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Implement traits for Cell #2421

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Merged
merged 1 commit into from
Mar 8, 2025
Merged

Implement traits for Cell #2421

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21 changes: 20 additions & 1 deletion src/impls.rs
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Expand Up @@ -7,7 +7,11 @@
// This file may not be copied, modified, or distributed except according to
// those terms.

use core::{cell::UnsafeCell, mem::MaybeUninit as CoreMaybeUninit, ptr::NonNull};
use core::{
cell::{Cell, UnsafeCell},
mem::MaybeUninit as CoreMaybeUninit,
ptr::NonNull,
};

use super::*;

Expand Down Expand Up @@ -862,6 +866,21 @@ safety_comment! {
}
assert_unaligned!(ManuallyDrop<()>, ManuallyDrop<u8>);

impl_for_transmute_from!(T: ?Sized + TryFromBytes => TryFromBytes for Cell<T>[UnsafeCell<T>]);
impl_for_transmute_from!(T: ?Sized + FromZeros => FromZeros for Cell<T>[UnsafeCell<T>]);
impl_for_transmute_from!(T: ?Sized + FromBytes => FromBytes for Cell<T>[UnsafeCell<T>]);
impl_for_transmute_from!(T: ?Sized + IntoBytes => IntoBytes for Cell<T>[UnsafeCell<T>]);
safety_comment! {
/// SAFETY:
/// `Cell<T>` has the same in-memory representation as `T` [1], and thus has
/// the same alignment as `T`.
///
/// [1] Per https://doc.rust-lang.org/1.81.0/core/cell/struct.Cell.html#memory-layout:
///
/// `Cell<T>` has the same in-memory representation as its inner type `T`.
unsafe_impl!(T: ?Sized + Unaligned => Unaligned for Cell<T>);
}

impl_for_transmute_from!(T: ?Sized + FromZeros => FromZeros for UnsafeCell<T>[<T>]);
impl_for_transmute_from!(T: ?Sized + FromBytes => FromBytes for UnsafeCell<T>[<T>]);
impl_for_transmute_from!(T: ?Sized + IntoBytes => IntoBytes for UnsafeCell<T>[<T>]);
Expand Down
22 changes: 10 additions & 12 deletions src/lib.rs
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Expand Up @@ -357,7 +357,7 @@ pub use crate::r#ref::*;
pub use crate::wrappers::*;

use core::{
cell::UnsafeCell,
cell::{Cell, UnsafeCell},
cmp::Ordering,
fmt::{self, Debug, Display, Formatter},
hash::Hasher,
Expand Down Expand Up @@ -983,29 +983,27 @@ impl_known_layout!(const N: usize, T => [T; N]);

safety_comment! {
/// SAFETY:
/// `str`, `ManuallyDrop<[T]>` [1], and `UnsafeCell<T>` [2] have the same
/// representations as `[u8]`, `[T]`, and `T` repsectively. `str` has
/// different bit validity than `[u8]`, but that doesn't affect the
/// soundness of this impl.
/// `str` has the same representation as `[u8]`. `ManuallyDrop<T>` [1],
/// `UnsafeCell<T>` [2], and `Cell<T>` [3] have the same representation as
/// `T`.
///
/// [1] Per https://doc.rust-lang.org/nightly/core/mem/struct.ManuallyDrop.html:
/// [1] Per https://doc.rust-lang.org/1.85.0/std/mem/struct.ManuallyDrop.html:
///
/// `ManuallyDrop<T>` is guaranteed to have the same layout and bit
/// validity as `T`
///
/// [2] Per https://doc.rust-lang.org/core/cell/struct.UnsafeCell.html#memory-layout:
/// [2] Per https://doc.rust-lang.org/1.85.0/core/cell/struct.UnsafeCell.html#memory-layout:
///
/// `UnsafeCell<T>` has the same in-memory representation as its inner
/// type `T`.
///
/// TODO(#429):
/// - Add quotes from docs.
/// - Once [1] (added in
/// https://github.com/rust-lang/rust/pull/115522) is available on stable,
/// quote the stable docs instead of the nightly docs.
/// [3] Per https://doc.rust-lang.org/1.85.0/core/cell/struct.Cell.html#memory-layout:
///
/// `Cell<T>` has the same in-memory representation as `T`.
unsafe_impl_known_layout!(#[repr([u8])] str);
unsafe_impl_known_layout!(T: ?Sized + KnownLayout => #[repr(T)] ManuallyDrop<T>);
unsafe_impl_known_layout!(T: ?Sized + KnownLayout => #[repr(T)] UnsafeCell<T>);
unsafe_impl_known_layout!(T: ?Sized + KnownLayout => #[repr(T)] Cell<T>);
}

