Implement Clone for @ and @mut types.

The borrowck-borrow-from-expr-block test had to be updated. I'm not sure why
it compiled before since ~int was already clonable.

src/libcore/clone.rs

@@ -36,6 +36,16 @@ impl<T:Clone> Clone for ~T {
     fn clone(&self) -> ~T { ~(**self).clone() }
 }
 
+impl<T:Clone> Clone for @T {
+    #[inline(always)]
+    fn clone(&self) -> @T { @(**self).clone() }
+}
+
+impl<T:Clone> Clone for @mut T {
+    #[inline(always)]
+    fn clone(&self) -> @mut T { @mut (**self).clone() }
+}
+
 macro_rules! clone_impl(
     ($t:ty) => {
         impl Clone for $t {

src/test/run-pass/borrowck-borrow-from-expr-block.rs

@@ -13,7 +13,7 @@ fn borrow(x: &int, f: &fn(x: &int)) {
 }
 
 fn test1(x: @~int) {
-    do borrow(&*x.clone()) |p| {
+    do borrow(&**x.clone()) |p| {
         let x_a = ptr::addr_of(&(**x));
         assert!((x_a as uint) != ptr::to_uint(p));
         assert!(unsafe{*x_a} == *p);

src/test/run-pass/clones.rs

@@ -0,0 +1,27 @@
+// 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.
+
+fn main() {
+    let a : ~int = ~5i;
+    let b : ~int = a.clone();
+
+    debug!(fmt!("a: %?, b: %?", a, b));
+
+    let a : @int = @5i;
+    let b : @int = a.clone();
+
+    debug!(fmt!("a: %?, b: %?", a, b));
+
+    let a : @mut int = @mut 5i;
+    let b : @mut int = a.clone();
+    *b = 6;
+
+    debug!(fmt!("a: %?, b: %?", a, b));
+}