remove InPlaceIterable marker from Peekable due to unsoundness

library/alloc/benches/vec.rs

@@ -468,7 +468,6 @@ fn bench_in_place_recycle(b: &mut Bencher) {
                 .enumerate()
                 .map(|(idx, e)| idx.wrapping_add(e))
                 .fuse()
-                .peekable()
                 .collect::<Vec<usize>>(),
         );
     });

library/alloc/tests/vec.rs

@@ -1002,7 +1002,6 @@ fn test_from_iter_specialization_with_iterator_adapters() {
         .zip(std::iter::repeat(1usize))
         .map(|(a, b)| a + b)
         .map_while(Option::Some)
-        .peekable()
         .skip(1)
         .map(|e| if e != usize::MAX { Ok(std::num::NonZeroUsize::new(e)) } else { Err(()) });
     assert_in_place_trait(&iter);
@@ -1095,6 +1094,18 @@ fn test_from_iter_specialization_panic_during_drop_leaks() {
     }
 }
 
+// regression test for issue #85322. Peekable previously implemented InPlaceIterable,
+// but due to an interaction with IntoIter's current Clone implementation it failed to uphold
+// the contract.
+#[test]
+fn test_collect_after_iterator_clone() {
+    let v = vec![0; 5];
+    let mut i = v.into_iter().map(|i| i + 1).peekable();
+    i.peek();
+    let v = i.clone().collect::<Vec<_>>();
+    assert_eq!(v, [1, 1, 1, 1, 1]);
+    assert!(v.len() <= v.capacity());
+}
 #[test]
 fn test_cow_from() {
     let borrowed: &[_] = &["borrowed", "(slice)"];

library/core/src/iter/adapters/peekable.rs

@@ -1,4 +1,4 @@
-use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable, TrustedLen};
+use crate::iter::{adapters::SourceIter, FusedIterator, TrustedLen};
 use crate::ops::{ControlFlow, Try};
 
 /// An iterator with a `peek()` that returns an optional reference to the next
@@ -356,6 +356,3 @@ where
         unsafe { SourceIter::as_inner(&mut self.iter) }
     }
 }
-
-#[unstable(issue = "none", feature = "inplace_iteration")]
-unsafe impl<I: InPlaceIterable> InPlaceIterable for Peekable<I> {}