Just warn on clashing keys but proceed with render

[sophiebits]

We've hit a couple bugs in prod now where keys are supposed to be distinct but aren't, which causes React to throw errors and render nothing.

It would be nice if React could instead warn and render all the components anyway (perhaps adding some suffix to make the keys unique) or render only one of the components with the same ID. Both of these seem preferable to completely dying (though maybe this is just our fault for not properly having our JS error reporting figured out…).

[plievone]

Because keys are optional, it should indeed just warn in prod, not break. But perhaps uniqueness is relied on in too many places to handle a special case of invalid keys nicely?

[sophiebits]

The fact that keys are optional has nothing to do with this. React should have the same behavior in dev and prod but it's perfectly reasonable to throw (as now) or warn.

[plievone]

@spicyj Sorry I meant that as an api user one could assume that keys are just to help react in reusing component instances and if one supplies invalid keys then one could assume that then they are just no help and slower way proceeds. So I support your cause :)