Use Ref::map to make ThreadSafeLayoutNode::style safe.

components/layout/construct.rs

@@ -667,7 +667,7 @@ impl<'a> FlowConstructor<'a> {
 
             self.create_fragments_for_node_text_content(&mut initial_fragments,
                                                         node,
-                                                        node.style());
+                                                        &*node.style());
         }
 
         self.build_flow_for_block_starting_with_fragments(flow, node, initial_fragments)

components/layout/css/node_style.rs

@@ -7,16 +7,17 @@
 use data::LayoutDataWrapper;
 use wrapper::{PseudoElementType, ThreadSafeLayoutNode};
 
-use std::mem;
 use style::properties::ComputedValues;
+
+use std::cell::Ref;
 use std::sync::Arc;
 
 /// Node mixin providing `style` method that returns a `NodeStyle`
 pub trait StyledNode {
-    fn get_style<'a>(&'a self, layout_data_ref: &'a LayoutDataWrapper) -> &'a Arc<ComputedValues>;
+    fn get_style<'a>(&self, layout_data_ref: &'a LayoutDataWrapper) -> &'a Arc<ComputedValues>;
     /// Returns the style results for the given node. If CSS selector matching has not yet been
     /// performed, fails.
-    fn style<'a>(&'a self) -> &'a Arc<ComputedValues>;
+    fn style<'a>(&'a self) -> Ref<'a, Arc<ComputedValues>>;
     /// Does this node have a computed style yet?
     fn has_style(&self) -> bool;
     /// Removes the style from this node.
@@ -34,14 +35,11 @@ impl<'ln> StyledNode for ThreadSafeLayoutNode<'ln> {
     }
 
     #[inline]
-    #[allow(unsafe_code)]
-    fn style<'a>(&'a self) -> &'a Arc<ComputedValues> {
-        unsafe {
-            let layout_data_ref = self.borrow_layout_data();
+    fn style<'a>(&'a self) -> Ref<'a, Arc<ComputedValues>> {
+        Ref::map(self.borrow_layout_data(), |layout_data_ref| {
             let layout_data = layout_data_ref.as_ref().expect("no layout data");
-            mem::transmute::<&Arc<ComputedValues>,
-                             &'a Arc<ComputedValues>>(self.get_style(&layout_data))
-        }
+            self.get_style(layout_data)
+        })
     }
 
     fn has_style(&self) -> bool {

components/layout/lib.rs

@@ -5,6 +5,7 @@
 #![feature(append)]
 #![feature(arc_unique)]
 #![feature(box_syntax)]
+#![feature(cell_extras)]
 #![feature(custom_derive)]
 #![feature(filling_drop)]
 #![feature(hashmap_hasher)]