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, 23 insertions, 10 deletions

diff --git a/src/components/script/dom/characterdata.rs b/src/components/script/dom/characterdata.rs
index f85246ee12c..2a41e1fee3b 100644
--- a/src/components/script/dom/characterdata.rs
+++ b/src/components/script/dom/characterdata.rs
@@ -5,7 +5,7 @@
 //! DOM bindings for `CharacterData`.
 
 use dom::bindings::codegen::InheritTypes::CharacterDataDerived;
-use dom::bindings::js::JS;
+use dom::bindings::js::JSRef;
 use dom::bindings::error::{Fallible, ErrorResult, IndexSize};
 use dom::bindings::utils::{Reflectable, Reflector};
 use dom::document::Document;
@@ -31,44 +31,57 @@ impl CharacterDataDerived for EventTarget {
 }
 
 impl CharacterData {
-    pub fn new_inherited(id: NodeTypeId, data: DOMString, document: JS<Document>) -> CharacterData {
+    pub fn new_inherited(id: NodeTypeId, data: DOMString, document: &JSRef<Document>) -> CharacterData {
         CharacterData {
             node: Node::new_inherited(id, document),
             data: data
         }
     }
+}
+
+pub trait CharacterDataMethods {
+    fn Data(&self) -> DOMString;
+    fn SetData(&mut self, arg: DOMString) -> ErrorResult;
+    fn Length(&self) -> u32;
+    fn SubstringData(&self, offset: u32, count: u32) -> Fallible<DOMString>;
+    fn AppendData(&mut self, arg: DOMString) -> ErrorResult;
+    fn InsertData(&mut self, _offset: u32, _arg: DOMString) -> ErrorResult;
+    fn DeleteData(&mut self, _offset: u32, _count: u32) -> ErrorResult;
+    fn ReplaceData(&mut self, _offset: u32, _count: u32, _arg: DOMString) -> ErrorResult;
+}
 
-    pub fn Data(&self) -> DOMString {
+impl<'a> CharacterDataMethods for JSRef<'a, CharacterData> {
+    fn Data(&self) -> DOMString {
         self.data.clone()
     }
 
-    pub fn SetData(&mut self, arg: DOMString) -> ErrorResult {
+    fn SetData(&mut self, arg: DOMString) -> ErrorResult {
         self.data = arg;
         Ok(())
     }
 
-    pub fn Length(&self) -> u32 {
+    fn Length(&self) -> u32 {
         self.data.len() as u32
     }
 
-    pub fn SubstringData(&self, offset: u32, count: u32) -> Fallible<DOMString> {
+    fn SubstringData(&self, offset: u32, count: u32) -> Fallible<DOMString> {
         Ok(self.data.slice(offset as uint, count as uint).to_str())
     }
 
-    pub fn AppendData(&mut self, arg: DOMString) -> ErrorResult {
+    fn AppendData(&mut self, arg: DOMString) -> ErrorResult {
         self.data.push_str(arg);
         Ok(())
     }
 
-    pub fn InsertData(&mut self, offset: u32, arg: DOMString) -> ErrorResult {
+    fn InsertData(&mut self, offset: u32, arg: DOMString) -> ErrorResult {
         self.ReplaceData(offset, 0, arg)
     }
 
-    pub fn DeleteData(&mut self, offset: u32, count: u32) -> ErrorResult {
+    fn DeleteData(&mut self, offset: u32, count: u32) -> ErrorResult {
         self.ReplaceData(offset, count, ~"")
     }
 
-    pub fn ReplaceData(&mut self, offset: u32, count: u32, arg: DOMString) -> ErrorResult {
+    fn ReplaceData(&mut self, offset: u32, count: u32, arg: DOMString) -> ErrorResult {
         let length = self.data.len() as u32;
         if offset > length {
             return Err(IndexSize);