[pointer] Support Box and Arc

gherrit-pr-id: I7fe90063e148d89e2f75b6fa63a960ad8b1dd432

Author: joshlf

src/impls.rs

@@ -648,7 +648,7 @@ unsafe impl<T: TryFromBytes + ?Sized> TryFromBytes for UnsafeCell<T> {
     }
 
     #[inline]
-    fn is_bit_valid<A: invariant::Reference>(candidate: Maybe<'_, Self, A>) -> bool {
+    fn is_bit_valid<A: invariant::ReadFoo>(candidate: Maybe<'_, Self, A>) -> bool {
         // The only way to implement this function is using an exclusive-aliased
         // pointer. `UnsafeCell`s cannot be read via shared-aliased pointers
         // (other than by using `unsafe` code, which we can't use since we can't
@@ -1124,15 +1124,15 @@ mod tests {
 
             pub(super) trait TestIsBitValidShared<T: ?Sized> {
                 #[allow(clippy::needless_lifetimes)]
-                fn test_is_bit_valid_shared<'ptr, A: invariant::Reference>(
+                fn test_is_bit_valid_shared<'ptr, A: invariant::ReadFoo>(
                     &self,
                     candidate: Maybe<'ptr, T, A>,
                 ) -> Option<bool>;
             }
 
             impl<T: TryFromBytes + Immutable + ?Sized> TestIsBitValidShared<T> for AutorefWrapper<T> {
                 #[allow(clippy::needless_lifetimes)]
-                fn test_is_bit_valid_shared<'ptr, A: invariant::Reference>(
+                fn test_is_bit_valid_shared<'ptr, A: invariant::ReadFoo>(
                     &self,
                     candidate: Maybe<'ptr, T, A>,
                 ) -> Option<bool> {
@@ -1222,7 +1222,7 @@ mod tests {
                 #[allow(unused, non_local_definitions)]
                 impl AutorefWrapper<$ty> {
                     #[allow(clippy::needless_lifetimes)]
-                    fn test_is_bit_valid_shared<'ptr, A: invariant::Reference>(
+                    fn test_is_bit_valid_shared<'ptr, A: invariant::ReadFoo>(
                         &mut self,
                         candidate: Maybe<'ptr, $ty, A>,
                     ) -> Option<bool> {

src/lib.rs

@@ -1321,7 +1321,7 @@ pub unsafe trait TryFromBytes {
     /// [`UnsafeCell`]: core::cell::UnsafeCell
     /// [`Shared`]: invariant::Shared
     #[doc(hidden)]
-    fn is_bit_valid<A: invariant::Reference>(candidate: Maybe<'_, Self, A>) -> bool;
+    fn is_bit_valid<A: invariant::ReadFoo>(candidate: Maybe<'_, Self, A>) -> bool;
 
     /// Attempts to interpret the given `source` as a `&Self`.
     ///
@@ -3469,10 +3469,23 @@ pub unsafe trait FromBytes: FromZeros {
     where
         Self: KnownLayout + Immutable,
     {
-        static_assert_dst_is_not_zst!(Self);
-        match Ptr::from_ref(source).try_cast_into_no_leftover::<_, BecauseImmutable>(None) {
-            Ok(ptr) => Ok(ptr.bikeshed_recall_valid().as_ref()),
-            Err(err) => Err(err.map_src(|src| src.as_ref())),
+        Self::from_bytes(source)
+    }
+
+    #[must_use = "has no side effects"]
+    #[inline]
+    fn from_bytes<'a, P: pointer::Pointer<'a, Self>, R>(
+        source: P::To<'a, [u8]>,
+    ) -> Result<P, CastError<P::To<'a, [u8]>, Self>>
+    where
+        R: invariant::ReadReason,
+        Self: 'a + KnownLayout + invariant::Read<P::Aliasing, R>,
+    {
+        match Ptr::<'_, _, (P::Aliasing, _, _)>::from_pointer(source)
+            .try_cast_into_no_leftover::<_, R>(None)
+        {
+            Ok(ptr) => Ok(ptr.bikeshed_recall_valid().into_pointer()),
+            Err(err) => Err(err.map_src(|src| src.into_pointer())),
         }
     }
 
@@ -3705,11 +3718,7 @@ pub unsafe trait FromBytes: FromZeros {
     where
         Self: IntoBytes + KnownLayout,
     {
-        static_assert_dst_is_not_zst!(Self);
-        match Ptr::from_mut(source).try_cast_into_no_leftover::<_, BecauseExclusive>(None) {
-            Ok(ptr) => Ok(ptr.bikeshed_recall_valid().as_mut()),
-            Err(err) => Err(err.map_src(|src| src.as_mut())),
-        }
+        Self::from_bytes(source)
     }
 
     /// Interprets the prefix of the given `source` as a `&mut Self` without

src/pointer/inner.rs

@@ -25,7 +25,8 @@ mod _def {
     /// `Ptr<'a, T>` is [covariant] in `'a` and `T`.
     ///
     /// [covariant]: https://doc.rust-lang.org/reference/subtyping.html
-    pub(crate) struct PtrInner<'a, T>
+    #[allow(missing_debug_implementations)]
+    pub struct PtrInner<'a, T>
     where
         T: ?Sized,
     {

src/pointer/invariant.rs

@@ -13,8 +13,6 @@
 //! Invariants are encoded as ([`Aliasing`], [`Alignment`], [`Validity`])
 //! triples implementing the [`Invariants`] trait.
 
