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[derive] Support KnownLayout for sized types #514

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Oct 25, 2023
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[derive] Support KnownLayout for sized types #514

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5 changes: 4 additions & 1 deletion src/byteorder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -276,11 +276,14 @@ example of how it can be used for parsing UDP packets.
[`AsBytes`]: crate::AsBytes
[`Unaligned`]: crate::Unaligned"),
#[derive(Copy, Clone, Eq, PartialEq, Hash)]
#[cfg_attr(any(feature = "derive", test), derive(FromZeroes, FromBytes, AsBytes, Unaligned))]
#[cfg_attr(any(feature = "derive", test), derive(KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned))]
#[repr(transparent)]
pub struct $name<O>([u8; $bytes], PhantomData<O>);
}

#[cfg(not(any(feature = "derive", test)))]
impl_known_layout!(O => $name<O>);

safety_comment! {
/// SAFETY:
/// `$name<O>` is `repr(transparent)`, and so it has the same layout
Expand Down
149 changes: 82 additions & 67 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -382,7 +382,9 @@ impl DstLayout {
/// # Safety
///
/// Unsafe code may assume that `DstLayout` is the correct layout for `T`.
const fn for_type<T>() -> DstLayout {
#[doc(hidden)]
#[inline]
pub const fn for_type<T>() -> DstLayout {
// SAFETY: `align` is correct by construction. `T: Sized`, and so it is
// sound to initialize `size_info` to `SizeInfo::Sized { size }`; the
// `size` field is also correct by construction.
Expand Down Expand Up @@ -643,7 +645,16 @@ impl DstLayout {
///
/// This trait does not convey any safety guarantees to code outside this crate.
#[doc(hidden)] // TODO: Remove this once KnownLayout is used by other APIs
pub unsafe trait KnownLayout: sealed::KnownLayoutSealed {
pub unsafe trait KnownLayout {
// The `Self: Sized` bound makes it so that `KnownLayout` can still be
// object safe. It's not currently object safe thanks to `const LAYOUT`, and
// it likely won't be in the future, but there's no reason not to be
// forwards-compatible with object safety.
#[doc(hidden)]
fn only_derive_is_allowed_to_implement_this_trait()
where
Self: Sized;

#[doc(hidden)]
const LAYOUT: DstLayout;

Expand All @@ -654,9 +665,14 @@ pub unsafe trait KnownLayout: sealed::KnownLayoutSealed {
fn raw_from_ptr_len(bytes: NonNull<u8>, elems: usize) -> NonNull<Self>;
}

impl<T: KnownLayout> sealed::KnownLayoutSealed for [T] {}
// SAFETY: Delegates safety to `DstLayout::for_slice`.
unsafe impl<T: KnownLayout> KnownLayout for [T] {
#[allow(clippy::missing_inline_in_public_items)]
fn only_derive_is_allowed_to_implement_this_trait()
where
Self: Sized,
{
}
const LAYOUT: DstLayout = DstLayout::for_slice::<T>();

// SAFETY: `.cast` preserves address and provenance. The returned pointer
Expand Down Expand Up @@ -3134,7 +3150,6 @@ where

mod sealed {
pub trait ByteSliceSealed {}
pub trait KnownLayoutSealed {}
}

// ByteSlice and ByteSliceMut abstract over [u8] references (&[u8], &mut [u8],
Expand Down Expand Up @@ -5023,78 +5038,78 @@ mod tests {
};
}

assert_impls!((): FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(u8: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(i8: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(u16: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(i16: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(u32: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(i32: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(u64: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(i64: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(u128: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(i128: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(usize: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(isize: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(f32: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(f64: FromZeroes, FromBytes, AsBytes, !Unaligned);

assert_impls!(bool: FromZeroes, AsBytes, Unaligned, !FromBytes);
assert_impls!(char: FromZeroes, AsBytes, !FromBytes, !Unaligned);
assert_impls!(str: FromZeroes, AsBytes, Unaligned, !FromBytes);

