move AsIntoIter helper trait and mark it as unsafe

library/alloc/src/collections/binary_heap.rs

@@ -1416,7 +1416,7 @@ unsafe impl<T> SourceIter for IntoIter<T> {
 #[doc(hidden)]
 unsafe impl<I> InPlaceIterable for IntoIter<I> {}
 
-impl<I> AsIntoIter for IntoIter<I> {
+unsafe impl<I> AsIntoIter for IntoIter<I> {
     type Item = I;
 
     fn as_into_iter(&mut self) -> &mut vec::IntoIter<Self::Item> {

library/alloc/src/vec/in_place_collect.rs

@@ -2,7 +2,7 @@ use core::iter::{InPlaceIterable, SourceIter, TrustedRandomAccessNoCoerce};
 use core::mem::{self, ManuallyDrop};
 use core::ptr::{self};
 
-use super::{AsIntoIter, InPlaceDrop, SpecFromIter, SpecFromIterNested, Vec};
+use super::{InPlaceDrop, SpecFromIter, SpecFromIterNested, Vec};
 
 /// Specialization marker for collecting an iterator pipeline into a Vec while reusing the
 /// source allocation, i.e. executing the pipeline in place.
@@ -154,3 +154,10 @@ where
         len
     }
 }
+
+// internal helper trait for in-place iteration specialization.
+#[rustc_specialization_trait]
+pub(crate) unsafe trait AsIntoIter {
+    type Item;
+    fn as_into_iter(&mut self) -> &mut super::IntoIter<Self::Item>;
+}

library/alloc/src/vec/into_iter.rs

@@ -1,3 +1,5 @@
+#[cfg(not(no_global_oom_handling))]
+use super::AsIntoIter;
 use crate::alloc::{Allocator, Global};
 use crate::raw_vec::RawVec;
 use core::fmt;
@@ -338,14 +340,8 @@ unsafe impl<T, A: Allocator> SourceIter for IntoIter<T, A> {
     }
 }
 
-// internal helper trait for in-place iteration specialization.
-#[rustc_specialization_trait]
-pub(crate) trait AsIntoIter {
-    type Item;
-    fn as_into_iter(&mut self) -> &mut IntoIter<Self::Item>;
-}
-
-impl<T> AsIntoIter for IntoIter<T> {
+#[cfg(not(no_global_oom_handling))]
+unsafe impl<T> AsIntoIter for IntoIter<T> {
     type Item = T;
 
     fn as_into_iter(&mut self) -> &mut IntoIter<Self::Item> {

library/alloc/src/vec/mod.rs

@@ -96,7 +96,7 @@ mod drain;
 mod cow;
 
 #[cfg(not(no_global_oom_handling))]
-pub(crate) use self::into_iter::AsIntoIter;
+pub(crate) use self::in_place_collect::AsIntoIter;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::into_iter::IntoIter;