-use super::*;
-
 /// The invariants of a [`Ptr`][super::Ptr].
 pub trait Invariants: Sealed {
     type Aliasing: Aliasing;
@@ -82,6 +80,15 @@ pub trait Aliasing:
     /// Aliasing>::Variance<'a, T>` to inherit this variance.
     #[doc(hidden)]
     type Variance<'a, T: 'a + ?Sized>;
+
+    // #[doc(hidden)]
+    // type Applied<'a, T: 'a + ?Sized>;
+
+    // #[doc(hidden)]
+    // fn into_ptr<'a, T: 'a + ?Sized>(ptr: Self::Applied<'a, T>) -> PtrInner<'a, T>;
+
+    // #[doc(hidden)]
+    // unsafe fn from_ptr<'a, T: 'a + ?Sized>(ptr: PtrInner<'a, T>) -> Self::Applied<'a, T>;
 }
 
 #[doc(hidden)]
@@ -136,14 +143,7 @@ impl<
 ///
 /// Given `A: Reference`, callers may assume that either `A = Shared` or `A =
 /// Exclusive`.
-pub trait Reference: Aliasing + Sealed {
-    fn with<'a, T, I, S, E, O>(ptr: Ptr<'a, T, I>, shared: S, exclusive: E) -> O
-    where
-        T: 'a + ?Sized,
-        I: Invariants<Aliasing = Self>,
-        S: FnOnce(Ptr<'a, T, I::WithAliasing<Shared>>) -> O,
-        E: FnOnce(Ptr<'a, T, I::WithAliasing<Exclusive>>) -> O;
-}
+pub trait Reference: ReadFoo + Sealed {}
 
 /// It is unknown whether any invariant holds.
 pub enum Unknown {}
@@ -189,18 +189,7 @@ impl Aliasing for Shared {
     const IS_EXCLUSIVE: bool = false;
     type Variance<'a, T: 'a + ?Sized> = &'a T;
 }
-impl Reference for Shared {
-    #[inline(always)]
-    fn with<'a, T, I, S, E, O>(ptr: Ptr<'a, T, I>, shared: S, _exclusive: E) -> O
-    where
-        T: 'a + ?Sized,
-        I: Invariants<Aliasing = Shared>,
-        S: FnOnce(Ptr<'a, T, I::WithAliasing<Shared>>) -> O,
-        E: FnOnce(Ptr<'a, T, I::WithAliasing<Exclusive>>) -> O,
-    {
-        shared(ptr.unify_invariants())
-    }
-}
+impl Reference for Shared {}
 
 /// The `Ptr<'a, T>` adheres to the aliasing rules of a `&'a mut T`.
 ///
@@ -215,16 +204,41 @@ impl Aliasing for Exclusive {
     const IS_EXCLUSIVE: bool = true;
     type Variance<'a, T: 'a + ?Sized> = &'a mut T;
 }
-impl Reference for Exclusive {
-    #[inline(always)]
-    fn with<'a, T, I, S, E, O>(ptr: Ptr<'a, T, I>, _shared: S, exclusive: E) -> O
-    where
-        T: 'a + ?Sized,
-        I: Invariants<Aliasing = Exclusive>,
-        S: FnOnce(Ptr<'a, T, I::WithAliasing<Shared>>) -> O,
-        E: FnOnce(Ptr<'a, T, I::WithAliasing<Exclusive>>) -> O,
-    {
-        exclusive(ptr.unify_invariants())
+impl Reference for Exclusive {}
+
+#[cfg(feature = "alloc")]
+pub use _alloc::*;
+#[cfg(feature = "alloc")]
+mod _alloc {
+    use alloc::boxed::Box as Bx;
+
+    use super::*;
+
+    pub enum Box {}
+    impl AliasingInner for Box {
+        type MappedTo<M: AliasingMapping> = M::FromBox;
+    }
+    impl Aliasing for Box {
+        const IS_EXCLUSIVE: bool = true;
+        type Variance<'a, T: 'a + ?Sized> = Bx<T>;
+    }
+}
+
+#[cfg(feature = "std")]
+pub use _std::*;
+#[cfg(feature = "std")]
+mod _std {
+    use std::sync::Arc as Ac;
+
+    use super::*;
+
+    pub enum Arc {}
+    impl AliasingInner for Arc {
+        type MappedTo<M: AliasingMapping> = M::FromArc;
+    }
+    impl Aliasing for Arc {
+        const IS_EXCLUSIVE: bool = true;
+        type Variance<'a, T: 'a + ?Sized> = Ac<T>;
     }
 }
 
