Add definition for React.forwardRef()

[motiz88]

Closes #6103. There is some context re: soundness in #6103 (comment).

The type of the render argument here diverges very slightly from that in React master at the moment, but see facebook/react#13100 for the reason why.

UPDATE: With facebook/react#13100 now merged, this is aligned with the React source code's own definition of forwardRef.

[AlmeroSteyn]

Hi!

Started introducing Flow into my React project last week. As we focus on accessibility a lot, there is a lot of focus management and therefore usage of Refs. So we immediately bumped into this one with forwardRef.

I understand how these projects go and therefore understand that everyone is busy, but could I ask if there is any idea when Flow will support the new 16.3 features fully?

Is there also some clear documentation/examples somewhere showing how to use Flow with React.createRef?

Thank you so much for building tools like this and maintaining it.

[motiz88]

Hey @AlmeroSteyn,

1. I think [meta] Bringing Flow types in line with 16.3 APIs react#12553 gives a complete picture of React 16.3 features in Flow and that's probably the best place to discuss them as a whole. I wish I could tell you anything about timelines, but your guess is as good as mine I'm afraid.

2. https://flow.org/en/docs/react/refs/ is probably due for an update documenting createRef (and forwardRef for that matter, when this is merged) since it only mentions ref functions at the moment. I'm not aware of any other source of documentation for this, but I'm sure a docs PR will be welcome 😉

[AlmeroSteyn]

@motiz88, thanks for the reponse.

Had to backtrack on using Flow as we use ref a lot for accessibility (focus control) and also could not find out how to properly type ...rest object spreads. So my code ended up in an any mess.

Thanks for the invite to participate with PR's, however other areas of focus are sapping my time currently. Not that it would help though, the problem is that I cannot get these types working at all LOL. Much less document them.

[motiz88]

@mrkev Any chance you could give this a look? I'm not overjoyed about the #6103 (comment) situation but I think it's the best we can get out of the current mechanics of Flow, and the drawbacks are outweighed by the benefits of providing some form of support for this React feature, 5 months now since its release.

[facebook-github-bot]

motiz88 has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[bvaughn]

I'm not at all familiar with the Flow codebase– so someone like @samwgoldman or @avikchaudhuri should have the final say here, but I think the forwardRef type looks right to me! 👍

[facebook-github-bot]

motiz88 has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[samwgoldman]

This was reviewed internally a while back, but we never updated this PR. Sorry about that. The proposed types here are not quite correct and lead to missed errors when the ref pseudo-prop of the forwardRef component is actually used.

Supporting forwardRef properly requires some deeper changes to Flow's React support, which @jbrown215 is working on.