Compare style attributes rather than rejecting them from the cache.

MozReview-Commit-ID: Jmu7Pie2mBP

components/selectors/matching.rs

@@ -23,14 +23,11 @@ bitflags! {
     pub flags StyleRelations: usize {
         /// Whether this element is affected by an ID selector.
         const AFFECTED_BY_ID_SELECTOR = 1 << 0,
-        /// Whether this element has a style attribute. Computed
-        /// externally.
-        const AFFECTED_BY_STYLE_ATTRIBUTE = 1 << 1,
         /// Whether this element is affected by presentational hints. This is
         /// computed externally (that is, in Servo).
-        const AFFECTED_BY_PRESENTATIONAL_HINTS = 1 << 2,
+        const AFFECTED_BY_PRESENTATIONAL_HINTS = 1 << 1,
         /// Whether this element has pseudo-element styles. Computed externally.
-        const AFFECTED_BY_PSEUDO_ELEMENTS = 1 << 3,
+        const AFFECTED_BY_PSEUDO_ELEMENTS = 1 << 2,
     }
 }
 

components/style/sharing/checks.rs

@@ -21,8 +21,7 @@ use stylearc::Arc;
 pub fn relations_are_shareable(relations: &StyleRelations) -> bool {
     use selectors::matching::*;
     !relations.intersects(AFFECTED_BY_ID_SELECTOR |
-                          AFFECTED_BY_PSEUDO_ELEMENTS |
-                          AFFECTED_BY_STYLE_ATTRIBUTE)
+                          AFFECTED_BY_PSEUDO_ELEMENTS)
 }
 
 /// Whether, given two elements, they have pointer-equal computed values.
@@ -44,11 +43,21 @@ pub fn same_computed_values<E>(first: Option<E>, second: Option<E>) -> bool
     eq
 }
 
-/// Whether a given element has presentational hints.
-///
-/// We consider not worth to share style with an element that has presentational
-/// hints, both because implementing the code that compares that the hints are
-/// equal is somewhat annoying, and also because it'd be expensive enough.
+/// Whether two elements have the same same style attribute (by pointer identity).
+pub fn have_same_style_attribute<E>(
+    target: &mut StyleSharingTarget<E>,
+    candidate: &mut StyleSharingCandidate<E>
+) -> bool
+    where E: TElement,
+{
+    match (target.style_attribute(), candidate.style_attribute()) {
+        (None, None) => true,
+        (Some(_), None) | (None, Some(_)) => false,
+        (Some(a), Some(b)) => Arc::ptr_eq(a, b)
+    }
+}
+
+/// Whether two elements have the same same presentational attributes.
 pub fn have_same_presentational_hints<E>(
     target: &mut StyleSharingTarget<E>,
     candidate: &mut StyleSharingCandidate<E>

components/style/sharing/mod.rs

@@ -126,6 +126,15 @@ pub struct StyleSharingCandidate<E: TElement> {
     validation_data: ValidationData,
 }
 
+impl<E: TElement> Deref for StyleSharingCandidate<E> {
+    type Target = E;
+
+    fn deref(&self) -> &Self::Target {
+        &self.element
+    }
+}
+
+
 impl<E: TElement> StyleSharingCandidate<E> {
     /// Get the classlist of this candidate.
     fn class_list(&mut self) -> &[Atom] {
@@ -409,12 +418,6 @@ impl<E: TElement> StyleSharingCandidateCache<E> {
             return StyleSharingResult::CannotShare;
         }
 
-        if target.style_attribute().is_some() {
-            debug!("{:?} Cannot share style: element has style attribute",
-                   target.element);
-            return StyleSharingResult::CannotShare
-        }
-
         if target.get_id().is_some() {
             debug!("{:?} Cannot share style: element has id", target.element);
             return StyleSharingResult::CannotShare
@@ -542,7 +545,7 @@ impl<E: TElement> StyleSharingCandidateCache<E> {
             miss!(IdAttr)
         }
 
-        if target.style_attribute().is_some() {
+        if !checks::have_same_style_attribute(target, candidate) {
             miss!(StyleAttr)
         }
 

components/style/stylist.rs

@@ -26,8 +26,8 @@ use selector_map::{SelectorMap, SelectorMapEntry};
 use selector_parser::{SelectorImpl, PseudoElement};
 use selectors::attr::NamespaceConstraint;
 use selectors::bloom::BloomFilter;
-use selectors::matching::{AFFECTED_BY_STYLE_ATTRIBUTE, AFFECTED_BY_PRESENTATIONAL_HINTS};
 use selectors::matching::{ElementSelectorFlags, matches_selector, MatchingContext, MatchingMode};
+use selectors::matching::AFFECTED_BY_PRESENTATIONAL_HINTS;
 use selectors::parser::{Combinator, Component, Selector, SelectorInner, SelectorIter, SelectorMethods};
 use selectors::visitor::SelectorVisitor;
 use shared_lock::{Locked, SharedRwLockReadGuard, StylesheetGuards};
@@ -1007,7 +1007,6 @@ impl Stylist {
 
             // Step 4: Normal style attributes.
             if let Some(sa) = style_attribute {
-                context.relations |= AFFECTED_BY_STYLE_ATTRIBUTE;
                 Push::push(
                     applicable_declarations,
                     ApplicableDeclarationBlock::from_declarations(sa.clone(),