library/compiler: add PointeeSized bounds

As core uses an extern type (`ptr::VTable`), the default `?Sized` to
`MetaSized` migration isn't sufficient, and some code that previously
accepted `VTable` needs relaxed to continue to accept extern types.

Similarly, the compiler uses many extern types in `rustc_codegen_llvm`
and in the `rustc_middle::ty::List` implementation (`OpaqueListContents`)
some bounds must be relaxed to continue to accept these types.

Unfortunately, due to the current inability to relax `Deref::Target`,
some of the bounds in the standard library are forced to be stricter than
they ideally would be.

Author: davidtwco

core/src/clone.rs

@@ -36,6 +36,8 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+use crate::marker::PointeeSized;
+
 mod uninit;
 
 /// A common trait that allows explicit creation of a duplicate value.
@@ -283,7 +285,7 @@ impl_use_cloned! {
     reason = "deriving hack, should not be public",
     issue = "none"
 )]
-pub struct AssertParamIsClone<T: Clone + ?Sized> {
+pub struct AssertParamIsClone<T: Clone + PointeeSized> {
     _field: crate::marker::PhantomData<T>,
 }
 #[doc(hidden)]
@@ -293,7 +295,7 @@ pub struct AssertParamIsClone<T: Clone + ?Sized> {
     reason = "deriving hack, should not be public",
     issue = "none"
 )]
-pub struct AssertParamIsCopy<T: Copy + ?Sized> {
+pub struct AssertParamIsCopy<T: Copy + PointeeSized> {
     _field: crate::marker::PhantomData<T>,
 }
 
@@ -530,6 +532,8 @@ unsafe impl CloneToUninit for crate::bstr::ByteStr {
 /// are implemented in `traits::SelectionContext::copy_clone_conditions()`
 /// in `rustc_trait_selection`.
 mod impls {
+    use crate::marker::PointeeSized;
+
     macro_rules! impl_clone {
         ($($t:ty)*) => {
             $(
@@ -560,15 +564,15 @@ mod impls {
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized> Clone for *const T {
+    impl<T: PointeeSized> Clone for *const T {
         #[inline(always)]
         fn clone(&self) -> Self {
             *self
         }
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized> Clone for *mut T {
+    impl<T: PointeeSized> Clone for *mut T {
         #[inline(always)]
         fn clone(&self) -> Self {
             *self
@@ -577,7 +581,7 @@ mod impls {
 
     /// Shared references can be cloned, but mutable references *cannot*!
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized> Clone for &T {
+    impl<T: PointeeSized> Clone for &T {
         #[inline(always)]
         #[rustc_diagnostic_item = "noop_method_clone"]
         fn clone(&self) -> Self {
@@ -587,5 +591,5 @@ mod impls {
 
     /// Shared references can be cloned, but mutable references *cannot*!
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized> !Clone for &mut T {}
+    impl<T: PointeeSized> !Clone for &mut T {}
 }

core/src/cmp.rs

@@ -29,6 +29,7 @@ mod bytewise;
 pub(crate) use bytewise::BytewiseEq;
 
 use self::Ordering::*;
+use crate::marker::PointeeSized;
 use crate::ops::ControlFlow;
 
 /// Trait for comparisons using the equality operator.
@@ -246,7 +247,7 @@ use crate::ops::ControlFlow;
     append_const_msg
 )]
 #[rustc_diagnostic_item = "PartialEq"]
-pub trait PartialEq<Rhs: ?Sized = Self> {
+pub trait PartialEq<Rhs: PointeeSized = Self>: PointeeSized {
     /// Tests for `self` and `other` values to be equal, and is used by `==`.
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -332,7 +333,7 @@ pub macro PartialEq($item:item) {
 #[doc(alias = "!=")]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "Eq"]
-pub trait Eq: PartialEq<Self> {
+pub trait Eq: PartialEq<Self> + PointeeSized {
     // this method is used solely by `impl Eq or #[derive(Eq)]` to assert that every component of a
     // type implements `Eq` itself. The current deriving infrastructure means doing this assertion
     // without using a method on this trait is nearly impossible.
@@ -361,7 +362,7 @@ pub macro Eq($item:item) {
 #[doc(hidden)]
 #[allow(missing_debug_implementations)]
 #[unstable(feature = "derive_eq", reason = "deriving hack, should not be public", issue = "none")]
-pub struct AssertParamIsEq<T: Eq + ?Sized> {
+pub struct AssertParamIsEq<T: Eq + PointeeSized> {
     _field: crate::marker::PhantomData<T>,
 }
 
@@ -954,7 +955,7 @@ impl<T: Clone> Clone for Reverse<T> {
 #[doc(alias = ">=")]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "Ord"]
-pub trait Ord: Eq + PartialOrd<Self> {
+pub trait Ord: Eq + PartialOrd<Self> + PointeeSized {
     /// This method returns an [`Ordering`] between `self` and `other`.
     ///
     /// By convention, `self.cmp(&other)` returns the ordering matching the expression
@@ -1337,7 +1338,8 @@ pub macro Ord($item:item) {
     append_const_msg
 )]
 #[rustc_diagnostic_item = "PartialOrd"]
-pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
+#[allow(multiple_supertrait_upcastable)] // FIXME(sized_hierarchy): remove this
+pub trait PartialOrd<Rhs: PointeeSized = Self>: PartialEq<Rhs> + PointeeSized {
     /// This method returns an ordering between `self` and `other` values if one exists.
     ///
     /// # Examples
@@ -1481,7 +1483,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     }
 }
 
