servo: Merge #19881 - Add layout RPC query for getting an element's style (from jonleighton:issue-19811); r=emilio

This enables us to implement Element::has_css_layout_box() in a more
direct way, and also enables us to remove some of the existing more
specific queries.

Fixes #19811.

r? @emilio

Source-Repo: https://github.com/servo/servo
Source-Revision: 2a46067587d63aec176621ab3b6112ef5200a248

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 715f36d9bedb88b8bba29eff16913cb31a426305

servo/components/layout/query.rs

@@ -16,9 +16,9 @@ use ipc_channel::ipc::IpcSender;
 use msg::constellation_msg::PipelineId;
 use opaque_node::OpaqueNodeMethods;
 use script_layout_interface::rpc::{ContentBoxResponse, ContentBoxesResponse, LayoutRPC};
-use script_layout_interface::rpc::{MarginStyleResponse, NodeGeometryResponse};
-use script_layout_interface::rpc::{NodeOverflowResponse, NodeScrollRootIdResponse};
-use script_layout_interface::rpc::{OffsetParentResponse, ResolvedStyleResponse, TextIndexResponse};
+use script_layout_interface::rpc::{NodeGeometryResponse, NodeScrollRootIdResponse};
+use script_layout_interface::rpc::{OffsetParentResponse, ResolvedStyleResponse, StyleResponse};
+use script_layout_interface::rpc::TextIndexResponse;
 use script_layout_interface::wrapper_traits::{LayoutNode, ThreadSafeLayoutElement, ThreadSafeLayoutNode};
 use script_traits::LayoutMsg as ConstellationMsg;
 use script_traits::UntrustedNodeAddress;
@@ -59,9 +59,6 @@ pub struct LayoutThreadData {
     /// A queued response for the scroll root id for a given node.
     pub scroll_root_id_response: Option<ClipId>,
 
-    /// A pair of overflow property in x and y
-    pub overflow_response: NodeOverflowResponse,
-
     /// A queued response for the scroll {top, left, width, height} of a node in pixels.
     pub scroll_area_response: Rect<i32>,
 
@@ -71,8 +68,8 @@ pub struct LayoutThreadData {
     /// A queued response for the offset parent/rect of a node.
     pub offset_parent_response: OffsetParentResponse,
 
-    /// A queued response for the offset parent/rect of a node.
-    pub margin_style_response: MarginStyleResponse,
+    /// A queued response for the style of a node.
+    pub style_response: StyleResponse,
 
     /// Scroll offsets of scrolling regions.
     pub scroll_offsets: ScrollOffsetMap,
@@ -128,10 +125,6 @@ impl LayoutRPC for LayoutRPCImpl {
         }
     }
 
-    fn node_overflow(&self) -> NodeOverflowResponse {
-        NodeOverflowResponse(self.0.lock().unwrap().overflow_response.0)
-    }
-
     fn node_scroll_area(&self) -> NodeGeometryResponse {
         NodeGeometryResponse {
             client_rect: self.0.lock().unwrap().scroll_area_response
@@ -157,10 +150,10 @@ impl LayoutRPC for LayoutRPCImpl {
         rw_data.offset_parent_response.clone()
     }
 
-    fn margin_style(&self) -> MarginStyleResponse {
+    fn style(&self) -> StyleResponse {
         let &LayoutRPCImpl(ref rw_data) = self;
         let rw_data = rw_data.lock().unwrap();
-        rw_data.margin_style_response.clone()
+        rw_data.style_response.clone()
     }
 
     fn text_index(&self) -> TextIndexResponse {
@@ -863,24 +856,10 @@ pub fn process_offset_parent_query<N: LayoutNode>(requested_node: N, layout_root
     }
 }
 
-pub fn process_node_overflow_request<N: LayoutNode>(requested_node: N) -> NodeOverflowResponse {
-    let layout_node = requested_node.to_threadsafe();
-    let style = &*layout_node.as_element().unwrap().resolved_style();
-    let style_box = style.get_box();
+pub fn process_style_query<N: LayoutNode>(requested_node: N)
+        -> StyleResponse {
+    let element = requested_node.as_element().unwrap();
+    let data = element.borrow_data();
 
