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Do not dereference in slice_from_raw_parts postcondition #627

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Do not dereference in slice_from_raw_parts postcondition #627

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7 changes: 6 additions & 1 deletion library/core/src/ptr/non_null.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1590,9 +1590,14 @@ impl<T> NonNull<[T]> {
#[rustc_const_stable(feature = "const_slice_from_raw_parts_mut", since = "1.83.0")]
#[must_use]
#[inline]
// `result.len()` reads the length from the wide-pointer metadata without
// creating a reference: `slice_from_raw_parts` is a safe function with no
// validity requirements on `data`, so the postcondition must not
// dereference the resulting pointer (`unsafe { result.as_ref() }.len()`,
// as used previously, is UB for dangling or misaligned `data`).
#[ensures(|result| !result.pointer.is_null()
&& result.pointer as *const T == data.pointer
&& unsafe { result.as_ref() }.len() == len)]
&& result.len() == len)]
pub const fn slice_from_raw_parts(data: NonNull<T>, len: usize) -> Self {
// SAFETY: `data` is a `NonNull` pointer which is necessarily non-null
unsafe { Self::new_unchecked(super::slice_from_raw_parts_mut(data.as_ptr(), len)) }
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