tree 9b9252b4995f259fcac8c37dcf4a0630be3201c5
parent abdd95b9af9163df03f954b52e1327029843792f
author Emilio Cobos Álvarez <emilio@crisal.io> 1578414237 +0000
committer moz-wptsync-bot <wptsync@mozilla.com> 1578576353 +0000

Ensure to not create transition rules for elements that don't have any transition effect.

There are multiple places where bogus non-empty transition rules can be created
before this patch when EffectSet's cascade information isn't up-to-date.  That
can happen as described in bug 1606176.

Anyhow, in this particular call site, this is only used to filter from
transition rules effects that are from running animations, to implement:

https://drafts.csswg.org/css-transitions/#application:

>  Implementations must add this value to the cascade if and only if that
>  property is not currently undergoing a CSS Animation ([CSS3-ANIMATIONS])
>  on the same element.

In the test-case, the EffectSet cascade info is empty, so we hit the "skip
everything" for animations (wrong), and "skip nothing for transitions" (also
wrong). This creates a transition rule node which then we never remove
(understandably, as the element never had a transition!).

This fixes the observables of this test-case, by checking the cascade level
(so that we don't create transition rule nodes with declarations coming from
animations). This is strictly more correct than what we were doing.

If we hit the proposed assertion after this change, this code may still create
transition rules that incorrectly override animations, but will never mint one
out of the blue which we'd then fail to remove (which is the problem the
test-case is hitting).

Differential Revision: https://phabricator.services.mozilla.com/D58333

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1605610
gecko-commit: d74a47ca0f779bd8244f5ebcf78efef85fa18dce
gecko-integration-branch: autoland
gecko-reviewers: hiro