layout: Move the `LayoutNode` wrapper from script into layout.

13 files changed, 370 insertions, 343 deletions

diff --git a/src/components/main/css/matching.rs b/src/components/main/css/matching.rs
index efd84f36b7e..ea1b6d30a37 100644
--- a/src/components/main/css/matching.rs
+++ b/src/components/main/css/matching.rs
@@ -7,9 +7,9 @@
 use css::node_style::StyledNode;
 use layout::incremental;
 use layout::util::LayoutDataAccess;
+use layout::wrapper::LayoutNode;
 
 use extra::arc::{Arc, RWArc};
-use script::dom::node::LayoutNode;
 use std::cast;
 use std::cell::Cell;
 use std::comm;
diff --git a/src/components/main/css/node_style.rs b/src/components/main/css/node_style.rs
index 824b50e991a..6810d9187ea 100644
--- a/src/components/main/css/node_style.rs
+++ b/src/components/main/css/node_style.rs
@@ -6,10 +6,10 @@
 
 use css::node_util::NodeUtil;
 use layout::incremental::RestyleDamage;
+use layout::wrapper::LayoutNode;
 
 use extra::arc::Arc;
 use style::ComputedValues;
-use script::dom::node::LayoutNode;
 
 /// Node mixin providing `style` method that returns a `NodeStyle`
 pub trait StyledNode {
diff --git a/src/components/main/css/node_util.rs b/src/components/main/css/node_util.rs
index 72acf5dc08c..a84fb5cc061 100644
--- a/src/components/main/css/node_util.rs
+++ b/src/components/main/css/node_util.rs
@@ -4,11 +4,11 @@
 
 use layout::incremental::RestyleDamage;
 use layout::util::LayoutDataAccess;
+use layout::wrapper::LayoutNode;
 
 use extra::arc::Arc;
 use std::cast;
 use style::{ComputedValues, TNode};
-use script::dom::node::LayoutNode;
 
 pub trait NodeUtil {
     fn get_css_select_results<'a>(&'a self) -> &'a Arc<ComputedValues>;
diff --git a/src/components/main/layout/box.rs b/src/components/main/layout/box.rs
index c2dfa213c9e..70cda196fc9 100644
--- a/src/components/main/layout/box.rs
+++ b/src/components/main/layout/box.rs
@@ -15,7 +15,6 @@ use gfx::display_list::{TextDisplayItemClass, TextDisplayItemFlags, ClipDisplayI
 use gfx::display_list::{ClipDisplayItemClass};
 use gfx::font::{FontStyle, FontWeight300};
 use gfx::text::text_run::TextRun;
-use script::dom::node::LayoutNode;
 use servo_msg::constellation_msg::{FrameRectMsg, PipelineId, SubpageId};
 use servo_net::image::holder::ImageHolder;
 use servo_net::local_image_cache::LocalImageCache;
@@ -40,6 +39,7 @@ use layout::flow::Flow;
 use layout::flow;
 use layout::model::{MaybeAuto, specified};
 use layout::util::OpaqueNode;
+use layout::wrapper::LayoutNode;
 
 /// Boxes (`struct Box`) are the leaves of the layout tree. They cannot position themselves. In
 /// general, boxes do not have a simple correspondence with CSS boxes in the specification:
diff --git a/src/components/main/layout/construct.rs b/src/components/main/layout/construct.rs
index 9c6f285047e..80a8ffb8a1b 100644
--- a/src/components/main/layout/construct.rs
+++ b/src/components/main/layout/construct.rs
@@ -30,11 +30,11 @@ use layout::flow::{Flow, FlowData, MutableFlowUtils};
 use layout::inline::InlineFlow;
 use layout::text::TextRunScanner;
 use layout::util::LayoutDataAccess;
+use layout::wrapper::{LayoutNode, PostorderNodeMutTraversal};
 
 use script::dom::element::{HTMLIframeElementTypeId, HTMLImageElementTypeId};
 use script::dom::node::{CommentNodeTypeId, DoctypeNodeTypeId, DocumentFragmentNodeTypeId};
-use script::dom::node::{DocumentNodeTypeId, ElementNodeTypeId, LayoutNode};
-use script::dom::node::{PostorderNodeMutTraversal, TextNodeTypeId};
+use script::dom::node::{DocumentNodeTypeId, ElementNodeTypeId, TextNodeTypeId};
 use servo_util::slot::Slot;
 use std::util;
 use style::computed_values::{display, float};
diff --git a/src/components/main/layout/extra.rs b/src/components/main/layout/extra.rs
index bef668c6788..c17bfc4e0e4 100644
--- a/src/components/main/layout/extra.rs
+++ b/src/components/main/layout/extra.rs
@@ -5,8 +5,7 @@
 //! Code for managing the layout data in the DOM.
 
