Implement traits for atomic types (#1028)

Makes progress on #1009. This commit doesn't implement all traits for
`AtomicPtr<T>`, so there's more work to do.

src/lib.rs

@@ -304,6 +304,10 @@ use core::{
     ops::{Deref, DerefMut},
     ptr::{self, NonNull},
     slice,
+    sync::atomic::{
+        AtomicBool, AtomicI16, AtomicI32, AtomicI8, AtomicIsize, AtomicPtr, AtomicU16, AtomicU32,
+        AtomicU8, AtomicUsize,
+    },
 };
 
 use crate::pointer::invariant;
@@ -1096,7 +1100,9 @@ impl_known_layout!(
     u8, i8, u16, i16, u32, i32, u64, i64, u128, i128, usize, isize, f32, f64,
     bool, char,
     NonZeroU8, NonZeroI8, NonZeroU16, NonZeroI16, NonZeroU32, NonZeroI32,
-    NonZeroU64, NonZeroI64, NonZeroU128, NonZeroI128, NonZeroUsize, NonZeroIsize
+    NonZeroU64, NonZeroI64, NonZeroU128, NonZeroI128, NonZeroUsize, NonZeroIsize,
+    AtomicBool, AtomicI16, AtomicI32, AtomicI8, AtomicIsize, AtomicU16, AtomicU32,
+    AtomicU8, AtomicUsize
 );
 #[rustfmt::skip]
 impl_known_layout!(
@@ -1106,6 +1112,7 @@ impl_known_layout!(
     T         => MaybeUninit<T>,
     T: ?Sized => *const T,
     T: ?Sized => *mut T,
+    T         => AtomicPtr<T>
 );
 impl_known_layout!(const N: usize, T => [T; N]);
 
@@ -3892,6 +3899,48 @@ safety_comment! {
     unsafe_impl_for_power_set!(A, B, C, D, E, F, G, H, I, J, K, L -> M => NoCell for opt_extern_c_fn!(...));
 }
 
+macro_rules! impl_traits_for_atomics {
+    ($($atomics:ident [$inners:ident]),* $(,)?) => {
+        $(
+            impl_for_transparent_wrapper!(TryFromBytes for $atomics [UnsafeCell<$inners>]);
+            impl_for_transparent_wrapper!(FromZeros for $atomics [UnsafeCell<$inners>]);
+            impl_for_transparent_wrapper!(FromBytes for $atomics [UnsafeCell<$inners>]);
+            impl_for_transparent_wrapper!(IntoBytes for $atomics [UnsafeCell<$inners>]);
+        )*
+    };
+}
+
+#[rustfmt::skip]
+impl_traits_for_atomics!(
+    AtomicBool [bool],
+    AtomicI16 [i16], AtomicI32 [i32], AtomicI8 [i8], AtomicIsize [isize],
+    AtomicU16 [u16], AtomicU32 [u32], AtomicU8 [u8], AtomicUsize [usize],
+);
+
+safety_comment! {
+    /// SAFETY:
+    /// Per [1], `AtomicBool`, `AtomicU8`, and `AtomicI8` have the same size as
+    /// `bool`, `u8`, and `i8` respectively. Since a type's alignment cannot be
+    /// smaller than 1 [2], and since its alignment cannot be greater than its
+    /// size [3], the only possible value for the alignment is 1. Thus, it is
+    /// sound to implement `Unaligned`.
+    ///
+    /// [1] TODO(#896), TODO(https://github.com/rust-lang/rust/pull/121943):
+    ///     Cite docs once they've landed.
+    ///
+    /// [2] Per https://doc.rust-lang.org/reference/type-layout.html#size-and-alignment:
+    ///
+    ///     Alignment is measured in bytes, and must be at least 1.
+    ///
+    /// [3] Per https://doc.rust-lang.org/reference/type-layout.html#size-and-alignment:
+    ///
+    ///     The size of a value is always a multiple of its alignment.
+    unsafe_impl!(AtomicBool: Unaligned);
+    unsafe_impl!(AtomicU8: Unaligned);
+    unsafe_impl!(AtomicI8: Unaligned);
+    assert_unaligned!(AtomicBool, AtomicU8, AtomicI8);
+}
+
 safety_comment! {
     /// SAFETY:
     /// Per reference [1]:

src/macros.rs

@@ -216,14 +216,15 @@ macro_rules! impl_for_transparent_wrapper {
         // - `f` can only compile if its internal call to
         //   `is_transparent_wrapper` compiles.
         //
-        // The definition of `is_transparent_wrapper` is generated by each
-        // `@is_transparent_wrapper` macro arm. Each arm is parameterized by
-        // `$trait`, and emits bounds which are sufficient to ensure that this
-        // is a sound implementation of `$trait for $ty` *so long as* `$tyvar:
-        // $trait`. Note that we require `$tyvar: $trait` in the `impl` block
-        // itself. Thus, so long as the bounds emitted by the
-        // `@is_transparent_wrapper` arm are sound, then this entire impl is
-        // sound.
+        // The definition of `is_transparent_wrapper<I, T, W>` is generated by
+        // each `@is_transparent_wrapper` macro arm. Each arm is parameterized
+        // by `$trait`, and emits bounds which are sufficient to ensure that
+        // this is a sound implementation of `$trait for W` *so long as* `T:
+        // $trait`. In `f`, we call `is_transparent_wrapper<I, $tyvar, $ty>`,
+        // and so if this code compiles, that guarantees that `$ty` satisfies
+        // the same bounds for all `$tyvar: $trait`. Thus, so long as the bounds
+        // emitted by the `@is_transparent_wrapper` arm are sound, then this
+        // entire impl is sound.
         //
         // Each `@is_transparent_wrapper` arm contains its own safety comment
         // which explains why its bounds are sound.
@@ -241,11 +242,61 @@ macro_rules! impl_for_transparent_wrapper {
 
