// SPDX-License-Identifier: (BSD-2-Clause OR Apache-2.0) OR MIT
//
// Copyright 2022 The Fuchsia Authors
//
// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
// This file may not be copied, modified, or distributed except according to
// those terms.
//! Utilities used by macros and by `zerocopy-derive`.
//!
//! These are defined here `zerocopy` rather than in code generated by macros or
//! by `zerocopy-derive` so that they can be compiled once rather than
//! recompiled for every invocation (e.g., if they were defined in generated
//! code, then deriving `IntoBytes` and `FromBytes` on three different types
//! would result in the code in question being emitted and compiled six
//! different times).
#![allow(missing_debug_implementations)]
// FIXME(#29), FIXME(https://github.com/rust-lang/rust/issues/69835): Remove
// this `cfg` when `size_of_val_raw` is stabilized.
#[cfg(__ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS)]
#[cfg(not(target_pointer_width = "16"))]
use core::ptr::{self, NonNull};
use core::{marker::PhantomData, mem, num::Wrapping};
use crate::{
pointer::{
cast::CastSized,
invariant::{Aligned, Initialized, Valid},
BecauseImmutable,
},
FromBytes, Immutable, IntoBytes, KnownLayout, Ptr, ReadOnly, TryFromBytes, ValidityError,
};
/// Projects the type of the field at `Index` in `Self` without regard for field
/// privacy.
///
/// The `Index` parameter is any sort of handle that identifies the field; its
/// definition is the obligation of the implementer.
///
/// # Safety
///
/// Unsafe code may assume that this accurately reflects the definition of
/// `Self`.
pub unsafe trait Field<Index> {
/// The type of the field at `Index`.
type Type: ?Sized;
}
#[cfg_attr(
not(no_zerocopy_diagnostic_on_unimplemented_1_78_0),
diagnostic::on_unimplemented(
message = "`{T}` has {PADDING_BYTES} total byte(s) of padding",
label = "types with padding cannot implement `IntoBytes`",
note = "consider using `zerocopy::Unalign` to lower the alignment of individual fields",
note = "consider adding explicit fields where padding would be",
note = "consider using `#[repr(packed)]` to remove padding"
)
)]
pub trait PaddingFree<T: ?Sized, const PADDING_BYTES: usize> {}
impl<T: ?Sized> PaddingFree<T, 0> for () {}
// FIXME(#1112): In the slice DST case, we should delegate to *both*
// `PaddingFree` *and* `DynamicPaddingFree` (and probably rename `PaddingFree`
// to `StaticPaddingFree` or something - or introduce a third trait with that
// name) so that we can have more clear error messages.
#[cfg_attr(
not(no_zerocopy_diagnostic_on_unimplemented_1_78_0),
diagnostic::on_unimplemented(
message = "`{T}` has one or more padding bytes",
label = "types with padding cannot implement `IntoBytes`",
note = "consider using `zerocopy::Unalign` to lower the alignment of individual fields",
note = "consider adding explicit fields where padding would be",
note = "consider using `#[repr(packed)]` to remove padding"
)
)]
pub trait DynamicPaddingFree<T: ?Sized, const HAS_PADDING: bool> {}
impl<T: ?Sized> DynamicPaddingFree<T, false> for () {}
#[cfg(__ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS)]
#[cfg(not(target_pointer_width = "16"))]
const _64K: usize = 1 << 16;
// FIXME(#29), FIXME(https://github.com/rust-lang/rust/issues/69835): Remove
// this `cfg` when `size_of_val_raw` is stabilized.
#[cfg(__ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS)]
#[cfg(not(target_pointer_width = "16"))]
#[repr(C, align(65536))]
struct Aligned64kAllocation([u8; _64K]);
/// A pointer to an aligned allocation of size 2^16.
///
/// # Safety
///
/// `ALIGNED_64K_ALLOCATION` is guaranteed to point to the entirety of an
/// allocation with size and alignment 2^16, and to have valid provenance.
// FIXME(#29), FIXME(https://github.com/rust-lang/rust/issues/69835): Remove
// this `cfg` when `size_of_val_raw` is stabilized.
#[cfg(__ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS)]
#[cfg(not(target_pointer_width = "16"))]
pub const ALIGNED_64K_ALLOCATION: NonNull<[u8]> = {
const REF: &Aligned64kAllocation = &Aligned64kAllocation([0; _64K]);
let ptr: *const Aligned64kAllocation = REF;
let ptr: *const [u8] = ptr::slice_from_raw_parts(ptr.cast(), _64K);
// SAFETY:
// - `ptr` is derived from a Rust reference, which is guaranteed to be
// non-null.
// - `ptr` is derived from an `&Aligned64kAllocation`, which has size and
// alignment `_64K` as promised. Its length is initialized to `_64K`,
// which means that it refers to the entire allocation.
// - `ptr` is derived from a Rust reference, which is guaranteed to have
// valid provenance.
//
// FIXME(#429): Once `NonNull::new_unchecked` docs document that it
// preserves provenance, cite those docs.
// FIXME: Replace this `as` with `ptr.cast_mut()` once our MSRV >= 1.65
#[allow(clippy::as_conversions)]
unsafe {
NonNull::new_unchecked(ptr as *mut _)
}
};
/// Computes the offset of the base of the field `$trailing_field_name` within
/// the type `$ty`.
///
/// `trailing_field_offset!` produces code which is valid in a `const` context.
// FIXME(#29), FIXME(https://github.com/rust-lang/rust/issues/69835): Remove
// this `cfg` when `size_of_val_raw` is stabilized.
#[cfg(__ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS)]
#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
#[macro_export]
macro_rules! trailing_field_offset {
($ty:ty, $trailing_field_name:tt) => {{
let min_size = {
let zero_elems: *const [()] =
$crate::util::macro_util::core_reexport::ptr::slice_from_raw_parts(
$crate::util::macro_util::core_reexport::ptr::NonNull::<()>::dangling()
.as_ptr()
.cast_const(),
0,
);
// SAFETY:
// - If `$ty` is `Sized`, `size_of_val_raw` is always safe to call.
// - Otherwise:
// - If `$ty` is not a slice DST, this pointer conversion will
// fail due to "mismatched vtable kinds", and compilation will
// fail.
// - If `$ty` is a slice DST, we have constructed `zero_elems` to
// have zero trailing slice elements. Per the `size_of_val_raw`
// docs, "For the special case where the dynamic tail length is
// 0, this function is safe to call." [1]
//
// [1] https://doc.rust-lang.org/nightly/std/mem/fn.size_of_val_raw.html
unsafe {
#[allow(clippy::as_conversions)]
$crate::util::macro_util::core_reexport::mem::size_of_val_raw(
zero_elems as *const $ty,
)
}
};
assert!(min_size <= _64K);
#[allow(clippy::as_conversions)]
let ptr = ALIGNED_64K_ALLOCATION.as_ptr() as *const $ty;
// SAFETY:
// - Thanks to the preceding `assert!`, we know that the value with zero
// elements fits in `_64K` bytes, and thus in the allocation addressed
// by `ALIGNED_64K_ALLOCATION`. The offset of the trailing field is
// guaranteed to be no larger than this size, so this field projection
// is guaranteed to remain in-bounds of its allocation.