 use layout::util::{LayoutData, LayoutDataAccess};
-
-use script::dom::node::LayoutNode;
+use layout::wrapper::LayoutNode;
 
 /// Functionality useful for querying the layout-specific data on DOM nodes.
 pub trait LayoutAuxMethods {
diff --git a/src/components/main/layout/flow.rs b/src/components/main/layout/flow.rs
index 4062e13a30c..d7d1f602f29 100644
--- a/src/components/main/layout/flow.rs
+++ b/src/components/main/layout/flow.rs
@@ -33,13 +33,13 @@ use layout::display_list_builder::{DisplayListBuilder, ExtraDisplayListData};
 use layout::float_context::{FloatContext, Invalid};
 use layout::incremental::RestyleDamage;
 use layout::inline::InlineFlow;
+use layout::wrapper::LayoutNode;
 
 use extra::dlist::{DList, DListIterator, MutDListIterator};
 use extra::container::Deque;
 use geom::point::Point2D;
 use geom::rect::Rect;
 use gfx::display_list::{ClipDisplayItemClass, DisplayList};
-use script::dom::node::LayoutNode;
 use servo_util::geometry::Au;
 use std::cast;
 use std::cell::Cell;
diff --git a/src/components/main/layout/layout_task.rs b/src/components/main/layout/layout_task.rs
index 2d83e0f1a6a..8f5edcfb3ab 100644
--- a/src/components/main/layout/layout_task.rs
+++ b/src/components/main/layout/layout_task.rs
@@ -17,6 +17,7 @@ use layout::flow::{PostorderFlowTraversal};
 use layout::flow;
 use layout::incremental::{RestyleDamage};
 use layout::util::{LayoutData, LayoutDataAccess, OpaqueNode};
+use layout::wrapper::LayoutNode;
 
 use extra::arc::{Arc, RWArc, MutexArc};
 use geom::point::Point2D;
@@ -28,7 +29,7 @@ use gfx::opts::Opts;
 use gfx::render_task::{RenderMsg, RenderChan, RenderLayer};
 use gfx::{render_task, color};
 use script::dom::event::ReflowEvent;
-use script::dom::node::{AbstractNode, ElementNodeTypeId, LayoutDataRef, LayoutNode};
+use script::dom::node::{AbstractNode, ElementNodeTypeId, LayoutDataRef};
 use script::dom::element::{HTMLBodyElementTypeId, HTMLHtmlElementTypeId};
 use script::layout_interface::{AddStylesheetMsg, ContentBoxQuery};
 use script::layout_interface::{ContentBoxesQuery, ContentBoxesResponse, ExitNowMsg, LayoutQuery};
diff --git a/src/components/main/layout/text.rs b/src/components/main/layout/text.rs
index 457b014ed9c..bc3059695d6 100644
--- a/src/components/main/layout/text.rs
+++ b/src/components/main/layout/text.rs
@@ -3,15 +3,16 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 //! Text layout.
-use extra::arc::Arc;
+
 use layout::box::{Box, ScannedTextBox, ScannedTextBoxInfo, UnscannedTextBox};
 use layout::context::LayoutContext;
 use layout::flow::Flow;
 
+use extra::arc::Arc;
 use gfx::text::text_run::TextRun;
 use gfx::text::util::{CompressWhitespaceNewline, transform_text};
-use std::vec;
 use servo_util::range::Range;
+use std::vec;
 
 /// A stack-allocated object for scanning an inline flow into `TextRun`-containing `TextBox`es.
 struct TextRunScanner {
diff --git a/src/components/main/layout/util.rs b/src/components/main/layout/util.rs
index 36168117e0a..90c85acb1aa 100644
--- a/src/components/main/layout/util.rs
+++ b/src/components/main/layout/util.rs
@@ -4,9 +4,10 @@
 
 use layout::box::Box;
 use layout::construct::{ConstructionResult, NoConstructionResult};
+use layout::wrapper::LayoutNode;
 
