Add key validation to React.Children.toArray

[clemmy]

Addresses #11549

This warns only on React.Children.toArray. I don't think the other children helper methods (forEach, map, and count) are dangerous.

[gaearon]

What's the rollout plan? Just enabling this is going to be painful for everyone who's intentionally using to suppress the key warning.

[aweary]

I don't think the other children helper methods (forEach, map, and count) are dangerous.

It looks like map can also be used to skip key validation since it also uses mapIntoWithKeyPrefixInternal

[clemmy]

@aweary Hmm, I imagined there would be a use case where .map is used to add keys to a child, but on second thought, that seems super awkward as you'd have to do something like:

React.Children.map(children, (child) => { <Child {...child.props} key={} /> })

[clemmy]

@gaearon Add keys or use JSX fragments! Outside of that, they might just have to deal with the fact that since they're doing something weird, we're going to warn them.

[gaearon]

Have you tried this on www and assessed how many new warnings this will cause?

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[gaearon]

I'll close because it's a bit stale and also needs somebody to assess the number of new warnings at FB, but @clemmy's internship has ended. Maybe we'll revisit this some time in the future. I'll keep the issue open.