Bugfix: 'ref' not available reliably

[bryphe]

Issue: Discovered this while working on a prototype slider control: bryphe/prototype/slider.

Snippet of code with the issue:

let (ref, setRef) = useState(None);
         ...
let onMouseDown = (_evt) => {
       switch(ref) {
       | Some(r) => print_endline("got ref: " ++ string_of_int(r#getInternalId()));
       | None => print_endline("no ref");
       };
}
         ...
<view onMouseDown style ref={(r) => setRef(r)}> 

Defect: The ref would not be available reliably. The ref callback is being called correctly, but when we use setRef it's happening at a time when the instance hasn't been mounted completely in the reconciler - so it's not able to persist the state. Later renders give back None.

Fix: My proposed fix for this is to have this event be 'queued' such that we only dispatch it when reconciliation is complete. This is doable since we have the ref model implemented completely in 'user-space' - in other words, reason-reactify doesn't model ref today.

This would create an event queue for nodes - and only dispatch it on request (which revery will flush these pending events after every render).

Open Questions

• Should we look at add ref as a primitive by default in reason-reactify. If so, would it make sense to have a useRef hook we include as well? If we push it to the framework - we might be able to come up with a more efficient implementation.
• This also seems related to the idea of batching updates used in ReactMini and mentioned in Hooks with slots reason-reactify#51 - which also makes me consider that the reconciler would be the right place to push-back this fix. Depending on how that issue is fixed - I suspect the batching updates - enforcing that 'useState' is called at a correct time with more precision - would also address the issue.

TODO:

• Add test case exercising the issue
• Implement event-queue fix
• Better comments in the Node module
• Fix formatting

[bryphe]

Fix with the upgrade to brisk-reconciler - no need to queue up ref callbacks anymore.