 use extra::arc::Arc;
-use script::dom::node::{AbstractNode, LayoutNode};
+use script::dom::node::AbstractNode;
 use servo_util::range::Range;
 use servo_util::slot::{MutSlotRef, SlotRef};
 use std::cast;
diff --git a/src/components/main/layout/wrapper.rs b/src/components/main/layout/wrapper.rs
new file mode 100644
index 00000000000..0f700552300
--- /dev/null
+++ b/src/components/main/layout/wrapper.rs
@@ -0,0 +1,352 @@
+/* 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/. */
+
+//! A safe wrapper for DOM nodes that prevents layout from mutating the DOM, from letting DOM nodes
+//! escape, and from generally doing anything that it isn't supposed to. This is accomplished via
+//! a simple whitelist of allowed operations.
+//!
+//! As a security wrapper is only as good as its whitelist, be careful when adding operations to
+//! this list. The cardinal rules are:
+//!
+//! (1) Layout is not allowed to mutate the DOM.
+//!
+//! (2) Layout is not allowed to see anything with `Abstract` in the name, because it could hang
+//!     onto these objects and cause use-after-free.
+
+use extra::url::Url;
+use script::dom::element::Element;
+use script::dom::htmliframeelement::HTMLIFrameElement;
+use script::dom::htmlimageelement::HTMLImageElement;
+use script::dom::node::{AbstractNode, DocumentNodeTypeId, ElementNodeTypeId, LayoutView, Node};
+use script::dom::node::{NodeTypeId};
+use script::dom::text::Text;
+use servo_msg::constellation_msg::{PipelineId, SubpageId};
+use std::cast;
+use style::TNode;
+
+/// A wrapper so that layout can access only the methods that it should have access to. Layout must
+/// only ever see these and must never see instances of `AbstractNode`.
+#[deriving(Clone, Eq)]
+pub struct LayoutNode<'self> {
+    /// The wrapped node.
+    priv node: AbstractNode,
+
+    /// Being chained to a value prevents `LayoutNode`s from escaping.
+    priv chain: &'self (),
+}
+
+impl<'self> LayoutNode<'self> {
+    /// Creates a new layout node, scoped to the given closure.
+    pub unsafe fn with_layout_node<R>(node: AbstractNode, f: &fn<'a>(LayoutNode<'a>) -> R) -> R {
+        let heavy_iron_ball = ();
+        f(LayoutNode {
+            node: node,
+            chain: &heavy_iron_ball,
+        })
+    }
+
+    /// Creates a new layout node with the same lifetime as this layout node.
+    unsafe fn new_with_this_lifetime(&self, node: AbstractNode) -> LayoutNode<'self> {
+        LayoutNode {
+            node: node,
+            chain: self.chain,
+        }
+    }
+
+    /// Returns the interior of this node as a `Node`. This is highly unsafe for layout to call
+    /// and as such is marked `unsafe`.
+    pub unsafe fn get<'a>(&'a self) -> &'a Node<LayoutView> {
+        cast::transmute(self.node.node())
+    }
+
+    /// Returns the first child of this node.
+    pub fn first_child(&self) -> Option<LayoutNode<'self>> {
+        unsafe {
+            self.node.first_child().map(|node| self.new_with_this_lifetime(node))
+        }
+    }
+
+    /// Returns the first child of this node.
+    pub fn last_child(&self) -> Option<LayoutNode<'self>> {
+        unsafe {
+            self.node.last_child().map(|node| self.new_with_this_lifetime(node))
+        }
+    }
+
+    /// Iterates over this node and all its descendants, in preorder.
+    ///
+    /// FIXME(pcwalton): Terribly inefficient. We should use parallelism.
+    pub fn traverse_preorder(&self) -> LayoutTreeIterator<'self> {
+        let mut nodes = ~[];
+        gather_layout_nodes(self, &mut nodes, false);
+        LayoutTreeIterator::new(nodes)
+    }
+
+    /// Returns an iterator over this node's children.
+    pub fn children(&self) -> LayoutNodeChildrenIterator<'self> {
+        LayoutNodeChildrenIterator {
+            current_node: self.first_child(),
+        }
+    }
+
+    /// Returns the type ID of this node. Fails if this node is borrowed mutably.
+    pub fn type_id(&self) -> NodeTypeId {
+        self.node.type_id()
+    }
+
+    /// If this is an image element, returns its URL. If this is not an image element, fails.
+    ///
+    /// FIXME(pcwalton): Don't copy URLs.
+    pub fn image_url(&self) -> Option<Url> {
