Update _nodeIndex when child changes

[thomasboyt]

This is pretty difficult & important.

When the following structure changes from:

<Main>
  <Composite : frag>
    <one />
    <two />
  </Composite>
  <Composite : frag>
    <one />
    <two />
  </Composite>
</Main>

to:

<Main>
  <Composite : frag>
    <one />
  </Composite>
  <Composite : frag>
    <one />
    <two />
  </Composite>
</Main>

the only update cycle that gets called is for the first composite, and the second one doesn't know that a previous sibling fragment was updated, so its _nodeIndex is now off by one.

[thomasboyt]

wonder if there's a way to trigger some index-updating cycle on Main, given that a child fragment changed...

[thomasboyt]

this is, if nothing else, a predicted problem: facebook#2127 (comment)

[referencing nodes by mountIndex] does not work when one "node" can suddenly become any number of nodes and this may happen without invoking the parent and it may also happen several components deep (wrapping)

[thomasboyt]

options:

• when a composite component's update cycle is hit, if its nodeCount changes, trigger some way to increase the nodeIndexes of subsequent siblings
  • concerned that there's not going to be a simple, and almost certainly not an efficient, way to look up siblings
• trigger the parent update cycle when a fragment changes
  • horrible performance indications, adds user-facing special-case behavior to fragments that we should be trying to avoid, this is a garbage option
• call some method on the parent that only updates nodeIndexes
  • basically equivalent to the first option
  • parent.updateNodeIndexes(thisIndex, newNodeCount)
  • how do we look up the parent in a performant way?
  • can the parent access the children after some nodeIndex in a performant manner? sounds like an expensive filter

[thomasboyt]

The frustrating thing about accessing the parent is that there doesn't seem to be a good way to do it, at all.

I'm imagining a CompositeComponent storing a reference to its parent, somehow, but I don't know if the parent could change out from under it after initial mount. Looking up by root ID seems to be (a) impossible and (b) a super-gross hack even if it was.