Add regression test for issue #30104

#30104

Author: memoryruins

src/test/ui/nll/issue-30104.rs

@@ -0,0 +1,52 @@
+// Copyright 2018 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 #30104
+
+// compile-pass
+
+#![feature(nll)]
+
+use std::ops::{Deref, DerefMut};
+
+fn box_two_field(v: &mut Box<(i32, i32)>) {
+    let _a = &mut v.0;
+    let _b = &mut v.1;
+}
+
+fn box_destructure(v: &mut Box<(i32, i32)>) {
+    let (ref mut _head, ref mut _tail) = **v;
+}
+
+struct Wrap<T>(T);
+
+impl<T> Deref for Wrap<T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        &self.0
+    }
+}
+
+impl<T> DerefMut for Wrap<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.0
+    }
+}
+
+fn smart_two_field(v: &mut Wrap<(i32, i32)>) {
+    let _a = &mut v.0;
+    let _b = &mut v.1;
+}
+
+fn smart_destructure(v: &mut Wrap<(i32, i32)>) {
+    let (ref mut _head, ref mut _tail) = **v;
+}
+
+fn main() {}