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 [email protected].

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