Improve ESLint and Babel help messages, when enabling ESLint integration

lib/plugins/eslint.js

@@ -40,6 +40,7 @@ If you prefer to create a ${chalk.yellow('.eslintrc.js')} file by yourself, here
 
 ${chalk.yellow(`// .eslintrc.js
 module.exports = {
+    root: true,
     parser: '@babel/eslint-parser',
     extends: ['eslint:recommended'],
 }
@@ -51,13 +52,37 @@ Install ${chalk.yellow('@babel/eslint-parser')} to prevent potential parsing iss
                 const babelConfig = babelLoaderUtil.getLoaders(webpackConfig)[0].options;
                 // cacheDirectory is a custom loader option, not a Babel option
                 delete babelConfig['cacheDirectory'];
+
+                (babelConfig['presets'] || []).forEach(preset => {
+                    if (!Array.isArray(preset)) {
+                        return;
+                    }
+
+                    if (typeof preset[0] === 'string' && preset[0].includes('@babel') && preset[0].includes('preset-env')) {
+                        // The goal is to replace the preset string with a require.resolve() call, executed at runtime.
+                        // Since we output the Babel config as JSON, we need to replace it with a placeholder.
+                        preset[0] = '__PATH_TO_BABEL_PRESET_ENV__';
+
+                        // The option "targets" is not necessary
+                        delete preset[1]['targets'];
+
+                        // If needed, specify the core-js version to use
+                        if (preset[1]['corejs'] === null) {
+                            preset[1]['corejs'] = packageHelper.getPackageVersion('core-js');
+                        }
+                    }
+                });
+
                 message += `
 
 You will also need to specify your Babel config in a separate file. The current
 configuration Encore has been adding for your is:
 
 ${chalk.yellow(`// babel.config.js
-module.exports = ${JSON.stringify(babelConfig, null, 4)}
+module.exports = ${
+    JSON.stringify(babelConfig, null, 4)
+        .replace('"__PATH_TO_BABEL_PRESET_ENV__"', 'require.resolve("@babel/preset-env")')
+}
 `)}`;
 
                 if (webpackConfig.babelConfigurationCallback) {