style: Handle TraversalRestyleBehavior::ForReconstruct in the Servo restyle.

components/style/build_gecko.rs

@@ -321,6 +321,7 @@ mod bindings {
             "mozilla::css::SheetParsingMode",
             "mozilla::HalfCorner",
             "mozilla::PropertyStyleAnimationValuePair",
+            "mozilla::TraversalRestyleBehavior",
             "mozilla::TraversalRootBehavior",
             "mozilla::StyleShapeRadius",
             "mozilla::StyleGrid.*",
@@ -616,6 +617,7 @@ mod bindings {
             "RawGeckoURLExtraData",
             "RefPtr",
             "CSSPseudoClassType",
+            "TraversalRestyleBehavior",
             "TraversalRootBehavior",
             "ComputedTimingFunction_BeforeFlag",
             "FontFamilyList",

components/style/data.rs

@@ -223,6 +223,13 @@ impl StoredRestyleHint {
         StoredRestyleHint(RESTYLE_SELF | RESTYLE_DESCENDANTS)
     }
 
+    /// Creates a restyle hint that forces the element and all its later
+    /// siblings to have their whole subtrees restyled, including the elements
+    /// themselves.
+    pub fn subtree_and_later_siblings() -> Self {
+        StoredRestyleHint(RESTYLE_SELF | RESTYLE_DESCENDANTS | RESTYLE_LATER_SIBLINGS)
+    }
+
     /// Returns true if the hint indicates that our style may be invalidated.
     pub fn has_self_invalidations(&self) -> bool {
         self.0.intersects(RestyleHint::for_self())

components/style/matching.rs

@@ -557,7 +557,7 @@ trait PrivateMatchMethods: TElement {
 
         // Accumulate restyle damage.
         if let Some(old) = old_values {
-            self.accumulate_damage(restyle.unwrap(), &old, &new_values, pseudo);
+            self.accumulate_damage(&context.shared, restyle.unwrap(), &old, &new_values, pseudo);
         }
 
         // Set the new computed values.
@@ -677,10 +677,16 @@ trait PrivateMatchMethods: TElement {
     /// Computes and applies non-redundant damage.
     #[cfg(feature = "gecko")]
     fn accumulate_damage(&self,
+                         shared_context: &SharedStyleContext,
                          restyle: &mut RestyleData,
                          old_values: &Arc<ComputedValues>,
                          new_values: &Arc<ComputedValues>,
                          pseudo: Option<&PseudoElement>) {
+        // Don't accumulate damage if we're in a restyle for reconstruction.
+        if shared_context.traversal_flags.for_reconstruct() {
+            return;
+        }
+
         // If an ancestor is already getting reconstructed by Gecko's top-down
         // frame constructor, no need to apply damage.
         if restyle.damage_handled.contains(RestyleDamage::reconstruct()) {
@@ -705,6 +711,7 @@ trait PrivateMatchMethods: TElement {
     /// Computes and applies restyle damage unless we've already maxed it out.
     #[cfg(feature = "servo")]
     fn accumulate_damage(&self,
+                         _shared_context: &SharedStyleContext,
                          restyle: &mut RestyleData,
                          old_values: &Arc<ComputedValues>,
                          new_values: &Arc<ComputedValues>,
@@ -1109,7 +1116,7 @@ pub trait MatchMethods : TElement {
                     let old_values = data.get_styles_mut()
                                          .and_then(|s| s.primary.values.take());
                     if let Some(old) = old_values {
-                        self.accumulate_damage(data.restyle_mut(), &old,
+                        self.accumulate_damage(shared_context, data.restyle_mut(), &old,
                                                shared_style.values(), None);
                     }
 

components/style/traversal.rs

@@ -31,12 +31,14 @@ pub struct PerLevelTraversalData {
 }
 
 bitflags! {
-    /// Represents that target elements of the traversal.
+    /// Flags that control the traversal process.
     pub flags TraversalFlags: u8 {
         /// Traverse only unstyled children.
         const UNSTYLED_CHILDREN_ONLY = 0x01,
-        /// Traverse only elements for animation restyles
+        /// Traverse only elements for animation restyles.
         const ANIMATION_ONLY = 0x02,
+        /// Traverse without generating any change hints.
+        const FOR_RECONSTRUCT = 0x04,
     }
 }
 
