1376482 - Some animations not detected in Browser Toolbox

Status: NEW

(DevTools :: Inspector: Animations, defect, P2)

Description

[Sam Foster [:sfoster] (he/him)]

Attachment: noAnimationsToolboxAnimationPanel.png

The attached screenshot shows a rule on an element that has a CSS animation defined using a selector #downloads-notification-anchor[notification="start"] > #downloads-indicator-notification. The notification attribute is set by js, and then removed later. The inspector shows the rule correctly, including the animation properties, but the animation panel says no animations found for the current element.

I'm not sure what the important variables are here - if this is a toolbox only bug, or specific to this kind of selector, or because the rule is only matched after "page" load?

Comment 1

[Patrick Brosset <:pbro>]

I think I tracked it down to somewhere in the initialization of AnimationPlayerActor in /devtools/server/actors/animation.js.
In there, this.walker may be null if AnimationsActor.setWalkerActor was never called. 
However, in the node getter in AnimationPlayerActor, we access this.walker without checking if it exists first.

Comment 2

[Patrick Brosset <:pbro>]

First, we should make sure that this.walker is defined before trying to access it here: https://searchfox.org/mozilla-central/rev/8839daefd69087d7ac2655b72790d3a25b6a815c/devtools/server/actors/animation.js#105

Second, we should investigate why this.walker is undefined in this case (note that this only occurs with the browser toolbox).
The walker is being set from the client-side here: https://searchfox.org/mozilla-central/rev/8839daefd69087d7ac2655b72790d3a25b6a815c/devtools/client/animationinspector/animation-controller.js#166
So, it means the trait hasSetWalkerActor method is falsy here for some reason.