+        unsafe {
+            self.with_image_element(|image_element| {
+                image_element.image.as_ref().map(|url| (*url).clone())
+            })
+        }
+    }
+
+    /// Downcasts this node to an image element and calls the given closure.
+    ///
+    /// FIXME(pcwalton): RAII.
+    unsafe fn with_image_element<R>(self, f: &fn(&HTMLImageElement) -> R) -> R {
+        if !self.node.is_image_element() {
+            fail!(~"node is not an image element");
+        }
+        self.node.transmute(f)
+    }
+
+    /// If this node is an iframe element, returns its pipeline and subpage IDs. If this node is
+    /// not an iframe element, fails.
+    pub fn iframe_pipeline_and_subpage_ids(&self) -> (PipelineId, SubpageId) {
+        unsafe {
+            self.with_iframe_element(|iframe_element| {
+                let size = iframe_element.size.unwrap();
+                (size.pipeline_id, size.subpage_id)
+            })
+        }
+    }
+
+    /// Downcasts this node to an iframe element and calls the given closure.
+    ///
+    /// FIXME(pcwalton): RAII.
+    unsafe fn with_iframe_element<R>(self, f: &fn(&HTMLIFrameElement) -> R) -> R {
+        if !self.node.is_iframe_element() {
+            fail!(~"node is not an iframe element");
+        }
+        self.node.transmute(f)
+    }
+
+    /// Returns true if this node is a text node or false otherwise.
+    #[inline]
+    pub fn is_text(self) -> bool {
+        self.node.is_text()
+    }
+
+    /// Returns true if this node consists entirely of ignorable whitespace and false otherwise.
+    /// Ignorable whitespace is defined as whitespace that would be removed per CSS 2.1 § 16.6.1.
+    pub fn is_ignorable_whitespace(&self) -> bool {
+        unsafe {
+            self.is_text() && self.with_text(|text| text.element.data.is_whitespace())
+        }
+    }
+
+    /// If this is a text node, copies out the text. If this is not a text node, fails.
+    ///
+    /// FIXME(pcwalton): Don't copy text. Atomically reference count instead.
+    pub fn text(&self) -> ~str {
+        unsafe {
+            self.with_text(|text| text.element.data.to_str())
+        }
+    }
+
+    /// Downcasts this node to a text node and calls the given closure.
+    ///
+    /// FIXME(pcwalton): RAII.
+    unsafe fn with_text<R>(self, f: &fn(&Text) -> R) -> R {
+        self.node.with_imm_text(f)
+    }
+
+    /// Dumps this node tree, for debugging.
+    pub fn dump(&self) {
+        self.node.dump()
+    }
+
+    /// Returns a string that describes this node, for debugging.
+    pub fn debug_str(&self) -> ~str {
+        self.node.debug_str()
+    }
+
+    /// Traverses the tree in postorder.
+    ///
+    /// TODO(pcwalton): Offer a parallel version with a compatible API.
+    pub fn traverse_postorder<T:PostorderNodeTraversal>(self, traversal: &T) -> bool {
+        if traversal.should_prune(self) {
+            return true
+        }
+
+        let mut opt_kid = self.first_child();
+        loop {
+            match opt_kid {
+                None => break,
+                Some(kid) => {
+                    if !kid.traverse_postorder(traversal) {
+                        return false
+                    }
+                    opt_kid = kid.next_sibling()
+                }
+            }
+        }
+
+        traversal.process(self)
+    }
+
+    /// Traverses the tree in postorder.
+    ///
+    /// TODO(pcwalton): Offer a parallel version with a compatible API.
+    pub fn traverse_postorder_mut<T:PostorderNodeMutTraversal>(mut self, traversal: &mut T)
+                                  -> bool {
+        if traversal.should_prune(self) {
+            return true
+        }
+
+        let mut opt_kid = self.first_child();
+        loop {
+            match opt_kid {
+                None => break,
+                Some(kid) => {
+                    if !kid.traverse_postorder_mut(traversal) {
+                        return false
+                    }
+                    opt_kid = kid.next_sibling()
+                }
+            }
+        }
+
+        traversal.process(self)
+    }
+}
+
+impl<'self> TNode<Element> for LayoutNode<'self> {
