VecDeque: fix for stacked borrows

src/liballoc/collections/vec_deque.rs

@@ -1026,7 +1026,10 @@ impl<T> VecDeque<T> {
             iter: Iter {
                 tail: drain_tail,
                 head: drain_head,
-                ring: unsafe { self.buffer_as_mut_slice() },
+                // Crucially, we only create shared references from `self` here and read from
+                // it.  We do not write to `self` nor reborrow to a mutable reference.
+                // Hence the raw pointer we created above, for `deque`, remains valid.
+                ring: unsafe { self.buffer_as_slice() },
             },
         }
     }

src/libcore/ptr.rs

@@ -2815,14 +2815,14 @@ impl<T: ?Sized> fmt::Pointer for Unique<T> {
 #[unstable(feature = "ptr_internals", issue = "0")]
 impl<'a, T: ?Sized> From<&'a mut T> for Unique<T> {
     fn from(reference: &'a mut T) -> Self {
-        Unique { pointer: unsafe { NonZero(reference as _) }, _marker: PhantomData }
+        Unique { pointer: unsafe { NonZero(reference as *mut T) }, _marker: PhantomData }
     }
 }
 
 #[unstable(feature = "ptr_internals", issue = "0")]
 impl<'a, T: ?Sized> From<&'a T> for Unique<T> {
     fn from(reference: &'a T) -> Self {
-        Unique { pointer: unsafe { NonZero(reference as _) }, _marker: PhantomData }
+        Unique { pointer: unsafe { NonZero(reference as *const T) }, _marker: PhantomData }
     }
 }
 
@@ -3025,14 +3025,14 @@ impl<T: ?Sized> From<Unique<T>> for NonNull<T> {
 impl<'a, T: ?Sized> From<&'a mut T> for NonNull<T> {
     #[inline]
     fn from(reference: &'a mut T) -> Self {
-        NonNull { pointer: unsafe { NonZero(reference as _) } }
+        NonNull { pointer: unsafe { NonZero(reference as *mut T) } }
     }
 }
 
 #[stable(feature = "nonnull", since = "1.25.0")]
 impl<'a, T: ?Sized> From<&'a T> for NonNull<T> {
     #[inline]
     fn from(reference: &'a T) -> Self {
-        NonNull { pointer: unsafe { NonZero(reference as _) } }
+        NonNull { pointer: unsafe { NonZero(reference as *const T) } }
     }
 }