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, 25 insertions, 15 deletions

diff --git a/src/components/script/dom/attr.rs b/src/components/script/dom/attr.rs
index 0ca2fb2889e..4822de7eb07 100644
--- a/src/components/script/dom/attr.rs
+++ b/src/components/script/dom/attr.rs
@@ -4,7 +4,7 @@
 
 use dom::bindings::codegen::BindingDeclarations::AttrBinding;
 use dom::bindings::codegen::InheritTypes::NodeCast;
-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::node::Node;
@@ -45,7 +45,7 @@ impl Reflectable for Attr {
 impl Attr {
     fn new_inherited(local_name: DOMString, value: DOMString,
                      name: DOMString, namespace: Namespace,
-                     prefix: Option<DOMString>, owner: JS<Element>) -> Attr {
+                     prefix: Option<DOMString>, owner: &JSRef<Element>) -> Attr {
         Attr {
             reflector_: Reflector::new(),
             local_name: local_name,
@@ -53,25 +53,26 @@ impl Attr {
             name: name, //TODO: Intern attribute names
             namespace: namespace,
             prefix: prefix,
-            owner: owner,
+            owner: owner.unrooted(),
         }
     }
 
-    pub fn new(window: &JS<Window>, local_name: DOMString, value: DOMString,
+    pub fn new(window: &JSRef<Window>, local_name: DOMString, value: DOMString,
                name: DOMString, namespace: Namespace,
-               prefix: Option<DOMString>, owner: JS<Element>) -> JS<Attr> {
+               prefix: Option<DOMString>, owner: &JSRef<Element>) -> Temporary<Attr> {
         let attr = Attr::new_inherited(local_name, value, name, namespace, prefix, owner);
         reflect_dom_object(~attr, window, AttrBinding::Wrap)
     }
 
     pub fn set_value(&mut self, set_type: AttrSettingType, value: DOMString) {
-        let node: JS<Node> = NodeCast::from(&self.owner);
+        let mut owner = self.owner.root();
+        let node: &mut JSRef<Node> = NodeCast::from_mut_ref(&mut *owner);
         let namespace_is_null = self.namespace == namespace::Null;
 
         match set_type {
             ReplacedAttr => {
                 if namespace_is_null {
-                    vtable_for(&node).before_remove_attr(self.local_name.clone(), self.value.clone());
+                    vtable_for(node).before_remove_attr(self.local_name.clone(), self.value.clone());
                 }
             }
             FirstSetAttr => {}
@@ -80,7 +81,7 @@ impl Attr {
         self.value = value;
 
         if namespace_is_null {
-            vtable_for(&node).after_set_attr(self.local_name.clone(), self.value.clone());
+            vtable_for(node).after_set_attr(self.local_name.clone(), self.value.clone());
         }
     }
 
@@ -89,31 +90,40 @@ impl Attr {
     }
 }
 
-impl Attr {
-    pub fn LocalName(&self) -> DOMString {
+pub trait AttrMethods {
+    fn LocalName(&self) -> DOMString;
+    fn Value(&self) -> DOMString;
+    fn SetValue(&mut self, value: DOMString);
+    fn Name(&self) -> DOMString;
+    fn GetNamespaceURI(&self) -> Option<DOMString>;
+    fn GetPrefix(&self) -> Option<DOMString>;
+}
+
+impl<'a> AttrMethods for JSRef<'a, Attr> {
+    fn LocalName(&self) -> DOMString {
         self.local_name.clone()
     }
 
-    pub fn Value(&self) -> DOMString {
+    fn Value(&self) -> DOMString {
         self.value.clone()
     }
 
-    pub fn SetValue(&mut self, value: DOMString) {
+    fn SetValue(&mut self, value: DOMString) {
         self.set_value(ReplacedAttr, value);
     }
 
-    pub fn Name(&self) -> DOMString {
+    fn Name(&self) -> DOMString {
         self.name.clone()
     }
 
-    pub fn GetNamespaceURI(&self) -> Option<DOMString> {
+    fn GetNamespaceURI(&self) -> Option<DOMString> {
         match self.namespace.to_str() {
             "" => None,
             url => Some(url.to_owned()),
         }
     }
 
-    pub fn GetPrefix(&self) -> Option<DOMString> {
+    fn GetPrefix(&self) -> Option<DOMString> {
         self.prefix.clone()
     }
 }