+    fn parent_node(&self) -> Option<LayoutNode<'self>> {
+        unsafe {
+            self.node.node().parent_node.map(|node| self.new_with_this_lifetime(node))
+        }
+    }
+
+    fn prev_sibling(&self) -> Option<LayoutNode<'self>> {
+        unsafe {
+            self.node.node().prev_sibling.map(|node| self.new_with_this_lifetime(node))
+        }
+    }
+    
+    fn next_sibling(&self) -> Option<LayoutNode<'self>> {
+        unsafe {
+            self.node.node().next_sibling.map(|node| self.new_with_this_lifetime(node))
+        }
+    }
+
+    fn is_element(&self) -> bool {
+        match self.node.type_id() {
+            ElementNodeTypeId(*) => true,
+            _ => false
+        }
+    }
+
+    fn is_document(&self) -> bool {
+        match self.node.type_id() {
+            DocumentNodeTypeId(*) => true,
+            _ => false
+        }
+    }
+
+    /// FIXME(pcwalton): Unsafe!
+    #[inline]
+    fn with_element<R>(&self, f: &fn(&Element) -> R) -> R {
+        self.node.with_imm_element(f)
+    }
+}
+
+pub struct LayoutNodeChildrenIterator<'self> {
+    priv current_node: Option<LayoutNode<'self>>,
+}
+
+impl<'self> Iterator<LayoutNode<'self>> for LayoutNodeChildrenIterator<'self> {
+    fn next(&mut self) -> Option<LayoutNode<'self>> {
+        let node = self.current_node;
+        self.current_node = do self.current_node.and_then |node| {
+            node.next_sibling()
+        };
+        node
+    }
+}
+
+// FIXME: Do this without precomputing a vector of refs.
+// Easy for preorder; harder for postorder.
+//
+// FIXME(pcwalton): Parallelism! Eventually this should just be nuked.
+pub struct LayoutTreeIterator<'self> {
+    priv nodes: ~[LayoutNode<'self>],
+    priv index: uint,
+}
+
+impl<'self> LayoutTreeIterator<'self> {
+    fn new(nodes: ~[LayoutNode<'self>]) -> LayoutTreeIterator<'self> {
+        LayoutTreeIterator {
+            nodes: nodes,
+            index: 0,
+        }
+    }
+}
+
+impl<'self> Iterator<LayoutNode<'self>> for LayoutTreeIterator<'self> {
+    fn next(&mut self) -> Option<LayoutNode<'self>> {
+        if self.index >= self.nodes.len() {
+            None
+        } else {
+            let v = self.nodes[self.index].clone();
+            self.index += 1;
+            Some(v)
+        }
+    }
+}
+
+/// FIXME(pcwalton): This is super inefficient.
+fn gather_layout_nodes<'a>(cur: &LayoutNode<'a>, refs: &mut ~[LayoutNode<'a>], postorder: bool) {
+    if !postorder {
+        refs.push(cur.clone());
+    }
+    for kid in cur.children() {
+        gather_layout_nodes(&kid, refs, postorder)
+    }
+    if postorder {
+        refs.push(cur.clone());
+    }
+}
+
+/// A bottom-up, parallelizable traversal.
+pub trait PostorderNodeTraversal {
+    /// The operation to perform. Return true to continue or false to stop.
+    fn process<'a>(&'a self, node: LayoutNode<'a>) -> bool;
+
+    /// Returns true if this node should be pruned. If this returns true, we skip the operation
+    /// entirely and do not process any descendant nodes. This is called *before* child nodes are
+    /// visited. The default implementation never prunes any nodes.
+    fn should_prune<'a>(&'a self, _node: LayoutNode<'a>) -> bool {
+        false
+    }
+}
+
+/// A bottom-up, parallelizable traversal.
+pub trait PostorderNodeMutTraversal {
+    /// The operation to perform. Return true to continue or false to stop.
+    fn process<'a>(&'a mut self, node: LayoutNode<'a>) -> bool;
+
+    /// Returns true if this node should be pruned. If this returns true, we skip the operation
+    /// entirely and do not process any descendant nodes. This is called *before* child nodes are
+    /// visited. The default implementation never prunes any nodes.
+    fn should_prune<'a>(&'a self, _node: LayoutNode<'a>) -> bool {
+        false
+    }
+}
+
diff --git a/src/components/main/servo.rc b/src/components/main/servo.rc
index e6584df38c7..cc451b4e7ce 100755
--- a/src/components/main/servo.rc
+++ b/src/components/main/servo.rc
@@ -88,6 +88,7 @@ pub mod layout {
     pub mod text;
     pub mod util;
     pub mod incremental;
+    pub mod wrapper;
     mod extra;
 }
 