// - Because the minimum size is no larger than `_64K` bytes, and
// because an object's size must always be a multiple of its alignment
// [1], we know that `$ty`'s alignment is no larger than `_64K`. The
// allocation addressed by `ALIGNED_64K_ALLOCATION` is guaranteed to
// be aligned to `_64K`, so `ptr` is guaranteed to satisfy `$ty`'s
// alignment.
// - As required by `addr_of!`, we do not write through `field`.
//
// Note that, as of [2], this requirement is technically unnecessary
// for Rust versions >= 1.75.0, but no harm in guaranteeing it anyway
// until we bump our MSRV.
//
// [1] Per https://doc.rust-lang.org/reference/type-layout.html:
//
// The size of a value is always a multiple of its alignment.
//
// [2] https://github.com/rust-lang/reference/pull/1387
let field = unsafe {
$crate::util::macro_util::core_reexport::ptr::addr_of!((*ptr).$trailing_field_name)
};
// SAFETY:
// - Both `ptr` and `field` are derived from the same allocated object.
// - By the preceding safety comment, `field` is in bounds of that
// allocated object.
// - The distance, in bytes, between `ptr` and `field` is required to be
// a multiple of the size of `u8`, which is trivially true because
// `u8`'s size is 1.
// - The distance, in bytes, cannot overflow `isize`. This is guaranteed
// because no allocated object can have a size larger than can fit in
// `isize`. [1]
// - The distance being in-bounds cannot rely on wrapping around the
// address space. This is guaranteed because the same is guaranteed of
// allocated objects. [1]
//
// [1] FIXME(#429), FIXME(https://github.com/rust-lang/rust/pull/116675):
// Once these are guaranteed in the Reference, cite it.
let offset = unsafe { field.cast::<u8>().offset_from(ptr.cast::<u8>()) };
// Guaranteed not to be lossy: `field` comes after `ptr`, so the offset
// from `ptr` to `field` is guaranteed to be positive.
assert!(offset >= 0);
Some(
#[allow(clippy::as_conversions)]
{
offset as usize
},
)
}};
}
/// Computes alignment of `$ty: ?Sized`.
///
/// `align_of!` produces code which is valid in a `const` context.
// FIXME(#29), FIXME(https://github.com/rust-lang/rust/issues/69835): Remove
// this `cfg` when `size_of_val_raw` is stabilized.
#[cfg(__ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS)]
#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
#[macro_export]
macro_rules! align_of {
($ty:ty) => {{
// SAFETY: `OffsetOfTrailingIsAlignment` is `repr(C)`, and its layout is
// guaranteed [1] to begin with the single-byte layout for `_byte`,
// followed by the padding needed to align `_trailing`, then the layout
// for `_trailing`, and finally any trailing padding bytes needed to
// correctly-align the entire struct.
//
// This macro computes the alignment of `$ty` by counting the number of
// bytes preceding `_trailing`. For instance, if the alignment of `$ty`
// is `1`, then no padding is required align `_trailing` and it will be
// located immediately after `_byte` at offset 1. If the alignment of
// `$ty` is 2, then a single padding byte is required before
// `_trailing`, and `_trailing` will be located at offset 2.
// This correspondence between offset and alignment holds for all valid
// Rust alignments, and we confirm this exhaustively (or, at least up to
// the maximum alignment supported by `trailing_field_offset!`) in
// `test_align_of_dst`.
//
// [1]: https://doc.rust-lang.org/nomicon/other-reprs.html#reprc
#[repr(C)]
struct OffsetOfTrailingIsAlignment {
_byte: u8,
_trailing: $ty,
}
trailing_field_offset!(OffsetOfTrailingIsAlignment, _trailing)
}};
}
mod size_to_tag {
pub trait SizeToTag<const SIZE: usize> {
type Tag;
}
impl SizeToTag<1> for () {
type Tag = u8;
}
impl SizeToTag<2> for () {
type Tag = u16;
}
impl SizeToTag<4> for () {
type Tag = u32;
}
impl SizeToTag<8> for () {
type Tag = u64;
}
impl SizeToTag<16> for () {
type Tag = u128;
}
}
/// An alias for the unsigned integer of the given size in bytes.
#[doc(hidden)]
pub type SizeToTag<const SIZE: usize> = <() as size_to_tag::SizeToTag<SIZE>>::Tag;
// We put `Sized` in its own module so it can have the same name as the standard
// library `Sized` without shadowing it in the parent module.
#[cfg(not(no_zerocopy_diagnostic_on_unimplemented_1_78_0))]
mod __size_of {
#[diagnostic::on_unimplemented(
message = "`{Self}` is unsized",
label = "`IntoBytes` needs all field types to be `Sized` in order to determine whether there is padding",
note = "consider using `#[repr(packed)]` to remove padding",
note = "`IntoBytes` does not require the fields of `#[repr(packed)]` types to be `Sized`"
)]
pub trait Sized: core::marker::Sized {}
impl<T: core::marker::Sized> Sized for T {}
#[inline(always)]
#[must_use]
#[allow(clippy::needless_maybe_sized)]
pub const fn size_of<T: Sized + ?core::marker::Sized>() -> usize {
core::mem::size_of::<T>()
}
}
#[cfg(no_zerocopy_diagnostic_on_unimplemented_1_78_0)]
pub use core::mem::size_of;
#[cfg(not(no_zerocopy_diagnostic_on_unimplemented_1_78_0))]
pub use __size_of::size_of;
/// How many padding bytes does the struct type `$t` have?
///
/// `$ts` is the list of the type of every field in `$t`. `$t` must be a struct
/// type, or else `struct_padding!`'s result may be meaningless.
///
/// Note that `struct_padding!`'s results are independent of `repcr` since they
/// only consider the size of the type and the sizes of the fields. Whatever the
/// repr, the size of the type already takes into account any padding that the
/// compiler has decided to add. Structs with well-defined representations (such
/// as `repr(C)`) can use this macro to check for padding. Note that while this
/// may yield some consistent value for some `repr(Rust)` structs, it is not
/// guaranteed across platforms or compilations.
#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
#[macro_export]
macro_rules! struct_padding {
($t:ty, $_align:expr, $_packed:expr, [$($ts:ty),*]) => {{
// The `align` and `packed` directives can be ignored here. Regardless
// of if and how they are set, comparing the size of `$t` to the sum of
// its field sizes is a reliable indicator of the presence of padding.
$crate::util::macro_util::size_of::<$t>() - (0 $(+ $crate::util::macro_util::size_of::<$ts>())*)
}};
}
/// Does the `repr(C)` struct type `$t` have padding?
///
/// `$ts` is the list of the type of every field in `$t`. `$t` must be a
/// `repr(C)` struct type, or else `struct_has_padding!`'s result may be
/// meaningless.
