[Webkit-unassigned] [Bug 218011] REGRESSION (r263729): transition doesn't restart

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=218011

--- Comment #4 from Antoine Quint <graouts at webkit.org> ---
Under the call to getAnimations(), we take this code branch:

    // A CSS Transition might have completed since the last time animations were updated so we must
    // update the running and completed transitions membership in that case.
    if (is<CSSTransition>(animation) && matchingBackingAnimation && styleable.hasRunningTransitionsForProperty(property) && animation->playState() == WebAnimation::PlayState::Finished) {
        styleable.ensureCompletedTransitionsByProperty().set(property, styleable.ensureRunningTransitionsByProperty().take(property));
        animation = nullptr;
    }

After this, styleable.hasRunningTransitionsForProperty(property) is false and styleable.hasCompletedTransitionsForProperty(property) is true.

Then, upon style recalc due to resetting the transition and transform styles on the target, we take this code branch:

    else if (styleable.hasCompletedTransitionsForProperty(property) && !propertyInStyleMatchesValueForTransitionInMap(property, afterChangeStyle, styleable.ensureCompletedTransitionsByProperty())) {
        // 2. Otherwise, if the element has a completed transition for the property and the end value of the completed transition is different from
        //    the after-change style for the property, then implementations must remove the completed transition from the set of completed transitions.
        styleable.ensureCompletedTransitionsByProperty().remove(property);
    }

After this, styleable.hasRunningTransitionsForProperty(property) and styleable.hasCompletedTransitionsForProperty(property) are both false.

However, the next time we enter AnimationTimeline::updateCSSTransitionsForStyleableAndProperty() upon attempting to restart a transition, styleable.hasRunningTransitionsForProperty(property) is false but styleable.hasCompletedTransitionsForProperty(property) is back to being true. That's the problem, there should not be a completed running transition for this property.

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