diff --git a/src/components/script/dom/node.rs b/src/components/script/dom/node.rs
index cbc7595b609..2d4e15ef8c8 100644
--- a/src/components/script/dom/node.rs
+++ b/src/components/script/dom/node.rs
@@ -14,14 +14,12 @@ use dom::documenttype::DocumentType;
 use dom::element::{Element, ElementTypeId, HTMLImageElementTypeId, HTMLIframeElementTypeId};
 use dom::element::{HTMLAnchorElementTypeId, HTMLStyleElementTypeId};
 use dom::eventtarget::{AbstractEventTarget, EventTarget, NodeTypeId};
-use dom::nodelist::{NodeList};
-use dom::htmlimageelement::HTMLImageElement;
 use dom::htmliframeelement::HTMLIFrameElement;
+use dom::htmlimageelement::HTMLImageElement;
+use dom::nodelist::{NodeList};
 use dom::text::Text;
 
-use extra::url::Url;
 use js::jsapi::{JSObject, JSContext};
-use servo_msg::constellation_msg::{PipelineId, SubpageId};
 use servo_util::slot::{MutSlotRef, Slot, SlotRef};
 use std::cast::transmute;
 use std::cast;
@@ -30,198 +28,6 @@ use std::util;
 use style::TNode;
 
 //
-// Layout's immutable, sanitized view of nodes.
-//
-
-/// A nonsense constant for layout nodes to point to just to establish a lifetime.
-///
-/// FIXME(pcwalton): Phantom lifetimes in Rust would be useful...
-static HEAVY_IRON_BALL: () = ();
-
-/// A wrapper so that layout can access only the methods that it should have access to. Layout must
-/// only ever see these and must never see instances of `AbstractNode`.
-#[deriving(Clone, Eq)]
-pub struct LayoutNode<'self> {
-    /// The wrapped node.
-    priv node: AbstractNode,
-
-    /// Being chained to a `HEAVY_IRON_BALL` prevents `LayoutNode`s from escaping.
-    priv chain: &'self (),
-}
-
-impl<'self> LayoutNode<'self> {
-    /// NB: Do not make this public.
-    ///
-    /// FIXME(pcwalton): Probably this should be marked `unsafe`.
-    /*PRIVATE-FOR-SECURITY-REASONS*/ fn new(node: AbstractNode) -> LayoutNode<'static> {
-        LayoutNode {
-            node: node,
-            chain: &HEAVY_IRON_BALL,
-        }
-    }
-
-    /// Returns the interior of this node as a `Node`. This is highly unsafe for layout to call
-    /// and as such is marked `unsafe`.
-    pub unsafe fn get<'a>(&'a self) -> &'a Node<LayoutView> {
-        cast::transmute(self.node.node())
-    }
-
-    /// Returns the first child of this node.
-    pub fn first_child(&self) -> Option<LayoutNode<'self>> {
-        self.node.first_child().map(|node| LayoutNode::new(node))
-    }
-
-    /// Returns the first child of this node.
-    pub fn last_child(&self) -> Option<LayoutNode<'self>> {
-        self.node.last_child().map(|node| LayoutNode::new(node))
-    }
-
-    /// Iterates over this node and all its descendants, in preorder.
-    ///
-    /// FIXME(pcwalton): Terribly inefficient. We should use parallelism.
-    pub fn traverse_preorder(&self) -> LayoutTreeIterator<'self> {
-        let mut nodes = ~[];
-        gather_layout_nodes(self, &mut nodes, false);
-        LayoutTreeIterator::new(nodes)
-    }
-
-    /// Returns an iterator over this node's children.
-    pub fn children(&self) -> LayoutNodeChildrenIterator<'self> {
-        LayoutNodeChildrenIterator {
-            current_node: self.first_child(),
-        }
-    }
-
-    /// Returns the type ID of this node. Fails if this node is borrowed mutably.
-    pub fn type_id(&self) -> NodeTypeId {
-        self.node.type_id()
-    }
-
-    /// If this is an image element, returns its URL. If this is not an image element, fails.
-    ///
-    /// FIXME(pcwalton): Don't copy URLs.
-    pub fn image_url(&self) -> Option<Url> {
-        self.with_image_element(|image_element| {
-            image_element.image.as_ref().map(|url| (*url).clone())
-        })
-    }
-
-    /// Downcasts this node to an image element and calls the given closure.
-    ///
-    /// NB: Do not make this public, as layout will be able to do unsafe things with `AbstractNode`
-    /// otherwise.
-    ///
-    /// FIXME(pcwalton): RAII.
