Include syntax-object-rest-spread in default Babel options for Node.j…

…s >= 8.3.0

Fixes #1554.

docs/recipes/babelrc.md

@@ -15,6 +15,12 @@ There are multiple options for configuring how AVA transpiles your tests using B
 
 AVA lets you use some nifty JavaScript features, like [async functions](https://github.com/avajs/ava#async-function-support). To make this work on older Node.js versions AVA transpiles the tests and helper files using the [`@ava/stage-4`](https://github.com/avajs/babel-preset-stage-4) Babel preset. This is great for projects where you do not use Babel for your source, but do want to use the newest JavaScript features for your tests.
 
+### Using object rest/spread properties
+
+As of Node.js [8.3.0](https://github.com/nodejs/node/blob/v8.3.0/doc/changelogs/CHANGELOG_V8.md#8.3.0) [object rest/spread properties](https://github.com/tc39/proposal-object-rest-spread) is supported directly. This new language feature however has not yet reached [stage 4](http://2ality.com/2015/11/tc39-process.html#stage-4-finished), which means that AVA won't support it by default. That said, if you're using Node.js 8.3.0 or newer, AVA will load the [`syntax-object-rest-spread`](https://www.npmjs.com/package/babel-plugin-syntax-object-rest-spread) plugin for you. This means you *can* use object rest/spread properties in your tests as long as you're not targeting older Node.js versions.
+
+Note that if you customize the Babel configuration you'll have to explicitly specify the `syntax-object-rest-spread` plugin.
+
 ## Customizing how AVA transpiles your tests
 
 You can override the default Babel configuration AVA uses for test transpilation in `package.json`. For example, the configuration below adds the Babel `rewire` plugin, and adds the Babel [`stage-3`](http://babeljs.io/docs/plugins/preset-stage-3/) preset.

lib/babel-config.js

@@ -6,6 +6,7 @@ const figures = require('figures');
 const configManager = require('hullabaloo-config-manager');
 const md5Hex = require('md5-hex');
 const makeDir = require('make-dir');
+const semver = require('semver');
 const colors = require('./colors');
 
 function validate(conf) {
@@ -99,6 +100,7 @@ function build(projectDir, cacheDir, userOptions, powerAssert) {
 
 	const baseOptions = {
 		babelrc: false,
+		plugins: [],
 		presets: [
 			['@ava/transform-test-files', {powerAssert}]
 		]
@@ -107,6 +109,12 @@ function build(projectDir, cacheDir, userOptions, powerAssert) {
 		baseOptions.presets.unshift('@ava/stage-4');
 	}
 
+	// Include object rest spread support for node versions that support it
+	// natively.
+	if (userOptions === 'default' && semver.satisfies(process.versions.node, '>= 8.3.0')) {
+		baseOptions.plugins.push('babel-plugin-syntax-object-rest-spread');
+	}
+
 	const baseConfig = configManager.createConfig({
 		dir: AVA_DIR, // Presets are resolved relative to this directory
 		hash: md5Hex(JSON.stringify(baseOptions)),

package.json

@@ -108,6 +108,7 @@
 		"ava-init": "^0.2.0",
 		"babel-core": "^6.17.0",
 		"babel-generator": "^6.26.0",
+		"babel-plugin-syntax-object-rest-spread": "^6.13.0",
 		"bluebird": "^3.0.0",
 		"caching-transform": "^1.0.0",
 		"chalk": "^2.0.1",
@@ -165,6 +166,7 @@
 		"require-precompiled": "^0.1.0",
 		"resolve-cwd": "^2.0.0",
 		"safe-buffer": "^5.1.1",
+		"semver": "^5.4.1",
 		"slash": "^1.0.0",
 		"source-map-support": "^0.4.0",
 		"stack-utils": "^1.0.1",

test/babel-config.js

@@ -9,6 +9,19 @@ const configManager = require('hullabaloo-config-manager');
 const babelConfigHelper = require('../lib/babel-config');
 
 const fixture = name => path.join(__dirname, 'fixture', name);
+const setNodeVersion = value => Object.defineProperty(process.versions, 'node', {value});
+const resetNodeVersion = setNodeVersion.bind(null, process.versions.node);
+
+// Execute `run` with a given stubbed node version, then reset to the real
+// version.
+function withNodeVersion(version, run) {
+	setNodeVersion(version);
+	const promise = new Promise(resolve => {
+		resolve(run());
+	});
+	promise.then(resetNodeVersion, resetNodeVersion);
+	return promise;
+}
 
 test('uses default presets when userOptions is "default"', t => {
 	const userOptions = 'default';
@@ -46,6 +59,7 @@ test('uses options from babelrc when userOptions is "inherit"', t => {
 			t.same(options.presets, [require.resolve('@ava/babel-preset-stage-4')]);
 			const envOptions = options.env[configManager.currentEnv()];
 			t.same(envOptions, {
+				plugins: [],
 				presets: [
 					[
 						require.resolve('@ava/babel-preset-transform-test-files'),
@@ -82,6 +96,43 @@ test('uses userOptions for babel options when userOptions is an object', t => {
 		});
 });
 
+test('adds babel-plugin-syntax-object-rest-spread for node versions > 8.3.0', t => {
+	const projectDir = uniqueTempDir();
+	const cacheDir = path.join(projectDir, 'cache');
+
+	return withNodeVersion('9.0.0', () => babelConfigHelper.build(projectDir, cacheDir, 'default', true))
+		.then(result => {
+			const options = result.getOptions();
+			t.same(options.plugins, [
+				require.resolve('babel-plugin-syntax-object-rest-spread')
+			]);
+		});
+});
+
+test('adds babel-plugin-syntax-object-rest-spread for node versions == 8.3.0', t => {
+	const projectDir = uniqueTempDir();
+	const cacheDir = path.join(projectDir, 'cache');
+
+	return withNodeVersion('8.3.0', () => babelConfigHelper.build(projectDir, cacheDir, 'default', true))
+		.then(result => {
+			const options = result.getOptions();
+			t.same(options.plugins, [
+				require.resolve('babel-plugin-syntax-object-rest-spread')
+			]);
+		});
+});
+
+test('does not add babel-plugin-syntax-object-rest-spread for node versions < 8.3.0', t => {
+	const projectDir = uniqueTempDir();
+	const cacheDir = path.join(projectDir, 'cache');
+
+	return withNodeVersion('8.2.0', () => babelConfigHelper.build(projectDir, cacheDir, 'default', true))
+		.then(result => {
+			const options = result.getOptions();
+			t.same(options.plugins, []);
+		});
+});
+
 test('should disable power-assert when powerAssert is false', t => {
 	const userOptions = 'default';
 	const powerAssert = false;