Add on_unimplemented note to Index

diff --git a/src/libcore/ops.rs b/src/libcore/ops.rs
index 372596cdd44ecfb3c30c5be0e7ec974f00c80c39..002c04f852ac2475f0d6c3935b6d417c0b19d721 100644 (file)
--- a/src/libcore/ops.rs
+++ b/src/libcore/ops.rs
@@ -895,6 +895,7 @@ macro_rules! shr_impl_all {
 /// }
 /// ```
 #[lang="index"]
+#[rustc_on_unimplemented = "the type `{Self}` cannot be indexed by `{Index}`"]
 #[stable]
 pub trait Index<Index: ?Sized> {
     type Output: ?Sized;
@@ -933,6 +934,7 @@ pub trait Index<Index: ?Sized> {
 /// }
 /// ```
 #[lang="index_mut"]
+#[rustc_on_unimplemented = "the type `{Self}` cannot be mutably indexed by `{Index}`"]
 #[stable]
 pub trait IndexMut<Index: ?Sized> {
     type Output: ?Sized;