assert_impls!(NonZeroU8: AsBytes, Unaligned, !FromZeroes, !FromBytes);
assert_impls!(NonZeroI8: AsBytes, Unaligned, !FromZeroes, !FromBytes);
assert_impls!(NonZeroU16: AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroI16: AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroU32: AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroI32: AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroU64: AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroI64: AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroU128: AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroI128: AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroUsize: AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroIsize: AsBytes, !FromZeroes, !FromBytes, !Unaligned);

assert_impls!(Option<NonZeroU8>: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(Option<NonZeroI8>: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(Option<NonZeroU16>: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroI16>: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroU32>: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroI32>: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroU64>: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroI64>: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroU128>: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroI128>: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroUsize>: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroIsize>: FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!((): KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(u8: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(i8: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(u16: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(i16: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(u32: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(i32: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(u64: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(i64: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(u128: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(i128: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(usize: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(isize: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(f32: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(f64: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);

assert_impls!(bool: KnownLayout, FromZeroes, AsBytes, Unaligned, !FromBytes);
assert_impls!(char: KnownLayout, FromZeroes, AsBytes, !FromBytes, !Unaligned);
assert_impls!(str: KnownLayout, FromZeroes, AsBytes, Unaligned, !FromBytes);

assert_impls!(NonZeroU8: KnownLayout, AsBytes, Unaligned, !FromZeroes, !FromBytes);
assert_impls!(NonZeroI8: KnownLayout, AsBytes, Unaligned, !FromZeroes, !FromBytes);
assert_impls!(NonZeroU16: KnownLayout, AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroI16: KnownLayout, AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroU32: KnownLayout, AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroI32: KnownLayout, AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroU64: KnownLayout, AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroI64: KnownLayout, AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroU128: KnownLayout, AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroI128: KnownLayout, AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroUsize: KnownLayout, AsBytes, !FromZeroes, !FromBytes, !Unaligned);
assert_impls!(NonZeroIsize: KnownLayout, AsBytes, !FromZeroes, !FromBytes, !Unaligned);

assert_impls!(Option<NonZeroU8>: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(Option<NonZeroI8>: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(Option<NonZeroU16>: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroI16>: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroU32>: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroI32>: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroU64>: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroI64>: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroU128>: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroI128>: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroUsize>: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);
assert_impls!(Option<NonZeroIsize>: KnownLayout, FromZeroes, FromBytes, AsBytes, !Unaligned);

// Implements none of the ZC traits.
struct NotZerocopy;

assert_impls!(PhantomData<NotZerocopy>: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(PhantomData<[u8]>: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(PhantomData<NotZerocopy>: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(PhantomData<[u8]>: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);

assert_impls!(ManuallyDrop<u8>: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(ManuallyDrop<[u8]>: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(ManuallyDrop<NotZerocopy>: !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!(ManuallyDrop<[NotZerocopy]>: !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!(ManuallyDrop<u8>: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(ManuallyDrop<[u8]>: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(ManuallyDrop<NotZerocopy>: !KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!(ManuallyDrop<[NotZerocopy]>: !KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);

assert_impls!(MaybeUninit<u8>: FromZeroes, FromBytes, Unaligned, !AsBytes);
assert_impls!(MaybeUninit<NotZerocopy>: !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!(MaybeUninit<u8>: KnownLayout, FromZeroes, FromBytes, Unaligned, !AsBytes);
assert_impls!(MaybeUninit<NotZerocopy>: KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);

assert_impls!(Wrapping<u8>: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(Wrapping<NotZerocopy>: !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!(Wrapping<u8>: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(Wrapping<NotZerocopy>: KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);

assert_impls!(Unalign<u8>: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(Unalign<NotZerocopy>: Unaligned, !FromZeroes, !FromBytes, !AsBytes);
assert_impls!(Unalign<u8>: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!(Unalign<NotZerocopy>: KnownLayout, Unaligned, !FromZeroes, !FromBytes, !AsBytes);

