[v4] Don’t use “JSX uses React” with new runtime

[gaearon]

When using the new JSX transform, we should disable the “jsx uses react” ESLint rule. Otherwise you can’t remove the React import — which is one of the points of the new transform.

We should verify that our default template works without the React import in App.js, including the test environment.

[mrmckeb]

I'll take a look at this alongside the other work - I think it will also apply to react/react-in-jsx-scope.

[gaearon]

Ahh yup that's actually the one that's the problem.