Test that reborrowing contents of an &'a mut &'b mut pointer can only

be done for at most lifetime `'a`

Fixes #8624

src/test/compile-fail/regions-reborrow-from-shorter-mut-ref-mut-ref.rs

@@ -0,0 +1,18 @@
+// Copyright 2012 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.
+
+// Issue #8624. Test for reborrowing with 3 levels, not just two.
+
+fn copy_borrowed_ptr<'a, 'b, 'c>(p: &'a mut &'b mut &'c mut int) -> &'b mut int {
+    &mut ***p //~ ERROR cannot infer an appropriate lifetime
+}
+
+fn main() {
+}

src/test/compile-fail/regions-reborrow-from-shorter-mut-ref.rs

@@ -0,0 +1,25 @@
+// Copyright 2012 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.
+
+// Issue #8624. Tests that reborrowing the contents of an `&'b mut`
+// pointer which is backed by another `&'a mut` can only be done
+// for `'a` (which must be a sublifetime of `'b`).
+
+fn copy_borrowed_ptr<'a, 'b>(p: &'a mut &'b mut int) -> &'b mut int {
+    &mut **p //~ ERROR lifetime of `p` is too short
+}
+
+fn main() {
+    let mut x = 1;
+    let mut y = &mut x;
+    let z = copy_borrowed_ptr(&mut y);
+    *y += 1;
+    *z += 1;
+}