style: Get rid of CurrentElementInfo.

It's out-of-band data I never liked, and the code has changed enough from when
it was introduced, that now all of the information it stores can be local.

components/style/context.rs

@@ -5,11 +5,11 @@
 //! The context within which style is calculated.
 
 #[cfg(feature = "servo")] use animation::Animation;
-#[cfg(feature = "servo")] use animation::PropertyAnimation;
 use app_units::Au;
 use bloom::StyleBloom;
 use data::{EagerPseudoStyles, ElementData};
-use dom::{OpaqueNode, TNode, TElement, SendElement};
+use dom::{TElement, SendElement};
+#[cfg(feature = "servo")] use dom::OpaqueNode;
 use euclid::ScaleFactor;
 use euclid::Size2D;
 use fnv::FnvHashMap;
@@ -285,23 +285,6 @@ impl ElementCascadeInputs {
     }
 }
 
-/// Information about the current element being processed. We group this
-/// together into a single struct within ThreadLocalStyleContext so that we can
-/// instantiate and destroy it easily at the beginning and end of element
-/// processing.
-pub struct CurrentElementInfo {
-    /// The element being processed. Currently we use an OpaqueNode since we
-    /// only use this for identity checks, but we could use SendElement if there
-    /// were a good reason to.
-    element: OpaqueNode,
-    /// Whether the element is being styled for the first time.
-    is_initial_style: bool,
-    /// A Vec of possibly expired animations. Used only by Servo.
-    #[allow(dead_code)]
-    #[cfg(feature = "servo")]
-    pub possibly_expired_animations: Vec<PropertyAnimation>,
-}
-
 /// Statistics gathered during the traversal. We gather statistics on each
 /// thread and then combine them after the threads join via the Add
 /// implementation below.
@@ -712,8 +695,6 @@ pub struct ThreadLocalStyleContext<E: TElement> {
     pub selector_flags: SelectorFlagsMap<E>,
     /// Statistics about the traversal.
     pub statistics: TraversalStatistics,
-    /// Information related to the current element, non-None during processing.
-    pub current_element_info: Option<CurrentElementInfo>,
     /// The struct used to compute and cache font metrics from style
     /// for evaluation of the font-relative em/ch units and font-size
     pub font_metrics_provider: E::FontMetricsProvider,
@@ -736,7 +717,6 @@ impl<E: TElement> ThreadLocalStyleContext<E> {
             tasks: SequentialTaskList(Vec::new()),
             selector_flags: SelectorFlagsMap::new(),
             statistics: TraversalStatistics::default(),
-            current_element_info: None,
             font_metrics_provider: E::FontMetricsProvider::create_from(shared),
             stack_limit_checker: StackLimitChecker::new(
                 (STYLE_THREAD_STACK_SIZE_KB - STACK_SAFETY_MARGIN_KB) * 1024),
@@ -754,55 +734,16 @@ impl<E: TElement> ThreadLocalStyleContext<E> {
             tasks: SequentialTaskList(Vec::new()),
             selector_flags: SelectorFlagsMap::new(),
             statistics: TraversalStatistics::default(),
-            current_element_info: None,
             font_metrics_provider: E::FontMetricsProvider::create_from(shared),
             stack_limit_checker: StackLimitChecker::new(
                 (STYLE_THREAD_STACK_SIZE_KB - STACK_SAFETY_MARGIN_KB) * 1024),
             nth_index_cache: NthIndexCache::default(),
         }
     }
-
-    #[cfg(feature = "gecko")]
-    /// Notes when the style system starts traversing an element.
-    pub fn begin_element(&mut self, element: E, data: &ElementData) {
-        debug_assert!(self.current_element_info.is_none());
-        self.current_element_info = Some(CurrentElementInfo {
-            element: element.as_node().opaque(),
-            is_initial_style: !data.has_styles(),
-        });
-    }
-
-    #[cfg(feature = "servo")]
-    /// Notes when the style system starts traversing an element.
-    pub fn begin_element(&mut self, element: E, data: &ElementData) {
-        debug_assert!(self.current_element_info.is_none());
-        self.current_element_info = Some(CurrentElementInfo {
-            element: element.as_node().opaque(),
-            is_initial_style: !data.has_styles(),
-            possibly_expired_animations: Vec::new(),
-        });
-    }
-
-    /// Notes when the style system finishes traversing an element.
-    pub fn end_element(&mut self, element: E) {
-        debug_assert!(self.current_element_info.is_some());
-        debug_assert!(self.current_element_info.as_ref().unwrap().element ==
-                      element.as_node().opaque());
-        self.current_element_info = None;
-    }
-
-    /// Returns true if the current element being traversed is being styled for
-    /// the first time.
-    ///
-    /// Panics if called while no element is being traversed.
-    pub fn is_initial_style(&self) -> bool {
-        self.current_element_info.as_ref().unwrap().is_initial_style
-    }
 }
 