-    /*PRIVATE-FOR-SECURITY-REASONS*/ fn with_image_element<R>(
-                                                           self,
-                                                           f: &fn(&HTMLImageElement) -> R)
-                                                           -> R {
-        if !self.node.is_image_element() {
-            fail!(~"node is not an image element");
-        }
-        self.node.transmute(f)
-    }
-
-    /// If this node is an iframe element, returns its pipeline and subpage IDs. If this node is
-    /// not an iframe element, fails.
-    pub fn iframe_pipeline_and_subpage_ids(&self) -> (PipelineId, SubpageId) {
-        self.with_iframe_element(|iframe_element| {
-            let size = iframe_element.size.unwrap();
-            (size.pipeline_id, size.subpage_id)
-        })
-    }
-
-    /// Downcasts this node to an iframe element and calls the given closure.
-    ///
-    /// NB: Do not make this public, as layout will be able to do unsafe things with `AbstractNode`
-    /// otherwise.
-    ///
-    /// FIXME(pcwalton): RAII.
-    /*PRIVATE-FOR-SECURITY-REASONS*/ fn with_iframe_element<R>(
-                                                            self,
-                                                            f: &fn(&HTMLIFrameElement) -> R)
-                                                            -> R {
-        if !self.node.is_iframe_element() {
-            fail!(~"node is not an iframe element");
-        }
-        self.node.transmute(f)
-    }
-
-    /// Returns true if this node is a text node or false otherwise.
-    #[inline]
-    pub fn is_text(self) -> bool {
-        self.node.is_text()
-    }
-
-    /// Returns true if this node consists entirely of ignorable whitespace and false otherwise.
-    /// Ignorable whitespace is defined as whitespace that would be removed per CSS 2.1 § 16.6.1.
-    pub fn is_ignorable_whitespace(&self) -> bool {
-        self.is_text() && self.with_text(|text| text.element.data.is_whitespace())
-    }
-
-    /// If this is a text node, copies out the text. If this is not a text node, fails.
-    ///
-    /// FIXME(pcwalton): Don't copy text. Atomically reference count instead.
-    pub fn text(&self) -> ~str {
-        self.with_text(|text| text.element.data.to_str())
-    }
-
-    /// Downcasts this node to a text node and calls the given closure.
-    ///
-    /// NB: Do not make this public, as layout will be able to do unsafe things with `AbstractNode`
-    /// otherwise.
-    ///
-    /// FIXME(pcwalton): RAII.
-    /*PRIVATE-FOR-SECURITY-REASONS*/ fn with_text<R>(self, f: &fn(&Text) -> R) -> R {
-        self.node.with_imm_text(f)
-    }
-
-    /// Dumps this node tree, for debugging.
-    pub fn dump(&self) {
-        self.node.dump()
-    }
-
-    /// Returns a string that describes this node, for debugging.
-    pub fn debug_str(&self) -> ~str {
-        self.node.debug_str()
-    }
-}
-
-impl<'self> TNode<Element> for LayoutNode<'self> {
-    fn parent_node(&self) -> Option<LayoutNode<'self>> {
-        self.node.node().parent_node.map(|node| LayoutNode::new(node))
-    }
-
-    fn prev_sibling(&self) -> Option<LayoutNode<'self>> {
-        self.node.node().prev_sibling.map(|node| LayoutNode::new(node))
-    }
-    
-    fn next_sibling(&self) -> Option<LayoutNode<'self>> {
-        self.node.node().next_sibling.map(|node| LayoutNode::new(node))
-    }
-
-    fn is_element(&self) -> bool {
-        match self.node.type_id() {
-            ElementNodeTypeId(*) => true,
-            _ => false
-        }
-    }
-
-    fn is_document(&self) -> bool {
-        match self.node.type_id() {
-            DocumentNodeTypeId(*) => true,
-            _ => false
-        }
-    }
-
-    /// FIXME(pcwalton): Unsafe!
-    #[inline]
-    fn with_element<R>(&self, f: &fn(&Element) -> R) -> R {
-        self.node.with_imm_element(f)
-    }
-}
-
-//
 // The basic Node structure
 //
 
