style: More useful logging for transition-related stuff.

Transitions are still broken, but I found these messages more helpful than the
previous ones when diagnosing problems.

components/layout/animation.rs

@@ -89,6 +89,8 @@ pub fn update_animation_state<E>(
                 },
             };
 
+            debug!("update_animation_state({:?}): {:?}", still_running, running_animation);
+
             if still_running {
                 animations_still_running.push(running_animation);
                 continue;

components/style/animation.rs

@@ -438,9 +438,16 @@ pub fn start_transitions_if_applicable(
                 .iter()
                 .any(|animation| animation.has_the_same_end_value_as(&property_animation))
             {
+                debug!(
+                    "Not initiating transition for {}, other transition \
+                     found with the same end value",
+                    property_animation.property_name()
+                );
                 continue;
             }
 
+            debug!("Kicking off transition of {:?}", property_animation);
+
             // Kick off the animation.
             let box_style = new_style.get_box();
             let now = timer.seconds();
@@ -451,7 +458,7 @@ pub fn start_transitions_if_applicable(
                     start_time,
                     AnimationFrame {
                         duration: box_style.transition_duration_mod(i).seconds() as f64,
-                        property_animation: property_animation,
+                        property_animation,
                     },
                 )).unwrap();
 
@@ -657,12 +664,11 @@ pub fn update_style_for_animation<E>(
 where
     E: TElement,
 {
-    debug!("update_style_for_animation: entering");
+    debug!("update_style_for_animation: {:?}", animation);
     debug_assert!(!animation.is_expired());
 
     match *animation {
         Animation::Transition(_, start_time, ref frame) => {
-            debug!("update_style_for_animation: transition found");
             let now = context.timer.seconds();
             let mut new_style = (*style).clone();
             let updated_style =
@@ -678,10 +684,6 @@ where
             AnimationUpdate::Regular
         },
         Animation::Keyframes(_, ref animation, ref name, ref state) => {
-            debug!(
-                "update_style_for_animation: animation found: \"{}\", {:?}",
-                name, state
-            );
             let duration = state.duration;
             let started_at = state.started_at;
 
@@ -716,11 +718,6 @@ where
                 total_progress = 1.;
             }
 
-            debug!(
-                "update_style_for_animation: anim \"{}\", steps: {:?}, state: {:?}, progress: {}",
-                name, animation.steps, state, total_progress
-            );
-
             // Get the target and the last keyframe position.
             let last_keyframe_position;
             let target_keyframe_position;
@@ -865,6 +862,7 @@ pub fn complete_expired_transitions(
         had_animations_to_expire = animations_to_expire.is_some();
         if let Some(ref animations) = animations_to_expire {
             for animation in *animations {
+                debug!("Updating expired animation {:?}", animation);
                 // TODO: support animation-fill-mode
                 if let Animation::Transition(_, _, ref frame) = *animation {
                     frame.property_animation.update(Arc::make_mut(style), 1.0);

components/style/matching.rs

@@ -602,17 +602,8 @@ trait PrivateMatchMethods: TElement {
 
         let mut all_running_animations = context.running_animations.write();
         for mut running_animation in all_running_animations.get_mut(&this_opaque).unwrap() {
-            // This shouldn't happen frequently, but under some circumstances
+            if let Animation::Transition(_, _, ref frame) = *running_animation {
-            // mainly huge load or debug builds, the constellation might be
+                possibly_expired_animations.push(frame.property_animation.clone());
-            // delayed in sending the `TickAllAnimations` message to layout.
-            //
-            // Thus, we can't assume all the animations have been already
-            // updated by layout, because other restyle due to script might be
-            // triggered by layout before the animation tick.
-            //
-            // See #12171 and the associated PR for an example where this
-            // happened while debugging other release panic.
-            if running_animation.is_expired() {
                 continue;
             }
 
@@ -624,9 +615,7 @@ trait PrivateMatchMethods: TElement {
             );
 
             match *running_animation {
-                Animation::Transition(_, _, ref frame) => {
+                Animation::Transition(..) => unreachable!(),
-                    possibly_expired_animations.push(frame.property_animation.clone())
-                }
                 Animation::Keyframes(_, _, _, ref mut state) => {
                     match update {
                         AnimationUpdate::Regular => {},

components/style/properties/helpers/animated_properties.mako.rs

@@ -127,17 +127,22 @@ pub enum AnimatedProperty {
 }
 
 impl AnimatedProperty {
-    /// Get the name of this property.
+    /// Get the id of the property we're animating.
-    pub fn name(&self) -> &'static str {
+    pub fn id(&self) -> LonghandId {
         match *self {
             % for prop in data.longhands:
-                % if prop.animatable and not prop.logical:
+            % if prop.animatable and not prop.logical:
-                    AnimatedProperty::${prop.camel_case}(..) => "${prop.name}",
+            AnimatedProperty::${prop.camel_case}(..) => LonghandId::${prop.camel_case},
-                % endif
+            % endif
             % endfor
         }
     }
 
+    /// Get the name of this property.
+    pub fn name(&self) -> &'static str {
+        self.id().name()
+    }
+
     /// Whether this interpolation does animate, that is, whether the start and
     /// end values are different.
     pub fn does_animate(&self) -> bool {

tests/wpt/metadata/css/css-fonts/variations/font-style-interpolation.html.ini

@@ -1,6 +1,6 @@
 [font-style-interpolation.html]
   bug: https://github.com/servo/servo/issues/21570
   expected: TIMEOUT
-  [font-style animation]
+  [font-style transition]
     expected: TIMEOUT
 

tests/wpt/metadata/css/css-variables/variable-transitions-transition-property-all-before-value.html.ini

@@ -0,0 +1,3 @@
+[variable-transitions-transition-property-all-before-value.html]
+  [Verify substituted color value after transition]
+    expected: FAIL

tests/wpt/metadata/css/css-variables/variable-transitions-value-before-transition-property-all.html.ini

@@ -0,0 +1,3 @@
+[variable-transitions-value-before-transition-property-all.html]
+  [Verify substituted color value after transition]
+    expected: FAIL