Rollup merge of #51358 - barzamin:tests-39963, r=oli-obk

Tests that #39963 is fixed on MIR borrowck

As title.

fixes #39963

src/test/run-pass/borrowck/borrowck-multiple-borrows-interior-boxes.rs

@@ -0,0 +1,29 @@
+// 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.
+
+// Test case from #39963.
+
+#![feature(nll)]
+
+#[derive(Clone)]
+struct Foo(Option<Box<Foo>>, Option<Box<Foo>>);
+
+fn test(f: &mut Foo) {
+  match *f {
+    Foo(Some(ref mut left), Some(ref mut right)) => match **left {
+      Foo(Some(ref mut left), Some(ref mut right)) => panic!(),
+      _ => panic!(),
+    },
+    _ => panic!(),
+  }
+}
+
+fn main() {
+}