#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
#[macro_export]
macro_rules! repr_c_struct_has_padding {
($t:ty, $align:expr, $packed:expr, [$($ts:tt),*]) => {{
let layout = $crate::DstLayout::for_repr_c_struct(
$align,
$packed,
&[$($crate::repr_c_struct_has_padding!(@field $ts),)*]
);
layout.requires_static_padding() || layout.requires_dynamic_padding()
}};
(@field ([$t:ty])) => {
<[$t] as $crate::KnownLayout>::LAYOUT
};
(@field ($t:ty)) => {
$crate::DstLayout::for_unpadded_type::<$t>()
};
(@field [$t:ty]) => {
<[$t] as $crate::KnownLayout>::LAYOUT
};
(@field $t:ty) => {
$crate::DstLayout::for_unpadded_type::<$t>()
};
}
/// Does the union type `$t` have padding?
///
/// `$ts` is the list of the type of every field in `$t`. `$t` must be a union
/// type, or else `union_padding!`'s result may be meaningless.
///
/// Note that `union_padding!`'s results are independent of `repr` since they
/// only consider the size of the type and the sizes of the fields. Whatever the
/// repr, the size of the type already takes into account any padding that the
/// compiler has decided to add. Unions with well-defined representations (such
/// as `repr(C)`) can use this macro to check for padding. Note that while this
/// may yield some consistent value for some `repr(Rust)` unions, it is not
/// guaranteed across platforms or compilations.
#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
#[macro_export]
macro_rules! union_padding {
($t:ty, $_align:expr, $_packed:expr, [$($ts:ty),*]) => {{
// The `align` and `packed` directives can be ignored here. Regardless
// of if and how they are set, comparing the size of `$t` to each of its
// field sizes is a reliable indicator of the presence of padding.
let mut max = 0;
$({
let padding = $crate::util::macro_util::size_of::<$t>() - $crate::util::macro_util::size_of::<$ts>();
if padding > max {
max = padding;
}
})*
max
}};
}
/// How many padding bytes does the enum type `$t` have?
///
/// `$disc` is the type of the enum tag, and `$ts` is a list of fields in each
/// square-bracket-delimited variant. `$t` must be an enum, or else
/// `enum_padding!`'s result may be meaningless. An enum has padding if any of
/// its variant structs [1][2] contain padding, and so all of the variants of an
/// enum must be "full" in order for the enum to not have padding.
///
/// The results of `enum_padding!` require that the enum is not `repr(Rust)`, as
/// `repr(Rust)` enums may niche the enum's tag and reduce the total number of
/// bytes required to represent the enum as a result. As long as the enum is
/// `repr(C)`, `repr(int)`, or `repr(C, int)`, this will consistently return
/// whether the enum contains any padding bytes.
///
/// [1]: https://doc.rust-lang.org/1.81.0/reference/type-layout.html#reprc-enums-with-fields
/// [2]: https://doc.rust-lang.org/1.81.0/reference/type-layout.html#primitive-representation-of-enums-with-fields
#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
#[macro_export]
macro_rules! enum_padding {
($t:ty, $_align:expr, $packed:expr, $disc:ty, $([$($ts:ty),*]),*) => {{
// The `align` and `packed` directives are irrelevant. `$align` can be
// ignored because regardless of if and how it is set, comparing the
// size of `$t` to each of its field sizes is a reliable indicator of
// the presence of padding. `$packed` is irrelevant because it is
// forbidden on enums.
#[allow(clippy::as_conversions)]
const _: [(); 1] = [(); $packed.is_none() as usize];
let mut max = 0;
$({
let padding = $crate::util::macro_util::size_of::<$t>()
- (
$crate::util::macro_util::size_of::<$disc>()
$(+ $crate::util::macro_util::size_of::<$ts>())*
);
if padding > max {
max = padding;
}
})*
max
}};
}
/// Unwraps an infallible `Result`.
#[doc(hidden)]
#[macro_export]
macro_rules! into_inner {
($e:expr) => {
match $e {
$crate::util::macro_util::core_reexport::result::Result::Ok(e) => e,
$crate::util::macro_util::core_reexport::result::Result::Err(i) => match i {},
}
};
}
/// Translates an identifier or tuple index into a numeric identifier.
#[doc(hidden)] // `#[macro_export]` bypasses this module's `#[doc(hidden)]`.
#[macro_export]
macro_rules! ident_id {
($field:ident) => {
$crate::util::macro_util::hash_name(stringify!($field))
};
($field:literal) => {
$field
};
}
/// Computes the hash of a string.
///
/// NOTE(#2749) on hash collisions: This function's output only needs to be
/// deterministic within a particular compilation. Thus, if a user ever reports
/// a hash collision (very unlikely given the <= 16-byte special case), we can
/// strengthen the hash function at that point and publish a new version. Since
/// this is computed at compile time on small strings, we can easily use more
/// expensive and higher-quality hash functions if need be.
#[inline(always)]
#[must_use]
#[allow(clippy::as_conversions, clippy::indexing_slicing, clippy::arithmetic_side_effects)]
pub const fn hash_name(name: &str) -> i128 {
let name = name.as_bytes();
// We guarantee freedom from hash collisions between any two strings of
// length 16 or less by having the hashes of such strings be equal to
// their value. There is still a possibility that such strings will have
// the same value as the hash of a string of length > 16.
if name.len() <= size_of::<u128>() {
let mut bytes = [0u8; 16];
let mut i = 0;
while i < name.len() {
bytes[i] = name[i];
i += 1;
}
return i128::from_ne_bytes(bytes);
};
// An implementation of FxHasher, although returning a u128. Probably
// not as strong as it could be, but probably more collision resistant
// than normal 64-bit FxHasher.
let mut hash = 0u128;
let mut i = 0;
while i < name.len() {
// This is just FxHasher's `0x517cc1b727220a95` constant
// concatenated back-to-back.
const K: u128 = 0x517cc1b727220a95517cc1b727220a95;
hash = (hash.rotate_left(5) ^ (name[i] as u128)).wrapping_mul(K);
i += 1;
}
i128::from_ne_bytes(hash.to_ne_bytes())
}
/// Attempts to transmute `Src` into `Dst`.
///
/// A helper for `try_transmute!`.
///
/// # Panics
///
/// `try_transmute` may either produce a post-monomorphization error or a panic
/// if `Dst` is bigger than `Src`. Otherwise, `try_transmute` panics under the
/// same circumstances as [`is_bit_valid`].
///
/// [`is_bit_valid`]: TryFromBytes::is_bit_valid
#[inline(always)]
pub fn try_transmute<Src, Dst>(src: Src) -> Result<Dst, ValidityError<Src, Dst>>
where
Src: IntoBytes,
Dst: TryFromBytes,
{
static_assert!(Src, Dst => mem::size_of::<Dst>() == mem::size_of::<Src>());
let mu_src = mem::MaybeUninit::new(src);
// SAFETY: `MaybeUninit` has no validity requirements.
let mu_dst: mem::MaybeUninit<ReadOnly<Dst>> =
unsafe { crate::util::transmute_unchecked(mu_src) };
let ptr = Ptr::from_ref(&mu_dst);
// SAFETY: Since `Src: IntoBytes`, and since `size_of::<Src>() ==
// size_of::<Dst>()` by the preceding assertion, all of `mu_dst`'s bytes are
// initialized. `MaybeUninit` has no validity requirements, so even if
// `ptr` is used to mutate its referent (which it actually can't be - it's
// a shared `ReadOnly` pointer), that won't violate its referent's validity.
let ptr = unsafe { ptr.assume_validity::<Initialized>() };
if Dst::is_bit_valid(ptr.cast::<_, CastSized, _>()) {
// SAFETY: Since `Dst::is_bit_valid`, we know that `ptr`'s referent is
// bit-valid for `Dst`. `ptr` points to `mu_dst`, and no intervening
// operations have mutated it, so it is a bit-valid `Dst`.
