Mixing with_children() and manual Parent insertion result in random children order

[djeedai]

Bevy version

0.6

Operating system & version

Windows 10 / likely irrelevant

What you did

1. Add some children with with_children()
2. Add other children by manually inserting the Parent component

What you expected to happen

Children (they're UI nodes) display in expected order according to FlexDirection

What actually happened

Random order. It seems that children from with_children() are inserted first, followed by any other one from manually adding Parent.

Additional information

Related to, or can be confused with, #1214, which is a different documentation-only bug.

[djeedai]

From Discord:

François 🥷🏻 — Today at 11:12 AM
when you insert the parent component yourself, there's another system cleaning up the hierarchy that's updating the children component of the parent. but as it happens in another system, it's not in the same command queue so ordering is lost

[alice-i-cecile]

@cart can we get a A-Hierarchy label?

[cart]

Done!

[JaySpruce]

Fixed by #17398 (Children is now updated by component hooks instead of a system).