Add a fast path in the cascade for anonymous boxes.

src/components/main/layout/box_.rs

@@ -44,7 +44,7 @@ use std::from_str::FromStr;
 use std::iter::AdditiveIterator;
 use std::mem;
 use std::num::Zero;
-use style::{ComputedValues, TElement, TNode, cascade};
+use style::{ComputedValues, TElement, TNode, cascade_anonymous};
 use style::computed_values::{LengthOrPercentageOrAuto, overflow, LPA_Auto, background_attachment};
 use style::computed_values::{background_repeat, border_style, clear, position, text_align};
 use style::computed_values::{text_decoration, vertical_align, visibility, white_space};
@@ -343,7 +343,7 @@ impl Box {
         //
         // Anonymous table boxes, TableRowBox and TableCellBox, are generated around `Foo`, but it shouldn't inherit the border.
 
-        let (node_style, _) = cascade(&[], false, Some(&**node.style()), None);
+        let node_style = cascade_anonymous(&**node.style());
         Box {
             node: OpaqueNodeMethods::from_thread_safe_layout_node(node),
             style: Arc::new(node_style),

src/components/style/properties.rs.mako

@@ -1911,6 +1911,36 @@ pub fn cascade(applicable_declarations: &[MatchedProperty],
 }
 
 
+/// Equivalent to `cascade()` with an empty `applicable_declarations`
+/// Performs the CSS cascade for an anonymous box.
+///
+///   * `parent_style`: Computed style of the element this anonymous box inherits from.
+pub fn cascade_anonymous(parent_style: &ComputedValues) -> ComputedValues {
+    let initial_values = &*INITIAL_VALUES;
+    let mut result = ComputedValues {
+        % for style_struct in STYLE_STRUCTS:
+            ${style_struct.name}:
+                % if style_struct.inherited:
+                    parent_style
+                % else:
+                    initial_values
+                % endif
+                .${style_struct.name}.clone(),
+        % endfor
+        shareable: false,
+    };
+    {
+        let border = result.Border.get_mut();
+        % for side in ["top", "right", "bottom", "left"]:
+            // Like calling to_computed_value, which wouldn't type check.
+            border.border_${side}_width = Au(0);
+        % endfor
+    }
+    // None of the teaks on 'display' apply here.
+    result
+}
+
+
 // Only re-export the types for computed values.
 pub mod computed_values {
     % for property in LONGHANDS:

src/components/style/style.rs

@@ -33,7 +33,8 @@ extern crate servo_util = "util";
 pub use stylesheets::{Stylesheet, CSSRule, StyleRule};
 pub use selector_matching::{Stylist, StylesheetOrigin, UserAgentOrigin, AuthorOrigin, UserOrigin};
 pub use selector_matching::{MatchedProperty};
-pub use properties::{cascade, PropertyDeclaration, ComputedValues, computed_values, style_structs};
+pub use properties::{cascade, cascade_anonymous};
+pub use properties::{PropertyDeclaration, ComputedValues, computed_values, style_structs};
 pub use properties::{PropertyDeclarationBlock, parse_style_attribute};  // Style attributes
 pub use properties::{CSSFloat, DeclaredValue, PropertyDeclarationParseResult};
 pub use properties::longhands;