Auto merge of #18641 - servo:ROOT-ALL-THE-THINGS, r=SimonSapin

Improve DomRoot<T>

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components/script/dom/bindings/refcounted.rs

@@ -22,7 +22,6 @@
 //! its hash table during the next GC. During GC, the entries of the hash table are counted
 //! as JS roots.
 
-use core::nonzero::NonZero;
 use dom::bindings::conversions::ToJSValConvertible;
 use dom::bindings::error::Error;
 use dom::bindings::reflector::{DomObject, Reflector};
@@ -185,7 +184,7 @@ impl<T: DomObject> Trusted<T> {
             self.owner_thread == (&*live_references) as *const _ as *const libc::c_void
         }));
         unsafe {
-            DomRoot::new(NonZero::new_unchecked(self.refcount.0 as *const T))
+            DomRoot::from_ref(&*(self.refcount.0 as *const T))
         }
     }
 }

components/script/dom/bindings/root.rs

@@ -558,10 +558,11 @@ pub unsafe fn trace_roots(tracer: *mut JSTracer) {
 /// are additive, so this object's destruction will not invalidate other roots
 /// for the same JS value. `Root`s cannot outlive the associated
 /// `RootCollection` object.
+#[allow(unrooted_must_root)]
 #[allow_unrooted_interior]
 pub struct DomRoot<T: DomObject> {
     /// Reference to rooted value that must not outlive this container
-    ptr: NonZero<*const T>,
+    ptr: Dom<T>,
     /// List that ensures correct dynamic root ordering
     root_list: *const RootCollection,
 }
@@ -591,11 +592,12 @@ impl<T: DomObject> DomRoot<T> {
     /// Create a new stack-bounded root for the provided JS-owned value.
     /// It cannot outlive its associated `RootCollection`, and it gives
     /// out references which cannot outlive this new `Root`.
-    pub fn new(unrooted: NonZero<*const T>) -> DomRoot<T> {
+    #[allow(unrooted_must_root)]
+    unsafe fn new(unrooted: Dom<T>) -> DomRoot<T> {
         debug_assert!(thread_state::get().is_script());
         STACK_ROOTS.with(|ref collection| {
             let RootCollectionPtr(collection) = collection.get().unwrap();
-            unsafe { (*collection).root(&*(*unrooted.get()).reflector()) }
+            (*collection).root(unrooted.reflector());
             DomRoot {
                 ptr: unrooted,
                 root_list: collection,
@@ -605,7 +607,7 @@ impl<T: DomObject> DomRoot<T> {
 
     /// Generate a new root from a reference
     pub fn from_ref(unrooted: &T) -> DomRoot<T> {
-        DomRoot::new(unsafe { NonZero::new_unchecked(unrooted) })
+        unsafe { DomRoot::new(Dom::from_ref(unrooted)) }
     }
 }
 
@@ -620,7 +622,7 @@ impl<T: DomObject> Deref for DomRoot<T> {
     type Target = T;
     fn deref(&self) -> &T {
         debug_assert!(thread_state::get().is_script());
-        unsafe { &*self.ptr.get() }
+        &self.ptr
     }
 }
 

components/script/dom/bindings/weakref.rs

@@ -86,7 +86,9 @@ impl<T: WeakReferenceable> WeakRef<T> {
 
     /// DomRoot a weak reference. Returns `None` if the object was already collected.
     pub fn root(&self) -> Option<DomRoot<T>> {
-        unsafe { &*self.ptr.get() }.value.get().map(DomRoot::new)
+        unsafe { &*self.ptr.get() }.value.get().map(|ptr| unsafe {
+            DomRoot::from_ref(&*ptr.get())
+        })
     }
 
     /// Return whether the weakly-referenced object is still alive.