-    NodeOverflowResponse(Some(Point2D::new(style_box.overflow_x, style_box.overflow_y)))
-}
-
-pub fn process_margin_style_query<N: LayoutNode>(requested_node: N)
-        -> MarginStyleResponse {
-    let layout_node = requested_node.to_threadsafe();
-    let style = &*layout_node.as_element().unwrap().resolved_style();
-    let margin = style.get_margin();
-
-    MarginStyleResponse {
-        top: margin.margin_top,
-        right: margin.margin_right,
-        bottom: margin.margin_bottom,
-        left: margin.margin_left,
-    }
+    StyleResponse(data.map(|d| d.styles.primary().clone()))
 }

servo/components/layout_thread/lib.rs

@@ -75,9 +75,9 @@ use layout::incremental::{LayoutDamageComputation, RelayoutMode, SpecialRestyleD
 use layout::layout_debug;
 use layout::parallel;
 use layout::query::{LayoutRPCImpl, LayoutThreadData, process_content_box_request, process_content_boxes_request};
-use layout::query::{process_margin_style_query, process_node_overflow_request, process_resolved_style_request};
 use layout::query::{process_node_geometry_request, process_node_scroll_area_request};
-use layout::query::{process_node_scroll_root_id_request, process_offset_parent_query};
+use layout::query::{process_node_scroll_root_id_request, process_offset_parent_query, process_resolved_style_request};
+use layout::query::process_style_query;
 use layout::sequential;
 use layout::traversal::{ComputeStackingRelativePositions, PreorderFlowTraversal, RecalcStyleAndConstructFlows};
 use layout::wrapper::LayoutNodeLayoutData;
@@ -94,7 +94,7 @@ use profile_traits::time::{self, TimerMetadata, profile};
 use profile_traits::time::{TimerMetadataFrameType, TimerMetadataReflowType};
 use script_layout_interface::message::{Msg, NewLayoutThreadInfo, NodesFromPointQueryType, Reflow};
 use script_layout_interface::message::{ReflowComplete, ReflowGoal, ScriptReflow};
-use script_layout_interface::rpc::{LayoutRPC, MarginStyleResponse, NodeOverflowResponse, OffsetParentResponse};
+use script_layout_interface::rpc::{LayoutRPC, StyleResponse, OffsetParentResponse};
 use script_layout_interface::rpc::TextIndexResponse;
 use script_layout_interface::wrapper_traits::LayoutNode;
 use script_traits::{ConstellationControlMsg, LayoutControlMsg, LayoutMsg as ConstellationMsg};
@@ -519,10 +519,9 @@ impl LayoutThread {
                     client_rect_response: Rect::zero(),
                     scroll_root_id_response: None,
                     scroll_area_response: Rect::zero(),
-                    overflow_response: NodeOverflowResponse(None),
                     resolved_style_response: String::new(),
                     offset_parent_response: OffsetParentResponse::empty(),
-                    margin_style_response: MarginStyleResponse::empty(),
+                    style_response: StyleResponse(None),
                     scroll_offsets: HashMap::new(),
                     text_index_response: TextIndexResponse(None),
                     nodes_from_point_response: vec![],
@@ -1092,9 +1091,6 @@ impl LayoutThread {
                     ReflowGoal::NodeScrollGeometryQuery(_) => {
                         rw_data.scroll_area_response = Rect::zero();
                     },
-                    ReflowGoal::NodeOverflowQuery(_) => {
-                        rw_data.overflow_response = NodeOverflowResponse(None);
-                    },
                     ReflowGoal::NodeScrollRootIdQuery(_) => {
                         rw_data.scroll_root_id_response = None;
                     },
@@ -1104,8 +1100,8 @@ impl LayoutThread {
                     ReflowGoal::OffsetParentQuery(_) => {
                         rw_data.offset_parent_response = OffsetParentResponse::empty();
                     },
-                    ReflowGoal::MarginStyleQuery(_) => {
-                        rw_data.margin_style_response = MarginStyleResponse::empty();
+                    ReflowGoal::StyleQuery(_) => {
+                        rw_data.style_response = StyleResponse(None);
                     },
                     ReflowGoal::TextIndexQuery(..) => {
                         rw_data.text_index_response = TextIndexResponse(None);
@@ -1379,10 +1375,6 @@ impl LayoutThread {
                 let node = unsafe { ServoLayoutNode::new(&node) };
                 rw_data.scroll_area_response = process_node_scroll_area_request(node, root_flow);
             },
-            ReflowGoal::NodeOverflowQuery(node) => {
-                let node = unsafe { ServoLayoutNode::new(&node) };
-                rw_data.overflow_response = process_node_overflow_request(node);
-            },
             ReflowGoal::NodeScrollRootIdQuery(node) => {
                 let node = unsafe { ServoLayoutNode::new(&node) };
                 rw_data.scroll_root_id_response = Some(process_node_scroll_root_id_request(self.id,
@@ -1401,9 +1393,9 @@ impl LayoutThread {
                 let node = unsafe { ServoLayoutNode::new(&node) };
                 rw_data.offset_parent_response = process_offset_parent_query(node, root_flow);
             },
-            ReflowGoal::MarginStyleQuery(node) => {
+            ReflowGoal::StyleQuery(node) => {
                 let node = unsafe { ServoLayoutNode::new(&node) };
-                rw_data.margin_style_response = process_margin_style_query(node);
+                rw_data.style_response = process_style_query(node);
             },
             ReflowGoal::NodesFromPointQuery(client_point, ref reflow_goal) => {
                 let mut flags = match reflow_goal {

