Update collect.rs

Author: HernandoR

library/core/src/iter/traits/collect.rs

@@ -154,6 +154,8 @@ pub trait FromIterator<A>: Sized {
 
 // implement `FromIterator` for type with Default and Extend
 impl<T, A: Default + Extend<T>> FromIterator<T> for A {
+    #[unstable(issue = "58659")]
+    #[rustc_diagnostic_item = "default_from_iter_fn"]
     default fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
         let mut collection = A::default();
         collection.extend(iter);