Added test for #45697

Author: davidtwco

src/test/ui/issue-45697.rs

@@ -0,0 +1,35 @@
+// 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.
+
+// Test that assignments to an `&mut` pointer which is found in a
+// borrowed (but otherwise non-aliasable) location is illegal.
+
+// compile-flags: -Z emit-end-regions -Z borrowck=compare
+
+struct S<'a> {
+    pointer: &'a mut isize
+}
+
+fn copy_borrowed_ptr<'a>(p: &'a mut S<'a>) -> S<'a> {
+    S { pointer: &mut *p.pointer }
+}
+
+fn main() {
+    let mut x = 1;
+
+    {
+        let mut y = S { pointer: &mut x };
+        let z = copy_borrowed_ptr(&mut y);
+        *y.pointer += 1;
+        //~^ ERROR cannot assign to `*y.pointer` because it is borrowed (Ast) [E0506]
+        //~| ERROR cannot assign to `*y.pointer` because it is borrowed (Mir) [E0506]
+        *z.pointer += 1;
+    }
+}

src/test/ui/issue-45697.stderr

@@ -0,0 +1,18 @@
+error[E0506]: cannot assign to `*y.pointer` because it is borrowed (Ast)
+  --> $DIR/issue-45697.rs:30:9
+   |
+29 |         let z = copy_borrowed_ptr(&mut y);
+   |                                        - borrow of `*y.pointer` occurs here
+30 |         *y.pointer += 1;
+   |         ^^^^^^^^^^^^^^^ assignment to borrowed `*y.pointer` occurs here
+
+error[E0506]: cannot assign to `*y.pointer` because it is borrowed (Mir)
+  --> $DIR/issue-45697.rs:30:9
+   |
+29 |         let z = copy_borrowed_ptr(&mut y);
+   |                                   ------ borrow of `*y.pointer` occurs here
+30 |         *y.pointer += 1;
+   |         ^^^^^^^^^^^^^^^ assignment to borrowed `*y.pointer` occurs here
+
+error: aborting due to 2 previous errors
+