servo/components/script/devtools.rs

@@ -154,12 +154,13 @@ pub fn handle_get_layout(documents: &Documents,
 }
 
 fn determine_auto_margins(window: &Window, node: &Node) -> AutoMargins {
-    let margin = window.margin_style_query(node.to_trusted_node_address());
+    let style = window.style_query(node.to_trusted_node_address()).unwrap();
+    let margin = style.get_margin();
     AutoMargins {
-        top: margin.top == margin_top::computed_value::T::Auto,
-        right: margin.right == margin_right::computed_value::T::Auto,
-        bottom: margin.bottom == margin_bottom::computed_value::T::Auto,
-        left: margin.left == margin_left::computed_value::T::Auto,
+        top: margin.margin_top == margin_top::computed_value::T::Auto,
+        right: margin.margin_right == margin_right::computed_value::T::Auto,
+        bottom: margin.margin_bottom == margin_bottom::computed_value::T::Auto,
+        left: margin.margin_left == margin_left::computed_value::T::Auto,
     }
 }
 

servo/components/script/dom/element.rs

@@ -348,27 +348,24 @@ impl Element {
     }
 
     // https://drafts.csswg.org/cssom-view/#css-layout-box
-    //
-    // We'll have no content box if there's no fragment for the node, and we use
-    // bounding_content_box, for simplicity, to detect this (rather than making a more specific
-    // query to the layout thread).
     fn has_css_layout_box(&self) -> bool {
-        self.upcast::<Node>().bounding_content_box().is_some()
+        let style = self.upcast::<Node>().style();
+
+        // style will be None for elements in a display: none subtree. otherwise, the element has a
+        // layout box iff it doesn't have display: none.
+        style.map_or(false, |s| !s.get_box().clone_display().is_none())
     }
 
     // https://drafts.csswg.org/cssom-view/#potentially-scrollable
     fn potentially_scrollable(&self) -> bool {
-        self.has_css_layout_box() &&
-        !self.overflow_x_is_visible() &&
-        !self.overflow_y_is_visible()
+        self.has_css_layout_box() && !self.has_any_visible_overflow()
     }
 