             impl_for_transparent_wrapper!(
                 @is_bit_valid
-                $tyvar: $($(? $optbound +)* $($bound +)*)?
-                => $trait for $ty
+                <$tyvar: $($(? $optbound +)* $($bound +)*)?>
+                $trait for $ty
             );
         }
     };
+    (
+        $(#[$attr:meta])*
+        for $ty:ty [$inner:ty] $(; |$candidate:ident $(: MaybeAligned<$ref_repr:ty>)? $(: Maybe<$ptr_repr:ty>)?| $is_bit_valid:expr)?
+    ) => {};
+    (
+        $(#[$attr:meta])*
+        $trait:ident $(, $traits:ident)* for $ty:ty [$inner:ty] $(; |$candidate:ident $(: MaybeAligned<$ref_repr:ty>)? $(: Maybe<$ptr_repr:ty>)?| $is_bit_valid:expr)?
+    ) => {
+        impl_for_transparent_wrapper!(
+            $(#[$attr])*
+            $($traits),* for $ty [$inner] $(; |$candidate $(: MaybeAligned<$ref_repr>)? $(: Maybe<$ptr_repr>)?| $is_bit_valid:expr)?
+        );
+
+        $(#[$attr])*
+        #[allow(non_local_definitions)]
+        // SAFETY:
+        // - We explicitly add a `$tyvar: $trait` bound (regardless of what
+        //   bounds the caller has provided).
+        // - Inside of `only_derive_is_allowed_to_implement_this_trait`, `f` is
+        //   generic over the any `I: Invariants`.
+        // - `f` can only compile if its internal call to
+        //   `is_transparent_wrapper` compiles.
+        //
+        // The definition of `is_transparent_wrapper<I, T, W>` is generated by
+        // each `@is_transparent_wrapper` macro arm. Each arm is parameterized
+        // by `$trait`, and emits bounds which are sufficient to ensure that
+        // this is a sound implementation of `$trait for W` *so long as* `T:
+        // $trait`. In `f`, we call `is_transparent_wrapper<I, $inner, $ty>`,
+        // and so if this code compiles, that guarantees that `$ty` satisfies
+        // the same bounds so long as `$inner: $trait`. Thus, so long as the
+        // bounds emitted by the `@is_transparent_wrapper` arm are sound, then
+        // this entire impl is sound.
+        //
+        // Each `@is_transparent_wrapper` arm contains its own safety comment
+        // which explains why its bounds are sound.
+        unsafe impl $trait for $ty {
+            #[allow(dead_code, clippy::missing_inline_in_public_items)]
+            fn only_derive_is_allowed_to_implement_this_trait() {
+                use crate::{pointer::invariant::Invariants, util::*};
+
+                impl_for_transparent_wrapper!(@is_transparent_wrapper $trait);
+
+                fn f<I: Invariants>() {
+                    is_transparent_wrapper::<I, $inner, $ty>();
+                }
+            }
+
+            impl_for_transparent_wrapper!(@is_bit_valid $trait for $ty);
+        }
+    };
     (@is_transparent_wrapper NoCell) => {
         // SAFETY: `W: TransparentWrapper<UnsafeCellVariance=Covariant>`
         // requires that `W` has `UnsafeCell`s at the same byte offsets as
@@ -299,8 +350,8 @@ macro_rules! impl_for_transparent_wrapper {
     };
     (
         @is_bit_valid
-        $tyvar:ident $(: $(? $optbound:ident $(+)?)* $($bound:ident $(+)?)* )?
-        => TryFromBytes for $ty:ty
+        $(<$tyvar:ident $(: $(? $optbound:ident $(+)?)* $($bound:ident $(+)?)* )?>)?
+        TryFromBytes for $ty:ty
     ) => {
         // SAFETY: See safety comment in `(@is_transparent_wrapper
         // TryFromBytes)` macro arm for an explanation of why this is a sound
@@ -312,8 +363,8 @@ macro_rules! impl_for_transparent_wrapper {
     };
     (
         @is_bit_valid
-        $tyvar:ident $(: $(? $optbound:ident $(+)?)* $($bound:ident $(+)?)* )?
-        => $trait:ident for $ty:ty
+        $(<$tyvar:ident $(: $(? $optbound:ident $(+)?)* $($bound:ident $(+)?)* )?>)?
+        $trait:ident for $ty:ty
     ) => {
         // Trait other than `TryFromBytes`; no `is_bit_valid` impl.
     };
@@ -553,15 +604,14 @@ macro_rules! unsafe_impl_known_layout {
 /// Note that `align_of<T>` requires `T: Sized`, so this macro doesn't work for
 /// unsized types.
 macro_rules! assert_unaligned {
-    ($ty:ty) => {
-        // We only compile this assertion under `cfg(test)` to avoid taking an
-        // extra non-dev dependency (and making this crate more expensive to
-        // compile for our dependents).
-        #[cfg(test)]
-        static_assertions::const_assert_eq!(core::mem::align_of::<$ty>(), 1);
-    };
-    ($($ty:ty),*) => {
-        $(assert_unaligned!($ty);)*
+    ($($tys:ty),*) => {
+        $(
+            // We only compile this assertion under `cfg(test)` to avoid taking
+            // an extra non-dev dependency (and making this crate more expensive
+            // to compile for our dependents).
+            #[cfg(test)]
+            static_assertions::const_assert_eq!(core::mem::align_of::<$tys>(), 1);
+        )*
     };
 }