feat: remove remaining React imports

[nickserv]

Follows up on #9853 and removes remaining React imports, as React 17 is supported and #9734 has been merged.

[nickserv]

A smoke test has the ESLint error 'React' is not defined react/jsx-no-undef in src/index.tsx. It seems like this is only an issue with TypeScript. Should we disable react/jsx-no-undef with TS like we already do with no-undef?

https://dev.azure.com/facebook/create-react-app/_build/results?buildId=2072&view=logs&j=2a983690-2011-537a-f1b1-93b016d28b7e&t=6a887007-3b70-5b2f-836b-0f0b425fc73a

[MichaelDeBoey]

Shouldn't this be handled automatically by eslint-plugin-react when React 17 is detected? 🤔

CC: @yannickcr

[yannickcr]

@MichaelDeBoey For eslint-plugsin-react and React 17 you only have to disable the react/jsx-uses-react and react/react-in-jsx-scope rules: https://reactjs.org/blog/2020/09/22/introducing-the-new-jsx-transform.html#eslint

For this case I'd say the React import should not be removed from here https://github.com/facebook/create-react-app/pull/9907/files#diff-64c681ba8886069f7e1af46ff0db7eb161244eb14a4a7c780d83eaae6c126cbf since it is still used for React.StrictMode

[n3tr]

The current version of TypeScript (4.0.x) doesn't support the new JSX transform (introducing in 4.1).

Removing import React from the typescript template might break the app unless the user installs typescript@4.1.0-beta.

There is code checking the ts version and switch to use new jsx configuration

• https://github.com/facebook/create-react-app/blob/master/packages/react-scripts/scripts/utils/verifyTypeScriptSetup.js#L148-L158

[nickserv]

@MichaelDeBoey @yannickcr Is it safe to remove those rules from eslint-config-react-app? It could cause confusion for any external users that still aren't using the new JSX transform, but CRA 4 users should be fine either way.

@n3tr There is an issue with TS 4.1 beta support in CRA 4 (#9868) that makes upgrading tricky anyway, and by the time that fix is published TS 4.1 may already be stable.

[nickserv]

TypeScript 4.1 is stable and #9868 has been closed, so this should be ready to merge once the review suggestions are resolved.

[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[nickserv]

I have an unresolved question:

Is it safe to remove those rules from eslint-config-react-app? It could cause confusion for any external users that still aren't using the new JSX transform, but CRA 4 users should be fine either way.

[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[MichaelDeBoey]

We should still merge this one

[nickserv]

This is ready to review again, but I'd still like to know the plan with the lint config