Ok(ReadOnly::into_inner(unsafe { mu_dst.assume_init() }))
} else {
// SAFETY: `MaybeUninit` has no validity requirements.
let mu_src: mem::MaybeUninit<Src> = unsafe { crate::util::transmute_unchecked(mu_dst) };
// SAFETY: `mu_dst`/`mu_src` was constructed from `src` and never
// modified, so it is still bit-valid.
Err(ValidityError::new(unsafe { mu_src.assume_init() }))
}
}
/// See `try_transmute_ref!` documentation.
pub trait TryTransmuteRefDst<'a> {
type Dst: ?Sized;
/// See `try_transmute_ref!` documentation.
fn try_transmute_ref(self) -> Result<&'a Self::Dst, ValidityError<&'a Self::Src, Self::Dst>>
where
Self: TryTransmuteRefSrc<'a>,
Self::Src: IntoBytes + Immutable + KnownLayout,
Self::Dst: TryFromBytes + Immutable + KnownLayout;
}
pub trait TryTransmuteRefSrc<'a> {
type Src: ?Sized;
}
impl<'a, Src, Dst> TryTransmuteRefSrc<'a> for Wrap<&'a Src, &'a Dst>
where
Src: ?Sized,
Dst: ?Sized,
{
type Src = Src;
}
impl<'a, Src, Dst> TryTransmuteRefDst<'a> for Wrap<&'a Src, &'a Dst>
where
Src: IntoBytes + Immutable + KnownLayout + ?Sized,
Dst: TryFromBytes + Immutable + KnownLayout + ?Sized,
{
type Dst = Dst;
#[inline(always)]
fn try_transmute_ref(
self,
) -> Result<
&'a Dst,
ValidityError<&'a <Wrap<&'a Src, &'a Dst> as TryTransmuteRefSrc<'a>>::Src, Dst>,
> {
let ptr = Ptr::from_ref(self.0);
#[rustfmt::skip]
let res = ptr.try_with(#[inline(always)] |ptr| {
let ptr = ptr.recall_validity::<Initialized, _>();
let ptr = ptr.cast::<_, crate::layout::CastFrom<Dst>, _>();
ptr.try_into_valid()
});
match res {
Ok(ptr) => {
static_assert!(Src: ?Sized + KnownLayout, Dst: ?Sized + KnownLayout => {
Src::LAYOUT.align.get() >= Dst::LAYOUT.align.get()
}, "cannot transmute reference when destination type has higher alignment than source type");
// SAFETY: We have checked that `Dst` does not have a stricter
// alignment requirement than `Src`.
let ptr = unsafe { ptr.assume_alignment::<Aligned>() };
Ok(ptr.as_ref())
}
Err(err) => Err(err.map_src(Ptr::as_ref)),
}
}
}
pub trait TryTransmuteMutDst<'a> {
type Dst: ?Sized;
/// See `try_transmute_mut!` documentation.
fn try_transmute_mut(
self,
) -> Result<&'a mut Self::Dst, ValidityError<&'a mut Self::Src, Self::Dst>>
where
Self: TryTransmuteMutSrc<'a>,
Self::Src: IntoBytes,
Self::Dst: TryFromBytes;
}
pub trait TryTransmuteMutSrc<'a> {
type Src: ?Sized;
}
impl<'a, Src, Dst> TryTransmuteMutSrc<'a> for Wrap<&'a mut Src, &'a mut Dst>
where
Src: ?Sized,
Dst: ?Sized,
{
type Src = Src;
}
impl<'a, Src, Dst> TryTransmuteMutDst<'a> for Wrap<&'a mut Src, &'a mut Dst>
where
Src: FromBytes + IntoBytes + KnownLayout + ?Sized,
Dst: TryFromBytes + IntoBytes + KnownLayout + ?Sized,
{
type Dst = Dst;
#[inline(always)]
fn try_transmute_mut(
self,
) -> Result<
&'a mut Dst,
ValidityError<&'a mut <Wrap<&'a mut Src, &'a mut Dst> as TryTransmuteMutSrc<'a>>::Src, Dst>,
> {
let ptr = Ptr::from_mut(self.0);
// SAFETY: The provided closure returns the only copy of `ptr`.
#[rustfmt::skip]
let res = unsafe {
ptr.try_with_unchecked(#[inline(always)] |ptr| {
let ptr = ptr.recall_validity::<Initialized, (_, (_, _))>();
let ptr = ptr.cast::<_, crate::layout::CastFrom<Dst>, _>();
ptr.try_into_valid()
})
};
match res {
Ok(ptr) => {
static_assert!(Src: ?Sized + KnownLayout, Dst: ?Sized + KnownLayout => {
Src::LAYOUT.align.get() >= Dst::LAYOUT.align.get()
}, "cannot transmute reference when destination type has higher alignment than source type");
// SAFETY: We have checked that `Dst` does not have a stricter
// alignment requirement than `Src`.
let ptr = unsafe { ptr.assume_alignment::<Aligned>() };
Ok(ptr.as_mut())
}
Err(err) => Err(err.map_src(Ptr::as_mut)),
}
}
}
// Used in `transmute_ref!` and friends.
//
// This permits us to use the autoref specialization trick to dispatch to
// associated functions for `transmute_ref` and `transmute_mut` when both `Src`
// and `Dst` are `Sized`, and to trait methods otherwise. The associated
// functions, unlike the trait methods, do not require a `KnownLayout` bound.
// This permits us to add support for transmuting references to unsized types
// without breaking backwards-compatibility (on v0.8.x) with the old
// implementation, which did not require a `KnownLayout` bound to transmute
// sized types.
