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Implement KnownLayout, FromZeroes for raw pointers #584

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Nov 2, 2023
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Implement KnownLayout, FromZeroes for raw pointers #584

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25 changes: 25 additions & 0 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -703,6 +703,8 @@ impl_known_layout!(
T: ?Sized => PhantomData<T>,
T => Wrapping<T>,
T => MaybeUninit<T>,
T: ?Sized => *const T,
T: ?Sized => *mut T,
);
impl_known_layout!(const N: usize, T => [T; N]);

Expand Down Expand Up @@ -1857,6 +1859,22 @@ safety_comment! {
unsafe_impl!(T: AsBytes => AsBytes for [T]);
unsafe_impl!(T: Unaligned => Unaligned for [T]);
}
safety_comment! {
/// SAFETY:
/// - `FromZeroes`: For thin pointers (note that `T: Sized`), the zero
/// pointer is considered "null". [1] No operations which require
/// provenance are legal on null pointers, so this is not a footgun.
///
/// NOTE(#170): Implementing `FromBytes` and `AsBytes` for raw pointers
/// would be sound, but carries provenance footguns. We want to support
/// `FromBytes` and `AsBytes` for raw pointers eventually, but we are
/// holding off until we can figure out how to address those footguns.
///
/// [1] TODO(https://github.com/rust-lang/rust/pull/116988): Cite the
/// documentation once this PR lands.
unsafe_impl!(T => FromZeroes for *const T);
unsafe_impl!(T => FromZeroes for *mut T);
}

// SIMD support
//
Expand Down Expand Up @@ -5375,6 +5393,13 @@ mod tests {
assert_impls!([u8; 1]: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!([NotZerocopy; 1]: KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);

assert_impls!(*const NotZerocopy: KnownLayout, FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!(*mut NotZerocopy: KnownLayout, FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!(*const [NotZerocopy]: KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!(*mut [NotZerocopy]: KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!(*const dyn Debug: KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!(*mut dyn Debug: KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);

#[cfg(feature = "simd")]
{
#[allow(unused_macros)]
Expand Down