[pointer] Make invariants opaque, more ergonomic

Closes #1876

Author: joshlf

src/pointer/invariant.rs

@@ -18,12 +18,40 @@ pub trait Invariants: Sealed {
     type Aliasing: Aliasing;
     type Alignment: Alignment;
     type Validity: Validity;
+
+    /// Invariants identical to `Self` except with a different aliasing
+    /// invariant.
+    type WithAliasing<A: Aliasing>: Invariants<
+        Aliasing = A,
+        Alignment = Self::Alignment,
+        Validity = Self::Validity,
+    >;
+
+    /// Invariants identical to `Self` except with a different alignment
+    /// invariant.
+    type WithAlignment<A: Alignment>: Invariants<
+        Aliasing = Self::Aliasing,
+        Alignment = A,
+        Validity = Self::Validity,
+    >;
+
+    /// Invariants identical to `Self` except with a different validity
+    /// invariant.
+    type WithValidity<V: Validity>: Invariants<
+        Aliasing = Self::Aliasing,
+        Alignment = Self::Alignment,
+        Validity = V,
+    >;
 }
 
 impl<A: Aliasing, AA: Alignment, V: Validity> Invariants for (A, AA, V) {
     type Aliasing = A;
     type Alignment = AA;
     type Validity = V;
+
+    type WithAliasing<AB: Aliasing> = (AB, AA, V);
+    type WithAlignment<AB: Alignment> = (A, AB, V);
+    type WithValidity<VB: Validity> = (A, AA, VB);
 }
 
 /// The aliasing invariant of a [`Ptr`][super::Ptr].
@@ -107,29 +135,29 @@ impl Alignment for Aligned {}
 /// The byte ranges initialized in `T` are also initialized in the referent.
 ///
 /// Formally: uninitialized bytes may only be present in `Ptr<T>`'s referent
-/// where they are guaranteed to be present in `T`. This is a dynamic property:
-/// if, at a particular byte offset, a valid enum discriminant is set, the
-/// subsequent bytes may only have uninitialized bytes as specificed by the
-/// corresponding enum.
+/// where they are guaranteed to be present in `T`. This is a dynamic
+/// property: if, at a particular byte offset, a valid enum discriminant is
+/// set, the subsequent bytes may only have uninitialized bytes as
+/// specificed by the corresponding enum.
 ///
-/// Formally, given `len = size_of_val_raw(ptr)`, at every byte offset, `b`, in
-/// the range `[0, len)`:
-/// - If, in any instance `t: T` of length `len`, the byte at offset `b` in `t`
-///   is initialized, then the byte at offset `b` within `*ptr` must be
+/// Formally, given `len = size_of_val_raw(ptr)`, at every byte offset, `b`,
+/// in the range `[0, len)`:
+/// - If, in any instance `t: T` of length `len`, the byte at offset `b` in
+///   `t` is initialized, then the byte at offset `b` within `*ptr` must be
 ///   initialized.
-/// - Let `c` be the contents of the byte range `[0, b)` in `*ptr`. Let `S` be
-///   the subset of valid instances of `T` of length `len` which contain `c` in
-///   the offset range `[0, b)`. If, in any instance of `t: T` in `S`, the byte
-///   at offset `b` in `t` is initialized, then the byte at offset `b` in `*ptr`
-///   must be initialized.
+/// - Let `c` be the contents of the byte range `[0, b)` in `*ptr`. Let `S`
+///   be the subset of valid instances of `T` of length `len` which contain
+///   `c` in the offset range `[0, b)`. If, in any instance of `t: T` in
+///   `S`, the byte at offset `b` in `t` is initialized, then the byte at
+///   offset `b` in `*ptr` must be initialized.
 ///
-///   Pragmatically, this means that if `*ptr` is guaranteed to contain an enum
-///   type at a particular offset, and the enum discriminant stored in `*ptr`
-///   corresponds to a valid variant of that enum type, then it is guaranteed
-///   that the appropriate bytes of `*ptr` are initialized as defined by that
-///   variant's bit validity (although note that the variant may contain another
-///   enum type, in which case the same rules apply depending on the state of
-///   its discriminant, and so on recursively).
+///   Pragmatically, this means that if `*ptr` is guaranteed to contain an
+///   enum type at a particular offset, and the enum discriminant stored in
+///   `*ptr` corresponds to a valid variant of that enum type, then it is
+///   guaranteed that the appropriate bytes of `*ptr` are initialized as
+///   defined by that variant's bit validity (although note that the variant
+///   may contain another enum type, in which case the same rules apply
+///   depending on the state of its discriminant, and so on recursively).
 pub enum AsInitialized {}
 impl Validity for AsInitialized {}
 