@@ -50,6 +52,11 @@ impl TraversalFlags {
     pub fn for_unstyled_children_only(&self) -> bool {
         self.contains(UNSTYLED_CHILDREN_ONLY)
     }
+
+    /// Returns true if the traversal is for a frame reconstruction.
+    pub fn for_reconstruct(&self) -> bool {
+        self.contains(FOR_RECONSTRUCT)
+    }
 }
 
 /// This structure exists to enforce that callers invoke pre_traverse, and also
@@ -148,6 +155,10 @@ pub trait DomTraversal<E: TElement> : Sync {
     fn pre_traverse(root: E, stylist: &Stylist, traversal_flags: TraversalFlags)
                     -> PreTraverseToken
     {
+        debug_assert!(!(traversal_flags.for_reconstruct() &&
+                        traversal_flags.for_unstyled_children_only()),
+                      "must not specify FOR_RECONSTRUCT in combination with UNSTYLED_CHILDREN_ONLY");
+
         if traversal_flags.for_unstyled_children_only() {
             if root.borrow_data().map_or(true, |d| d.has_styles() && d.styles().is_display_none()) {
                 return PreTraverseToken {
@@ -165,12 +176,18 @@ pub trait DomTraversal<E: TElement> : Sync {
         // we need a special case for the root.
         //
         // Expanding snapshots here may create a LATER_SIBLINGS restyle hint, which
-        // we will drop on the floor. To prevent missed restyles, we assert against
+        // we propagate to the next sibling element.
-        // restyling a root with later siblings.
         if let Some(mut data) = root.mutate_data() {
             if let Some(r) = data.get_restyle_mut() {
-                debug_assert!(root.next_sibling_element().is_none());
+                let later_siblings = r.compute_final_hint(root, stylist);
-                let _later_siblings = r.compute_final_hint(root, stylist);
+                if later_siblings {
+                    if let Some(next) = root.next_sibling_element() {
+                        if let Some(mut next_data) = next.mutate_data() {
+                            let hint = StoredRestyleHint::subtree_and_later_siblings();
+                            next_data.ensure_restyle().hint.insert(&hint);
+                        }
+                    }
+                }
             }
         }
 
@@ -195,6 +212,10 @@ pub trait DomTraversal<E: TElement> : Sync {
             return true;
         }
 
+        if traversal_flags.for_reconstruct() {
+            return true;
+        }
+
         match node.as_element() {
             None => Self::text_node_needs_traversal(node),
             Some(el) => {
@@ -264,7 +285,11 @@ pub trait DomTraversal<E: TElement> : Sync {
                 // Servo uses the post-order traversal for flow construction, so
                 // we need to traverse any element with damage so that we can perform
                 // fixup / reconstruction on our way back up the tree.
-                if cfg!(feature = "servo") &&
+                //
+                // We also need to traverse nodes with explicit damage and no other
+                // restyle data, so that this damage can be cleared.
+                if (cfg!(feature = "servo") ||
+                    traversal_flags.for_reconstruct()) &&
                    data.get_restyle().map_or(false, |r| r.damage != RestyleDamage::empty())
                 {
                     return true;
@@ -342,11 +367,15 @@ pub trait DomTraversal<E: TElement> : Sync {
 
         for kid in parent.as_node().children() {
             if Self::node_needs_traversal(kid, self.shared_context().traversal_flags) {
-                let el = kid.as_element();
+                // If we are in a restyle for reconstruction, there is no need to
-                if el.as_ref().and_then(|el| el.borrow_data())
+                // perform a post-traversal, so we don't need to set the dirty
-                              .map_or(false, |d| d.has_styles())
+                // descendants bit on the parent.
-                {
+                if !self.shared_context().traversal_flags.for_reconstruct() {
-                    unsafe { parent.set_dirty_descendants(); }
+                    let el = kid.as_element();
+                    if el.as_ref().and_then(|el| el.borrow_data())
+                                  .map_or(false, |d| d.has_styles()) {
+                        unsafe { parent.set_dirty_descendants(); }
+                    }
                 }
                 f(thread_local, kid);
             }
@@ -557,20 +586,34 @@ pub fn recalc_style_at<E, D>(traversal: &D,
                             inherited_style_changed);
     }
 
