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Fix Pin::set bounds regression #129668

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Aug 28, 2024
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21 changes: 12 additions & 9 deletions library/core/src/pin.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1370,7 +1370,15 @@ impl<Ptr: Deref> Pin<Ptr> {
// SAFETY: see documentation on this function
unsafe { Pin::new_unchecked(&*self.__pointer) }
}
}

// These methods being in a `Ptr: DerefMut` impl block concerns semver stability.
// Currently, calling e.g. `.set()` on a `Pin<&T>` sees that `Ptr: DerefMut`
// doesn't hold, and goes to check for a `.set()` method on `T`. But, if the
// `where Ptr: DerefMut` bound is moved to the method, rustc sees the impl block
// as a valid candidate, and doesn't go on to check other candidates when it
// sees that the bound on the method.
impl<Ptr: DerefMut> Pin<Ptr> {
/// Gets a mutable reference to the pinned value this `Pin<Ptr>` points to.
///
/// This is a generic method to go from `&mut Pin<Pointer<T>>` to `Pin<&mut T>`.
Expand Down Expand Up @@ -1402,10 +1410,7 @@ impl<Ptr: Deref> Pin<Ptr> {
/// ```
#[stable(feature = "pin", since = "1.33.0")]
#[inline(always)]
pub fn as_mut(&mut self) -> Pin<&mut Ptr::Target>
where
Ptr: DerefMut,
{
pub fn as_mut(&mut self) -> Pin<&mut Ptr::Target> {
// SAFETY: see documentation on this function
unsafe { Pin::new_unchecked(&mut *self.__pointer) }
}
Expand All @@ -1420,10 +1425,7 @@ impl<Ptr: Deref> Pin<Ptr> {
#[unstable(feature = "pin_deref_mut", issue = "86918")]
#[must_use = "`self` will be dropped if the result is not used"]
#[inline(always)]
pub fn as_deref_mut(self: Pin<&mut Pin<Ptr>>) -> Pin<&mut Ptr::Target>
where
Ptr: DerefMut,
{
pub fn as_deref_mut(self: Pin<&mut Pin<Ptr>>) -> Pin<&mut Ptr::Target> {
// SAFETY: What we're asserting here is that going from
//
// Pin<&mut Pin<Ptr>>
Expand Down Expand Up @@ -1475,12 +1477,13 @@ impl<Ptr: Deref> Pin<Ptr> {
#[inline(always)]
pub fn set(&mut self, value: Ptr::Target)
where
Ptr: DerefMut,
Ptr::Target: Sized,
{
*(self.__pointer) = value;
}
}

impl<Ptr: Deref> Pin<Ptr> {
/// Unwraps this `Pin<Ptr>`, returning the underlying `Ptr`.
///
/// # Safety
Expand Down
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