Allow canonicalizing the `array::map` loop in trusted cases

2 files changed, 12 insertions, 1 deletions

diff --git a/library/core/src/slice/iter.rs b/library/core/src/slice/iter.rs
index 90ab43d1289..c4317799bcc 100644
--- a/library/core/src/slice/iter.rs
+++ b/library/core/src/slice/iter.rs
@@ -7,7 +7,9 @@ use crate::cmp;
 use crate::cmp::Ordering;
 use crate::fmt;
 use crate::intrinsics::assume;
-use crate::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
+use crate::iter::{
+    FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce, UncheckedIterator,
+};
 use crate::marker::{PhantomData, Send, Sized, Sync};
 use crate::mem::{self, SizedTypeProperties};
 use crate::num::NonZeroUsize;
diff --git a/library/core/src/slice/iter/macros.rs b/library/core/src/slice/iter/macros.rs
index 0fd57b197aa..89b92a7d597 100644
--- a/library/core/src/slice/iter/macros.rs
+++ b/library/core/src/slice/iter/macros.rs
@@ -384,6 +384,15 @@ macro_rules! iterator {
 
         #[unstable(feature = "trusted_len", issue = "37572")]
         unsafe impl<T> TrustedLen for $name<'_, T> {}
+
+        impl<'a, T> UncheckedIterator for $name<'a, T> {
+            unsafe fn next_unchecked(&mut self) -> $elem {
+                // SAFETY: The caller promised there's at least one more item.
+                unsafe {
+                    next_unchecked!(self)
+                }
+            }
+        }
     }
 }