Auto merge of #16148 - emilio:cleanup-animation-only-restyle, r=hiikezoe

style: Cleanup a bit the restyle hint propagation code.

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components/style/data.rs

@@ -135,13 +135,20 @@ pub struct StoredRestyleHint(RestyleHint);
 
 impl StoredRestyleHint {
     /// Propagates this restyle hint to a child element.
-    pub fn propagate(&self) -> Self {
-        // If we have RESTYLE_CSS_ANIMATIONS restyle hint, it means we are in the
-        // middle of an animation only restyle.  In that case, we don't need to
-        // propagate any restyle hints.
-        StoredRestyleHint(if self.0.contains(RESTYLE_CSS_ANIMATIONS) {
-            RestyleHint::empty()
-        } else if self.0.contains(RESTYLE_DESCENDANTS) {
+    pub fn propagate(&mut self) -> Self {
+        use std::mem;
+
+        // If we have RESTYLE_CSS_ANIMATIONS restyle hint, it means we are in
+        // the middle of an animation only restyle. In that case, we don't need
+        // to propagate any restyle hints, and we need to remove ourselves.
+        if self.0.contains(RESTYLE_CSS_ANIMATIONS) {
+            self.0.remove(RESTYLE_CSS_ANIMATIONS);
+            return Self::empty();
+        }
+
+        // Else we should clear ourselves, and return the propagated hint.
+        let hint = mem::replace(&mut self.0, RestyleHint::empty());
+        StoredRestyleHint(if hint.contains(RESTYLE_DESCENDANTS) {
             RESTYLE_SELF | RESTYLE_DESCENDANTS
         } else {
             RestyleHint::empty()
@@ -180,11 +187,6 @@ impl StoredRestyleHint {
         self.0 |= other.0
     }
 
-    /// Remove animation restyle hint.
-    pub fn remove_animation_hint(&mut self) {
-        self.0.remove(RESTYLE_CSS_ANIMATIONS)
-    }
-
     /// Returns true if the hint has animation-only restyle.
     pub fn has_animation_hint(&self) -> bool {
         self.0.contains(RESTYLE_CSS_ANIMATIONS)

components/style/traversal.rs

@@ -15,7 +15,6 @@ use restyle_hints::{RESTYLE_DESCENDANTS, RESTYLE_SELF};
 use selector_parser::RestyleDamage;
 use servo_config::opts;
 use std::borrow::BorrowMut;
-use std::mem;
 use stylist::Stylist;
 
 /// A per-traversal-level chunk of data. This is sent down by the traversal, and
@@ -484,37 +483,46 @@ pub fn recalc_style_at<E, D>(traversal: &D,
 
     // Now that matching and cascading is done, clear the bits corresponding to
     // those operations and compute the propagated restyle hint.
-    let empty_hint = StoredRestyleHint::empty();
     let propagated_hint = match data.get_restyle_mut() {
-        None => empty_hint,
+        None => StoredRestyleHint::empty(),
         Some(r) => {
+            debug_assert!(context.shared.animation_only_restyle ||
+                          !r.hint.has_animation_hint(),
+                          "animation restyle hint should be handled during \
+                           animation-only restyles");
             r.recascade = false;
-            if r.hint.has_animation_hint() {
-                debug_assert!(context.shared.animation_only_restyle,
-                              "animation restyle hint should be handled during animation-only restyles");
-                // Drop animation restyle hint.
-                let propagated_hint = r.hint.propagate();
-                r.hint.remove_animation_hint();
-                propagated_hint
-            } else {
-                mem::replace(&mut r.hint, empty_hint).propagate()
-            }
+            r.hint.propagate()
         },
     };
     debug_assert!(data.has_current_styles() || context.shared.animation_only_restyle,
                   "Should have computed style or haven't yet valid computed style in case of animation-only restyle");
-    trace!("propagated_hint={:?}, inherited_style_changed={:?}", propagated_hint, inherited_style_changed);
+    trace!("propagated_hint={:?}, inherited_style_changed={:?}",
+           propagated_hint, inherited_style_changed);
+
+    let has_dirty_descendants_for_this_restyle =
+        if context.shared.animation_only_restyle {
+            element.has_animation_only_dirty_descendants()
+        } else {
+            element.has_dirty_descendants()
+        };
 
     // Preprocess children, propagating restyle hints and handling sibling relationships.
-    if traversal.should_traverse_children(&mut context.thread_local, element, &data, DontLog) &&
-       ((!context.shared.animation_only_restyle && element.has_dirty_descendants()) ||
-        (context.shared.animation_only_restyle && element.has_animation_only_dirty_descendants()) ||
-        !propagated_hint.is_empty() ||
-        inherited_style_changed) {
+    if traversal.should_traverse_children(&mut context.thread_local,
+                                          element,
+                                          &data,
+                                          DontLog) &&
+        (has_dirty_descendants_for_this_restyle ||
+         !propagated_hint.is_empty() ||
+         inherited_style_changed) {
         let damage_handled = data.get_restyle().map_or(RestyleDamage::empty(), |r| {
             r.damage_handled() | r.damage.handled_for_descendants()
         });
-        preprocess_children(traversal, element, propagated_hint, damage_handled, inherited_style_changed);
+
+        preprocess_children(traversal,
+                            element,
+                            propagated_hint,
+                            damage_handled,
+                            inherited_style_changed);
     }
 
     if context.shared.animation_only_restyle {