+    // If we are in a restyle for reconstruction, drop the existing restyle
+    // data here, since we won't need to perform a post-traversal to pick up
+    // any change hints.
+    if context.shared.traversal_flags.for_reconstruct() {
+        data.clear_restyle();
+    }
+
     if context.shared.traversal_flags.for_animation_only() {
         unsafe { element.unset_animation_only_dirty_descendants(); }
     }
 
-    // Make sure the dirty descendants bit is not set for the root of a
+    // There are two cases when we want to clear the dity descendants bit
-    // display:none subtree, even if the style didn't change (since, if
+    // here after styling this element.
-    // the style did change, we'd have already cleared it above).
+    //
+    // The first case is when this element is the root of a display:none
+    // subtree, even if the style didn't change (since, if the style did
+    // change, we'd have already cleared it above).
     //
     // This keeps the tree in a valid state without requiring the DOM to
     // check display:none on the parent when inserting new children (which
     // can be moderately expensive). Instead, DOM implementations can
     // unconditionally set the dirty descendants bit on any styled parent,
     // and let the traversal sort it out.
-    if data.styles().is_display_none() {
+    //
+    // The second case is when we are in a restyle for reconstruction,
+    // where we won't need to perform a post-traversal to pick up any
+    // change hints.
+    if data.styles().is_display_none() || context.shared.traversal_flags.for_reconstruct() {
         unsafe { element.unset_dirty_descendants(); }
     }
 }

ports/geckolib/glue.rs

@@ -85,7 +85,7 @@ use style::stylesheets::StylesheetLoader as StyleStylesheetLoader;
 use style::supports::parse_condition_or_declaration;
 use style::thread_state;
 use style::timer::Timer;
-use style::traversal::{ANIMATION_ONLY, UNSTYLED_CHILDREN_ONLY};
+use style::traversal::{ANIMATION_ONLY, FOR_RECONSTRUCT, UNSTYLED_CHILDREN_ONLY};
 use style::traversal::{resolve_style, DomTraversal, TraversalDriver, TraversalFlags};
 use style_traits::ToCss;
 use super::stylesheet_loader::StylesheetLoader;
@@ -207,13 +207,20 @@ fn traverse_subtree(element: GeckoElement, raw_data: RawServoStyleSetBorrowed,
 #[no_mangle]
 pub extern "C" fn Servo_TraverseSubtree(root: RawGeckoElementBorrowed,
                                         raw_data: RawServoStyleSetBorrowed,
-                                        behavior: structs::TraversalRootBehavior) -> bool {
+                                        root_behavior: structs::TraversalRootBehavior,
+                                        restyle_behavior: structs::TraversalRestyleBehavior)
+                                        -> bool {
+    use self::structs::TraversalRestyleBehavior as Restyle;
+    use self::structs::TraversalRootBehavior as Root;
+
     let element = GeckoElement(root);
     debug!("Servo_TraverseSubtree: {:?}", element);
 
-    let traversal_flags = match behavior {
+    let traversal_flags = match (root_behavior, restyle_behavior) {
-        structs::TraversalRootBehavior::UnstyledChildrenOnly => UNSTYLED_CHILDREN_ONLY,
+        (Root::Normal, Restyle::Normal) => TraversalFlags::empty(),
-        _ => TraversalFlags::empty(),
+        (Root::UnstyledChildrenOnly, Restyle::Normal) => UNSTYLED_CHILDREN_ONLY,
+        (Root::Normal, Restyle::ForReconstruct) => FOR_RECONSTRUCT,
+        _ => panic!("invalid combination of TraversalRootBehavior and TraversalRestyleBehavior"),
     };
 
     if element.has_animation_only_dirty_descendants() ||