style: Refactor the traversal so it's more easy to read and straight-…

…forward.

components/style/data.rs

@@ -9,7 +9,7 @@
 use dom::TElement;
 use properties::ComputedValues;
 use properties::longhands::display::computed_value as display;
-use restyle_hints::{RESTYLE_LATER_SIBLINGS, RESTYLE_SELF, RESTYLE_STYLE_ATTRIBUTE, RestyleHint};
+use restyle_hints::{RESTYLE_LATER_SIBLINGS, RESTYLE_SELF, RestyleHint};
 use rule_tree::StrongRuleNode;
 use selector_parser::{PseudoElement, RestyleDamage, Snapshot};
 use std::collections::HashMap;
@@ -168,7 +168,7 @@ pub struct StoredRestyleHint {
     ///
     /// This hint is stripped down, and only contains hints that are a subset of
     /// RestyleHint::for_single_element().
-    pub for_self: RestyleHint,
+    pub self_: RestyleHint,
     /// Whether the descendants of this element need to be restyled.
     pub descendants: DescendantRestyleHint,
 }
@@ -177,7 +177,7 @@ impl StoredRestyleHint {
     /// Propagates this restyle hint to a child element.
     pub fn propagate(&self) -> Self {
         StoredRestyleHint {
-            for_self: if self.descendants == DescendantRestyleHint::Empty {
+            self_: if self.descendants == DescendantRestyleHint::Empty {
                 RestyleHint::empty()
             } else {
                 RESTYLE_SELF
@@ -189,7 +189,7 @@ impl StoredRestyleHint {
     /// Creates an empty `StoredRestyleHint`.
     pub fn empty() -> Self {
         StoredRestyleHint {
-            for_self: RestyleHint::empty(),
+            self_: RestyleHint::empty(),
             descendants: DescendantRestyleHint::Empty,
         }
     }
@@ -198,24 +198,25 @@ impl StoredRestyleHint {
     /// including the element.
     pub fn subtree() -> Self {
         StoredRestyleHint {
-            for_self: RESTYLE_SELF,
+            self_: RESTYLE_SELF,
             descendants: DescendantRestyleHint::Descendants,
         }
     }
 
-    /// Whether the restyle hint is empty (nothing requires to be restyled).
-    pub fn is_empty(&self) -> bool {
-        !self.needs_restyle_self() && self.descendants == DescendantRestyleHint::Empty
+    /// Returns true if the hint indicates that our style may be invalidated.
+    pub fn has_self_invalidations(&self) -> bool {
+        !self.self_.is_empty()
     }
 
-    /// Whether the element holding the hint needs to be restyled on some way.
-    pub fn needs_restyle_self(&self) -> bool {
-        !self.for_self.is_empty()
+    /// Whether the restyle hint is empty (nothing requires to be restyled).
+    pub fn is_empty(&self) -> bool {
+        !self.has_self_invalidations() &&
+            self.descendants == DescendantRestyleHint::Empty
     }
 
     /// Insert another restyle hint, effectively resulting in the union of both.
     pub fn insert(&mut self, other: &Self) {
-        self.for_self |= other.for_self;
+        self.self_ |= other.self_;
         self.descendants = self.descendants.union(other.descendants);
     }
 }
@@ -232,7 +233,7 @@ impl From<RestyleHint> for StoredRestyleHint {
         use self::DescendantRestyleHint::*;
         debug_assert!(!hint.contains(RESTYLE_LATER_SIBLINGS), "Caller should apply sibling hints");
         StoredRestyleHint {
-            for_self: hint & RestyleHint::for_single_element(),
+            self_: hint & RestyleHint::for_self(),
             descendants: if hint.contains(RESTYLE_DESCENDANTS) { Descendants } else { Empty },
         }
     }
@@ -348,7 +349,7 @@ impl RestyleData {
 
