Cache the first base element with an href attribute on the Document.

components/script/dom/document.rs

@@ -155,6 +155,8 @@ pub struct Document {
     current_parser: MutNullableHeap<JS<ServoHTMLParser>>,
     /// When we should kick off a reflow. This happens during parsing.
     reflow_timeout: Cell<Option<u64>>,
+    /// The cached first `base` element with an `href` attribute.
+    base_element: MutNullableHeap<JS<HTMLBaseElement>>,
 }
 
 impl PartialEq for Document {
@@ -241,6 +243,8 @@ pub trait DocumentHelpers<'a> {
     fn base_url(self) -> Url;
     /// Returns the first `base` element in the DOM that has an `href` attribute.
     fn base_element(self) -> Option<Root<HTMLBaseElement>>;
+    /// Refresh the cached first base element in the DOM.
+    fn refresh_base_element(self);
     fn quirks_mode(self) -> QuirksMode;
     fn set_quirks_mode(self, mode: QuirksMode);
     fn set_encoding_name(self, name: DOMString);
@@ -370,11 +374,17 @@ impl<'a> DocumentHelpers<'a> for &'a Document {
 
     /// Returns the first `base` element in the DOM that has an `href` attribute.
     fn base_element(self) -> Option<Root<HTMLBaseElement>> {
-        NodeCast::from_ref(self)
+        self.base_element.get().map(Root::from_rooted)
+    }
+
+    /// Refresh the cached first base element in the DOM.
+    fn refresh_base_element(self) {
+        let base = NodeCast::from_ref(self)
             .traverse_preorder()
             .filter_map(HTMLBaseElementCast::to_root)
             .filter(|element| ElementCast::from_ref(&**element).has_attribute(&atom!("href")))
-            .next()
+            .next();
+        self.base_element.set(base.map(|element| JS::from_ref(&*element)));
     }
 
     fn quirks_mode(self) -> QuirksMode {
@@ -1131,6 +1141,7 @@ impl Document {
             loader: DOMRefCell::new(doc_loader),
             current_parser: Default::default(),
             reflow_timeout: Cell::new(None),
+            base_element: Default::default(),
         }
     }
 

components/script/dom/htmlbaseelement.rs

@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use dom::attr::AttrHelpers;
+use dom::attr::{Attr, AttrHelpers};
 use dom::bindings::codegen::Bindings::HTMLBaseElementBinding;
 use dom::bindings::codegen::InheritTypes::ElementCast;
 use dom::bindings::codegen::InheritTypes::HTMLBaseElementDerived;
@@ -55,10 +55,52 @@ impl HTMLBaseElement {
         let parsed = UrlParser::new().base_url(&base).parse(&href.value());
         parsed.unwrap_or(base)
     }
+
+    /// Update the cached base element in response to adding or removing an
+    /// attribute.
+    pub fn add_remove_attr(&self, attr: &Attr) {
+        if *attr.local_name() == atom!("href") {
+            let document = document_from_node(self);
+            document.refresh_base_element();
+        }
+    }
+
+    /// Update the cached base element in response to binding or unbinding from
+    /// a tree.
+    pub fn bind_unbind(&self, tree_in_doc: bool) {
+        if !tree_in_doc {
+            return;
+        }
+
+        if ElementCast::from_ref(self).has_attribute(&atom!("href")) {
+            let document = document_from_node(self);
+            document.refresh_base_element();
+        }
+    }
 }
 
 impl<'a> VirtualMethods for &'a HTMLBaseElement {
     fn super_type<'b>(&'b self) -> Option<&'b VirtualMethods> {
         Some(HTMLElementCast::from_borrowed_ref(self) as &VirtualMethods)
     }
+
+    fn after_set_attr(&self, attr: &Attr) {
+        self.super_type().unwrap().after_set_attr(attr);
+        self.add_remove_attr(attr);
+    }
+
+    fn before_remove_attr(&self, attr: &Attr) {
+        self.super_type().unwrap().before_remove_attr(attr);
+        self.add_remove_attr(attr);
+    }
+
+    fn bind_to_tree(&self, tree_in_doc: bool) {
+        self.super_type().unwrap().bind_to_tree(tree_in_doc);
+        self.bind_unbind(tree_in_doc);
+    }
+
+    fn unbind_from_tree(&self, tree_in_doc: bool) {
+        self.super_type().unwrap().unbind_from_tree(tree_in_doc);
+        self.bind_unbind(tree_in_doc);
+    }
 }