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, 12 insertions, 7 deletions

diff --git a/src/components/script/dom/htmlbrelement.rs b/src/components/script/dom/htmlbrelement.rs
index 1cf175468ae..bb1e57a2370 100644
--- a/src/components/script/dom/htmlbrelement.rs
+++ b/src/components/script/dom/htmlbrelement.rs
@@ -5,7 +5,7 @@
 use dom::bindings::codegen::BindingDeclarations::HTMLBRElementBinding;
 use dom::bindings::codegen::InheritTypes::HTMLBRElementDerived;
 use dom::bindings::error::ErrorResult;
-use dom::bindings::js::JS;
+use dom::bindings::js::{JSRef, Temporary};
 use dom::document::Document;
 use dom::element::HTMLBRElementTypeId;
 use dom::eventtarget::{EventTarget, NodeTargetTypeId};
@@ -28,24 +28,29 @@ impl HTMLBRElementDerived for EventTarget {
 }
 
 impl HTMLBRElement {
-    pub fn new_inherited(localName: DOMString, document: JS<Document>) -> HTMLBRElement {
+    pub fn new_inherited(localName: DOMString, document: &JSRef<Document>) -> HTMLBRElement {
         HTMLBRElement {
             htmlelement: HTMLElement::new_inherited(HTMLBRElementTypeId, localName, document)
         }
     }
 
-    pub fn new(localName: DOMString, document: &JS<Document>) -> JS<HTMLBRElement> {
-        let element = HTMLBRElement::new_inherited(localName, document.clone());
+    pub fn new(localName: DOMString, document: &JSRef<Document>) -> Temporary<HTMLBRElement> {
+        let element = HTMLBRElement::new_inherited(localName, document);
         Node::reflect_node(~element, document, HTMLBRElementBinding::Wrap)
     }
 }
 
-impl HTMLBRElement {
-    pub fn Clear(&self) -> DOMString {
+pub trait HTMLBRElementMethods {
+    fn Clear(&self) -> DOMString;
+    fn SetClear(&mut self, _text: DOMString) -> ErrorResult;
+}
+
+impl<'a> HTMLBRElementMethods for JSRef<'a, HTMLBRElement> {
+    fn Clear(&self) -> DOMString {
         ~""
     }
 
-    pub fn SetClear(&mut self, _text: DOMString) -> ErrorResult {
+    fn SetClear(&mut self, _text: DOMString) -> ErrorResult {
         Ok(())
     }
 }