Rollup merge of #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 #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`.

8 files changed, 35 insertions, 29 deletions

diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
index 7780ceda1c1..896d000233a 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
@@ -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 {
diff --git a/library/core/src/pin.rs b/library/core/src/pin.rs
index bb6c81a486a..a0227d9130b 100644
--- a/library/core/src/pin.rs
+++ b/library/core/src/pin.rs
@@ -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.
@@ -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
     }
 }
 
@@ -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.
@@ -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`.
@@ -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
     }
 }
 
@@ -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>`.
@@ -1455,7 +1461,7 @@ impl<Ptr: DerefMut> Pin<Ptr> {
     where
         Ptr::Target: Sized,
     {
-        *(self.pointer) = value;
+        *(self.__pointer) = value;
     }
 }
 
@@ -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
@@ -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
     }
 }
 
@@ -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`.
@@ -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`.
@@ -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.
@@ -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)
     }
 }
 
@@ -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 } }
 }
diff --git a/src/etc/natvis/libcore.natvis b/src/etc/natvis/libcore.natvis
index 624d8cc5cc5..f8569ef2594 100644
--- a/src/etc/natvis/libcore.natvis
+++ b/src/etc/natvis/libcore.natvis
@@ -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>
 
diff --git a/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-abort.diff b/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-abort.diff
index 8e53427e7e0..a38b8246bde 100644
--- a/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-abort.diff
+++ b/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-abort.diff
@@ -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@$DIR/inline_coroutine.rs:19:5: 19:8}> { __pointer: _3 };
 +         StorageDead(_3);
 +         StorageLive(_5);
 +         _5 = const false;
diff --git a/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-unwind.diff b/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-unwind.diff
index b06db41af9d..dc6628ab44c 100644
--- a/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-unwind.diff
+++ b/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-unwind.diff
@@ -36,7 +36,7 @@
 -         _4 = g() -> [return: bb1, unwind continue];
 +         _4 = {coroutine@$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;
diff --git a/tests/ui/feature-gates/feature-gate-unsafe_pin_internals.rs b/tests/ui/feature-gates/feature-gate-unsafe_pin_internals.rs
index 134ea25b75a..594a2672d43 100644
--- a/tests/ui/feature-gates/feature-gate-unsafe_pin_internals.rs
+++ b/tests/ui/feature-gates/feature-gate-unsafe_pin_internals.rs
@@ -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() {
diff --git a/tests/ui/pin-macro/cant_access_internals.rs b/tests/ui/pin-macro/cant_access_internals.rs
index 5826a18b571..4aeb6a643d9 100644
--- a/tests/ui/pin-macro/cant_access_internals.rs
+++ b/tests/ui/pin-macro/cant_access_internals.rs
@@ -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'
 }
diff --git a/tests/ui/pin-macro/cant_access_internals.stderr b/tests/ui/pin-macro/cant_access_internals.stderr
index 2737b84f599..444314a9d8b 100644
--- a/tests/ui/pin-macro/cant_access_internals.stderr
+++ b/tests/ui/pin-macro/cant_access_internals.stderr
@@ -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