stylo: Remove a lot of the restyle damage related complexity.

The only reason why we had the `existing_style_for_style_damage` bit is to apply
some optimizations that we don't have anymore.

I still want to reintroduce a few of them, at least for the non-eager
pseudo-element case... But I think I won't need this at all.

This allows us to remove a fair amount of Gecko code too.

10 files changed, 76 insertions, 199 deletions

diff --git a/components/layout/animation.rs b/components/layout/animation.rs
index ebbba82fcc6..19f621f7fdc 100644
--- a/components/layout/animation.rs
+++ b/components/layout/animation.rs
@@ -161,9 +161,10 @@ pub fn recalc_style_for_animations(context: &LayoutContext,
                                            &mut fragment.style,
                                            &ServoMetricsProvider);
                 let difference =
-                    RestyleDamage::compute_style_difference(&old_style,
-                                                            &old_style,
-                                                            &fragment.style);
+                    RestyleDamage::compute_style_difference(
+                        &old_style,
+                        &fragment.style,
+                    );
                 damage |= difference.damage;
             }
         }
diff --git a/components/layout_thread/dom_wrapper.rs b/components/layout_thread/dom_wrapper.rs
index beb929d5e16..d35536c627f 100644
--- a/components/layout_thread/dom_wrapper.rs
+++ b/components/layout_thread/dom_wrapper.rs
@@ -444,14 +444,6 @@ impl<'le> TElement for ServoLayoutElement<'le> {
         }
     }
 
-    #[inline]
-    fn existing_style_for_restyle_damage<'a>(&'a self,
-                                             current_cv: &'a ComputedValues,
-                                             _pseudo_element: Option<&PseudoElement>)
-                                             -> Option<&'a ComputedValues> {
-        Some(current_cv)
-    }
-
     fn has_dirty_descendants(&self) -> bool {
         unsafe { self.as_node().node.get_flag(HAS_DIRTY_DESCENDANTS) }
     }
diff --git a/components/style/dom.rs b/components/style/dom.rs
index 8673a50e203..4e699017c64 100644
--- a/components/style/dom.rs
+++ b/components/style/dom.rs
@@ -20,7 +20,7 @@ use properties::{AnimationRules, ComputedValues, PropertyDeclarationBlock};
 #[cfg(feature = "gecko")] use properties::animated_properties::AnimationValue;
 #[cfg(feature = "gecko")] use properties::animated_properties::TransitionProperty;
 use rule_tree::CascadeLevel;
-use selector_parser::{AttrValue, ElementExt, PreExistingComputedValues};
+use selector_parser::{AttrValue, ElementExt};
 use selector_parser::{PseudoClassStringArg, PseudoElement};
 use selectors::matching::{ElementSelectorFlags, VisitedHandlingMode};
 use selectors::sink::Push;
@@ -378,18 +378,6 @@ pub trait TElement : Eq + PartialEq + Debug + Hash + Sized + Copy + Clone +
     /// Internal iterator for the classes of this element.
     fn each_class<F>(&self, callback: F) where F: FnMut(&Atom);
 
-    /// Get the pre-existing style to calculate restyle damage (change hints).
-    ///
-    /// This needs to be generic since it varies between Servo and Gecko.
-    ///
-    /// XXX(emilio): It's a bit unfortunate we need to pass the current computed
-    /// values as an argument here, but otherwise Servo would crash due to
-    /// double borrows to return it.
-    fn existing_style_for_restyle_damage<'a>(&'a self,
-                                             current_computed_values: &'a ComputedValues,
-                                             pseudo: Option<&PseudoElement>)
-                                             -> Option<&'a PreExistingComputedValues>;
-
     /// Whether a given element may generate a pseudo-element.
     ///
     /// This is useful to avoid computing, for example, pseudo styles for
diff --git a/components/style/gecko/pseudo_element.rs b/components/style/gecko/pseudo_element.rs
index 05e2ebbfb6a..fba462171f7 100644
--- a/components/style/gecko/pseudo_element.rs
+++ b/components/style/gecko/pseudo_element.rs
@@ -75,10 +75,22 @@ impl PseudoElement {
         EAGER_PSEUDOS[i].clone()
     }
 