#[derive(Copy, Clone)]
pub struct Wrap<Src, Dst>(pub Src, pub PhantomData<Dst>);
impl<Src, Dst> Wrap<Src, Dst> {
#[inline(always)]
pub const fn new(src: Src) -> Self {
Wrap(src, PhantomData)
}
}
impl<'a, Src, Dst> Wrap<&'a Src, &'a Dst>
where
Src: ?Sized,
Dst: ?Sized,
{
#[allow(clippy::must_use_candidate, clippy::missing_inline_in_public_items, clippy::empty_loop)]
pub const fn transmute_ref_inference_helper(self) -> &'a Dst {
loop {}
}
}
impl<'a, Src, Dst> Wrap<&'a Src, &'a Dst> {
/// # Safety
/// The caller must guarantee that:
/// - `Src: IntoBytes + Immutable`
/// - `Dst: FromBytes + Immutable`
///
/// # PME
///
/// Instantiating this method PMEs unless both:
/// - `mem::size_of::<Dst>() == mem::size_of::<Src>()`
/// - `mem::align_of::<Dst>() <= mem::align_of::<Src>()`
#[inline(always)]
#[must_use]
pub const unsafe fn transmute_ref(self) -> &'a Dst {
static_assert!(Src, Dst => mem::size_of::<Dst>() == mem::size_of::<Src>());
static_assert!(Src, Dst => mem::align_of::<Dst>() <= mem::align_of::<Src>());
let src: *const Src = self.0;
let dst = src.cast::<Dst>();
// SAFETY:
// - We know that it is sound to view the target type of the input
// reference (`Src`) as the target type of the output reference
// (`Dst`) because the caller has guaranteed that `Src: IntoBytes`,
// `Dst: FromBytes`, and `size_of::<Src>() == size_of::<Dst>()`.
// - We know that there are no `UnsafeCell`s, and thus we don't have to
// worry about `UnsafeCell` overlap, because `Src: Immutable` and
// `Dst: Immutable`.
// - The caller has guaranteed that alignment is not increased.
// - We know that the returned lifetime will not outlive the input
// lifetime thanks to the lifetime bounds on this function.
//
// FIXME(#67): Once our MSRV is 1.58, replace this `transmute` with
// `&*dst`.
#[allow(clippy::transmute_ptr_to_ref)]
unsafe {
mem::transmute(dst)
}
}
#[inline(always)]
pub fn try_transmute_ref(self) -> Result<&'a Dst, ValidityError<&'a Src, Dst>>
where
Src: IntoBytes + Immutable,
Dst: TryFromBytes + Immutable,
{
static_assert!(Src => mem::align_of::<Src>() == mem::align_of::<Wrapping<Src>>());
static_assert!(Dst => mem::align_of::<Dst>() == mem::align_of::<Wrapping<Dst>>());
// SAFETY: By the preceding assert, `Src` and `Wrapping<Src>` have the
// same alignment.
let src: &Wrapping<Src> =
unsafe { crate::util::transmute_ref::<_, _, BecauseImmutable>(self.0) };
let src = Wrap::new(src);
<Wrap<&'a Wrapping<Src>, &'a Wrapping<Dst>> as TryTransmuteRefDst<'a>>::try_transmute_ref(
src,
)
.map(
// SAFETY: By the preceding assert, `Dst` and `Wrapping<Dst>` have
// the same alignment.
#[inline(always)]
|dst| unsafe { crate::util::transmute_ref::<_, _, BecauseImmutable>(dst) },
)
.map_err(
#[inline(always)]
|err| {
// SAFETY: By the preceding assert, `Src` and `Wrapping<Src>` have the
// same alignment.
ValidityError::new(unsafe {
crate::util::transmute_ref::<_, _, BecauseImmutable>(err.into_src())
})
},
)
}
}
impl<'a, Src, Dst> Wrap<&'a mut Src, &'a mut Dst>
where
Src: ?Sized,
Dst: ?Sized,
{
#[allow(clippy::must_use_candidate, clippy::missing_inline_in_public_items, clippy::empty_loop)]
pub fn transmute_mut_inference_helper(self) -> &'a mut Dst {
loop {}
}
}
impl<'a, Src, Dst> Wrap<&'a mut Src, &'a mut Dst> {
/// Transmutes a mutable reference of one type to a mutable reference of
/// another type.
///
/// # PME
///
/// Instantiating this method PMEs unless both:
/// - `mem::size_of::<Dst>() == mem::size_of::<Src>()`
/// - `mem::align_of::<Dst>() <= mem::align_of::<Src>()`
#[inline(always)]
#[must_use]
pub fn transmute_mut(self) -> &'a mut Dst
where
Src: FromBytes + IntoBytes,
Dst: FromBytes + IntoBytes,
{
static_assert!(Src, Dst => mem::size_of::<Dst>() == mem::size_of::<Src>());
static_assert!(Src, Dst => mem::align_of::<Dst>() <= mem::align_of::<Src>());
let src: *mut Src = self.0;
let dst = src.cast::<Dst>();
// SAFETY:
// - We know that it is sound to view the target type of the input
// reference (`Src`) as the target type of the output reference
// (`Dst`) and vice-versa because `Src: FromBytes + IntoBytes`, `Dst:
// FromBytes + IntoBytes`, and (as asserted above) `size_of::<Src>()
// == size_of::<Dst>()`.
// - We asserted above that alignment will not increase.
// - We know that the returned lifetime will not outlive the input
// lifetime thanks to the lifetime bounds on this function.
unsafe { &mut *dst }
}
#[inline(always)]
pub fn try_transmute_mut(self) -> Result<&'a mut Dst, ValidityError<&'a mut Src, Dst>>
where
Src: FromBytes + IntoBytes,
Dst: TryFromBytes + IntoBytes,
{
static_assert!(Src => mem::align_of::<Src>() == mem::align_of::<Wrapping<Src>>());
static_assert!(Dst => mem::align_of::<Dst>() == mem::align_of::<Wrapping<Dst>>());
// SAFETY: By the preceding assert, `Src` and `Wrapping<Src>` have the
// same alignment.
let src: &mut Wrapping<Src> =
unsafe { crate::util::transmute_mut::<_, _, (_, (_, _))>(self.0) };
let src = Wrap::new(src);
<Wrap<&'a mut Wrapping<Src>, &'a mut Wrapping<Dst>> as TryTransmuteMutDst<'a>>
::try_transmute_mut(src)
// SAFETY: By the preceding assert, `Dst` and `Wrapping<Dst>` have the
// same alignment.
.map(|dst| unsafe { crate::util::transmute_mut::<_, _, (_, (_, _))>(dst) })
.map_err(|err| {
// SAFETY: By the preceding assert, `Src` and `Wrapping<Src>` have the
// same alignment.
ValidityError::new(unsafe {
crate::util::transmute_mut::<_, _, (_, (_, _))>(err.into_src())
})
})
}
}
pub trait TransmuteRefDst<'a> {
type Dst: ?Sized;
#[must_use]
fn transmute_ref(self) -> &'a Self::Dst;
}
impl<'a, Src: ?Sized, Dst: ?Sized> TransmuteRefDst<'a> for Wrap<&'a Src, &'a Dst>
where
Src: KnownLayout + IntoBytes + Immutable,
Dst: KnownLayout<PointerMetadata = usize> + FromBytes + Immutable,
{
type Dst = Dst;
#[inline(always)]
fn transmute_ref(self) -> &'a Dst {
let ptr = Ptr::from_ref(self.0)
.recall_validity::<Initialized, _>()
.transmute_with::<Dst, Initialized, crate::layout::CastFrom<Dst>, (crate::pointer::BecauseMutationCompatible, _)>()
.recall_validity::<Valid, _>();
static_assert!(Src: ?Sized + KnownLayout, Dst: ?Sized + KnownLayout => {
Src::LAYOUT.align.get() >= Dst::LAYOUT.align.get()
}, "cannot transmute reference when destination type has higher alignment than source type");
// SAFETY: The preceding `static_assert!` ensures that
// `Src::LAYOUT.align >= Dst::LAYOUT.align`. Since `self` is
// validly-aligned for `Src`, it is also validly-aligned for `Dst`.
