rollup merge of #21392: japaric/iter

closes #20953
closes #21361

---

In the future, we will likely derive these `impl`s via syntax extensions or using compiler magic (see #20617). For the time being we can use these manual `impl`s.

r? @aturon
cc @burntsushi @Kroisse

2 files changed, 17 insertions, 0 deletions

diff --git a/src/liballoc/boxed.rs b/src/liballoc/boxed.rs
index a2cc98c7d01..92ac41e2058 100644
--- a/src/liballoc/boxed.rs
+++ b/src/liballoc/boxed.rs
@@ -18,6 +18,7 @@ use core::cmp::{PartialEq, PartialOrd, Eq, Ord, Ordering};
 use core::default::Default;
 use core::fmt;
 use core::hash::{self, Hash};
+use core::iter::Iterator;
 use core::marker::Sized;
 use core::mem;
 use core::option::Option;
@@ -187,6 +188,20 @@ impl<T: ?Sized> DerefMut for Box<T> {
     fn deref_mut(&mut self) -> &mut T { &mut **self }
 }
 
+// FIXME(#21363) remove `old_impl_check` when bug is fixed
+#[old_impl_check]
+impl<'a, T> Iterator for Box<Iterator<Item=T> + 'a> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<T> {
+        (**self).next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (**self).size_hint()
+    }
+}
+
 #[cfg(test)]
 mod test {
     #[test]
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 811e32e747d..47715fe9e5d 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -70,6 +70,8 @@
 #![feature(lang_items, unsafe_destructor)]
 #![feature(box_syntax)]
 #![feature(optin_builtin_traits)]
+// FIXME(#21363) remove `old_impl_check` when bug is fixed
+#![feature(old_impl_check)]
 #![allow(unknown_features)] #![feature(int_uint)]
 
 #[macro_use]