-fn default_chaining_impl<T: ?Sized, U: ?Sized>(
+fn default_chaining_impl<T: PointeeSized, U: PointeeSized>(
     lhs: &T,
     rhs: &U,
     p: impl FnOnce(Ordering) -> bool,
@@ -1803,6 +1805,7 @@ where
 mod impls {
     use crate::cmp::Ordering::{self, Equal, Greater, Less};
     use crate::hint::unreachable_unchecked;
+    use crate::marker::PointeeSized;
     use crate::ops::ControlFlow::{self, Break, Continue};
 
     macro_rules! partial_eq_impl {
@@ -2015,7 +2018,7 @@ mod impls {
     // & pointers
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &A
+    impl<A: PointeeSized, B: PointeeSized> PartialEq<&B> for &A
     where
         A: PartialEq<B>,
     {
@@ -2029,7 +2032,7 @@ mod impls {
         }
     }
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized, B: ?Sized> PartialOrd<&B> for &A
+    impl<A: PointeeSized, B: PointeeSized> PartialOrd<&B> for &A
     where
         A: PartialOrd<B>,
     {
@@ -2071,7 +2074,7 @@ mod impls {
         }
     }
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized> Ord for &A
+    impl<A: PointeeSized> Ord for &A
     where
         A: Ord,
     {
@@ -2081,12 +2084,12 @@ mod impls {
         }
     }
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized> Eq for &A where A: Eq {}
+    impl<A: PointeeSized> Eq for &A where A: Eq {}
 
     // &mut pointers
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &mut A
+    impl<A: PointeeSized, B: PointeeSized> PartialEq<&mut B> for &mut A
     where
         A: PartialEq<B>,
     {
@@ -2100,7 +2103,7 @@ mod impls {
         }
     }
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized, B: ?Sized> PartialOrd<&mut B> for &mut A
+    impl<A: PointeeSized, B: PointeeSized> PartialOrd<&mut B> for &mut A
     where
         A: PartialOrd<B>,
     {
@@ -2142,7 +2145,7 @@ mod impls {
         }
     }
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized> Ord for &mut A
+    impl<A: PointeeSized> Ord for &mut A
     where
         A: Ord,
     {
@@ -2152,10 +2155,10 @@ mod impls {
         }
     }
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized> Eq for &mut A where A: Eq {}
+    impl<A: PointeeSized> Eq for &mut A where A: Eq {}
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized, B: ?Sized> PartialEq<&mut B> for &A
+    impl<A: PointeeSized, B: PointeeSized> PartialEq<&mut B> for &A
     where
         A: PartialEq<B>,
     {
@@ -2170,7 +2173,7 @@ mod impls {
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &mut A
+    impl<A: PointeeSized, B: PointeeSized> PartialEq<&B> for &mut A
     where
         A: PartialEq<B>,
     {

core/src/convert/mod.rs

@@ -38,6 +38,7 @@
 use crate::error::Error;
 use crate::fmt;
 use crate::hash::{Hash, Hasher};
+use crate::marker::PointeeSized;
 
 mod num;
 
@@ -215,7 +216,7 @@ pub const fn identity<T>(x: T) -> T {
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "AsRef"]
-pub trait AsRef<T: ?Sized> {
+pub trait AsRef<T: PointeeSized>: PointeeSized {
     /// Converts this type into a shared reference of the (usually inferred) input type.
     #[stable(feature = "rust1", since = "1.0.0")]
     fn as_ref(&self) -> &T;
@@ -366,7 +367,7 @@ pub trait AsRef<T: ?Sized> {
 /// `&mut Vec<u8>`, for example, is the better choice (callers need to pass the correct type then).
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "AsMut"]
-pub trait AsMut<T: ?Sized> {
+pub trait AsMut<T: PointeeSized>: PointeeSized {
     /// Converts this type into a mutable reference of the (usually inferred) input type.
     #[stable(feature = "rust1", since = "1.0.0")]
     fn as_mut(&mut self) -> &mut T;
@@ -701,7 +702,7 @@ pub trait TryFrom<T>: Sized {
 
 // As lifts over &
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized, U: ?Sized> AsRef<U> for &T
+impl<T: PointeeSized, U: PointeeSized> AsRef<U> for &T
 where
     T: AsRef<U>,
 {
@@ -713,7 +714,7 @@ where
 
 // As lifts over &mut
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized, U: ?Sized> AsRef<U> for &mut T
+impl<T: PointeeSized, U: PointeeSized> AsRef<U> for &mut T
 where
     T: AsRef<U>,
 {
@@ -733,7 +734,7 @@ where
 
 // AsMut lifts over &mut
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized, U: ?Sized> AsMut<U> for &mut T
+impl<T: PointeeSized, U: PointeeSized> AsMut<U> for &mut T
 where
     T: AsMut<U>,
 {