src/pointer/ptr.rs

@@ -416,9 +416,7 @@ mod _conversions {
     {
         /// Converts a `Ptr` an unaligned `T` into a `Ptr` to an aligned
         /// `Unalign<T>`.
-        pub(crate) fn into_unalign(
-            self,
-        ) -> Ptr<'a, crate::Unalign<T>, (I::Aliasing, Aligned, I::Validity)> {
+        pub(crate) fn into_unalign(self) -> Ptr<'a, crate::Unalign<T>, I::WithAlignment<Aligned>> {
             // SAFETY:
             // - This cast preserves provenance.
             // - This cast preserves address. `Unalign<T>` promises to have the
@@ -436,7 +434,7 @@ mod _conversions {
             // SAFETY: `Unalign<T>` promises to have alignment 1, and so it is
             // trivially aligned.
             let ptr = unsafe { ptr.assume_alignment::<Aligned>() };
-            ptr
+            ptr.unify_invariants()
         }
     }
 }
@@ -461,7 +459,7 @@ mod _transitions {
         #[inline]
         pub(crate) fn into_exclusive_or_post_monomorphization_error(
             self,
-        ) -> Ptr<'a, T, (Exclusive, I::Alignment, I::Validity)> {
+        ) -> Ptr<'a, T, I::WithAliasing<Exclusive>> {
             // NOTE(https://github.com/rust-lang/rust/issues/131625): We do this
             // rather than just having `Aliasing::IS_EXCLUSIVE` have the panic
             // behavior because doing it that way causes rustdoc to fail while
@@ -521,7 +519,7 @@ mod _transitions {
         #[inline]
         pub(crate) const unsafe fn assume_aliasing<A: Aliasing>(
             self,
-        ) -> Ptr<'a, T, (A, I::Alignment, I::Validity)> {
+        ) -> Ptr<'a, T, I::WithAliasing<A>> {
             // SAFETY: The caller promises that `self` satisfies the aliasing
             // requirements of `A`.
             unsafe { self.assume_invariants() }
@@ -538,7 +536,7 @@ mod _transitions {
         #[inline]
         pub(crate) const unsafe fn assume_exclusive(
             self,
-        ) -> Ptr<'a, T, (Exclusive, I::Alignment, I::Validity)> {
+        ) -> Ptr<'a, T, I::WithAliasing<Exclusive>> {
             // SAFETY: The caller promises that `self` satisfies the aliasing
             // requirements of `Exclusive`.
             unsafe { self.assume_aliasing::<Exclusive>() }
@@ -554,7 +552,7 @@ mod _transitions {
         #[inline]
         pub(crate) const unsafe fn assume_alignment<A: Alignment>(
             self,
-        ) -> Ptr<'a, T, (I::Aliasing, A, I::Validity)> {
+        ) -> Ptr<'a, T, I::WithAlignment<A>> {
             // SAFETY: The caller promises that `self`'s referent is
             // well-aligned for `T` if required by `A` .
             unsafe { self.assume_invariants() }
@@ -564,7 +562,7 @@ mod _transitions {
         /// on success.
         pub(crate) fn bikeshed_try_into_aligned(
             self,
-        ) -> Result<Ptr<'a, T, (I::Aliasing, Aligned, I::Validity)>, AlignmentError<Self, T>>
+        ) -> Result<Ptr<'a, T, I::WithAlignment<Aligned>>, AlignmentError<Self, T>>
         where
             T: Sized,
         {
@@ -582,9 +580,7 @@ mod _transitions {
         #[inline]
         // TODO(#859): Reconsider the name of this method before making it
         // public.
-        pub(crate) const fn bikeshed_recall_aligned(
-            self,
-        ) -> Ptr<'a, T, (I::Aliasing, Aligned, I::Validity)>
