Rollup merge of #34136 - imjacobclark:ice-test-case-25579, r=nikomatsakis

Test case for borrowk ICE #25579

r? @nikomatsakis

Fixes #25579

src/test/compile-fail/issue-25579.rs

@@ -0,0 +1,27 @@
+// 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.
+
+enum Sexpression {
+    Num(()),
+    Cons(&'static mut Sexpression)
+}
+
+fn causes_ice(mut l: &mut Sexpression) {
+    loop { match l {
+        &mut Sexpression::Num(ref mut n) => {},
+        &mut Sexpression::Cons(ref mut expr) => { //~ ERROR cannot borrow `l.0`
+            //~| ERROR cannot borrow `l.0`
+            l = &mut **expr; //~ ERROR cannot assign to `l`
+        }
+    }}
+}
+
+fn main() {
+}