that indicates that the possessor
Expand Down Expand Up @@ -166,6 +167,9 @@ impl<T: ?Sized, U: ?Sized> CoerceUnsized<Unique<U>> for Unique<T> where T: Unsiz
#[unstable(feature = "ptr_internals", issue = "none")]
impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Unique<U>> for Unique<T> where T: Unsize<U> {}

#[unstable(feature = "pin_coerce_unsized_trait", issue = "123430")]
unsafe impl<T: ?Sized> PinCoerceUnsized for Unique<T> {}

#[unstable(feature = "ptr_internals", issue = "none")]
impl<T: ?Sized> fmt::Debug for Unique<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
Expand Down
46 changes: 46 additions & 0 deletions library/core/tests/pin.rs
Original file line number Diff line number Diff line change
Expand Up @@ -29,3 +29,49 @@ fn pin_const() {

pin_mut_const();
}

#[allow(unused)]
mod pin_coerce_unsized {
use core::cell::{Cell, RefCell, UnsafeCell};
use core::pin::Pin;
use core::ptr::NonNull;

pub trait MyTrait {}
impl MyTrait for String {}

// These Pins should continue to compile.
// Do note that these instances of Pin types cannot be used
// meaningfully because all methods require a Deref/DerefMut
// bounds on the pointer type and Cell, RefCell and UnsafeCell
// do not implement Deref/DerefMut.

pub fn cell(arg: Pin<Cell<Box<String>>>) -> Pin<Cell<Box<dyn MyTrait>>> {
arg
}
pub fn ref_cell(arg: Pin<RefCell<Box<String>>>) -> Pin<RefCell<Box<dyn MyTrait>>> {
arg
}
pub fn unsafe_cell(arg: Pin<UnsafeCell<Box<String>>>) -> Pin<UnsafeCell<Box<dyn MyTrait>>> {
arg
}

// These sensible Pin coercions are possible.
pub fn pin_mut_ref(arg: Pin<&mut String>) -> Pin<&mut dyn MyTrait> {
arg
}
pub fn pin_ref(arg: Pin<&String>) -> Pin<&dyn MyTrait> {
arg
}
pub fn pin_ptr(arg: Pin<*const String>) -> Pin<*const dyn MyTrait> {
arg
}
pub fn pin_ptr_mut(arg: Pin<*mut String>) -> Pin<*mut dyn MyTrait> {
arg
}
pub fn pin_non_null(arg: Pin<NonNull<String>>) -> Pin<NonNull<dyn MyTrait>> {
arg
}
pub fn nesting_pins(arg: Pin<Pin<&String>>) -> Pin<Pin<&dyn MyTrait>> {
arg
}
}
1 change: 1 addition & 0 deletions library/std/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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)]
Expand Down
4 changes: 4 additions & 0 deletions library/std/src/sys/pal/sgx/abi/usercalls/alloc.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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};
Expand Down Expand Up @@ -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
Expand Down

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