-    /// Whether this pseudo-element is ::before or ::after.
+    /// Whether the current pseudo element is ::before or ::after.
     #[inline]
     pub fn is_before_or_after(&self) -> bool {
-        matches!(*self, PseudoElement::Before | PseudoElement::After)
+        self.is_before() || self.is_after()
+    }
+
+    /// Whether this pseudo-element is the ::before pseudo.
+    #[inline]
+    pub fn is_before(&self) -> bool {
+        *self == PseudoElement::Before
+    }
+
+    /// Whether this pseudo-element is the ::after pseudo.
+    #[inline]
+    pub fn is_after(&self) -> bool {
+        *self == PseudoElement::After
     }
 
     /// Whether this pseudo-element is ::first-letter.
diff --git a/components/style/gecko/restyle_damage.rs b/components/style/gecko/restyle_damage.rs
index 6ba02600e12..67a4366718e 100644
--- a/components/style/gecko/restyle_damage.rs
+++ b/components/style/gecko/restyle_damage.rs
@@ -6,7 +6,7 @@
 
 use gecko_bindings::bindings;
 use gecko_bindings::structs;
-use gecko_bindings::structs::{nsChangeHint, nsStyleContext, nsStyleStructID};
+use gecko_bindings::structs::nsChangeHint;
 use matching::{StyleChange, StyleDifference};
 use properties::ComputedValues;
 use std::ops::{BitAnd, BitOr, BitOrAssign, Not};
@@ -46,49 +46,22 @@ impl GeckoRestyleDamage {
     /// structs, so they effectively only diff structs that have ever been
     /// accessed from layout.
     pub fn compute_style_difference(
-        source: &nsStyleContext,
         old_style: &ComputedValues,
         new_style: &ComputedValues,
     ) -> StyleDifference {
         let mut any_style_changed: bool = false;
         let hint = unsafe {
-            bindings::Gecko_CalcStyleDifference(old_style,
-                                                new_style,
-                                                source.mBits,
-                                                &mut any_style_changed)
+            bindings::Gecko_CalcStyleDifference(
+                old_style,
+                new_style,
+                structs::NS_STYLE_INHERIT_MASK as u64,
+                &mut any_style_changed
+            )
         };
         let change = if any_style_changed { StyleChange::Changed } else { StyleChange::Unchanged };
         StyleDifference::new(GeckoRestyleDamage(nsChangeHint(hint)), change)
     }
 
-    /// Computes the `StyleDifference` between the two `ComputedValues` objects
-    /// for the case where the old and new style are both `display: none`.
-    ///
-    /// In general we don't need to generate damage for such elements, but we
-    /// do need to generate a frame reconstruction for `-moz-binding` changes,
-    /// so that we can start loading the new binding.
-    pub fn compute_undisplayed_style_difference(
-        old_style: &ComputedValues,
-        new_style: &ComputedValues,
-    ) -> StyleDifference {
-        let mut any_style_changed: bool = false;
-
-        // Just compute the Display struct's difference.
-        let display_struct_bit = 1 << (nsStyleStructID::eStyleStruct_Display as u32);
-        let hint = unsafe {
-            bindings::Gecko_CalcStyleDifference(old_style,
-                                                new_style,
-                                                display_struct_bit,
-                                                &mut any_style_changed)
-        };
-
-        // Only pay attention to a reconstruct change hint.
-        let damage = GeckoRestyleDamage(nsChangeHint(hint)) & Self::reconstruct();
-
-        let change = if damage.is_empty() { StyleChange::Changed } else { StyleChange::Unchanged };
-        StyleDifference::new(damage, change)
-    }
-
     /// Returns true if this restyle damage contains all the damage of |other|.
     pub fn contains(self, other: Self) -> bool {
         self & other == other
diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index e4e0936c203..ee2210fa2f0 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -45,7 +45,6 @@ use gecko_bindings::bindings::Gecko_GetExtraContentStyleDeclarations;
 use gecko_bindings::bindings::Gecko_GetHTMLPresentationAttrDeclarationBlock;
 use gecko_bindings::bindings::Gecko_GetSMILOverrideDeclarationBlock;
 use gecko_bindings::bindings::Gecko_GetStyleAttrDeclarationBlock;
-use gecko_bindings::bindings::Gecko_GetStyleContext;
 use gecko_bindings::bindings::Gecko_GetUnvisitedLinkAttrDeclarationBlock;
 use gecko_bindings::bindings::Gecko_GetVisitedLinkAttrDeclarationBlock;
 use gecko_bindings::bindings::Gecko_IsSignificantChild;
@@ -55,7 +54,7 @@ use gecko_bindings::bindings::Gecko_UnsetDirtyStyleAttr;
 use gecko_bindings::bindings::Gecko_UpdateAnimations;
 use gecko_bindings::structs;
 use gecko_bindings::structs::{RawGeckoElement, RawGeckoNode, RawGeckoXBLBinding};
-use gecko_bindings::structs::{nsIAtom, nsIContent, nsINode_BooleanFlag, nsStyleContext};
+use gecko_bindings::structs::{nsIAtom, nsIContent, nsINode_BooleanFlag};
 use gecko_bindings::structs::ELEMENT_HANDLED_SNAPSHOT;
 use gecko_bindings::structs::ELEMENT_HAS_ANIMATION_ONLY_DIRTY_DESCENDANTS_FOR_SERVO;
 use gecko_bindings::structs::ELEMENT_HAS_DIRTY_DESCENDANTS_FOR_SERVO;
@@ -1020,18 +1019,6 @@ impl<'le> TElement for GeckoElement<'le> {
                                      Gecko_ClassOrClassList)
     }
 
