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node_modules/@vue/cli-plugin-babel/migrator/index.js

@@ -0,0 +1,18 @@
+const { chalk } = require('@vue/cli-shared-utils')
+
+module.exports = (api) => {
+  api.transformScript('babel.config.js', require('../codemods/usePluginPreset'))
+
+  if (api.fromVersion('^3')) {
+    api.extendPackage({
+      dependencies: {
+        'core-js': '^3.4.3'
+      }
+    }, true)
+
+    // TODO: implement a codemod to migrate polyfills
+    api.exitLog(`core-js has been upgraded from v2 to v3.
+If you have any custom polyfills defined in ${chalk.yellow('babel.config.js')}, please be aware their names may have been changed.
+For more complete changelog, see https://github.com/zloirock/core-js/blob/master/CHANGELOG.md#300---20190319`)
+  }
+}