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Unrolled build for rust-lang#119562
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Rollup merge of rust-lang#119562 - LegionMammal978:rename-pin-pointer, r=Amanieu,dtolnay

Rename `pointer` field on `Pin`

A few days ago, I was helping another user create a self-referential type using `PhantomPinned`. However, I noticed an odd behavior when I tried to access one of the type's fields via `Pin`'s `Deref` impl:

```rust
use std::{marker::PhantomPinned, ptr};

struct Pinned {
    data: i32,
    pointer: *const i32,
    _pin: PhantomPinned,
}

fn main() {
    let mut b = Box::pin(Pinned {
        data: 42,
        pointer: ptr::null(),
        _pin: PhantomPinned,
    });
    {
        let pinned = unsafe { b.as_mut().get_unchecked_mut() };
        pinned.pointer = &pinned.data;
    }
    println!("{}", unsafe { *b.pointer });
}
```

```rust
error[E0658]: use of unstable library feature 'unsafe_pin_internals'
  --> <source>:19:30
   |
19 |     println!("{}", unsafe { *b.pointer });
   |                              ^^^^^^^^^

error[E0277]: `Pinned` doesn't implement `std::fmt::Display`
  --> <source>:19:20
   |
19 |     println!("{}", unsafe { *b.pointer });
   |                    ^^^^^^^^^^^^^^^^^^^^^ `Pinned` cannot be formatted with the default formatter
   |
   = help: the trait `std::fmt::Display` is not implemented for `Pinned`
   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
```

Since the user named their field `pointer`, it conflicts with the `pointer` field on `Pin`, which is public but unstable since Rust 1.60.0 with rust-lang#93176. On versions from 1.33.0 to 1.59.0, where the field on `Pin` is private, this program compiles and prints `42` as expected.

To avoid this confusing behavior, this PR renames `pointer` to `__pointer`, so that it's less likely to conflict with a `pointer` field on the underlying type, as accessed through the `Deref` impl. This is technically a breaking change for anyone who names their field `__pointer` on the inner type; if this is undesirable, it could be renamed to something more longwinded. It's also a nightly breaking change for any external users of `unsafe_pin_internals`.
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rust-timer authored Jan 27, 2024
2 parents c073f56 + bc3fb52 commit af4e223
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Showing 8 changed files with 35 additions and 29 deletions.
2 changes: 1 addition & 1 deletion compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2040,7 +2040,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
let field_is_local = sole_field.did.is_local();
let field_is_accessible =
sole_field.vis.is_accessible_from(expr.hir_id.owner.def_id, self.tcx)
// Skip suggestions for unstable public fields (for example `Pin::pointer`)
// Skip suggestions for unstable public fields (for example `Pin::__pointer`)
&& matches!(self.tcx.eval_stability(sole_field.did, None, expr.span, None), EvalResult::Allow | EvalResult::Unmarked);

if !field_is_local && !field_is_accessible {
Expand Down
46 changes: 26 additions & 20 deletions library/core/src/pin.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1092,14 +1092,20 @@ pub struct Pin<Ptr> {
// - deter downstream users from accessing it (which would be unsound!),
// - let the `pin!` macro access it (such a macro requires using struct
// literal syntax in order to benefit from lifetime extension).
// Long-term, `unsafe` fields or macro hygiene are expected to offer more robust alternatives.
//
// However, if the `Deref` impl exposes a field with the same name as this
// field, then the two will collide, resulting in a confusing error when the
// user attempts to access the field through a `Pin<Ptr>`. Therefore, the
// name `__pointer` is designed to be unlikely to collide with any other
// field. Long-term, macro hygiene is expected to offer a more robust
// alternative, alongside `unsafe` fields.
#[unstable(feature = "unsafe_pin_internals", issue = "none")]
#[doc(hidden)]
pub pointer: Ptr,
pub __pointer: Ptr,
}

// The following implementations aren't derived in order to avoid soundness
// issues. `&self.pointer` should not be accessible to untrusted trait
// issues. `&self.__pointer` should not be accessible to untrusted trait
// implementations.
//
// See <https://internals.rust-lang.org/t/unsoundness-in-pin/11311/73> for more details.
Expand Down Expand Up @@ -1212,7 +1218,7 @@ impl<Ptr: Deref<Target: Unpin>> Pin<Ptr> {
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
#[stable(feature = "pin_into_inner", since = "1.39.0")]
pub const fn into_inner(pin: Pin<Ptr>) -> Ptr {
pin.pointer
pin.__pointer
}
}

