Check if there is a .babelrc file before ejecting #1066

[gustavogodoi]

To verify this change:

1. I ran the tests (yarn test).
2. I ran the react-scripts eject in a project with .babelrc in the root (eject failed with the message).
3. I ran the react-scripts eject in a project without .babelrc in the root and it was ejected.

[facebook-github-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file. In order for us to review and merge your code, please sign up at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need the corporate CLA signed.

If you have received this in error or have any questions, please contact us at cla@fb.com. Thanks!

[gaearon]

This is not enough because there might be a .babelrc higher up in the tree. There are also other ways to specify Babel config, such as package.json files up the tree.

I think we should somehow let the Babel do resolution, and complain if it found anything.

[facebook-github-bot]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

[ahmadawais]

@gaearon In a recent app that I built I chose to put .babelrc in the package.json for this very reason.

// Add Babel config.
		console.log( `  ➕  Adding ${ green( 'Babel' ) } preset.` );
		appPackage.babel = {
			presets: [
				[
					'env',
					{
						modules: false,
						targets: {
							browsers: [
								'last 2 Chrome versions',
								'last 2 Firefox versions',
								'last 2 Safari versions',
								'last 2 iOS versions',
								'last 1 Android version',
								'last 1 ChromeAndroid version',
								'ie 11',
							],
						},
					},
				],
			],
			plugins: [
				[ 'transform-object-rest-spread' ],
				[
					'transform-object-rest-spread',
					{
						useBuiltIns: true,
					},
				],
				[
					'transform-react-jsx',
					{
						pragma: 'wp.element.createElement',
					},
				],
				[
					'transform-runtime',
					{
						helpers: false,
						polyfill: false,
						regenerator: true,
					},
				],
			],
		};

		fs.writeFileSync(
			path.join( appPath, 'package.json' ),
			JSON.stringify( appPackage, null, 2 ) + '\n'
		);