safety_comment! {
Expand Down
36 changes: 30 additions & 6 deletions src/pointer/transmute.rs
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Expand Up @@ -7,7 +7,7 @@
// those terms.

use core::{
cell::UnsafeCell,
cell::{Cell, UnsafeCell},
mem::{ManuallyDrop, MaybeUninit},
num::Wrapping,
ptr::NonNull,
Expand Down Expand Up @@ -405,20 +405,44 @@ safety_comment! {
unsafe_impl_invariants_eq!(T => T, Wrapping<T>);

/// SAFETY:
/// - `Unalign<T>` has the same size as `T` [1].
/// - Per [1], `Unalign<T>` has the same bit validity as `T`. Technically
/// - `UnsafeCell<T>` has the same size as `T` [1].
/// - Per [1], `UnsafeCell<T>` has the same bit validity as `T`. Technically
/// the term "representation" doesn't guarantee this, but the subsequent
/// sentence in the documentation makes it clear that this is the
/// intention.
///
/// [1] Per https://doc.rust-lang.org/1.81.0/core/cell/struct.UnsafeCell.html#memory-layout:
///
/// `UnsafeCell<T>` has the same in-memory representation as its inner type
/// `T`. A consequence of this guarantee is that it is possible to convert
/// between `T` and `UnsafeCell<T>`.
/// `UnsafeCell<T>` has the same in-memory representation as its inner
/// type `T`. A consequence of this guarantee is that it is possible to
/// convert between `T` and `UnsafeCell<T>`.
unsafe_impl_for_transparent_wrapper!(T: ?Sized => UnsafeCell<T>);

/// SAFETY:
/// - `Cell<T>` has the same size as `T` [1].
/// - Per [1], `Cell<T>` has the same bit validity as `T`. Technically the
/// term "representation" doesn't guarantee this, but it does promise to
/// have the "same memory layout and caveats as `UnsafeCell<T>`." The
/// `UnsafeCell` docs [2] make it clear that bit validity is the intention
/// even if that phrase isn't used.
///
/// [1] Per https://doc.rust-lang.org/1.85.0/std/cell/struct.Cell.html#memory-layout:
///
/// `Cell<T>` has the same memory layout and caveats as `UnsafeCell<T>`.
/// In particular, this means that `Cell<T>` has the same in-memory
/// representation as its inner type `T`.
///
/// [2] Per https://doc.rust-lang.org/1.81.0/core/cell/struct.UnsafeCell.html#memory-layout:
///
/// `UnsafeCell<T>` has the same in-memory representation as its inner
/// type `T`. A consequence of this guarantee is that it is possible to
/// convert between `T` and `UnsafeCell<T>`.
unsafe_impl_for_transparent_wrapper!(T: ?Sized => Cell<T>);
}

impl_transitive_transmute_from!(T: ?Sized => Cell<T> => T => UnsafeCell<T>);
impl_transitive_transmute_from!(T: ?Sized => UnsafeCell<T> => T => Cell<T>);

