Add test for #4666, which didn't *quite* seem to be covered by

existing tests. The bug itself was fixed as part of recent borrowck
reform.

Fixes #4666.

src/test/run-pass/borrowck-scope-of-deref-issue-4666.rs

@@ -0,0 +1,50 @@
+// Copyright 2012-2013 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.
+
+// Tests that the scope of the pointer returned from `get()` is
+// limited to the deref operation itself, and does not infect the
+// block as a whole.
+
+struct Box {
+    x: uint
+}
+
+impl Box {
+    fn get<'a>(&'a self) -> &'a uint {
+        &self.x
+    }
+    fn set(&mut self, x: uint) {
+        self.x = x;
+    }
+}
+
+fn fun1() {
+    // in the past, borrow checker behaved differently when
+    // init and decl of `v` were distinct
+    let v;
+    let mut box = Box {x: 0};
+    box.set(22);
+    v = *box.get();
+    box.set(v+1);
+    assert_eq!(23, *box.get());
+}
+
+fn fun2() {
+    let mut box = Box {x: 0};
+    box.set(22);
+    let v = *box.get();
+    box.set(v+1);
+    assert_eq!(23, *box.get());
+}
+
+pub fn main() {
+    fun1();
+    fun2();
+}