auto merge of #2101 : jdm/servo/newroot_rebase, r=Ms2ger

As described in #1764, this strategy uses the following properties:
* DOM members are `JS<T>` types. These cannot be used with being explicitly rooted, but they are required for compiler-derived trace hooks.
* Methods that take DOM type arguments receive `&[mut] JSRef<T>`. These are rooted value references that are cloneable but cannot escape.
* Methods that return DOM values use `Unrooted<T>`. These are values that may or may not be rooted elsewhere, but callers must root them in order to interact with them in any way. One unsoundness hole exists - `Unrooted` values must be rooted ASAP, or there exists the danger that JSAPI calls could be made that could cause the underlying JS value to be GCed.
* All methods are implemented on `JSRef<T>`, enforcing the requirement that all DOM values are rooted for the duration of a method call (with a few exceptions for layout-related code, which cannot root values and therefore interacts with `JS<T>` and `&T` values - this is safe under the assumption that layout code interacts with DOM nodes that are in the tree, therefore rooted, and does not run concurrently with content code)

1 files changed, 19 insertions, 11 deletions

diff --git a/src/components/script/dom/attrlist.rs b/src/components/script/dom/attrlist.rs
index cfa6c2c083f..e707a42b13f 100644
--- a/src/components/script/dom/attrlist.rs
+++ b/src/components/script/dom/attrlist.rs
@@ -4,7 +4,7 @@
 
 use dom::attr::Attr;
 use dom::bindings::codegen::BindingDeclarations::AttrListBinding;
-use dom::bindings::js::JS;
+use dom::bindings::js::{JS, JSRef, Temporary};
 use dom::bindings::utils::{Reflectable, Reflector, reflect_dom_object};
 use dom::element::Element;
 use dom::window::Window;
@@ -17,28 +17,36 @@ pub struct AttrList {
 }
 
 impl AttrList {
-    pub fn new_inherited(window: JS<Window>, elem: JS<Element>) -> AttrList {
+    pub fn new_inherited(window: &JSRef<Window>, elem: &JSRef<Element>) -> AttrList {
         AttrList {
             reflector_: Reflector::new(),
-            window: window,
-            owner: elem
+            window: window.unrooted(),
+            owner: elem.unrooted(),
         }
     }
 
-    pub fn new(window: &JS<Window>, elem: &JS<Element>) -> JS<AttrList> {
-        reflect_dom_object(~AttrList::new_inherited(window.clone(), elem.clone()),
+    pub fn new(window: &JSRef<Window>, elem: &JSRef<Element>) -> Temporary<AttrList> {
+        reflect_dom_object(~AttrList::new_inherited(window, elem),
                            window, AttrListBinding::Wrap)
     }
+}
+
+pub trait AttrListMethods {
+    fn Length(&self) -> u32;
+    fn Item(&self, index: u32) -> Option<Temporary<Attr>>;
+    fn IndexedGetter(&self, index: u32, found: &mut bool) -> Option<Temporary<Attr>>;
+}
 
-    pub fn Length(&self) -> u32 {
-        self.owner.get().attrs.len() as u32
+impl<'a> AttrListMethods for JSRef<'a, AttrList> {
+    fn Length(&self) -> u32 {
+        self.owner.root().attrs.len() as u32
     }
 
-    pub fn Item(&self, index: u32) -> Option<JS<Attr>> {
-        self.owner.get().attrs.as_slice().get(index as uint).map(|x| x.clone())
+    fn Item(&self, index: u32) -> Option<Temporary<Attr>> {
+        self.owner.root().attrs.as_slice().get(index as uint).map(|x| Temporary::new(x.clone()))
     }
 
-    pub fn IndexedGetter(&self, index: u32, found: &mut bool) -> Option<JS<Attr>> {
+    fn IndexedGetter(&self, index: u32, found: &mut bool) -> Option<Temporary<Attr>> {
         let item = self.Item(index);
         *found = item.is_some();
         item