assert_impls!([u8]: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!([NotZerocopy]: !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!([u8; 0]: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!([NotZerocopy; 0]: !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!([u8; 1]: FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!([NotZerocopy; 1]: !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!([u8]: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!([NotZerocopy]: !KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!([u8; 0]: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!([NotZerocopy; 0]: KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);
assert_impls!([u8; 1]: KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned);
assert_impls!([NotZerocopy; 1]: KnownLayout, !FromZeroes, !FromBytes, !AsBytes, !Unaligned);

#[cfg(feature = "simd")]
{
Expand Down
8 changes: 6 additions & 2 deletions src/macros.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -211,9 +211,11 @@ macro_rules! impl_known_layout {
const _: () = {
use core::ptr::NonNull;

impl<$(const $constvar : $constty,)? $($tyvar $(: ?$optbound)?)?> sealed::KnownLayoutSealed for $ty {}
// SAFETY: Delegates safety to `DstLayout::for_type`.
unsafe impl<$(const $constvar : $constty,)? $($tyvar $(: ?$optbound)?)?> KnownLayout for $ty {
#[allow(clippy::missing_inline_in_public_items)]
fn only_derive_is_allowed_to_implement_this_trait() where Self: Sized {}

const LAYOUT: DstLayout = DstLayout::for_type::<$ty>();

// SAFETY: `.cast` preserves address and provenance.
Expand Down Expand Up @@ -245,8 +247,10 @@ macro_rules! unsafe_impl_known_layout {
const _: () = {
use core::ptr::NonNull;

impl<$($tyvar: ?Sized + KnownLayout)?> sealed::KnownLayoutSealed for $ty {}
unsafe impl<$($tyvar: ?Sized + KnownLayout)?> KnownLayout for $ty {
#[allow(clippy::missing_inline_in_public_items)]
fn only_derive_is_allowed_to_implement_this_trait() {}

const LAYOUT: DstLayout = <$repr as KnownLayout>::LAYOUT;

// SAFETY: All operations preserve address and provenance.
Expand Down
15 changes: 12 additions & 3 deletions src/util.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -572,7 +572,18 @@ pub(crate) mod testutil {
// Though `u64` has alignment 8 on some platforms, it's not guaranteed.
// By contrast, `AU64` is guaranteed to have alignment 8.
#[derive(
FromZeroes, FromBytes, AsBytes, Eq, PartialEq, Ord, PartialOrd, Default, Debug, Copy, Clone,
KnownLayout,
FromZeroes,
FromBytes,
AsBytes,
Eq,
PartialEq,
Ord,
PartialOrd,
Default,
Debug,
Copy,
Clone,
)]
#[repr(C, align(8))]
pub(crate) struct AU64(pub(crate) u64);
Expand All @@ -589,8 +600,6 @@ pub(crate) mod testutil {
Display::fmt(&self.0, f)
}
}

impl_known_layout!(AU64);
}

#[cfg(test)]
Expand Down
8 changes: 7 additions & 1 deletion src/wrappers.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -58,10 +58,16 @@ use super::*;
// [3] https://github.com/google/zerocopy/issues/209
#[allow(missing_debug_implementations)]
#[derive(Default, Copy)]
#[cfg_attr(any(feature = "derive", test), derive(FromZeroes, FromBytes, AsBytes, Unaligned))]
#[cfg_attr(
any(feature = "derive", test),
derive(KnownLayout, FromZeroes, FromBytes, AsBytes, Unaligned)
)]
#[repr(C, packed)]
pub struct Unalign<T>(T);

#[cfg(not(any(feature = "derive", test)))]
impl_known_layout!(T => Unalign<T>);

safety_comment! {
/// SAFETY:
/// - `Unalign<T>` is `repr(packed)`, so it is unaligned regardless of the
Expand Down
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