-    fn existing_style_for_restyle_damage<'a>(&'a self,
-                                             _existing_values: &'a ComputedValues,
-                                             pseudo: Option<&PseudoElement>)
-                                             -> Option<&'a nsStyleContext> {
-        // TODO(emilio): Migrate this to CSSPseudoElementType.
-        let atom_ptr = pseudo.map_or(ptr::null_mut(), |p| p.atom().as_ptr());
-        unsafe {
-            let context_ptr = Gecko_GetStyleContext(self.0, atom_ptr);
-            context_ptr.as_ref()
-        }
-    }
-
     fn has_snapshot(&self) -> bool {
         self.flags() & (ELEMENT_HAS_SNAPSHOT as u32) != 0
     }
diff --git a/components/style/matching.rs b/components/style/matching.rs
index 25f2fef7c5d..47b03fbb477 100644
--- a/components/style/matching.rs
+++ b/components/style/matching.rs
@@ -14,7 +14,6 @@ use invalidation::element::restyle_hints::{RESTYLE_CSS_ANIMATIONS, RESTYLE_CSS_T
 use invalidation::element::restyle_hints::{RESTYLE_SMIL, RESTYLE_STYLE_ATTRIBUTE};
 use invalidation::element::restyle_hints::RestyleHint;
 use properties::ComputedValues;
-use properties::longhands::display::computed_value as display;
 use rule_tree::{CascadeLevel, StrongRuleNode};
 use selector_parser::{PseudoElement, RestyleDamage};
 use selectors::matching::ElementSelectorFlags;
@@ -152,14 +151,16 @@ trait PrivateMatchMethods: TElement {
     }
 
     #[cfg(feature = "gecko")]
-    fn needs_animations_update(&self,
-                               context: &mut StyleContext<Self>,
-                               old_values: Option<&Arc<ComputedValues>>,
-                               new_values: &ComputedValues)
-                               -> bool {
+    fn needs_animations_update(
+        &self,
+        context: &mut StyleContext<Self>,
+        old_values: Option<&Arc<ComputedValues>>,
+        new_values: &ComputedValues,
+    ) -> bool {
+        use properties::longhands::display::computed_value as display;
+
         let new_box_style = new_values.get_box();
-        let has_new_animation_style = new_box_style.animation_name_count() >= 1 &&
-                                      new_box_style.animation_name_at(0).0.is_some();
+        let has_new_animation_style = new_box_style.specifies_animations();
         let has_animations = self.has_css_animations();
 
         old_values.map_or(has_new_animation_style, |old| {
@@ -175,7 +176,7 @@ trait PrivateMatchMethods: TElement {
             // and update only animations corresponding to those @keyframes.
             (context.shared.traversal_flags.contains(traversal_flags::ForCSSRuleChanges) &&
              has_new_animation_style) ||
-            !old_box_style.animations_equals(&new_box_style) ||
+            !old_box_style.animations_equals(new_box_style) ||
              (old_display_style == display::T::none &&
               new_display_style != display::T::none &&
               has_new_animation_style) ||
@@ -188,14 +189,17 @@ trait PrivateMatchMethods: TElement {
     /// Create a SequentialTask for resolving descendants in a SMIL display property
     /// animation if the display property changed from none.
     #[cfg(feature = "gecko")]
-    fn handle_display_change_for_smil_if_needed(&self,
-                                                context: &mut StyleContext<Self>,
-                                                old_values: Option<&ComputedValues>,
-                                                new_values: &ComputedValues,
-                                                restyle_hints: RestyleHint) {
+    fn handle_display_change_for_smil_if_needed(
+        &self,
+        context: &mut StyleContext<Self>,
+        old_values: Option<&ComputedValues>,
+        new_values: &ComputedValues,
+        restyle_hints: RestyleHint
+    ) {
         use context::DISPLAY_CHANGED_FROM_NONE_FOR_SMIL;
+        use properties::longhands::display::computed_value as display;
 