@@ -851,20 +657,6 @@ impl Iterator<AbstractNode> for AbstractNodeChildrenIterator {
     }
 }
 
-pub struct LayoutNodeChildrenIterator<'self> {
-    priv current_node: Option<LayoutNode<'self>>,
-}
-
-impl<'self> Iterator<LayoutNode<'self>> for LayoutNodeChildrenIterator<'self> {
-    fn next(&mut self) -> Option<LayoutNode<'self>> {
-        let node = self.current_node;
-        self.current_node = do self.current_node.and_then |node| {
-            node.next_sibling()
-        };
-        node
-    }
-}
-
 pub struct AncestorIterator {
     priv current: Option<AbstractNode>,
 }
@@ -922,49 +714,6 @@ fn gather_abstract_nodes(cur: &AbstractNode, refs: &mut ~[AbstractNode], postord
     }
 }
 
-// FIXME: Do this without precomputing a vector of refs.
-// Easy for preorder; harder for postorder.
-//
-// FIXME(pcwalton): Parallelism! Eventually this should just be nuked.
-pub struct LayoutTreeIterator<'self> {
-    priv nodes: ~[LayoutNode<'self>],
-    priv index: uint,
-}
-
-impl<'self> LayoutTreeIterator<'self> {
-    fn new(nodes: ~[LayoutNode<'self>]) -> LayoutTreeIterator<'self> {
-        LayoutTreeIterator {
-            nodes: nodes,
-            index: 0,
-        }
-    }
-}
-
-impl<'self> Iterator<LayoutNode<'self>> for LayoutTreeIterator<'self> {
-    fn next(&mut self) -> Option<LayoutNode<'self>> {
-        if self.index >= self.nodes.len() {
-            None
-        } else {
-            let v = self.nodes[self.index].clone();
-            self.index += 1;
-            Some(v)
-        }
-    }
-}
-
-/// FIXME(pcwalton): This is super inefficient.
-fn gather_layout_nodes<'a>(cur: &LayoutNode<'a>, refs: &mut ~[LayoutNode<'a>], postorder: bool) {
-    if !postorder {
-        refs.push(cur.clone());
-    }
-    for kid in cur.children() {
-        gather_layout_nodes(&kid, refs, postorder)
-    }
-    if postorder {
-        refs.push(cur.clone());
-    }
-}
-
 impl AbstractNode {
     /// Iterates over all ancestors of this node.
     pub fn ancestors(&self) -> AncestorIterator {
@@ -1629,80 +1378,3 @@ impl Reflectable for Node<ScriptView> {
     }
 }
 
-/// A bottom-up, parallelizable traversal.
-pub trait PostorderNodeTraversal {
-    /// The operation to perform. Return true to continue or false to stop.
-    fn process<'a>(&'a self, node: LayoutNode<'a>) -> bool;
-
-    /// Returns true if this node should be pruned. If this returns true, we skip the operation
-    /// entirely and do not process any descendant nodes. This is called *before* child nodes are
-    /// visited. The default implementation never prunes any nodes.
-    fn should_prune<'a>(&'a self, _node: LayoutNode<'a>) -> bool {
-        false
-    }
-}
-
-/// A bottom-up, parallelizable traversal.
-pub trait PostorderNodeMutTraversal {
-    /// The operation to perform. Return true to continue or false to stop.
-    fn process<'a>(&'a mut self, node: LayoutNode<'a>) -> bool;
-
-    /// Returns true if this node should be pruned. If this returns true, we skip the operation
-    /// entirely and do not process any descendant nodes. This is called *before* child nodes are
-    /// visited. The default implementation never prunes any nodes.
-    fn should_prune<'a>(&'a self, _node: LayoutNode<'a>) -> bool {
-        false
-    }
-}
-
-impl<'self> LayoutNode<'self> {
-    /// Traverses the tree in postorder.
-    ///
-    /// TODO(pcwalton): Offer a parallel version with a compatible API.
-    pub fn traverse_postorder<T:PostorderNodeTraversal>(self, traversal: &T) -> bool {
-        if traversal.should_prune(self) {
-            return true
-        }
-
-        let mut opt_kid = self.first_child();
-        loop {
-            match opt_kid {
-                None => break,
-                Some(kid) => {
-                    if !kid.traverse_postorder(traversal) {
-                        return false
-                    }
-                    opt_kid = kid.next_sibling()
-                }
-            }
-        }
-
-        traversal.process(self)
-    }
-
-    /// Traverses the tree in postorder.
-    ///
-    /// TODO(pcwalton): Offer a parallel version with a compatible API.
-    pub fn traverse_postorder_mut<T:PostorderNodeMutTraversal>(mut self, traversal: &mut T)
-                                  -> bool {
-        if traversal.should_prune(self) {
-            return true
-        }
-
-        let mut opt_kid = self.first_child();
-        loop {
-            match opt_kid {
-                None => break,
-                Some(kid) => {
-                    if !kid.traverse_postorder_mut(traversal) {
-                        return false
-                    }
-                    opt_kid = kid.next_sibling()
-                }
-            }
-        }
-
-        traversal.process(self)
-    }
-
-}