5 files changed, 25 insertions, 6 deletions
diff --git a/components/script/Cargo.toml b/components/script/Cargo.toml
index 4730eeeb18a..c9edde464ee 100644
--- a/components/script/Cargo.toml
+++ b/components/script/Cargo.toml
@@ -62,7 +62,7 @@ metrics = {path = "../metrics"}
 mitochondria = "1.1.2"
 mime = "0.2.1"
 mime_guess = "1.8.0"
-mozjs = { version = "0.3", features = ["promises"]}
+mozjs = { version = "0.4", features = ["promises"]}
 msg = {path = "../msg"}
 net_traits = {path = "../net_traits"}
 num-traits = "0.1.32"
diff --git a/components/script/dom/bindings/reflector.rs b/components/script/dom/bindings/reflector.rs
index 0fef0a30678..97d88cb4357 100644
--- a/components/script/dom/bindings/reflector.rs
+++ b/components/script/dom/bindings/reflector.rs
@@ -46,7 +46,8 @@ impl Reflector {
     /// Get the reflector.
     #[inline]
     pub fn get_jsobject(&self) -> HandleObject {
-        self.object.handle()
+        // We're rooted, so it's safe to hand out a handle to object in Heap
+        unsafe { self.object.handle() }
     }
 
     /// Initialize the reflector. (May be called only once.)
diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 423b053cbbf..be38b14a540 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -59,9 +59,9 @@ use hyper::mime::Mime;
 use hyper::status::StatusCode;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
 use js::glue::{CallObjectTracer, CallValueTracer};
-use js::jsapi::{GCTraceKindToAscii, Heap, JSObject, JSTracer, TraceKind};
+use js::jsapi::{GCTraceKindToAscii, Heap, Handle, JSObject, JSTracer, TraceKind};
 use js::jsval::JSVal;
-use js::rust::Runtime;
+use js::rust::{GCMethods, Runtime};
 use js::typedarray::TypedArray;
 use js::typedarray::TypedArrayElement;
 use metrics::{InteractiveMetrics, InteractiveWindow};
@@ -788,6 +788,16 @@ impl<T: JSTraceable + 'static> RootedTraceableBox<T> {
     }
 }
 
+impl<T> RootedTraceableBox<Heap<T>>
+    where
+        Heap<T>: JSTraceable + 'static,
+        T: GCMethods + Copy,
+{
+    pub fn handle(&self) -> Handle<T> {
+        unsafe { (*self.ptr).handle() }
+    }
+}
+
 impl<T: JSTraceable + Default> Default for RootedTraceableBox<T> {
     fn default() -> RootedTraceableBox<T> {
         RootedTraceableBox::new(T::default())
diff --git a/components/script/dom/customelementregistry.rs b/components/script/dom/customelementregistry.rs
index a208f99def6..123b0bef2cb 100644
--- a/components/script/dom/customelementregistry.rs
+++ b/components/script/dom/customelementregistry.rs
@@ -604,7 +604,8 @@ impl CustomElementReaction {
         match *self {
             CustomElementReaction::Upgrade(ref definition) => upgrade_element(definition.clone(), element),
             CustomElementReaction::Callback(ref callback, ref arguments) => {
-                let arguments = arguments.iter().map(|arg| arg.handle()).collect();
+                // We're rooted, so it's safe to hand out a handle to objects in Heap
+                let arguments = arguments.iter().map(|arg| unsafe { arg.handle() }).collect();
                 let _ = callback.Call_(&*element, arguments, ExceptionHandling::Report);
             }
         }
diff --git a/components/script/timers.rs b/components/script/timers.rs
index 4bc4bf37fff..a5e7020095f 100644
--- a/components/script/timers.rs
+++ b/components/script/timers.rs
@@ -500,7 +500,7 @@ impl JsTimerTask {
                     code_str, rval.handle_mut());
             },
             InternalTimerCallback::FunctionTimerCallback(ref function, ref arguments) => {
-                let arguments = arguments.iter().map(|arg| arg.handle()).collect();
+                let arguments = self.collect_heap_args(arguments);
                 let _ = function.Call_(this, arguments, Report);
             },
         };
@@ -516,4 +516,11 @@ impl JsTimerTask {
             timers.initialize_and_schedule(&this.global(), self);
         }
     }
+
+    // Returning Handles directly from Heap values is inherently unsafe, but here it's
+    // always done via rooted JsTimers, which is safe.
+    #[allow(unsafe_code)]
+    fn collect_heap_args(&self, args: &[Heap<JSVal>]) -> Vec<HandleValue> {
+        args.iter().map(|arg| unsafe { arg.handle() }).collect()
+    }
 }