-        let display_changed_from_none = old_values.as_ref().map_or(false, |old| {
+        let display_changed_from_none = old_values.map_or(false, |old| {
             let old_display_style = old.get_box().clone_display();
             let new_display_style = new_values.get_box().clone_display();
             old_display_style == display::T::none &&
@@ -669,19 +673,22 @@ pub trait MatchMethods : TElement {
         // damage calculation for themselves, when there's an actual pseudo.
         let is_existing_before_or_after =
             cfg!(feature = "gecko") &&
-            pseudo.map_or(false, |p| p.is_before_or_after()) &&
-            self.existing_style_for_restyle_damage(old_values, pseudo)
-                .is_some();
+            pseudo.map_or(false, |p| {
+                (p.is_before() && self.before_pseudo_element().is_some()) ||
+                (p.is_after() && self.after_pseudo_element().is_some())
+            });
 
         if is_existing_before_or_after {
             return ChildCascadeRequirement::CanSkipCascade;
         }
 
-        self.accumulate_damage_for(shared_context,
-                                   restyle,
-                                   old_values,
-                                   new_values,
-                                   pseudo)
+        self.accumulate_damage_for(
+            shared_context,
+            restyle,
+            old_values,
+            new_values,
+            pseudo
+        )
     }
 
     /// Updates the rule nodes without re-running selector matching, using just
@@ -821,81 +828,7 @@ pub trait MatchMethods : TElement {
         pseudo: Option<&PseudoElement>
     ) -> StyleDifference {
         debug_assert!(pseudo.map_or(true, |p| p.is_eager()));
-        if let Some(source) = self.existing_style_for_restyle_damage(old_values, pseudo) {
-            return RestyleDamage::compute_style_difference(source, old_values, new_values)
-        }
-
-        let new_display = new_values.get_box().clone_display();
-        let old_display = old_values.get_box().clone_display();
-
-        let new_style_is_display_none = new_display == display::T::none;
-        let old_style_is_display_none = old_display == display::T::none;
-
-        // If there's no style source, that likely means that Gecko couldn't
-        // find a style context.
-        //
-        // This happens with display:none elements, and not-yet-existing
-        // pseudo-elements.
-        if new_style_is_display_none && old_style_is_display_none {
-            // The style remains display:none.  The only case we need to care
-            // about is if -moz-binding changed, and to generate a reconstruct
-            // so that we can start the binding load.  Otherwise, there is no
-            // need for damage.
-            return RestyleDamage::compute_undisplayed_style_difference(old_values, new_values);
-        }
-
-        if pseudo.map_or(false, |p| p.is_before_or_after()) {
-            // FIXME(bz) This duplicates some of the logic in
-            // PseudoElement::should_exist, but it's not clear how best to share
-            // that logic without redoing the "get the display" work.
-            let old_style_generates_no_pseudo =
-                old_style_is_display_none ||
-                old_values.ineffective_content_property();
-
-            let new_style_generates_no_pseudo =
-                new_style_is_display_none ||
-                new_values.ineffective_content_property();
-
-            if old_style_generates_no_pseudo != new_style_generates_no_pseudo {
-                return StyleDifference::new(RestyleDamage::reconstruct(), StyleChange::Changed)
-            }
-
-            // The pseudo-element will remain undisplayed, so just avoid
-            // triggering any change.
-            //
-            // NOTE(emilio): We will only arrive here for pseudo-elements that
-            // aren't generated (see the is_existing_before_or_after check in
-            // accumulate_damage).
-            //
-            // However, it may be the case that the style of this element would
-            // make us think we need a pseudo, but we don't, like for pseudos in
-            // replaced elements, that's why we need the old != new instead of
-            // just check whether the new style would generate a pseudo.
-            return StyleDifference::new(RestyleDamage::empty(), StyleChange::Unchanged)
-        }
-
-        if pseudo.map_or(false, |p| p.is_first_letter() || p.is_first_line()) {
-            // No one cares about this pseudo, and we've checked above that
-            // we're not switching from a "cares" to a "doesn't care" state
-            // or vice versa.
-            return StyleDifference::new(RestyleDamage::empty(),
-                                        StyleChange::Unchanged)
-        }
-
-        // If we are changing display property we need to accumulate
-        // reconstruction damage for the change.
-        // FIXME: Bug 1378972: This is a workaround for bug 1374175, we should
-        // generate more accurate restyle damage in fallback cases.
-        let needs_reconstruction = new_display != old_display;
-        let damage = if needs_reconstruction {
-            RestyleDamage::reconstruct()
-        } else {
-            RestyleDamage::empty()
-        };
-        // We don't really know if there was a change in any style (since we
-        // didn't actually call compute_style_difference) but we return
-        // StyleChange::Changed conservatively.
-        StyleDifference::new(damage, StyleChange::Changed)
+        RestyleDamage::compute_style_difference(old_values, new_values)
     }
 }
 
