Rename pointer field on Pin

The internal, unstable field of `Pin` can conflict with fields from the
inner type accessed via the `Deref` impl. Rename it from `pointer` to
`__pointer`, to make it less likely to conflict with anything else.

Author: LegionMammal978

library/core/src/pin.rs

@@ -411,14 +411,20 @@ pub struct Pin<P> {
     //   - 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 `P::Deref` 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<P>`. 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: P,
+    pub __pointer: P,
 }
 
 // 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.
@@ -525,7 +531,7 @@ impl<P: Deref<Target: Unpin>> Pin<P> {
     #[rustc_const_unstable(feature = "const_pin", issue = "76654")]
     #[stable(feature = "pin_into_inner", since = "1.39.0")]
     pub const fn into_inner(pin: Pin<P>) -> P {
-        pin.pointer
+        pin.__pointer
     }
 }
 
@@ -654,7 +660,7 @@ impl<P: Deref> Pin<P> {
     #[rustc_const_unstable(feature = "const_pin", issue = "76654")]
     #[stable(feature = "pin", since = "1.33.0")]
     pub const unsafe fn new_unchecked(pointer: P) -> Pin<P> {
-        Pin { pointer }
+        Pin { __pointer: pointer }
     }
 
     /// Gets a pinned shared reference from this pinned pointer.
@@ -668,7 +674,7 @@ impl<P: Deref> Pin<P> {
     #[inline(always)]
     pub fn as_ref(&self) -> Pin<&P::Target> {
         // SAFETY: see documentation on this function
-        unsafe { Pin::new_unchecked(&*self.pointer) }
+        unsafe { Pin::new_unchecked(&*self.__pointer) }
     }
 
     /// Unwraps this `Pin<P>` returning the underlying pointer.
@@ -688,7 +694,7 @@ impl<P: Deref> Pin<P> {
     #[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<P>) -> P {
-        pin.pointer
+        pin.__pointer
     }
 }
 
@@ -725,7 +731,7 @@ impl<P: DerefMut> Pin<P> {
     #[inline(always)]
     pub fn as_mut(&mut self) -> Pin<&mut P::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 behind the pinned reference.
@@ -750,7 +756,7 @@ impl<P: DerefMut> Pin<P> {
     where
         P::Target: Sized,
     {
-        *(self.pointer) = value;
+        *(self.__pointer) = value;
     }
 }
 
@@ -776,7 +782,7 @@ 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
@@ -806,7 +812,7 @@ 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
     }
 }
 
@@ -817,7 +823,7 @@ 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`.
@@ -837,7 +843,7 @@ 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`.
@@ -855,7 +861,7 @@ 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.
@@ -978,21 +984,21 @@ impl<P: Receiver> Receiver for Pin<P> {}
 #[stable(feature = "pin", since = "1.33.0")]
 impl<P: fmt::Debug> fmt::Debug for Pin<P> {
     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<P: fmt::Display> fmt::Display for Pin<P> {
     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<P: fmt::Pointer> fmt::Pointer for Pin<P> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Pointer::fmt(&self.pointer, f)
+        fmt::Pointer::fmt(&self.__pointer, f)
     }
 }
 
@@ -1235,16 +1241,16 @@ 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 } }
 }

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() {

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'
 }

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