+        pub(crate) const fn bikeshed_recall_aligned(self) -> Ptr<'a, T, I::WithAlignment<Aligned>>
         where
             T: crate::Unaligned,
         {
@@ -603,9 +599,7 @@ mod _transitions {
         #[doc(hidden)]
         #[must_use]
         #[inline]
-        pub const unsafe fn assume_validity<V: Validity>(
-            self,
-        ) -> Ptr<'a, T, (I::Aliasing, I::Alignment, V)> {
+        pub const unsafe fn assume_validity<V: Validity>(self) -> Ptr<'a, T, I::WithValidity<V>> {
             // SAFETY: The caller promises that `self`'s referent conforms to
             // the validity requirement of `V`.
             unsafe { self.assume_invariants() }
@@ -620,9 +614,7 @@ mod _transitions {
         #[doc(hidden)]
         #[must_use]
         #[inline]
-        pub const unsafe fn assume_initialized(
-            self,
-        ) -> Ptr<'a, T, (I::Aliasing, I::Alignment, Initialized)> {
+        pub const unsafe fn assume_initialized(self) -> Ptr<'a, T, I::WithValidity<Initialized>> {
             // SAFETY: The caller has promised to uphold the safety
             // preconditions.
             unsafe { self.assume_validity::<Initialized>() }
@@ -637,7 +629,7 @@ mod _transitions {
         #[doc(hidden)]
         #[must_use]
         #[inline]
-        pub const unsafe fn assume_valid(self) -> Ptr<'a, T, (I::Aliasing, I::Alignment, Valid)> {
+        pub const unsafe fn assume_valid(self) -> Ptr<'a, T, I::WithValidity<Valid>> {
             // SAFETY: The caller has promised to uphold the safety
             // preconditions.
             unsafe { self.assume_validity::<Valid>() }
@@ -649,7 +641,7 @@ mod _transitions {
         #[inline]
         // TODO(#859): Reconsider the name of this method before making it
         // public.
-        pub const fn bikeshed_recall_valid(self) -> Ptr<'a, T, (I::Aliasing, I::Alignment, Valid)>
+        pub const fn bikeshed_recall_valid(self) -> Ptr<'a, T, I::WithValidity<Valid>>
         where
             T: crate::FromBytes,
             I: Invariants<Validity = Initialized>,
@@ -676,7 +668,7 @@ mod _transitions {
         #[inline]
         pub(crate) fn try_into_valid(
             mut self,
-        ) -> Result<Ptr<'a, T, (I::Aliasing, I::Alignment, Valid)>, ValidityError<Self, T>>
+        ) -> Result<Ptr<'a, T, I::WithValidity<Valid>>, ValidityError<Self, T>>
         where
             T: TryFromBytes,
             I::Aliasing: Reference,
@@ -685,7 +677,7 @@ mod _transitions {
             // 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
             // fix before returning.
-            if T::is_bit_valid(self.reborrow().forget_aligned()) {
+            if T::is_bit_valid(self.reborrow().forget_aligned().unify_invariants()) {
                 // SAFETY: If `T::is_bit_valid`, code may assume that `self`
                 // contains a bit-valid instance of `Self`.
                 Ok(unsafe { self.assume_valid() })
@@ -698,7 +690,7 @@ mod _transitions {
         #[doc(hidden)]
         #[must_use]
         #[inline]
-        pub const fn forget_aligned(self) -> Ptr<'a, T, (I::Aliasing, Any, I::Validity)> {
+        pub const fn forget_aligned(self) -> Ptr<'a, T, I::WithAlignment<Any>> {
             // SAFETY: `Any` is less restrictive than `Aligned`.
             unsafe { self.assume_invariants() }
         }