1 files changed, 6 insertions, 0 deletions
diff --git a/library/core/src/iter/adapters/flatten.rs b/library/core/src/iter/adapters/flatten.rs
index 520ec9abcf0..2568aaf34f3 100644
--- a/library/core/src/iter/adapters/flatten.rs
+++ b/library/core/src/iter/adapters/flatten.rs
@@ -310,6 +310,7 @@ where
 /// Real logic of both `Flatten` and `FlatMap` which simply delegate to
 /// this type.
 #[derive(Clone, Debug)]
+#[unstable(feature = "trusted_len", issue = "37572")]
 struct FlattenCompat<I, U> {
     iter: Fuse<I>,
     frontiter: Option<U>,
@@ -463,6 +464,7 @@ where
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
 impl<I, U> Iterator for FlattenCompat<I, U>
 where
     I: Iterator<Item: IntoIterator<IntoIter = U, Item = U::Item>>,
@@ -577,6 +579,7 @@ where
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
 impl<I, U> DoubleEndedIterator for FlattenCompat<I, U>
 where
     I: DoubleEndedIterator<Item: IntoIterator<IntoIter = U, Item = U::Item>>,
@@ -646,6 +649,7 @@ where
     }
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
 unsafe impl<const N: usize, I, T> TrustedLen
     for FlattenCompat<I, <[T; N] as IntoIterator>::IntoIter>
 where
@@ -653,6 +657,7 @@ where
 {
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
 unsafe impl<'a, const N: usize, I, T> TrustedLen
     for FlattenCompat<I, <&'a [T; N] as IntoIterator>::IntoIter>
 where
@@ -660,6 +665,7 @@ where
 {
 }
 
+#[unstable(feature = "trusted_len", issue = "37572")]
 unsafe impl<'a, const N: usize, I, T> TrustedLen
     for FlattenCompat<I, <&'a mut [T; N] as IntoIterator>::IntoIter>
 where