Make Node::is_in_doc O(1)

Added a flags variable inside Node to represent boolean flags, with
is_in_doc being the first of them. It is updated whenever a node is
appended or removed from a parent.

This patch is for:
https://github.com/mozilla/servo/issues/1030

src/components/script/dom/node.rs

@@ -91,6 +91,9 @@ pub struct Node<View> {
     /// The live list of children return by .childNodes.
     child_list: Option<@mut NodeList>,
 
+    /// A bitfield of flags for node items.
+    priv flags: NodeFlags,
+
     /// Layout information. Only the layout task may touch this data.
     ///
     /// FIXME(pcwalton): We need to send these back to the layout task to be destroyed when this
@@ -98,6 +101,23 @@ pub struct Node<View> {
     layout_data: LayoutDataRef,
 }
 
+/// Flags for node items.
+pub struct NodeFlags(u8);
+
+impl NodeFlags {
+    pub fn new(type_id: NodeTypeId) -> NodeFlags {
+        let mut flags = NodeFlags(0);
+        match type_id {
+            DocumentNodeTypeId(_) => { flags.set_is_in_doc(true); }
+            _ => {}
+        }
+        flags
+    }
+}
+
+/// Specifies whether this node is in a document.
+bitfield!(NodeFlags, is_in_doc, set_is_in_doc, 0x01)
+
 #[unsafe_destructor]
 impl<T> Drop for Node<T> {
     fn drop(&mut self) {
@@ -546,9 +566,8 @@ impl<'self, View> AbstractNode<View> {
         self.node().children()
     }
 
-    // Issue #1030: should not walk the tree
     pub fn is_in_doc(&self) -> bool {
-        self.ancestors().any(|node| node.is_document())
+        self.node().flags.is_in_doc()
     }
 }
 
@@ -649,6 +668,8 @@ impl Node<ScriptView> {
             owner_doc: doc,
             child_list: None,
 
+            flags: NodeFlags::new(type_id),
+
             layout_data: LayoutDataRef::init(),
         }
     }
@@ -1002,6 +1023,7 @@ impl Node<ScriptView> {
         // Step 8.
         for node in nodes.iter() {
             parent.add_child(*node, child);
+            node.mut_node().flags.set_is_in_doc(parent.is_in_doc());
         }
 
         // Step 9.
@@ -1080,6 +1102,7 @@ impl Node<ScriptView> {
         // Step 6-7: mutation observers.
         // Step 8.
         parent.remove_child(node);
+        node.mut_node().flags.set_is_in_doc(false);
 
         // Step 9.
         if !suppress_observers {

src/components/script/macros.rs

@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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/. */
+
+#[macro_escape];
+
+macro_rules! bitfield(
+    ($bitfieldname:ident, $getter:ident, $setter:ident, $value:expr) => (
+        impl $bitfieldname {
+            #[inline]
+            pub fn $getter(self) -> bool {
+                (*self & $value) != 0
+            }
+
+            #[inline]
+            pub fn $setter(&mut self, value: bool) {
+                *self = $bitfieldname((**self & !$value) | (if value { $value } else { 0 }))
+            }
+        }
+    )
+)
+

src/components/script/script.rc

@@ -23,6 +23,9 @@ extern mod style;
 extern mod servo_msg (name = "msg");
 extern mod extra;
 
+// Macros
+mod macros;
+
 pub mod dom {
     pub mod bindings {
         pub mod element;