Tweak .custom API, validate options hook - it cant be async

Author: Andarist

src/index.js

@@ -35,8 +35,15 @@ function createBabelPluginFactory(customCallback = returnObject) {
 	return pluginOptions => {
 		let customOptions = null;
 
-		if (overrides.customOptions) {
-			({ custom: customOptions = null, plugin: pluginOptions } = overrides.customOptions(pluginOptions));
+		if (overrides.options) {
+			const overridden = overrides.options(pluginOptions);
+
+			if (typeof overridden.then === 'function') {
+				throw new Error(
+					".options hook can't be asynchronous. It should return `{ customOptions, pluginsOptions }` synchronously.",
+				);
+			}
+			({ customOptions = null, pluginOptions } = overridden);
 		}
 
 		const {

test/test.js

@@ -291,9 +291,9 @@ describe('rollup-plugin-babel', function() {
 	it('supports overriding the plugin options in custom loader', () => {
 		const customBabelPlugin = babelPlugin.custom(() => {
 			return {
-				customOptions(options) {
+				options(options) {
 					// Ignore the js extension to test overriding the options
-					return { plugin: Object.assign({}, options, { extensions: ['.x'] }) };
+					return { pluginOptions: Object.assign({}, options, { extensions: ['.x'] }) };
 				},
 				config(cfg) {
 					return Object.assign({}, cfg.options, {