let ptr = unsafe { ptr.assume_alignment() };
ptr.as_ref()
}
}
pub trait TransmuteMutDst<'a> {
type Dst: ?Sized;
#[must_use]
fn transmute_mut(self) -> &'a mut Self::Dst;
}
impl<'a, Src: ?Sized, Dst: ?Sized> TransmuteMutDst<'a> for Wrap<&'a mut Src, &'a mut Dst>
where
Src: KnownLayout + FromBytes + IntoBytes,
Dst: KnownLayout<PointerMetadata = usize> + FromBytes + IntoBytes,
{
type Dst = Dst;
#[inline(always)]
fn transmute_mut(self) -> &'a mut Dst {
let ptr = Ptr::from_mut(self.0)
.recall_validity::<Initialized, (_, (_, _))>()
.transmute_with::<Dst, Initialized, crate::layout::CastFrom<Dst>, _>()
.recall_validity::<Valid, (_, (_, _))>();
static_assert!(Src: ?Sized + KnownLayout, Dst: ?Sized + KnownLayout => {
Src::LAYOUT.align.get() >= Dst::LAYOUT.align.get()
}, "cannot transmute reference when destination type has higher alignment than source type");
// SAFETY: The preceding `static_assert!` ensures that
// `Src::LAYOUT.align >= Dst::LAYOUT.align`. Since `self` is
// validly-aligned for `Src`, it is also validly-aligned for `Dst`.
let ptr = unsafe { ptr.assume_alignment() };
ptr.as_mut()
}
}
/// A function which emits a warning if its return value is not used.
#[must_use]
#[inline(always)]
pub const fn must_use<T>(t: T) -> T {
t
}
// NOTE: We can't change this to a `pub use core as core_reexport` until [1] is
// fixed or we update to a semver-breaking version (as of this writing, 0.8.0)
// on the `main` branch.
//
// [1] https://github.com/obi1kenobi/cargo-semver-checks/issues/573
pub mod core_reexport {
pub use core::*;
pub mod mem {
pub use core::mem::*;
}
}
#[cfg(test)]
mod tests {
use core::num::NonZeroUsize;
use crate::util::testutil::*;
#[cfg(__ZEROCOPY_INTERNAL_USE_ONLY_NIGHTLY_FEATURES_IN_TESTS)]
mod nightly {
use super::super::*;
use crate::util::testutil::*;
// FIXME(#29), FIXME(https://github.com/rust-lang/rust/issues/69835):
// Remove this `cfg` when `size_of_val_raw` is stabilized.
#[allow(clippy::decimal_literal_representation)]
#[test]
fn test_trailing_field_offset() {
assert_eq!(mem::align_of::<Aligned64kAllocation>(), _64K);
macro_rules! test {
(#[$cfg:meta] ($($ts:ty),* ; $trailing_field_ty:ty) => $expect:expr) => {{
#[$cfg]
struct Test($(#[allow(dead_code)] $ts,)* #[allow(dead_code)] $trailing_field_ty);
assert_eq!(test!(@offset $($ts),* ; $trailing_field_ty), $expect);
}};
(#[$cfg:meta] $(#[$cfgs:meta])* ($($ts:ty),* ; $trailing_field_ty:ty) => $expect:expr) => {
test!(#[$cfg] ($($ts),* ; $trailing_field_ty) => $expect);
test!($(#[$cfgs])* ($($ts),* ; $trailing_field_ty) => $expect);
};
(@offset ; $_trailing:ty) => { trailing_field_offset!(Test, 0) };
(@offset $_t:ty ; $_trailing:ty) => { trailing_field_offset!(Test, 1) };
}
test!(#[repr(C)] #[repr(transparent)] #[repr(packed)](; u8) => Some(0));
test!(#[repr(C)] #[repr(transparent)] #[repr(packed)](; [u8]) => Some(0));
test!(#[repr(C)] #[repr(C, packed)] (u8; u8) => Some(1));
test!(#[repr(C)] (; AU64) => Some(0));
test!(#[repr(C)] (; [AU64]) => Some(0));
test!(#[repr(C)] (u8; AU64) => Some(8));
test!(#[repr(C)] (u8; [AU64]) => Some(8));
#[derive(
Immutable, FromBytes, Eq, PartialEq, Ord, PartialOrd, Default, Debug, Copy, Clone,
)]
#[repr(C)]
pub(crate) struct Nested<T, U: ?Sized> {
_t: T,
_u: U,
}
test!(#[repr(C)] (; Nested<u8, AU64>) => Some(0));
test!(#[repr(C)] (; Nested<u8, [AU64]>) => Some(0));
test!(#[repr(C)] (u8; Nested<u8, AU64>) => Some(8));
test!(#[repr(C)] (u8; Nested<u8, [AU64]>) => Some(8));
// Test that `packed(N)` limits the offset of the trailing field.
test!(#[repr(C, packed( 1))] (u8; elain::Align< 2>) => Some( 1));
test!(#[repr(C, packed( 2))] (u8; elain::Align< 4>) => Some( 2));
test!(#[repr(C, packed( 4))] (u8; elain::Align< 8>) => Some( 4));
test!(#[repr(C, packed( 8))] (u8; elain::Align< 16>) => Some( 8));
test!(#[repr(C, packed( 16))] (u8; elain::Align< 32>) => Some( 16));
test!(#[repr(C, packed( 32))] (u8; elain::Align< 64>) => Some( 32));
test!(#[repr(C, packed( 64))] (u8; elain::Align< 128>) => Some( 64));
test!(#[repr(C, packed( 128))] (u8; elain::Align< 256>) => Some( 128));
test!(#[repr(C, packed( 256))] (u8; elain::Align< 512>) => Some( 256));
test!(#[repr(C, packed( 512))] (u8; elain::Align< 1024>) => Some( 512));
test!(#[repr(C, packed( 1024))] (u8; elain::Align< 2048>) => Some( 1024));
test!(#[repr(C, packed( 2048))] (u8; elain::Align< 4096>) => Some( 2048));
test!(#[repr(C, packed( 4096))] (u8; elain::Align< 8192>) => Some( 4096));
test!(#[repr(C, packed( 8192))] (u8; elain::Align< 16384>) => Some( 8192));
test!(#[repr(C, packed( 16384))] (u8; elain::Align< 32768>) => Some( 16384));
test!(#[repr(C, packed( 32768))] (u8; elain::Align< 65536>) => Some( 32768));
test!(#[repr(C, packed( 65536))] (u8; elain::Align< 131072>) => Some( 65536));
/* Alignments above 65536 are not yet supported.