diff --git a/components/style/selector_parser.rs b/components/style/selector_parser.rs
index 7443c4534c1..1960f9b8010 100644
--- a/components/style/selector_parser.rs
+++ b/components/style/selector_parser.rs
@@ -35,16 +35,6 @@ pub use servo::restyle_damage::ServoRestyleDamage as RestyleDamage;
 #[cfg(feature = "gecko")]
 pub use gecko::restyle_damage::GeckoRestyleDamage as RestyleDamage;
 
-/// A type that represents the previous computed values needed for restyle
-/// damage calculation.
-#[cfg(feature = "servo")]
-pub type PreExistingComputedValues = ::properties::ComputedValues;
-
-/// A type that represents the previous computed values needed for restyle
-/// damage calculation.
-#[cfg(feature = "gecko")]
-pub type PreExistingComputedValues = ::gecko_bindings::structs::nsStyleContext;
-
 /// Servo's selector parser.
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub struct SelectorParser<'a> {
diff --git a/components/style/servo/restyle_damage.rs b/components/style/servo/restyle_damage.rs
index 1b7e4636e13..fcec01bbe64 100644
--- a/components/style/servo/restyle_damage.rs
+++ b/components/style/servo/restyle_damage.rs
@@ -60,26 +60,15 @@ impl HeapSizeOf for ServoRestyleDamage {
 impl ServoRestyleDamage {
     /// Compute the `StyleDifference` (including the appropriate restyle damage)
     /// for a given style change between `old` and `new`.
-    pub fn compute_style_difference(_source: &ComputedValues,
-                                    old: &ComputedValues,
-                                    new: &ComputedValues)
-                                    -> StyleDifference {
+    pub fn compute_style_difference(
+        old: &ComputedValues,
+        new: &ComputedValues,
+    ) -> StyleDifference {
         let damage = compute_damage(old, new);
         let change = if damage.is_empty() { StyleChange::Unchanged } else { StyleChange::Changed };
         StyleDifference::new(damage, change)
     }
 
-    /// Computes the `StyleDifference` between the two `ComputedValues` objects
-    /// for the case where the old and new style are both `display: none`.
-    ///
-    /// For Servo we never need to generate any damage for such elements.
-    pub fn compute_undisplayed_style_difference(
-        _old_style: &ComputedValues,
-        _new_style: &ComputedValues,
-    ) -> StyleDifference {
-        StyleDifference::new(Self::empty(), StyleChange::Unchanged)
-    }
-
     /// Returns a bitmask that represents a flow that needs to be rebuilt and
     /// reflowed.
     ///
diff --git a/components/style/servo/selector_parser.rs b/components/style/servo/selector_parser.rs
index 4a1170a9a8d..9fcce17bde2 100644
--- a/components/style/servo/selector_parser.rs
+++ b/components/style/servo/selector_parser.rs
@@ -130,10 +130,22 @@ impl PseudoElement {
         result
     }
 
-    /// Whether the current pseudo element is :before or :after.
+    /// Whether the current pseudo element is ::before or ::after.
     #[inline]
     pub fn is_before_or_after(&self) -> bool {
-        matches!(*self, PseudoElement::After | PseudoElement::Before)
+        self.is_before() || self.is_after()
+    }
+
+    /// Whether this pseudo-element is the ::before pseudo.
+    #[inline]
+    pub fn is_before(&self) -> bool {
+        *self == PseudoElement::Before
+    }
+
+    /// Whether this pseudo-element is the ::after pseudo.
+    #[inline]
+    pub fn is_after(&self) -> bool {
+        *self == PseudoElement::After
     }
 
     /// Whether the current pseudo element is :first-letter