     // https://drafts.csswg.org/cssom-view/#scrolling-box
     fn has_scrolling_box(&self) -> bool {
         // TODO: scrolling mechanism, such as scrollbar (We don't have scrollbar yet)
         //       self.has_scrolling_mechanism()
-        self.overflow_x_is_hidden() ||
-        self.overflow_y_is_hidden()
+        self.has_any_hidden_overflow()
     }
 
     fn has_overflow(&self) -> bool {
@@ -376,32 +373,33 @@ impl Element {
         self.ScrollWidth() > self.ClientWidth()
     }
 
-    // used value of overflow-x is "visible"
-    fn overflow_x_is_visible(&self) -> bool {
-        let window = window_from_node(self);
-        let overflow_pair = window.overflow_query(self.upcast::<Node>().to_trusted_node_address());
-        overflow_pair.x == overflow_x::computed_value::T::Visible
+    // TODO: Once #19183 is closed (overflow-x/y types moved out of mako), then we could implement
+    //       a more generic `fn has_some_overflow(&self, overflow: Overflow)` rather than have
+    //       these two `has_any_{visible,hidden}_overflow` methods which are very structurally
+    //       similar.
+
+    /// Computed value of overflow-x or overflow-y is "visible"
+    fn has_any_visible_overflow(&self) -> bool {
+        let style = self.upcast::<Node>().style();
+
+        style.map_or(false, |s| {
+            let box_ = s.get_box();
+
+            box_.clone_overflow_x() == overflow_x::computed_value::T::Visible ||
+                box_.clone_overflow_y() == overflow_y::computed_value::T::Visible
+        })
     }
 
-    // used value of overflow-y is "visible"
-    fn overflow_y_is_visible(&self) -> bool {
-        let window = window_from_node(self);
-        let overflow_pair = window.overflow_query(self.upcast::<Node>().to_trusted_node_address());
-        overflow_pair.y == overflow_y::computed_value::T::Visible
-    }
+    /// Computed value of overflow-x or overflow-y is "hidden"
+    fn has_any_hidden_overflow(&self) -> bool {
+        let style = self.upcast::<Node>().style();
 
-    // used value of overflow-x is "hidden"
-    fn overflow_x_is_hidden(&self) -> bool {
-        let window = window_from_node(self);
-        let overflow_pair = window.overflow_query(self.upcast::<Node>().to_trusted_node_address());
-        overflow_pair.x == overflow_x::computed_value::T::Hidden
-    }
+        style.map_or(false, |s| {
+            let box_ = s.get_box();
 
-    // used value of overflow-y is "hidden"
-    fn overflow_y_is_hidden(&self) -> bool {
-        let window = window_from_node(self);
-        let overflow_pair = window.overflow_query(self.upcast::<Node>().to_trusted_node_address());
-        overflow_pair.y == overflow_y::computed_value::T::Hidden
+            box_.clone_overflow_x() == overflow_x::computed_value::T::Hidden ||
+                box_.clone_overflow_y() == overflow_y::computed_value::T::Hidden
+        })
     }
 }
 

servo/components/script/dom/node.rs

@@ -82,6 +82,7 @@ use std::mem;
 use std::ops::Range;
 use style::context::QuirksMode;
 use style::dom::OpaqueNode;
+use style::properties::ComputedValues;
 use style::selector_parser::{SelectorImpl, SelectorParser};
 use style::stylesheets::Stylesheet;
 use style::thread_state;
@@ -619,6 +620,10 @@ impl Node {
         window_from_node(self).client_rect_query(self.to_trusted_node_address())
     }
 
