Implement in-place iteratation markers for iter::{Copied, Cloned}

library/alloc/tests/vec.rs

@@ -1166,10 +1166,14 @@ fn test_from_iter_partially_drained_in_place_specialization() {
 #[test]
 fn test_from_iter_specialization_with_iterator_adapters() {
     fn assert_in_place_trait<T: InPlaceIterable>(_: &T) {}
-    let src: Vec<usize> = vec![0usize; 256];
+    let owned: Vec<usize> = vec![0usize; 256];
+    let refd: Vec<&usize> = owned.iter().collect();
+    let src: Vec<&&usize> = refd.iter().collect();
     let srcptr = src.as_ptr();
     let iter = src
         .into_iter()
+        .copied()
+        .cloned()
         .enumerate()
         .map(|i| i.0 + i.1)
         .zip(std::iter::repeat(1usize))
@@ -1180,7 +1184,7 @@ fn test_from_iter_specialization_with_iterator_adapters() {
     assert_in_place_trait(&iter);
     let sink = iter.collect::<Result<Vec<_>, _>>().unwrap();
     let sinkptr = sink.as_ptr();
-    assert_eq!(srcptr, sinkptr as *const usize);
+    assert_eq!(srcptr as *const usize, sinkptr as *const usize);
 }
 
 #[test]

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

@@ -1,8 +1,9 @@
 use crate::iter::adapters::{
-    zip::try_get_unchecked, TrustedRandomAccess, TrustedRandomAccessNoCoerce,
+    zip::try_get_unchecked, SourceIter, TrustedRandomAccess, TrustedRandomAccessNoCoerce,
 };
-use crate::iter::{FusedIterator, TrustedLen, UncheckedIterator};
+use crate::iter::{FusedIterator, InPlaceIterable, TrustedLen, UncheckedIterator};
 use crate::ops::Try;
+use core::num::NonZeroUsize;
 
 /// An iterator that clones the elements of an underlying iterator.
 ///
@@ -167,3 +168,23 @@ impl<I: Default> Default for Cloned<I> {
         Self::new(Default::default())
     }
 }
+
+#[unstable(issue = "none", feature = "inplace_iteration")]
+unsafe impl<I> SourceIter for Cloned<I>
+where
+    I: SourceIter,
+{
+    type Source = I::Source;
+
+    #[inline]
+    unsafe fn as_inner(&mut self) -> &mut I::Source {
+        // SAFETY: unsafe function forwarding to unsafe function with the same requirements
+        unsafe { SourceIter::as_inner(&mut self.it) }
+    }
+}
+
+#[unstable(issue = "none", feature = "inplace_iteration")]
+unsafe impl<I: InPlaceIterable> InPlaceIterable for Cloned<I> {
+    const EXPAND_BY: Option<NonZeroUsize> = I::EXPAND_BY;
+    const MERGE_BY: Option<NonZeroUsize> = I::MERGE_BY;
+}

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

@@ -1,7 +1,7 @@
 use crate::iter::adapters::{
-    zip::try_get_unchecked, TrustedRandomAccess, TrustedRandomAccessNoCoerce,
+    zip::try_get_unchecked, SourceIter, TrustedRandomAccess, TrustedRandomAccessNoCoerce,
 };
-use crate::iter::{FusedIterator, TrustedLen};
+use crate::iter::{FusedIterator, InPlaceIterable, TrustedLen};
 use crate::mem::MaybeUninit;
 use crate::mem::SizedTypeProperties;
 use crate::num::NonZeroUsize;
@@ -255,3 +255,23 @@ impl<I: Default> Default for Copied<I> {
         Self::new(Default::default())
     }
 }
+
+#[unstable(issue = "none", feature = "inplace_iteration")]
+unsafe impl<I> SourceIter for Copied<I>
+where
+    I: SourceIter,
+{
+    type Source = I::Source;
+
+    #[inline]
+    unsafe fn as_inner(&mut self) -> &mut I::Source {
+        // SAFETY: unsafe function forwarding to unsafe function with the same requirements
+        unsafe { SourceIter::as_inner(&mut self.it) }
+    }
+}
+
+#[unstable(issue = "none", feature = "inplace_iteration")]
+unsafe impl<I: InPlaceIterable> InPlaceIterable for Copied<I> {
+    const EXPAND_BY: Option<NonZeroUsize> = I::EXPAND_BY;
+    const MERGE_BY: Option<NonZeroUsize> = I::MERGE_BY;
+}