bring back some lost Freezes

Author: RalfJung

library/alloc/src/rc.rs

@@ -318,7 +318,7 @@ pub struct Rc<
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
 > {
     ptr: NonNull<RcBox<T>>,
-    phantom: PhantomData<RcBox<T>>,
+    phantom: PhantomData<Box<RcBox<T>>>,
     alloc: A,
 }
 
@@ -3400,7 +3400,7 @@ fn data_offset_align(align: usize) -> usize {
 #[derive(Debug)]
 pub struct UniqueRc<T> {
     ptr: NonNull<RcBox<T>>,
-    phantom: PhantomData<RcBox<T>>,
+    phantom: PhantomData<Box<RcBox<T>>>,
 }
 
 impl<T> UniqueRc<T> {

library/alloc/src/sync.rs

@@ -251,7 +251,7 @@ pub struct Arc<
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
 > {
     ptr: NonNull<ArcInner<T>>,
-    phantom: PhantomData<ArcInner<T>>,
+    phantom: PhantomData<Box<ArcInner<T>>>,
     alloc: A,
 }
 

library/core/src/ptr/unique.rs

@@ -1,6 +1,6 @@
 use crate::convert::From;
 use crate::fmt;
-use crate::marker::{PhantomData, Unsize};
+use crate::marker::{Freeze, PhantomData, Unsize};
 use crate::ops::{CoerceUnsized, DispatchFromDyn};
 use crate::ptr::NonNull;
 
@@ -58,6 +58,10 @@ unsafe impl<T: Send + ?Sized> Send for Unique<T> {}
 #[unstable(feature = "ptr_internals", issue = "none")]
 unsafe impl<T: Sync + ?Sized> Sync for Unique<T> {}
 
+/// `Unique` pointers are always `Freeze` since any interior mutability that might exist in `T` is
+/// masked by the pointer indirection.
+unsafe impl<T: ?Sized> Freeze for Unique<T> {}
+
 #[unstable(feature = "ptr_internals", issue = "none")]
 impl<T: Sized> Unique<T> {
     /// Creates a new `Unique` that is dangling, but well-aligned.