add regression test for #52057

Fixes #52057

Author: nikomatsakis

src/test/ui/issue-52057.rs

@@ -0,0 +1,35 @@
+// Copyright 2016 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.
+
+// Regression test for #52057. There is an implied bound
+// that `I: 'a` where `'a` is the lifetime of `self` in `parse_first`;
+// but to observe that, one must normalize first.
+//
+// run-pass
+
+#![feature(nll)]
+
+pub trait Parser {
+    type Input;
+
+    #[inline(always)]
+    fn parse_first(input: &mut Self::Input);
+}
+
+impl<'a, I, P: ?Sized> Parser for &'a mut P
+where
+    P: Parser<Input = I>,
+{
+    type Input = I;
+
+    fn parse_first(_: &mut Self::Input) {}
+}
+
+fn main() {}