As determined in #39766, RootedVec<JSVal> is not a safe construct; GC values that live in heap memory need to stored in Heap wrappers, which enforces the correct barriers. However, it also isn't safe to use RootedVec<Heap<JSVal>> in case the underlying vector moves in memory during resizing.

This is a problem for code that is using a RootedVec to safely create a HandleValueArray; I think we need an alternative RootedArray which is a fixed size with inline memory and can be used with the rooted! macro. We should then remove the ability to create a HandleValueArray from a RootedVec and lint against RootedVec<JSVal>.

Existing uses that I've found:

• servo/components/script/dom/defaultteeunderlyingsource.rs

  Lines 199 to 201 in cbff958

  	rooted_vec!(let mut reasons_values);
  	reasons_values.push(self.reason_1.get());
  	reasons_values.push(self.reason_2.get());

• servo/components/script/dom/paintworkletglobalscope.rs

  Lines 315 to 319 in cbff958

  	rooted_vec!(let mut arguments_values);
  	for argument in arguments {
  	let style_value = CSSStyleValue::new(self.upcast(), argument.clone(), can_gc);
  	arguments_values.push(ObjectValue(style_value.reflector().get_jsobject().get()));
  	}

• servo/components/script/dom/paintworkletglobalscope.rs

  Lines 323 to 329 in cbff958

  	rooted_vec!(let mut callback_args);
  	callback_args.push(ObjectValue(
  	rendering_context.reflector().get_jsobject().get(),
  	));
  	callback_args.push(ObjectValue(paint_size.reflector().get_jsobject().get()));
  	callback_args.push(ObjectValue(properties.reflector().get_jsobject().get()));
  	callback_args.push(ObjectValue(argument_object.get()));

• servo/components/script/indexed_db.rs

  Line 70 in cbff958

  rooted_vec!(let mut values <- repeat_n(UndefinedValue(), a.len()));