impl TrustedRandomAccess for ArrayWindows

(cherry picked from commit 129d552d3f)

library/core/src/slice/iter.rs

@@ -2232,6 +2232,14 @@ impl<'a, T, const N: usize> Iterator for ArrayWindows<'a, T, N> {
     fn last(self) -> Option<Self::Item> {
         self.v.last_chunk()
     }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        // SAFETY: since the caller guarantees that `idx` is in bounds,
+        // which means that `idx` cannot overflow an `isize`, and the
+        // "slice" created by `cast_array` is a subslice of `self.v`
+        // thus is guaranteed to be valid for the lifetime `'a` of `self.v`.
+        unsafe { &*self.v.as_ptr().add(idx).cast_array() }
+    }
 }
 
 #[stable(feature = "array_windows", since = "1.94.0")]
@@ -2266,6 +2274,16 @@ unsafe impl<T, const N: usize> TrustedLen for ArrayWindows<'_, T, N> {}
 #[stable(feature = "array_windows", since = "1.94.0")]
 impl<T, const N: usize> FusedIterator for ArrayWindows<'_, T, N> {}
 
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<T, const N: usize> TrustedRandomAccess for ArrayWindows<'_, T, N> {}
+
+#[doc(hidden)]
+#[unstable(feature = "trusted_random_access", issue = "none")]
+unsafe impl<T, const N: usize> TrustedRandomAccessNoCoerce for ArrayWindows<'_, T, N> {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
 /// An iterator over a slice in (non-overlapping) chunks (`chunk_size` elements at a
 /// time), starting at the end of the slice.
 ///