Commit 037d8e74 authored by bors's avatar bors

Auto merge of #74488 - CAD97:layout_for_value_raw, r=hanna-kruppe

re-add Layout::for_value_raw

Tracking issue: #69835

This was accidentally removed in #70362 56cbf2f2.
Originally added in #69079.
parents 73ca84df 1821e3d7
......@@ -131,7 +131,42 @@ impl Layout {
pub fn for_value<T: ?Sized>(t: &T) -> Self {
let (size, align) = (mem::size_of_val(t), mem::align_of_val(t));
debug_assert!(Layout::from_size_align(size, align).is_ok());
// SAFETY: see rationale in `new` for why this is using an unsafe variant below
// SAFETY: see rationale in `new` for why this is using the unsafe variant
unsafe { Layout::from_size_align_unchecked(size, align) }
}
/// Produces layout describing a record that could be used to
/// allocate backing structure for `T` (which could be a trait
/// or other unsized type like a slice).
///
/// # Safety
///
/// This function is only safe to call if the following conditions hold:
///
/// - If `T` is `Sized`, this function is always safe to call.
/// - If the unsized tail of `T` is:
/// - a [slice], then the length of the slice tail must be an intialized
/// integer, and the size of the *entire value*
/// (dynamic tail length + statically sized prefix) must fit in `isize`.
/// - a [trait object], then the vtable part of the pointer must point
/// to a valid vtable for the type `T` acquired by an unsizing coersion,
/// and the size of the *entire value*
/// (dynamic tail length + statically sized prefix) must fit in `isize`.
/// - an (unstable) [extern type], then this function is always safe to
/// call, but may panic or otherwise return the wrong value, as the
/// extern type's layout is not known. This is the same behavior as
/// [`Layout::for_value`] on a reference to an extern type tail.
/// - otherwise, it is conservatively not allowed to call this function.
///
/// [slice]: ../../std/primitive.slice.html
/// [trait object]: ../../book/ch17-02-trait-objects.html
/// [extern type]: ../../unstable-book/language-features/extern-types.html
#[unstable(feature = "layout_for_ptr", issue = "69835")]
pub unsafe fn for_value_raw<T: ?Sized>(t: *const T) -> Self {
// SAFETY: we pass along the prerequisites of these functions to the caller
let (size, align) = unsafe { (mem::size_of_val_raw(t), mem::align_of_val_raw(t)) };
debug_assert!(Layout::from_size_align(size, align).is_ok());
// SAFETY: see rationale in `new` for why this is using the unsafe variant
unsafe { Layout::from_size_align_unchecked(size, align) }
}
......
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