add regression test for #52078

Fixes #52078

Author: nikomatsakis

src/test/ui/nll/issue-52078.rs

@@ -0,0 +1,37 @@
+// Copyright 2017 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.
+
+#![feature(nll)]
+#![allow(unused_variables)]
+
+// Regression test for #52078: we were failing to infer a relationship
+// between `'a` and `'b` below due to inference variables introduced
+// during the normalization process.
+//
+// compile-pass
+
+struct Drain<'a, T: 'a> {
+    _marker: ::std::marker::PhantomData<&'a T>,
+}
+
+trait Join {
+    type Value;
+    fn get(value: &mut Self::Value);
+}
+
+impl<'a, T> Join for Drain<'a, T> {
+    type Value = &'a mut Option<T>;
+
+    fn get<'b>(value: &'b mut Self::Value) {
+    }
+}
+
+fn main() {
+}