Auto merge of #17400 - hiikezoe:dont-do-normal-traversal-for-animation-only-restyle-element, r=heycam

Don't run normal traversal for animation only restyle element

<!-- Please describe your changes on the following line: -->
https://bugzilla.mozilla.org/show_bug.cgi?id=1356141

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

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components/style/invalidation/element/invalidator.rs

@@ -239,7 +239,7 @@ impl<'a, 'b: 'a, E> TreeStyleInvalidator<'a, 'b, E>
         let mut any_invalidated = false;
 
         while let Some(sibling) = current {
-            let mut sibling_data = sibling.get_data().map(|d| d.borrow_mut());
+            let mut sibling_data = sibling.mutate_data();
             let sibling_data = sibling_data.as_mut().map(|d| &mut **d);
 
             let mut sibling_invalidator = TreeStyleInvalidator::new(
@@ -302,7 +302,7 @@ impl<'a, 'b: 'a, E> TreeStyleInvalidator<'a, 'b, E>
                 None => continue,
             };
 
-            let mut child_data = child.get_data().map(|d| d.borrow_mut());
+            let mut child_data = child.mutate_data();
             let child_data = child_data.as_mut().map(|d| &mut **d);
 
             let mut child_invalidator = TreeStyleInvalidator::new(

components/style/traversal.rs

@@ -326,14 +326,21 @@ pub trait DomTraversal<E: TElement> : Sync {
         // the element if the element has animation only dirty
         // descendants bit, animation-only restyle hint or recascade.
         if traversal_flags.for_animation_only() {
-            if el.has_animation_only_dirty_descendants() {
-                return true;
-            }
-
+            // Skip elements that have no style data since animation-only
+            // restyle is not necessary for the elements.
             let data = match el.borrow_data() {
                 Some(d) => d,
                 None => return false,
             };
+
+            if !data.has_styles() {
+                return false;
+            }
+
+            if el.has_animation_only_dirty_descendants() {
+                return true;
+            }
+
             return data.restyle.hint.has_animation_hint() ||
                    data.restyle.hint.has_recascade_self();
         }
@@ -455,7 +462,11 @@ pub trait DomTraversal<E: TElement> : Sync {
                     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(); }
+                        if self.shared_context().traversal_flags.for_animation_only() {
+                            unsafe { parent.set_animation_only_dirty_descendants(); }
+                        } else {
+                            unsafe { parent.set_dirty_descendants(); }
+                        }
                     }
                 }
                 f(thread_local, kid);
@@ -855,14 +866,14 @@ where
             None => continue,
         };
 
-        let mut child_data =
-            unsafe { D::ensure_element_data(&child).borrow_mut() };
-
         // If the child is unstyled, we don't need to set up any restyling.
-        if !child_data.has_styles() {
+        if child.borrow_data().map_or(true, |d| !d.has_styles()) {
             continue;
         }
 
+        let mut child_data =
+            unsafe { D::ensure_element_data(&child).borrow_mut() };
+
         trace!(" > {:?} -> {:?} + {:?}, pseudo: {:?}",
                child,
                child_data.restyle.hint,

ports/geckolib/glue.rs

@@ -300,7 +300,9 @@ pub extern "C" fn Servo_TraverseSubtree(root: RawGeckoElementBorrowed,
         return false;
     }
 
-    element.has_dirty_descendants() || element.borrow_data().unwrap().restyle.contains_restyle_data()
+    element.has_dirty_descendants() ||
+    element.has_animation_only_dirty_descendants() ||
+    element.borrow_data().unwrap().restyle.contains_restyle_data()
 }
 
 /// Checks whether the rule tree has crossed its threshold for unused nodes, and
@@ -2801,7 +2803,9 @@ pub extern "C" fn Servo_AssertTreeIsClean(root: RawGeckoElementBorrowed) {
 
     let root = GeckoElement(root);
     fn assert_subtree_is_clean<'le>(el: GeckoElement<'le>) {
-        debug_assert!(!el.has_dirty_descendants() && !el.has_animation_only_dirty_descendants());
+        debug_assert!(!el.has_dirty_descendants() && !el.has_animation_only_dirty_descendants(),
+                      "{:?} has still dirty bit {:?} or animation-only dirty bit {:?}",
+                      el, el.has_dirty_descendants(), el.has_animation_only_dirty_descendants());
         for child in el.as_node().traversal_children() {
             if let Some(child) = child.as_element() {
                 assert_subtree_is_clean(child);