fix: module issue with plugin-transform-runtime

It makes babel assume every file is module. So set source to
unambiguous.

See #479

Author: swashata

packages/babel-preset-base/@types/babel-helper-plugin-utils.d.ts

@@ -3,13 +3,21 @@ declare module '@babel/helper-plugin-utils' {
 	// I have written all these under `__mocks__/@babel/helper-plugin-utils.ts`
 	// Is there any way to reuse it?
 	namespace helper {
-		type assertversion = (v:number) => boolean;
+		type assertversion = (v: number) => boolean;
 		interface Api {
-			assertVersion:assertversion;
+			assertVersion: assertversion;
 		}
-		type Options = { [x: string]: string | Options[] | Options };
-		type declareHandler = (api: Api, opts: Options, dirname?: string) => any;
-		function declare(builder:declareHandler) : (api:Api, options:Options, dirname?:string) => any;
+		interface Options {
+			[x: string]: string | Options[] | Options;
+		}
+		type declareHandler = (
+			api: Api,
+			opts: Options,
+			dirname?: string
+		) => any;
+		function declare(
+			builder: declareHandler
+		): (api: Api, options: Options, dirname?: string) => any;
 	}
 	export = helper;
 }

packages/babel-preset-base/src/preset.ts

@@ -29,6 +29,14 @@ export type babelPresetConfiguration = {
 export type babelPreset = [string] | [string, babelPresetConfiguration];
 
 export const preset = (opts: PresetOptions | null = {}) => {
+	// from CRA
+	// This is similar to how `env` works in Babel:
+	// https://babeljs.io/docs/usage/babelrc/#env-option
+	// We are not using `env` because it’s ignored in versions > [email protected]:
+	// https://github.com/babel/babel/issues/4539
+	// https://github.com/facebook/create-react-app/issues/720
+	// It’s also nice that we can enforce `NODE_ENV` being specified.
+	const env = process.env.BABEL_ENV || process.env.NODE_ENV;
 	// Extract this preset specific options and pass the rest to @babel/preset-env
 	const {
 		presetEnv = {},
@@ -55,7 +63,7 @@ export const preset = (opts: PresetOptions | null = {}) => {
 				// Put development based on BABEL_ENV
 				// Adds component stack to warning messages
 				// Adds __self attribute to JSX which React will use for some warnings
-				development: process.env.BABEL_ENV !== 'production',
+				development: env !== 'production',
 				// Will use the native built-in instead of trying to polyfill
 				// behavior for any plugins that require one.
 				useBuiltIns: true,
@@ -81,7 +89,8 @@ export const preset = (opts: PresetOptions | null = {}) => {
 				corejs: false,
 				helpers: true,
 				regenerator: true,
-				useESModules: true,
+				// We might wanna turn it on once node LTS has ESModules support
+				useESModules: env !== 'test',
 			},
 		],
 	};

packages/scripts/__tests__/config/__snapshots__/WebpackConfigHelper.spec.ts.snap

@@ -44,6 +44,7 @@ Object {
     ],
   ],
   "sourceMaps": false,
+  "sourceType": "unambiguous",
 }
 `;
 
@@ -137,6 +138,7 @@ Object {
               ],
             ],
             "sourceMaps": false,
+            "sourceType": "unambiguous",
           },
         },
       ],

packages/scripts/src/config/WebpackConfigHelper.ts

@@ -494,6 +494,11 @@ ${bannerConfig.copyrightText}${bannerConfig.credit ? creditNote : ''}`,
 					options: {
 						// cache
 						...babelLoaderCacheOptions,
+						// Babel assumes ES Modules, which isn't safe until CommonJS
+						// dies. This changes the behavior to assume CommonJS unless
+						// an `import` or `export` is present in the file.
+						// https://github.com/webpack/webpack/issues/4039#issuecomment-419284940
+						sourceType: 'unambiguous',
 						// preset from our own package
 						presets: getBabelPresets({ hasReact: false }),
 						// If an error happens in a package, it's possible to be