+    pub fn style(&self) -> Option<Arc<ComputedValues>> {
+        window_from_node(self).style_query(self.to_trusted_node_address())
+    }
+
     // https://drafts.csswg.org/cssom-view/#dom-element-scrollwidth
     // https://drafts.csswg.org/cssom-view/#dom-element-scrollheight
     // https://drafts.csswg.org/cssom-view/#dom-element-scrolltop

servo/components/script/dom/window.rs

@@ -72,8 +72,7 @@ use script_layout_interface::{TrustedNodeAddress, PendingImageState};
 use script_layout_interface::message::{Msg, Reflow, ReflowGoal, ScriptReflow};
 use script_layout_interface::reporter::CSSErrorReporter;
 use script_layout_interface::rpc::{ContentBoxResponse, ContentBoxesResponse, LayoutRPC};
-use script_layout_interface::rpc::{MarginStyleResponse, NodeScrollRootIdResponse};
-use script_layout_interface::rpc::{ResolvedStyleResponse, TextIndexResponse};
+use script_layout_interface::rpc::{NodeScrollRootIdResponse, ResolvedStyleResponse, TextIndexResponse};
 use script_runtime::{CommonScriptMsg, ScriptChan, ScriptPort, ScriptThreadEventCategory, Runtime};
 use script_thread::{ImageCacheMsg, MainThreadScriptChan, MainThreadScriptMsg};
 use script_thread::{ScriptThread, SendableMainThreadScriptChan};
@@ -82,6 +81,7 @@ use script_traits::{ScriptToConstellationChan, ScriptMsg, ScrollState, TimerEven
 use script_traits::{TimerSchedulerMsg, UntrustedNodeAddress, WindowSizeData, WindowSizeType};
 use script_traits::webdriver_msg::{WebDriverJSError, WebDriverJSResult};
 use selectors::attr::CaseSensitivity;
+use servo_arc;
 use servo_config::opts;
 use servo_config::prefs::PREFS;
 use servo_geometry::{f32_rect_to_au_rect, MaxRect};
@@ -102,8 +102,7 @@ use std::sync::mpsc::{Sender, channel};
 use std::sync::mpsc::TryRecvError::{Disconnected, Empty};
 use style::media_queries;
 use style::parser::ParserContext as CssParserContext;
-use style::properties::PropertyId;
-use style::properties::longhands::overflow_x;
+use style::properties::{ComputedValues, PropertyId};
 use style::selector_parser::PseudoElement;
 use style::str::HTML_SPACE_CHARACTERS;
 use style::stylesheets::CssRuleType;
@@ -1403,16 +1402,6 @@ impl Window {
         self.layout_rpc.node_scroll_area().client_rect
     }
 
-    pub fn overflow_query(&self,
-                          node: TrustedNodeAddress) -> Point2D<overflow_x::computed_value::T> {
-        // NB: This is only called if the document is fully active, and the only
-        // reason to bail out from a query is if there's no viewport, so this
-        // *must* issue a reflow.
-        assert!(self.reflow(ReflowGoal::NodeOverflowQuery(node), ReflowReason::Query));
-
-        self.layout_rpc.node_overflow().0.unwrap()
-    }
-
     pub fn scroll_offset_query(&self, node: &Node) -> Vector2D<f32> {
         if let Some(scroll_offset) = self.scroll_offsets
                                          .borrow()
@@ -1477,11 +1466,11 @@ impl Window {
         (element, response.rect)
     }
 
-    pub fn margin_style_query(&self, node: TrustedNodeAddress) -> MarginStyleResponse {
-        if !self.reflow(ReflowGoal::MarginStyleQuery(node), ReflowReason::Query) {
-            return MarginStyleResponse::empty();
+    pub fn style_query(&self, node: TrustedNodeAddress) -> Option<servo_arc::Arc<ComputedValues>> {
+        if !self.reflow(ReflowGoal::StyleQuery(node), ReflowReason::Query) {
+            return None
         }
-        self.layout_rpc.margin_style()
+        self.layout_rpc.style().0
     }
 
