Children nodes are inserted to new parent without first removing them from their old parent

[scofalik]

I spotted a bug that crashed editor during rendering. It appeared that Renderer wants to re-render a part of a tree that is detached from main tree. What was weird about that tree was that detached-root had a child but that child's parent property was set to null. Similarly, that child also had a child which also had parent set to null.

After debugging it appeared that in view.Writer some nodes were supposed to be moved from one node to another, however those nodes were not removed from their original parent before appending to new parent, which caused this bug.

[scofalik]

While I am at it, I'll check the whole code for appendChildren and insertChildren usage and will fix it where needed.

[Reinmar]

Is it https://github.com/ckeditor/ckeditor5-engine/issues/1038?

[scofalik]

Yes, it is.

Alternatively, we can solve it by adding more logic in appendChildren/insertChildren.

I can change the solution.

[Reinmar]

I'm for more logic inside appendChildren() (or whichever is the lowest level method).

[Reinmar]

PJ is too:

I agree that appendChild should remove them from the previous parent. In the model, #4009 will (should) solver it. However, we should solve it in the view too.