Add test for #25439

Closes #25439.

src/test/run-pass/issue-25439.rs

@@ -0,0 +1,19 @@
+// Copyright 2015 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.
+
+struct Helper<'a, F: 'a>(&'a F);
+
+fn fix<F>(f: F) -> i32 where F: Fn(Helper<F>, i32) -> i32 {
+    f(Helper(&f), 8)
+}
+
+fn main() {
+    fix(|_, x| x);
+}