fix #6687 out-in transition getting stuck with v-if

[neelance]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

An out-in transition could get stuck if the child with v-if was not yet shown and then replaced with a different child. In this case, "afterLeave" would never get fired, thus "_leaving" stayed true indefinitely. This was likely to happen with vue-router and asynchronous data loading before the new page is shown.

Fixes #6687.

[neelance]

Flow is unhappy with Node.COMMENT_NODE. I don't have that much experience with flow. What's the best way to fix this?

[dsonet]

I guess just use the constant value 8 would be fine.

[neelance]

I've changed it to the constant value. One of the tests is still failing. I don't know enough about this code to say if this failure is really something bad or if the behavior is still fine this way and the test could be changed. Can someone with more knowledge on this please help me here?

[dsonet]

Seems you have to update the test to reflect your fix.
The failed test is 'async components with transition-mode out-in'.
But also maybe your fix introduced new bug.

[jkzing]

oldChild.elm could be undefined, so checking existence would be necessary.

oldChild.elm && oldChild.elm.nodeType !== 8

[neelance]

In which situation would this happen?

[jkzing]

This is why 'async components with transition-mode out-in' test failing. 🙂

[neelance]

@jkzing You are right, this indeed fixed the test. Thanks!

I'm a bit surprised, because the log output of the test failure didn't show any error related to undefined.

Is this good to merge now?

[neelance]

Any update?

[yyx990803]

Thanks for the PR @neelance ! I tweaked the implementation a little bit because the transition component is reused in Weex and should ideally be decoupled from the DOM.

[neelance]

@yyx990803 Cool! Thanks for merging.