test!(#[repr(C, packed( 131072))] (u8; elain::Align< 262144>) => Some( 131072));
test!(#[repr(C, packed( 262144))] (u8; elain::Align< 524288>) => Some( 262144));
test!(#[repr(C, packed( 524288))] (u8; elain::Align< 1048576>) => Some( 524288));
test!(#[repr(C, packed( 1048576))] (u8; elain::Align< 2097152>) => Some( 1048576));
test!(#[repr(C, packed( 2097152))] (u8; elain::Align< 4194304>) => Some( 2097152));
test!(#[repr(C, packed( 4194304))] (u8; elain::Align< 8388608>) => Some( 4194304));
test!(#[repr(C, packed( 8388608))] (u8; elain::Align< 16777216>) => Some( 8388608));
test!(#[repr(C, packed( 16777216))] (u8; elain::Align< 33554432>) => Some( 16777216));
test!(#[repr(C, packed( 33554432))] (u8; elain::Align< 67108864>) => Some( 33554432));
test!(#[repr(C, packed( 67108864))] (u8; elain::Align< 33554432>) => Some( 67108864));
test!(#[repr(C, packed( 33554432))] (u8; elain::Align<134217728>) => Some( 33554432));
test!(#[repr(C, packed(134217728))] (u8; elain::Align<268435456>) => Some(134217728));
test!(#[repr(C, packed(268435456))] (u8; elain::Align<268435456>) => Some(268435456));
*/
// Test that `align(N)` does not limit the offset of the trailing field.
test!(#[repr(C, align( 1))] (u8; elain::Align< 2>) => Some( 2));
test!(#[repr(C, align( 2))] (u8; elain::Align< 4>) => Some( 4));
test!(#[repr(C, align( 4))] (u8; elain::Align< 8>) => Some( 8));
test!(#[repr(C, align( 8))] (u8; elain::Align< 16>) => Some( 16));
test!(#[repr(C, align( 16))] (u8; elain::Align< 32>) => Some( 32));
test!(#[repr(C, align( 32))] (u8; elain::Align< 64>) => Some( 64));
test!(#[repr(C, align( 64))] (u8; elain::Align< 128>) => Some( 128));
test!(#[repr(C, align( 128))] (u8; elain::Align< 256>) => Some( 256));
test!(#[repr(C, align( 256))] (u8; elain::Align< 512>) => Some( 512));
test!(#[repr(C, align( 512))] (u8; elain::Align< 1024>) => Some( 1024));
test!(#[repr(C, align( 1024))] (u8; elain::Align< 2048>) => Some( 2048));
test!(#[repr(C, align( 2048))] (u8; elain::Align< 4096>) => Some( 4096));
test!(#[repr(C, align( 4096))] (u8; elain::Align< 8192>) => Some( 8192));
test!(#[repr(C, align( 8192))] (u8; elain::Align< 16384>) => Some( 16384));
test!(#[repr(C, align( 16384))] (u8; elain::Align< 32768>) => Some( 32768));
test!(#[repr(C, align( 32768))] (u8; elain::Align< 65536>) => Some( 65536));
/* Alignments above 65536 are not yet supported.
test!(#[repr(C, align( 65536))] (u8; elain::Align< 131072>) => Some( 131072));
test!(#[repr(C, align( 131072))] (u8; elain::Align< 262144>) => Some( 262144));
test!(#[repr(C, align( 262144))] (u8; elain::Align< 524288>) => Some( 524288));
test!(#[repr(C, align( 524288))] (u8; elain::Align< 1048576>) => Some( 1048576));
test!(#[repr(C, align( 1048576))] (u8; elain::Align< 2097152>) => Some( 2097152));
test!(#[repr(C, align( 2097152))] (u8; elain::Align< 4194304>) => Some( 4194304));
test!(#[repr(C, align( 4194304))] (u8; elain::Align< 8388608>) => Some( 8388608));
test!(#[repr(C, align( 8388608))] (u8; elain::Align< 16777216>) => Some( 16777216));
test!(#[repr(C, align( 16777216))] (u8; elain::Align< 33554432>) => Some( 33554432));
test!(#[repr(C, align( 33554432))] (u8; elain::Align< 67108864>) => Some( 67108864));
test!(#[repr(C, align( 67108864))] (u8; elain::Align< 33554432>) => Some( 33554432));
test!(#[repr(C, align( 33554432))] (u8; elain::Align<134217728>) => Some(134217728));
test!(#[repr(C, align(134217728))] (u8; elain::Align<268435456>) => Some(268435456));
*/
}
// FIXME(#29), FIXME(https://github.com/rust-lang/rust/issues/69835):
// Remove this `cfg` when `size_of_val_raw` is stabilized.
#[allow(clippy::decimal_literal_representation)]
#[test]
fn test_align_of_dst() {
// Test that `align_of!` correctly computes the alignment of DSTs.
assert_eq!(align_of!([elain::Align<1>]), Some(1));
assert_eq!(align_of!([elain::Align<2>]), Some(2));
assert_eq!(align_of!([elain::Align<4>]), Some(4));
assert_eq!(align_of!([elain::Align<8>]), Some(8));
assert_eq!(align_of!([elain::Align<16>]), Some(16));
assert_eq!(align_of!([elain::Align<32>]), Some(32));
assert_eq!(align_of!([elain::Align<64>]), Some(64));
assert_eq!(align_of!([elain::Align<128>]), Some(128));
assert_eq!(align_of!([elain::Align<256>]), Some(256));
assert_eq!(align_of!([elain::Align<512>]), Some(512));
assert_eq!(align_of!([elain::Align<1024>]), Some(1024));
assert_eq!(align_of!([elain::Align<2048>]), Some(2048));
assert_eq!(align_of!([elain::Align<4096>]), Some(4096));
assert_eq!(align_of!([elain::Align<8192>]), Some(8192));
assert_eq!(align_of!([elain::Align<16384>]), Some(16384));
assert_eq!(align_of!([elain::Align<32768>]), Some(32768));
assert_eq!(align_of!([elain::Align<65536>]), Some(65536));
/* Alignments above 65536 are not yet supported.
assert_eq!(align_of!([elain::Align<131072>]), Some(131072));
assert_eq!(align_of!([elain::Align<262144>]), Some(262144));
assert_eq!(align_of!([elain::Align<524288>]), Some(524288));
assert_eq!(align_of!([elain::Align<1048576>]), Some(1048576));
assert_eq!(align_of!([elain::Align<2097152>]), Some(2097152));
assert_eq!(align_of!([elain::Align<4194304>]), Some(4194304));
assert_eq!(align_of!([elain::Align<8388608>]), Some(8388608));
assert_eq!(align_of!([elain::Align<16777216>]), Some(16777216));
assert_eq!(align_of!([elain::Align<33554432>]), Some(33554432));
assert_eq!(align_of!([elain::Align<67108864>]), Some(67108864));
assert_eq!(align_of!([elain::Align<33554432>]), Some(33554432));
assert_eq!(align_of!([elain::Align<134217728>]), Some(134217728));
assert_eq!(align_of!([elain::Align<268435456>]), Some(268435456));
*/
}
}
#[test]
fn test_enum_casts() {
// Test that casting the variants of enums with signed integer reprs to
// unsigned integers obeys expected signed -> unsigned casting rules.