     pub fn text_index_query(
@@ -1898,12 +1887,11 @@ fn debug_reflow_events(id: PipelineId, reflow_goal: &ReflowGoal, reason: &Reflow
         ReflowGoal::ContentBoxesQuery(_n) => "\tContentBoxesQuery",
         ReflowGoal::NodesFromPointQuery(..) => "\tNodesFromPointQuery",
         ReflowGoal::NodeGeometryQuery(_n) => "\tNodeGeometryQuery",
-        ReflowGoal::NodeOverflowQuery(_n) => "\tNodeOverFlowQuery",
         ReflowGoal::NodeScrollGeometryQuery(_n) => "\tNodeScrollGeometryQuery",
         ReflowGoal::NodeScrollRootIdQuery(_n) => "\tNodeScrollRootIdQuery",
         ReflowGoal::ResolvedStyleQuery(_, _, _) => "\tResolvedStyleQuery",
         ReflowGoal::OffsetParentQuery(_n) => "\tOffsetParentQuery",
-        ReflowGoal::MarginStyleQuery(_n) => "\tMarginStyleQuery",
+        ReflowGoal::StyleQuery(_n) => "\tStyleQuery",
         ReflowGoal::TextIndexQuery(..) => "\tTextIndexQuery",
         ReflowGoal::TickAnimations => "\tTickAnimations",
     });

servo/components/script_layout_interface/message.rs

@@ -113,13 +113,12 @@ pub enum ReflowGoal {
     TickAnimations,
     ContentBoxQuery(TrustedNodeAddress),
     ContentBoxesQuery(TrustedNodeAddress),
-    NodeOverflowQuery(TrustedNodeAddress),
     NodeScrollRootIdQuery(TrustedNodeAddress),
     NodeGeometryQuery(TrustedNodeAddress),
     NodeScrollGeometryQuery(TrustedNodeAddress),
     ResolvedStyleQuery(TrustedNodeAddress, Option<PseudoElement>, PropertyId),
     OffsetParentQuery(TrustedNodeAddress),
-    MarginStyleQuery(TrustedNodeAddress),
+    StyleQuery(TrustedNodeAddress),
     TextIndexQuery(TrustedNodeAddress, Point2D<f32>),
     NodesFromPointQuery(Point2D<f32>, NodesFromPointQueryType),
 }
@@ -133,9 +132,9 @@ impl ReflowGoal {
             ReflowGoal::TickAnimations | ReflowGoal::Full => true,
             ReflowGoal::ContentBoxQuery(_) | ReflowGoal::ContentBoxesQuery(_) |
             ReflowGoal::NodeGeometryQuery(_) | ReflowGoal::NodeScrollGeometryQuery(_) |
-            ReflowGoal::NodeOverflowQuery(_) | ReflowGoal::NodeScrollRootIdQuery(_) |
+            ReflowGoal::NodeScrollRootIdQuery(_) |
             ReflowGoal::ResolvedStyleQuery(..) | ReflowGoal::OffsetParentQuery(_) |
-            ReflowGoal::MarginStyleQuery(_)  => false,
+            ReflowGoal::StyleQuery(_)  => false,
         }
     }
 
@@ -143,10 +142,10 @@ impl ReflowGoal {
     /// false if a layout_thread display list is sufficient.
     pub fn needs_display(&self) -> bool {
         match *self {
-            ReflowGoal::MarginStyleQuery(_)  | ReflowGoal::TextIndexQuery(..) |
+            ReflowGoal::StyleQuery(_)  | ReflowGoal::TextIndexQuery(..) |
             ReflowGoal::ContentBoxQuery(_) | ReflowGoal::ContentBoxesQuery(_) |
             ReflowGoal::NodeGeometryQuery(_) | ReflowGoal::NodeScrollGeometryQuery(_) |
-            ReflowGoal::NodeOverflowQuery(_) | ReflowGoal::NodeScrollRootIdQuery(_) |
+            ReflowGoal::NodeScrollRootIdQuery(_) |
             ReflowGoal::ResolvedStyleQuery(..) |
             ReflowGoal::OffsetParentQuery(_) => false,
             ReflowGoal::NodesFromPointQuery(..) | ReflowGoal::Full |

servo/components/script_layout_interface/rpc.rs

@@ -5,7 +5,9 @@
 use app_units::Au;
 use euclid::{Point2D, Rect};
 use script_traits::UntrustedNodeAddress;
-use style::properties::longhands::{margin_top, margin_right, margin_bottom, margin_left, overflow_x};
+use servo_arc::Arc;
+use style::properties::ComputedValues;
+use style::properties::longhands::overflow_x;
 use webrender_api::ClipId;
 
