1 files changed, 77 insertions, 0 deletions
diff --git a/tests/ui/delegation/generics/impl-trait-to-trait-method-pass.rs b/tests/ui/delegation/generics/impl-trait-to-trait-method-pass.rs
new file mode 100644
index 00000000000..72440fe82d4
--- /dev/null
+++ b/tests/ui/delegation/generics/impl-trait-to-trait-method-pass.rs
@@ -0,0 +1,77 @@
+//@ run-pass
+
+#![feature(fn_delegation)]
+#![allow(incomplete_features)]
+
+use std::iter::{Iterator, Map};
+
+pub mod same_trait {
+    use super::*;
+
+    pub struct MapOuter<I, F> {
+        pub inner: Map<I, F>
+    }
+
+    impl<B, I: Iterator, F> Iterator for MapOuter<I, F>
+    where
+        F: FnMut(I::Item) -> B,
+    {
+        type Item = <Map<I, F> as Iterator>::Item;
+
+        reuse Iterator::{next, fold} { self.inner }
+    }
+}
+use same_trait::MapOuter;
+
+mod another_trait {
+    use super::*;
+
+    trait ZipImpl<A, B> {
+        type Item;
+
+        fn next(&mut self) -> Option<Self::Item>;
+    }
+
+    pub struct Zip<A, B> {
+        pub a: A,
+        pub b: B,
+    }
+
+    impl<A: Iterator, B: Iterator> ZipImpl<A, B> for Zip<A, B> {
+        type Item = (A::Item, B::Item);
+
+        fn next(&mut self) -> Option<(A::Item, B::Item)> {
+            let x = self.a.next()?;
+            let y = self.b.next()?;
+            Some((x, y))
+        }
+    }
+
+    impl<A: Iterator, B: Iterator> Iterator for Zip<A, B> {
+        type Item = (A::Item, B::Item);
+
+        // Parameters are inherited from `Iterator::next`, not from `ZipImpl::next`.
+        // Otherwise, there would be a compilation error due to an unconstrained parameter.
+        reuse ZipImpl::next;
+    }
+}
+use another_trait::Zip;
+
+fn main() {
+    {
+        let x = vec![1, 2, 3];
+        let iter = x.iter().map(|val| val * 2);
+        let outer_iter = MapOuter { inner: iter };
+        let val = outer_iter.fold(0, |acc, x| acc + x);
+        assert_eq!(val, 12);
+    }
+
+    {
+        let x = vec![1, 2];
+        let y = vec![4, 5];
+
+        let mut zip = Zip { a: x.iter(), b: y.iter() };
+        assert_eq!(zip.next(), Some((&1, &4)));
+        assert_eq!(zip.next(), Some((&2, &5)));
+    }
+}