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Document explicitly that Weak::from_raw(ptr::null()) is ub #114525

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Document explicitly that Weak::from_raw(ptr::null()) is ub #114525

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26 changes: 22 additions & 4 deletions library/alloc/src/rc.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2776,8 +2776,16 @@ impl<T: ?Sized> Weak<T> {
///
/// # Safety
///
/// The pointer must have originated from the [`into_raw`] and must still own its potential
/// weak reference, and `ptr` must point to a block of memory allocated by the global allocator.
/// The pointer must have originated from the [`into_raw`] or [`into_raw_and_alloc`] functions
/// and must still own its potential weak reference, and `ptr` must point to a block of
/// memory allocated by `alloc`.
///
/// Note that `from_raw` expects values that actually originated from a call to one of these
/// functions and have not been used with `from_raw` yet, not what these functions can maybe
/// return, or are documented to potentially return.
/// For example, [`into_raw`] can return dangling pointers, but this doesn't allow you to create
/// a dangling pointer yourself and pass it to `from_raw`. Even if it has the same address
/// as a pointer created by [`into_raw`], use [`Weak::new`] instead.
Comment on lines +2787 to +2788
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Suggested change
/// a dangling pointer yourself and pass it to `from_raw`. Even if it has the same address
/// as a pointer created by [`into_raw`], use [`Weak::new`] instead.
/// a dangling pointer yourself and pass it to `from_raw`, even if it has the same address
/// as a pointer created by [`into_raw`]. Use [`Weak::new`] instead.

///
/// It is allowed for the strong count to be 0 at the time of calling this. Nevertheless, this
/// takes ownership of one weak reference currently represented as a raw pointer (the weak
Expand Down Expand Up @@ -2806,6 +2814,7 @@ impl<T: ?Sized> Weak<T> {
/// ```
///
/// [`into_raw`]: Weak::into_raw
/// [`into_raw_and_alloc`]: Weak::into_raw_and_alloc
/// [`upgrade`]: Weak::upgrade
/// [`new`]: Weak::new
#[inline]
Expand Down Expand Up @@ -2942,8 +2951,16 @@ impl<T: ?Sized, A: Allocator> Weak<T, A> {
///
/// # Safety
///
/// The pointer must have originated from the [`into_raw`] and must still own its potential
/// weak reference, and `ptr` must point to a block of memory allocated by `alloc`.
/// The pointer must have originated from the [`into_raw`] or [`into_raw_and_alloc`] functions
/// and must still own its potential weak reference, and `ptr` must point to a block of
/// memory allocated by `alloc`.
///
/// Note that `from_raw` expects values that actually originated from a call to one of these
/// functions and have not been used with `from_raw` yet, not what these functions can maybe
/// return, or are documented to potentially return.
/// For example, [`into_raw`] can return dangling pointers, but this doesn't allow you to create
/// a dangling pointer yourself and pass it to `from_raw`. Even if it has the same address
/// as a pointer created by [`into_raw`], use [`Weak::new`] instead.
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same diff as above

///
/// It is allowed for the strong count to be 0 at the time of calling this. Nevertheless, this
/// takes ownership of one weak reference currently represented as a raw pointer (the weak
Expand Down Expand Up @@ -2972,6 +2989,7 @@ impl<T: ?Sized, A: Allocator> Weak<T, A> {
/// ```
///
/// [`into_raw`]: Weak::into_raw
/// [`into_raw_and_alloc`]: Weak::into_raw_and_alloc
/// [`upgrade`]: Weak::upgrade
/// [`new`]: Weak::new
#[inline]
Expand Down
11 changes: 9 additions & 2 deletions library/alloc/src/sync.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2686,8 +2686,15 @@ impl<T: ?Sized, A: Allocator> Weak<T, A> {
///
/// # Safety
///
/// The pointer must have originated from the [`into_raw`] and must still own its potential
/// weak reference, and must point to a block of memory allocated by `alloc`.
/// The pointer must have originated from the [`into_raw`] function and must still own its
/// potential weak reference, and must point to a block of memory allocated by `alloc`.
///
/// Note that `from_raw_in` expects values that actually originated from a call to [`into_raw`]
/// and have not been used with `from_raw` yet, not what [`into_raw`] can maybe return,
/// or is documented to potentially return.
/// For example, [`into_raw`] can return dangling pointers, but this doesn't allow you to create
/// a dangling pointer yourself and pass it to `from_raw`. Even if it has the same address
/// as a pointer created by [`into_raw`], use [`Weak::new`] instead.
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and yet another time

///
/// It is allowed for the strong count to be 0 at the time of calling this. Nevertheless, this
/// takes ownership of one weak reference currently represented as a raw pointer (the weak
Expand Down