[pointer] Remove ReadReason from Read trait (#2409)

gherrit-pr-id: I7694dcd7b9c01e25ac8ad9ee1915de16dbc00fdd

Author: joshlf

src/pointer/invariant.rs

@@ -155,27 +155,22 @@ unsafe impl<ST: ?Sized, DT: ?Sized> CastableFrom<ST, Initialized, Initialized> f
 ///
 /// As a consequence, if `T: Read<A, R>`, then any `Ptr<T, (A, ...)>` is
 /// permitted to perform unsynchronized reads from its referent.
-pub trait Read<A: Aliasing, R: ReadReason> {}
+pub trait Read<A: Aliasing, R> {}
 
 impl<A: Aliasing, T: ?Sized + crate::Immutable> Read<A, BecauseImmutable> for T {}
 impl<T: ?Sized> Read<Exclusive, BecauseExclusive> for T {}
 
-/// Used to disambiguate [`Read`] impls.
-pub trait ReadReason: Sealed {}
-
 /// Unsynchronized reads are permitted because only one live [`Ptr`](crate::Ptr)
 /// or reference may exist to the referent bytes at a time.
 #[derive(Copy, Clone, Debug)]
 #[doc(hidden)]
 pub enum BecauseExclusive {}
-impl ReadReason for BecauseExclusive {}
 
 /// Unsynchronized reads are permitted because no live [`Ptr`](crate::Ptr)s or
 /// references permit interior mutation.
 #[derive(Copy, Clone, Debug)]
 #[doc(hidden)]
 pub enum BecauseImmutable {}
-impl ReadReason for BecauseImmutable {}
 
 use sealed::Sealed;
 mod sealed {

src/pointer/mod.rs

@@ -14,7 +14,7 @@ pub mod invariant;
 mod ptr;
 
 #[doc(hidden)]
-pub use invariant::{BecauseExclusive, BecauseImmutable, Read, ReadReason};
+pub use invariant::{BecauseExclusive, BecauseImmutable, Read};
 #[doc(hidden)]
 pub use ptr::Ptr;
 
@@ -48,7 +48,6 @@ where
     pub fn read_unaligned<R>(self) -> T
     where
         T: Copy,
-        R: invariant::ReadReason,
         T: invariant::Read<Aliasing, R>,
     {
         // SAFETY: By invariant on `MaybeAligned`, `raw` contains

src/pointer/ptr.rs

@@ -805,7 +805,6 @@ mod _transitions {
             T: TryFromBytes + Read<I::Aliasing, R>,
             I::Aliasing: Reference,
             I: Invariants<Validity = Initialized>,
-            R: crate::pointer::ReadReason,
         {
             // This call may panic. If that happens, it doesn't cause any soundness
             // issues, as we have not generated any invalid state which we need to
@@ -897,8 +896,6 @@ mod _casts {
         where
             T: Read<I::Aliasing, R>,
             U: 'a + ?Sized + Read<I::Aliasing, S> + CastableFrom<T, I::Validity, I::Validity>,
-            R: ReadReason,
-            S: ReadReason,
             F: FnOnce(*mut T) -> *mut U,
         {
             // SAFETY: Because `T` and `U` both implement `Read<I::Aliasing, _>`,
@@ -921,7 +918,6 @@ mod _casts {
         #[allow(clippy::wrong_self_convention)]
         pub(crate) fn as_bytes<R>(self) -> Ptr<'a, [u8], (I::Aliasing, Aligned, Valid)>
         where
-            R: ReadReason,
             T: Read<I::Aliasing, R>,
             I::Aliasing: Reference,
         {
@@ -1019,7 +1015,6 @@ mod _casts {
             CastError<Self, U>,
         >
         where
-            R: ReadReason,
             I::Aliasing: Reference,
             U: 'a + ?Sized + KnownLayout + Read<I::Aliasing, R>,
         {
@@ -1082,7 +1077,6 @@ mod _casts {
         where
             I::Aliasing: Reference,
             U: 'a + ?Sized + KnownLayout + Read<I::Aliasing, R>,
-            R: ReadReason,
         {
             // TODO(#67): Remove this allow. See NonNulSlicelExt for more
             // details.

src/util/macro_util.rs

@@ -25,7 +25,7 @@ use core::mem::{self, ManuallyDrop};
 use core::ptr::{self, NonNull};
 
 use crate::{
-    pointer::invariant::{self, BecauseExclusive, BecauseImmutable, Invariants, ReadReason},
+    pointer::invariant::{self, BecauseExclusive, BecauseImmutable, Invariants},
     FromBytes, Immutable, IntoBytes, Ptr, TryFromBytes, ValidityError,
 };
 
@@ -561,7 +561,6 @@ where
     Dst: TryFromBytes + invariant::Read<I::Aliasing, R>,
     I: Invariants<Validity = invariant::Initialized>,
     I::Aliasing: invariant::Reference,
-    R: ReadReason,
 {
     static_assert!(Src, Dst => mem::size_of::<Dst>() == mem::size_of::<Src>());