Expand Down Expand Up @@ -1349,7 +1355,7 @@ impl<Ptr: Deref> Pin<Ptr> {
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
#[stable(feature = "pin", since = "1.33.0")]
pub const unsafe fn new_unchecked(pointer: Ptr) -> Pin<Ptr> {
Pin { pointer }
Pin { __pointer: pointer }
}

/// Gets a shared reference to the pinned value this [`Pin`] points to.
Expand All @@ -1363,7 +1369,7 @@ impl<Ptr: Deref> Pin<Ptr> {
#[inline(always)]
pub fn as_ref(&self) -> Pin<&Ptr::Target> {
// SAFETY: see documentation on this function
unsafe { Pin::new_unchecked(&*self.pointer) }
unsafe { Pin::new_unchecked(&*self.__pointer) }
}

/// Unwraps this `Pin<Ptr>`, returning the underlying `Ptr`.
Expand All @@ -1388,7 +1394,7 @@ impl<Ptr: Deref> Pin<Ptr> {
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
#[stable(feature = "pin_into_inner", since = "1.39.0")]
pub const unsafe fn into_inner_unchecked(pin: Pin<Ptr>) -> Ptr {
pin.pointer
pin.__pointer
}
}

Expand Down Expand Up @@ -1426,7 +1432,7 @@ impl<Ptr: DerefMut> Pin<Ptr> {
#[inline(always)]
pub fn as_mut(&mut self) -> Pin<&mut Ptr::Target> {
// SAFETY: see documentation on this function
unsafe { Pin::new_unchecked(&mut *self.pointer) }
unsafe { Pin::new_unchecked(&mut *self.__pointer) }
}

/// Assigns a new value to the memory location pointed to by the `Pin<Ptr>`.
Expand Down Expand Up @@ -1455,7 +1461,7 @@ impl<Ptr: DerefMut> Pin<Ptr> {
where
Ptr::Target: Sized,
{
*(self.pointer) = value;
*(self.__pointer) = value;
}
}

Expand All @@ -1481,7 +1487,7 @@ impl<'a, T: ?Sized> Pin<&'a T> {
U: ?Sized,
F: FnOnce(&T) -> &U,
{
let pointer = &*self.pointer;
let pointer = &*self.__pointer;
let new_pointer = func(pointer);

// SAFETY: the safety contract for `new_unchecked` must be
Expand Down Expand Up @@ -1511,7 +1517,7 @@ impl<'a, T: ?Sized> Pin<&'a T> {
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
#[stable(feature = "pin", since = "1.33.0")]
pub const fn get_ref(self) -> &'a T {
self.pointer
self.__pointer
}
}

Expand All @@ -1522,7 +1528,7 @@ impl<'a, T: ?Sized> Pin<&'a mut T> {
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
#[stable(feature = "pin", since = "1.33.0")]
pub const fn into_ref(self) -> Pin<&'a T> {
Pin { pointer: self.pointer }
Pin { __pointer: self.__pointer }
}

/// Gets a mutable reference to the data inside of this `Pin`.
Expand All @@ -1542,7 +1548,7 @@ impl<'a, T: ?Sized> Pin<&'a mut T> {
where
T: Unpin,
{
self.pointer
self.__pointer
}

/// Gets a mutable reference to the data inside of this `Pin`.
Expand All @@ -1560,7 +1566,7 @@ impl<'a, T: ?Sized> Pin<&'a mut T> {
#[stable(feature = "pin", since = "1.33.0")]
#[rustc_const_unstable(feature = "const_pin", issue = "76654")]
pub const unsafe fn get_unchecked_mut(self) -> &'a mut T {
self.pointer
self.__pointer
}

/// Construct a new pin by mapping the interior value.
Expand Down Expand Up @@ -1684,21 +1690,21 @@ impl<Ptr: Receiver> Receiver for Pin<Ptr> {}
#[stable(feature = "pin", since = "1.33.0")]
impl<Ptr: fmt::Debug> fmt::Debug for Pin<Ptr> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&self.pointer, f)
fmt::Debug::fmt(&self.__pointer, f)
}
}

#[stable(feature = "pin", since = "1.33.0")]
impl<Ptr: fmt::Display> fmt::Display for Pin<Ptr> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt(&self.pointer, f)
fmt::Display::fmt(&self.__pointer, f)
}
}