// SAFETY: `MaybeUninit<T>` has no validity requirements. Currently this is not
// explicitly guaranteed, but it's obvious from `MaybeUninit`'s documentation
// that this is the intention:
Expand Down
2 changes: 1 addition & 1 deletion tests/ui-nightly/diagnostic-not-implemented-unaligned.stderr
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Expand Up @@ -10,10 +10,10 @@ error[E0277]: the trait bound `NotZerocopy: zerocopy::Unaligned` is not satisfie
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
note: required by a bound in `takes_unaligned`
--> tests/ui-nightly/diagnostic-not-implemented-unaligned.rs:21:23
Expand Down
2 changes: 1 addition & 1 deletion tests/ui-stable/diagnostic-not-implemented-unaligned.stderr
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Expand Up @@ -10,10 +10,10 @@ error[E0277]: the trait bound `NotZerocopy: zerocopy::Unaligned` is not satisfie
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
note: required by a bound in `takes_unaligned`
--> tests/ui-stable/diagnostic-not-implemented-unaligned.rs:21:23
Expand Down
2 changes: 1 addition & 1 deletion zerocopy-derive/tests/ui-nightly/derive_transparent.stderr
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Expand Up @@ -126,10 +126,10 @@ error[E0277]: the trait bound `NotZerocopy: zerocopy::Unaligned` is not satisfie
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
note: required for `TransparentStruct<NotZerocopy>` to implement `zerocopy::Unaligned`
--> tests/ui-nightly/derive_transparent.rs:24:32
Expand Down
6 changes: 3 additions & 3 deletions zerocopy-derive/tests/ui-nightly/late_compile_pass.stderr
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Expand Up @@ -186,10 +186,10 @@ error[E0277]: the trait bound `AU16: zerocopy::Unaligned` is not satisfied
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
= help: see issue #48214
= note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -210,10 +210,10 @@ error[E0277]: the trait bound `AU16: zerocopy::Unaligned` is not satisfied
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
= help: see issue #48214
= note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -234,10 +234,10 @@ error[E0277]: the trait bound `AU16: zerocopy::Unaligned` is not satisfied
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
= help: see issue #48214
= note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand Down
4 changes: 2 additions & 2 deletions zerocopy-derive/tests/ui-nightly/struct.stderr
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Expand Up @@ -284,10 +284,10 @@ error[E0277]: the trait bound `AU16: zerocopy::Unaligned` is not satisfied
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand Down Expand Up @@ -386,10 +386,10 @@ error[E0277]: the trait bound `AU16: zerocopy::Unaligned` is not satisfied
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
note: required for `IntoBytes11<AU16>` to implement `zerocopy::IntoBytes`
--> tests/ui-nightly/struct.rs:150:10
Expand Down
2 changes: 1 addition & 1 deletion zerocopy-derive/tests/ui-stable/derive_transparent.stderr
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Expand Up @@ -126,10 +126,10 @@ error[E0277]: the trait bound `NotZerocopy: zerocopy::Unaligned` is not satisfie
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
note: required for `TransparentStruct<NotZerocopy>` to implement `zerocopy::Unaligned`
--> tests/ui-stable/derive_transparent.rs:24:32
Expand Down
6 changes: 3 additions & 3 deletions zerocopy-derive/tests/ui-stable/late_compile_pass.stderr
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Expand Up @@ -158,10 +158,10 @@ error[E0277]: the trait bound `AU16: zerocopy::Unaligned` is not satisfied
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
= help: see issue #48214
= note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -178,10 +178,10 @@ error[E0277]: the trait bound `AU16: zerocopy::Unaligned` is not satisfied
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
= help: see issue #48214
= note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand All @@ -198,10 +198,10 @@ error[E0277]: the trait bound `AU16: zerocopy::Unaligned` is not satisfied
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
= help: see issue #48214
= note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand Down
4 changes: 2 additions & 2 deletions zerocopy-derive/tests/ui-stable/struct.stderr
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Expand Up @@ -257,10 +257,10 @@ error[E0277]: the trait bound `AU16: zerocopy::Unaligned` is not satisfied
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
Expand Down Expand Up @@ -347,10 +347,10 @@ error[E0277]: the trait bound `AU16: zerocopy::Unaligned` is not satisfied
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
I16<O>
and $N others
note: required for `IntoBytes11<AU16>` to implement `zerocopy::IntoBytes`
--> tests/ui-stable/struct.rs:150:10
Expand Down
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