AutoVector exposes [Mutable]Handle through operator[]. Given that [Mutable]TraceableVectorOperations is only used via Rooted primitives, I think it is safe to add such there as well. Once we do that (and fix up the AutoShapeVector usage), converting from AutoPropertyDescriptorVector to Rooted<TraceableVector<PropertyDescriptor>> is as trivial as changing the names.

Comment on attachment 8642498 [details] [diff] [review] auto_propdesc_vec-v1.diff Review of attachment 8642498 [details] [diff] [review]: ----------------------------------------------------------------- Looks good! ::: js/public/TraceableVector.h @@ +96,5 @@ > T& back() { return vec().back(); } > > + JS::MutableHandle<T> operator[](size_t aIndex) { > + return JS::MutableHandle<T>::fromMarkedLocation(&vec().operator[](aIndex)); > + } You may need to add the const version here as well, as per bug 1189722.