#[stable(feature = "pin", since = "1.33.0")]
impl<Ptr: fmt::Pointer> fmt::Pointer for Pin<Ptr> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Pointer::fmt(&self.pointer, f)
fmt::Pointer::fmt(&self.__pointer, f)
}
}

Expand Down Expand Up @@ -1941,16 +1947,16 @@ pub macro pin($value:expr $(,)?) {
// instead, dropped _at the end of the enscoping block_.
// For instance,
// ```rust
// let p = Pin { pointer: &mut <temporary> };
// let p = Pin { __pointer: &mut <temporary> };
// ```
// becomes:
// ```rust
// let mut anon = <temporary>;
// let p = Pin { pointer: &mut anon };
// let p = Pin { __pointer: &mut anon };
// ```
// which is *exactly* what we want.
//
// See https://doc.rust-lang.org/1.58.1/reference/destructors.html#temporary-lifetime-extension
// for more info.
$crate::pin::Pin::<&mut _> { pointer: &mut { $value } }
$crate::pin::Pin::<&mut _> { __pointer: &mut { $value } }
}
4 changes: 2 additions & 2 deletions src/etc/natvis/libcore.natvis
Original file line number Diff line number Diff line change
Expand Up @@ -99,9 +99,9 @@
</Type>

<Type Name="core::pin::Pin&lt;*&gt;">
<DisplayString>Pin({(void*)pointer}: {pointer})</DisplayString>
<DisplayString>Pin({(void*)__pointer}: {__pointer})</DisplayString>
<Expand>
<ExpandedItem>pointer</ExpandedItem>
<ExpandedItem>__pointer</ExpandedItem>
</Expand>
</Type>

Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,7 @@
- _4 = g() -> [return: bb1, unwind unreachable];
+ _4 = {coroutine@$DIR/inline_coroutine.rs:19:5: 19:8 (#0)};
+ _3 = &mut _4;
+ _2 = Pin::<&mut {coroutine@$DIR/inline_coroutine.rs:19:5: 19:8}> { pointer: _3 };
+ _2 = Pin::<&mut {coroutine@$DIR/inline_coroutine.rs:19:5: 19:8}> { __pointer: _3 };
+ StorageDead(_3);
+ StorageLive(_5);
+ _5 = const false;
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,7 @@
- _4 = g() -> [return: bb1, unwind continue];
+ _4 = {coroutine@$DIR/inline_coroutine.rs:19:5: 19:8 (#0)};
+ _3 = &mut _4;
+ _2 = Pin::<&mut {coroutine@$DIR/inline_coroutine.rs:19:5: 19:8}> { pointer: _3 };
+ _2 = Pin::<&mut {coroutine@$DIR/inline_coroutine.rs:19:5: 19:8}> { __pointer: _3 };
+ StorageDead(_3);
+ StorageLive(_5);
+ _5 = const false;
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ use core::{marker::PhantomPinned, pin::Pin};

/// The `unsafe_pin_internals` is indeed unsound.
fn non_unsafe_pin_new_unchecked<T>(pointer: &mut T) -> Pin<&mut T> {
Pin { pointer }
Pin { __pointer: pointer }
}

fn main() {
Expand Down
2 changes: 1 addition & 1 deletion tests/ui/pin-macro/cant_access_internals.rs
Original file line number Diff line number Diff line change
Expand Up @@ -8,5 +8,5 @@ use core::{

fn main() {
let mut phantom_pinned = pin!(PhantomPinned);
mem::take(phantom_pinned.pointer); //~ ERROR use of unstable library feature 'unsafe_pin_internals'
mem::take(phantom_pinned.__pointer); //~ ERROR use of unstable library feature 'unsafe_pin_internals'
}
4 changes: 2 additions & 2 deletions tests/ui/pin-macro/cant_access_internals.stderr
Original file line number Diff line number Diff line change
@@ -1,8 +1,8 @@
error[E0658]: use of unstable library feature 'unsafe_pin_internals'
--> $DIR/cant_access_internals.rs:11:15
|
LL | mem::take(phantom_pinned.pointer);
| ^^^^^^^^^^^^^^^^^^^^^^
LL | mem::take(phantom_pinned.__pointer);
| ^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: add `#![feature(unsafe_pin_internals)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
Expand Down

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