     /// Returns true if this RestyleData might invalidate the current style.
     pub fn has_invalidations(&self) -> bool {
-        self.hint.needs_restyle_self() ||
+        self.hint.has_self_invalidations() ||
             self.recascade ||
             self.snapshot.is_some()
     }
@@ -369,6 +370,19 @@ pub struct ElementData {
     restyle: Option<Box<RestyleData>>,
 }
 
+/// The kind of restyle that a single element should do.
+pub enum RestyleKind {
+    /// We need to run selector matching plus re-cascade, that is, a full
+    /// restyle.
+    MatchAndCascade,
+    /// We need to recascade with some replacement rule, such as the style
+    /// attribute, or animation rules.
+    CascadeWithReplacements(RestyleHint),
+    /// We only need to recascade, for example, because only inherited
+    /// properties in the parent changed.
+    CascadeOnly,
+}
+
 impl ElementData {
     /// Trivially construct an ElementData.
     pub fn new(existing: Option<ElementStyles>) -> Self {
@@ -387,16 +401,31 @@ impl ElementData {
     /// invalidation.
     pub fn has_current_styles(&self) -> bool {
         self.has_styles() &&
-        self.restyle.as_ref().map_or(true, |r| !r.has_invalidations())
+            self.restyle.as_ref().map_or(true, |r| !r.has_invalidations())
     }
 
-    /// Returns true if this element and its pseudo elements do not need
-    /// selector matching, and can just go on with a style attribute update in
-    /// the rule tree plus re-cascade.
-    pub fn needs_only_style_attribute_update(&self) -> bool {
+    /// Returns the kind of restyling that we're going to need to do on this
+    /// element, based of the stored restyle hint.
+    pub fn restyle_kind(&self) -> RestyleKind {
         debug_assert!(!self.has_current_styles(), "Should've stopped earlier");
-        self.has_styles() &&
-            self.restyle.as_ref().map_or(false, |r| r.hint.for_self == RESTYLE_STYLE_ATTRIBUTE)
+        if !self.has_styles() {
+            return RestyleKind::MatchAndCascade;
+        }
+
+        debug_assert!(self.restyle.is_some());
+        let restyle_data = self.restyle.as_ref().unwrap();
+        let hint = restyle_data.hint.self_;
+        if hint.contains(RESTYLE_SELF) {
+            return RestyleKind::MatchAndCascade;
+        }
+
+        if !hint.is_empty() {
+            return RestyleKind::CascadeWithReplacements(hint);
+        }
+
+        debug_assert!(restyle_data.recascade,
+                      "We definitely need to do something!");
+        return RestyleKind::CascadeOnly;
     }
 
     /// Gets the element styles, if any.

components/style/matching.rs

@@ -17,6 +17,7 @@ use data::{ComputedStyle, ElementData, ElementStyles, PseudoRuleNodes, PseudoSty
 use dom::{SendElement, TElement, TNode};
 use properties::{CascadeFlags, ComputedValues, SHAREABLE, SKIP_ROOT_AND_ITEM_BASED_DISPLAY_FIXUP, cascade};
 use properties::longhands::display::computed_value as display;
+use restyle_hints::{RESTYLE_STYLE_ATTRIBUTE, RestyleHint};
 use rule_tree::{CascadeLevel, StrongRuleNode};
 use selector_parser::{PseudoElement, RestyleDamage, SelectorImpl};
 use selectors::MatchAttr;
@@ -627,31 +628,50 @@ pub trait MatchMethods : TElement {
         }
     }
 
-    /// Updates the style attribute rule nodes without re-running selector
-    /// matching, using just the rule tree.
-    fn update_style_attribute(&self,
-                              context: &StyleContext<Self>,
-                              data: &mut AtomicRefMut<ElementData>)
-                              -> MatchResults {
-        let style_attribute = self.style_attribute();
+    /// Get the appropriate MatchResults from the current styles, to perform a
+    /// recascade.
+    ///
+    /// TODO(emilio): Stop using `MachResults`, use an enum, or something.
+    fn match_results_from_current_style(&self, data: &ElementData) -> MatchResults {
+        let rule_node = data.styles().primary.rules.clone();
+        MatchResults {
+            primary: rule_node,
+            // FIXME(emilio): Same concern as below.
+            relations: StyleRelations::empty(),
+            // The per-pseudo rule-nodes haven't changed, but still need to be
+            // recascaded.
+            per_pseudo: data.styles().pseudos.get_rules(),
+        }
 
