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/htmldataelement.rs b/src/components/script/dom/htmldataelement.rs
index e242be54d9d..26090be7632 100644
--- a/src/components/script/dom/htmldataelement.rs
+++ b/src/components/script/dom/htmldataelement.rs
@@ -4,7 +4,7 @@
 
 use dom::bindings::codegen::BindingDeclarations::HTMLDataElementBinding;
 use dom::bindings::codegen::InheritTypes::HTMLDataElementDerived;
-use dom::bindings::js::JS;
+use dom::bindings::js::{JSRef, Temporary};
 use dom::bindings::error::ErrorResult;
 use dom::document::Document;
 use dom::element::HTMLDataElementTypeId;
@@ -28,24 +28,29 @@ impl HTMLDataElementDerived for EventTarget {
 }
 
 impl HTMLDataElement {
-    pub fn new_inherited(localName: DOMString, document: JS<Document>) -> HTMLDataElement {
+    pub fn new_inherited(localName: DOMString, document: &JSRef<Document>) -> HTMLDataElement {
         HTMLDataElement {
             htmlelement: HTMLElement::new_inherited(HTMLDataElementTypeId, localName, document)
         }
     }
 
-    pub fn new(localName: DOMString, document: &JS<Document>) -> JS<HTMLDataElement> {
-        let element = HTMLDataElement::new_inherited(localName, document.clone());
+    pub fn new(localName: DOMString, document: &JSRef<Document>) -> Temporary<HTMLDataElement> {
+        let element = HTMLDataElement::new_inherited(localName, document);
         Node::reflect_node(~element, document, HTMLDataElementBinding::Wrap)
     }
 }
 
-impl HTMLDataElement {
-    pub fn Value(&self) -> DOMString {
+pub trait HTMLDataElementMethods {
+    fn Value(&self) -> DOMString;
+    fn SetValue(&mut self, _value: DOMString) -> ErrorResult;
+}
+
+impl<'a> HTMLDataElementMethods for JSRef<'a, HTMLDataElement> {
+    fn Value(&self) -> DOMString {
         ~""
     }
 
-    pub fn SetValue(&mut self, _value: DOMString) -> ErrorResult {
+    fn SetValue(&mut self, _value: DOMString) -> ErrorResult {
         Ok(())
     }
 }