 /// Synchronous messages that script can send to layout.
@@ -23,8 +25,6 @@ pub trait LayoutRPC {
     fn content_boxes(&self) -> ContentBoxesResponse;
     /// Requests the geometry of this node. Used by APIs such as `clientTop`.
     fn node_geometry(&self) -> NodeGeometryResponse;
-    /// Requests the overflow-x and overflow-y of this node. Used by `scrollTop` etc.
-    fn node_overflow(&self) -> NodeOverflowResponse;
     /// Requests the scroll geometry of this node. Used by APIs such as `scrollTop`.
     fn node_scroll_area(&self) -> NodeGeometryResponse;
     /// Requests the scroll root id of this node. Used by APIs such as `scrollTop`
@@ -32,8 +32,9 @@ pub trait LayoutRPC {
     /// Query layout for the resolved value of a given CSS property
     fn resolved_style(&self) -> ResolvedStyleResponse;
     fn offset_parent(&self) -> OffsetParentResponse;
-    /// Query layout for the resolve values of the margin properties for an element.
-    fn margin_style(&self) -> MarginStyleResponse;
+    /// Requests the styles for an element. Contains a `None` value if the element is in a `display:
+    /// none` subtree.
+    fn style(&self) -> StyleResponse;
     fn text_index(&self) -> TextIndexResponse;
     /// Requests the list of nodes from the given point.
     fn nodes_from_point_response(&self) -> Vec<UntrustedNodeAddress>;
@@ -70,23 +71,7 @@ impl OffsetParentResponse {
 }
 
 #[derive(Clone)]
-pub struct MarginStyleResponse {
-    pub top: margin_top::computed_value::T,
-    pub right: margin_right::computed_value::T,
-    pub bottom: margin_bottom::computed_value::T,
-    pub left: margin_left::computed_value::T,
-}
-
-impl MarginStyleResponse {
-    pub fn empty() -> MarginStyleResponse {
-        MarginStyleResponse {
-            top: margin_top::computed_value::T::Auto,
-            right: margin_right::computed_value::T::Auto,
-            bottom: margin_bottom::computed_value::T::Auto,
-            left: margin_left::computed_value::T::Auto,
-        }
-    }
-}
+pub struct StyleResponse(pub Option<Arc<ComputedValues>>);
 
 #[derive(Clone)]
 pub struct TextIndexResponse(pub Option<usize>);

servo/components/style/data.rs

@@ -11,7 +11,6 @@ use invalidation::element::restyle_hints::RestyleHint;
 #[cfg(feature = "gecko")]
 use malloc_size_of::MallocSizeOfOps;
 use properties::ComputedValues;
-use properties::longhands::display::computed_value::T as Display;
 use rule_tree::StrongRuleNode;
 use selector_parser::{EAGER_PSEUDO_COUNT, PseudoElement, RestyleDamage};
 use selectors::NthIndexCache;
@@ -169,7 +168,7 @@ impl ElementStyles {
 
     /// Whether this element `display` value is `none`.
     pub fn is_display_none(&self) -> bool {
-        self.primary().get_box().clone_display() == Display::None
+        self.primary().get_box().clone_display().is_none()
     }
 
     #[cfg(feature = "gecko")]

servo/components/style/values/specified/box.rs

@@ -216,6 +216,12 @@ impl Display {
             other => other,
         }
     }
+
+    /// Returns true if the value is `None`
+    #[inline]
+    pub fn is_none(&self) -> bool {
+        *self == Display::None
+    }
 }
 
 /// A specified value for the `vertical-align` property.