#[repr(i8)]
enum ReprI8 {
MinusOne = -1,
Zero = 0,
Min = i8::MIN,
Max = i8::MAX,
}
#[allow(clippy::as_conversions)]
let x = ReprI8::MinusOne as u8;
assert_eq!(x, u8::MAX);
#[allow(clippy::as_conversions)]
let x = ReprI8::Zero as u8;
assert_eq!(x, 0);
#[allow(clippy::as_conversions)]
let x = ReprI8::Min as u8;
assert_eq!(x, 128);
#[allow(clippy::as_conversions)]
let x = ReprI8::Max as u8;
assert_eq!(x, 127);
}
#[test]
fn test_struct_padding() {
// Test that, for each provided repr, `struct_padding!` reports the
// expected value.
macro_rules! test {
(#[$cfg:meta] ($($ts:ty),*) => $expect:expr) => {{
#[$cfg]
#[allow(dead_code)]
struct Test($($ts),*);
assert_eq!(struct_padding!(Test, None::<NonZeroUsize>, None::<NonZeroUsize>, [$($ts),*]), $expect);
}};
(#[$cfg:meta] $(#[$cfgs:meta])* ($($ts:ty),*) => $expect:expr) => {
test!(#[$cfg] ($($ts),*) => $expect);
test!($(#[$cfgs])* ($($ts),*) => $expect);
};
}
test!(#[repr(C)] #[repr(transparent)] #[repr(packed)] () => 0);
test!(#[repr(C)] #[repr(transparent)] #[repr(packed)] (u8) => 0);
test!(#[repr(C)] #[repr(transparent)] #[repr(packed)] (u8, ()) => 0);
test!(#[repr(C)] #[repr(packed)] (u8, u8) => 0);
test!(#[repr(C)] (u8, AU64) => 7);
// Rust won't let you put `#[repr(packed)]` on a type which contains a
// `#[repr(align(n > 1))]` type (`AU64`), so we have to use `u64` here.
// It's not ideal, but it definitely has align > 1 on /some/ of our CI
// targets, and this isn't a particularly complex macro we're testing
// anyway.
test!(#[repr(packed)] (u8, u64) => 0);
}
#[test]
fn test_repr_c_struct_padding() {
// Test that, for each provided repr, `repr_c_struct_padding!` reports
// the expected value.
macro_rules! test {
(($($ts:tt),*) => $expect:expr) => {{
#[repr(C)]
#[allow(dead_code)]
struct Test($($ts),*);
assert_eq!(repr_c_struct_has_padding!(Test, None::<NonZeroUsize>, None::<NonZeroUsize>, [$($ts),*]), $expect);
}};
}
// Test static padding
test!(() => false);
test!(([u8]) => false);
test!((u8) => false);
test!((u8, [u8]) => false);
test!((u8, ()) => false);
test!((u8, (), [u8]) => false);
test!((u8, u8) => false);
test!((u8, u8, [u8]) => false);
test!((u8, AU64) => true);
test!((u8, AU64, [u8]) => true);
// Test dynamic padding
test!((AU64, [AU64]) => false);
test!((u8, [AU64]) => true);
#[repr(align(4))]
struct AU32(#[allow(unused)] u32);
test!((AU64, [AU64]) => false);
test!((AU64, [AU32]) => true);
}
#[test]
fn test_union_padding() {
// Test that, for each provided repr, `union_padding!` reports the
// expected value.
macro_rules! test {
(#[$cfg:meta] {$($fs:ident: $ts:ty),*} => $expect:expr) => {{
#[$cfg]
#[allow(unused)] // fields are never read
union Test{ $($fs: $ts),* }
assert_eq!(union_padding!(Test, None::<NonZeroUsize>, None::<usize>, [$($ts),*]), $expect);
}};
(#[$cfg:meta] $(#[$cfgs:meta])* {$($fs:ident: $ts:ty),*} => $expect:expr) => {
test!(#[$cfg] {$($fs: $ts),*} => $expect);
test!($(#[$cfgs])* {$($fs: $ts),*} => $expect);
};
}
test!(#[repr(C)] #[repr(packed)] {a: u8} => 0);
test!(#[repr(C)] #[repr(packed)] {a: u8, b: u8} => 0);
// Rust won't let you put `#[repr(packed)]` on a type which contains a
// `#[repr(align(n > 1))]` type (`AU64`), so we have to use `u64` here.
// It's not ideal, but it definitely has align > 1 on /some/ of our CI
// targets, and this isn't a particularly complex macro we're testing
// anyway.
test!(#[repr(C)] #[repr(packed)] {a: u8, b: u64} => 7);
}
#[test]
fn test_enum_padding() {
// Test that, for each provided repr, `enum_has_padding!` reports the
// expected value.
macro_rules! test {
(#[repr($disc:ident $(, $c:ident)?)] { $($vs:ident ($($ts:ty),*),)* } => $expect:expr) => {
test!(@case #[repr($disc $(, $c)?)] { $($vs ($($ts),*),)* } => $expect);
};
(#[repr($disc:ident $(, $c:ident)?)] #[$cfg:meta] $(#[$cfgs:meta])* { $($vs:ident ($($ts:ty),*),)* } => $expect:expr) => {
test!(@case #[repr($disc $(, $c)?)] #[$cfg] { $($vs ($($ts),*),)* } => $expect);
test!(#[repr($disc $(, $c)?)] $(#[$cfgs])* { $($vs ($($ts),*),)* } => $expect);
};
(@case #[repr($disc:ident $(, $c:ident)?)] $(#[$cfg:meta])? { $($vs:ident ($($ts:ty),*),)* } => $expect:expr) => {{
#[repr($disc $(, $c)?)]
$(#[$cfg])?
#[allow(unused)] // variants and fields are never used
enum Test {
$($vs ($($ts),*),)*
}
assert_eq!(
enum_padding!(Test, None::<NonZeroUsize>, None::<NonZeroUsize>, $disc, $([$($ts),*]),*),
$expect
);
}};
}
#[allow(unused)]
#[repr(align(2))]
struct U16(u16);
#[allow(unused)]
#[repr(align(4))]
struct U32(u32);
test!(#[repr(u8)] #[repr(C)] {
A(u8),
} => 0);
test!(#[repr(u16)] #[repr(C)] {
A(u8, u8),
B(U16),
} => 0);
test!(#[repr(u32)] #[repr(C)] {
A(u8, u8, u8, u8),
B(U16, u8, u8),
C(u8, u8, U16),
D(U16, U16),
E(U32),
} => 0);
// `repr(int)` can pack the discriminant more efficiently
test!(#[repr(u8)] {
A(u8, U16),
} => 0);
test!(#[repr(u8)] {
A(u8, U16, U32),
} => 0);
// `repr(C)` cannot
test!(#[repr(u8, C)] {
A(u8, U16),
} => 2);
test!(#[repr(u8, C)] {
A(u8, u8, u8, U32),
} => 4);
// And field ordering can always cause problems
test!(#[repr(u8)] #[repr(C)] {
A(U16, u8),
} => 2);
test!(#[repr(u8)] #[repr(C)] {
A(U32, u8, u8, u8),
} => 4);
}
}