@@ -279,6 +293,27 @@ impl ValidityInner for Valid {
     type MappedTo<M: ValidityMapping> = M::FromValid;
 }
 
+// Aliasing modes that permit reading at all (ie, everything but Inaccessible).
+pub trait ReadFoo: Aliasing {}
+impl ReadFoo for Shared {}
+impl ReadFoo for Exclusive {}
+#[cfg(feature = "alloc")]
+impl ReadFoo for Box {}
+#[cfg(feature = "std")]
+impl ReadFoo for Arc {}
+
+// Shared, Arc, etc
+pub trait SharedFoo: Aliasing {}
+impl SharedFoo for Shared {}
+#[cfg(feature = "std")]
+impl SharedFoo for Arc {}
+
+// Exclusive, Box, etc
+pub trait ExclusiveFoo: Aliasing {}
+impl ExclusiveFoo for Exclusive {}
+#[cfg(feature = "alloc")]
+impl ExclusiveFoo for Box {}
+
 /// [`Ptr`](crate::Ptr) referents that permit unsynchronized read operations.
 ///
 /// `T: Read<A, R>` implies that a pointer to `T` with aliasing `A` permits
@@ -295,8 +330,8 @@ impl ValidityInner for Valid {
 /// permitted to perform unsynchronized reads from its referent.
 pub trait Read<A: Aliasing, R: ReadReason> {}
 
-impl<A: Reference, T: ?Sized + crate::Immutable> Read<A, BecauseImmutable> for T {}
-impl<T: ?Sized> Read<Exclusive, BecauseExclusive> for T {}
+impl<A: ReadFoo, T: ?Sized + crate::Immutable> Read<A, BecauseImmutable> for T {}
+impl<A: ExclusiveFoo, T: ?Sized> Read<A, BecauseExclusive> for T {}
 
 /// Used to disambiguate [`Read`] impls.
 pub trait ReadReason: Sealed {}
@@ -326,6 +361,10 @@ mod sealed {
     impl Sealed for Inaccessible {}
     impl Sealed for Shared {}
     impl Sealed for Exclusive {}
+    #[cfg(feature = "alloc")]
+    impl Sealed for Box {}
+    #[cfg(feature = "std")]
+    impl Sealed for Arc {}
 
     impl Sealed for Aligned {}
 
@@ -389,6 +428,10 @@ mod mapping {
         type FromInaccessible: Aliasing;
         type FromShared: Aliasing;
         type FromExclusive: Aliasing;
+        #[cfg(feature = "alloc")]
+        type FromBox: Aliasing;
+        #[cfg(feature = "std")]
+        type FromArc: Aliasing;
     }
 
     /// A mapping from one [`Alignment`] type to another.
@@ -457,12 +500,20 @@ mod mapping {
         type FromInaccessible = FromInaccessible;
         type FromShared = FromShared;
         type FromExclusive = FromExclusive;
+        #[cfg(feature = "alloc")]
+        type FromBox = Inaccessible;
+        #[cfg(feature = "std")]
+        type FromArc = Inaccessible;
     }
 
     impl AliasingMapping for Inaccessible {
         type FromInaccessible = Inaccessible;
         type FromShared = Inaccessible;
         type FromExclusive = Inaccessible;
+        #[cfg(feature = "alloc")]
+        type FromBox = Inaccessible;
+        #[cfg(feature = "std")]
+        type FromArc = Inaccessible;
     }
 
     pub enum UnsafeCellMismatch {}
@@ -471,24 +522,40 @@ mod mapping {
         type FromInaccessible = Inaccessible;
         type FromShared = Inaccessible;
         type FromExclusive = Exclusive;
+        #[cfg(feature = "alloc")]
+        type FromBox = Box;
+        #[cfg(feature = "std")]
+        type FromArc = Inaccessible;
     }
 
     impl AliasingMapping for Preserved {
         type FromInaccessible = Inaccessible;
         type FromShared = Shared;
         type FromExclusive = Exclusive;
+        #[cfg(feature = "alloc")]
+        type FromBox = Box;
+        #[cfg(feature = "std")]
+        type FromArc = Arc;
     }
 
     impl AliasingMapping for Shared {
         type FromInaccessible = Shared;
         type FromShared = Shared;
         type FromExclusive = Shared;
+        #[cfg(feature = "alloc")]
+        type FromBox = Shared;
+        #[cfg(feature = "std")]
+        type FromArc = Shared;
     }
 
     impl AliasingMapping for Exclusive {
         type FromInaccessible = Exclusive;
         type FromShared = Exclusive;
         type FromExclusive = Exclusive;
+        #[cfg(feature = "alloc")]
+        type FromBox = Exclusive;
+        #[cfg(feature = "std")]
+        type FromArc = Exclusive;
     }
 
     impl<FromUnknown: Alignment, FromAligned: Alignment> AlignmentMapping