Added test for #49579.

Author: davidtwco

src/test/ui/issue-49579.rs

@@ -0,0 +1,27 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+
+// compile-pass
+
+#![feature(nll)]
+
+fn fibs(n: u32) -> impl Iterator<Item=u128> {
+    (0 .. n)
+    .scan((0, 1), |st, _| {
+        *st = (st.1, st.0 + st.1);
+        Some(*st)
+    })
+    .map(&|(f, _)| f)
+}
+
+fn main() {
+    println!("{:?}", fibs(10).collect::<Vec<_>>());
+}