hide binary_heap::IntoIter internals behind impl Trait

library/alloc/src/collections/binary_heap.rs

@@ -1175,7 +1175,7 @@ impl<T> FusedIterator for IntoIter<T> {}
 
 #[unstable(issue = "0", feature = "inplace_iteration")]
 unsafe impl<T> SourceIter for IntoIter<T> {
-    type Source = crate::vec::IntoIter<T>;
+    type Source = impl Iterator<Item = T>;
 
     #[inline]
     fn as_inner(&mut self) -> &mut Self::Source {

library/alloc/src/lib.rs

@@ -136,6 +136,7 @@
 #![feature(maybe_uninit_extra, maybe_uninit_slice)]
 #![feature(alloc_layout_extra)]
 #![feature(try_trait)]
+#![feature(type_alias_impl_trait)]
 #![feature(associated_type_bounds)]
 // Allow testing this library