 impl<E: TElement> Drop for ThreadLocalStyleContext<E> {
     fn drop(&mut self) {
-        debug_assert!(self.current_element_info.is_none());
         debug_assert!(thread_state::get() == ThreadState::LAYOUT);
 
         // Apply any slow selector flags that need to be set on parents.

components/style/matching.rs

@@ -298,13 +298,11 @@ trait PrivateMatchMethods: TElement {
         use animation;
         use dom::TNode;
 
-        let possibly_expired_animations =
+        let mut possibly_expired_animations = vec![];
-            &mut context.thread_local.current_element_info.as_mut().unwrap()
-                        .possibly_expired_animations;
         let shared_context = context.shared;
         if let Some(ref mut old) = *old_values {
             self.update_animations_for_cascade(shared_context, old,
-                                               possibly_expired_animations,
+                                               &mut possibly_expired_animations,
                                                &context.thread_local.font_metrics_provider);
         }
 

components/style/traversal.rs

@@ -273,6 +273,7 @@ pub trait DomTraversal<E: TElement> : Sync {
         &self,
         context: &mut StyleContext<E>,
         parent: E,
+        is_initial_style: bool,
         parent_data: &ElementData,
     ) -> bool {
         debug_assert!(cfg!(feature = "gecko") ||
@@ -304,7 +305,7 @@ pub trait DomTraversal<E: TElement> : Sync {
         // happens, we may just end up doing wasted work, since Gecko
         // recursively drops Servo ElementData when the XBL insertion parent of
         // an Element is changed.
-        if cfg!(feature = "gecko") && context.thread_local.is_initial_style() &&
+        if cfg!(feature = "gecko") && is_initial_style &&
             parent_data.styles.primary().has_moz_binding()
         {
             debug!("Parent {:?} has XBL binding, deferring traversal", parent);
@@ -427,7 +428,8 @@ where
     use traversal_flags::TraversalFlags;
 
     let flags = context.shared.traversal_flags;
-    context.thread_local.begin_element(element, data);
+    let is_initial_style = !data.has_styles();
+
     context.thread_local.statistics.elements_traversed += 1;
     debug_assert!(flags.intersects(TraversalFlags::AnimationOnly | TraversalFlags::UnstyledOnly) ||
                   !element.has_snapshot() || element.handled_snapshot(),
@@ -524,8 +526,9 @@ where
                                 data.reconstructed_self() ||
                                 is_servo_nonincremental_layout();
 
-    traverse_children = traverse_children &&
+    traverse_children =
-                        !traversal.should_cull_subtree(context, element, &data);
+        traverse_children &&
+        !traversal.should_cull_subtree(context, element, is_initial_style, &data);
 
     // Examine our children, and enqueue the appropriate ones for traversal.
     if traverse_children {
@@ -535,6 +538,7 @@ where
             data,
             propagated_hint,
             child_cascade_requirement,
+            is_initial_style,
             note_child
         );
     }
@@ -550,8 +554,6 @@ where
                   !element.has_animation_only_dirty_descendants(),
                   "Should have cleared animation bits already");
     clear_state_after_traversing(element, data, flags);
-
-    context.thread_local.end_element(element);
 }
 
 fn clear_state_after_traversing<E>(
@@ -776,6 +778,7 @@ fn note_children<E, D, F>(
     data: &ElementData,
     propagated_hint: RestyleHint,
     cascade_requirement: ChildCascadeRequirement,
+    is_initial_style: bool,
     mut note_child: F,
 )
 where
@@ -785,7 +788,6 @@ where
 {
     trace!("note_children: {:?}", element);
     let flags = context.shared.traversal_flags;
-    let is_initial_style = context.thread_local.is_initial_style();
 
     // Loop over all the traversal children.
     for child_node in element.traversal_children() {