-        let mut new_rule_node = data.styles().primary.rules.clone();
+    }
 
-        new_rule_node = context.shared.stylist.rule_tree
-            .replace_rule_at_level_if_applicable(CascadeLevel::StyleAttributeNormal,
-                                                 style_attribute,
-                                                 new_rule_node);
+    /// Updates the rule nodes without re-running selector matching, using just
+    /// the rule tree.
+    fn cascade_with_replacements(&self,
+                                 hint: RestyleHint,
+                                 context: &StyleContext<Self>,
+                                 data: &mut AtomicRefMut<ElementData>)
+                                 -> MatchResults {
+        let mut rule_node = data.styles().primary.rules.clone();
 
-        new_rule_node = context.shared.stylist.rule_tree
-            .replace_rule_at_level_if_applicable(CascadeLevel::StyleAttributeImportant,
-                                                 style_attribute,
-                                                 new_rule_node);
+        if hint.contains(RESTYLE_STYLE_ATTRIBUTE) {
+            let style_attribute = self.style_attribute();
+
+            rule_node = context.shared.stylist.rule_tree
+                .update_rule_at_level(CascadeLevel::StyleAttributeNormal,
+                                      style_attribute,
+                                      rule_node);
+
+            rule_node = context.shared.stylist.rule_tree
+                .update_rule_at_level(CascadeLevel::StyleAttributeImportant,
+                                      style_attribute,
+                                      rule_node);
+        }
 
         MatchResults {
-            primary: new_rule_node,
-            // FIXME(emilio): This is ok, for now at least, because it disables
-            // style sharing. That being said, it's not ideal, probably should
-            // be optional?
+            primary: rule_node,
+            // FIXME(emilio): This is ok, for now, we shouldn't need to fake
+            // this.
             relations: AFFECTED_BY_STYLE_ATTRIBUTE,
             // The per-pseudo rule-nodes haven't changed, but still need to be
             // recomputed.
@@ -675,6 +695,10 @@ pub trait MatchMethods : TElement {
             return StyleSharingResult::CannotShare
         }
 
+        if self.parent_element().is_none() {
+            return StyleSharingResult::CannotShare
+        }
+
         if self.style_attribute().is_some() {
             return StyleSharingResult::CannotShare
         }

components/style/restyle_hints.rs

@@ -53,7 +53,7 @@ bitflags! {
 impl RestyleHint {
     /// The subset hints that affect the styling of a single element during the
     /// traversal.
-    pub fn for_single_element() -> Self {
+    pub fn for_self() -> Self {
         RESTYLE_SELF | RESTYLE_STYLE_ATTRIBUTE
     }
 }

components/style/rule_tree/mod.rs

@@ -184,13 +184,11 @@ impl RuleTree {
     /// Replaces a rule in a given level (if present) for another rule.
     ///
     /// Returns the resulting node that represents the new path.
-    ///
-    /// TODO(emilio): Maybe this should be in `StrongRuleNode`?
-    pub fn replace_rule_at_level_if_applicable(&self,
-                                               level: CascadeLevel,
-                                               pdb: Option<&Arc<RwLock<PropertyDeclarationBlock>>>,
-                                               path: StrongRuleNode)
-                                               -> StrongRuleNode {
+    pub fn update_rule_at_level(&self,
+                                level: CascadeLevel,
+                                pdb: Option<&Arc<RwLock<PropertyDeclarationBlock>>>,
+                                path: StrongRuleNode)
+                                -> StrongRuleNode {
         debug_assert!(level.is_unique_per_element());
         // TODO(emilio): Being smarter with lifetimes we could avoid a bit of
         // the refcount churn.