Add unrooted_must_root lint for enums and structs containing JS<T>, as well as functions with JS<T> in their parameter list

For safe wrappers over JS<T> (eg Temporary<T>) use #[allow(unrooted_must_root)].
For all other types containing a #[must_root] value, annotate the type with #[must_root] to ensure that it is never used unrooted

components/script/dom/formdata.rs

@@ -19,12 +19,14 @@ use std::cell::RefCell;
 use std::collections::hashmap::HashMap;
 
 #[deriving(Encodable, Clone)]
+#[must_root]
 pub enum FormDatum {
     StringData(DOMString),
     FileData(JS<File>)
 }
 
 #[deriving(Encodable)]
+#[must_root]
 pub struct FormData {
     data: Traceable<RefCell<HashMap<DOMString, Vec<FormDatum>>>>,
     reflector_: Reflector,