Add diagnostic item for std::iter::Enumerate

Author: CBSpeir

core/src/iter/adapters/enumerate.rs

@@ -15,6 +15,7 @@ use crate::ops::Try;
 #[derive(Clone, Debug)]
 #[must_use = "iterators are lazy and do nothing unless consumed"]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "Enumerate")]
 pub struct Enumerate<I> {
     iter: I,
     count: usize,