Change Babel options used for test compilation

Always extend the project's Babel configuration, if any.

Always apply the `@ava/stage-4` preset. Fixes #1488. Users can disable
this preset by adding it to the AVA's Babel configuration with the
`false` option:

```
"ava": {
	"babel": {
		"presets": [
			["ava/stage-4", false]
		]
	}
}

And yes, `ava/stage-4` so now an alias for the preset, which means it
can be used even if the preset is not installed as a top-level
dependency. Fixes #1225.

`@ava/transform-test-files` is applied as part of the test compilation,
but cannot be overridden by users like `@ava/stage-4` can.

Author: novemberborn

lib/babel-config.js

@@ -9,6 +9,10 @@ const makeDir = require('make-dir');
 const semver = require('semver');
 const colors = require('./colors');
 
+const stage4Path = require.resolve('../stage-4');
+const syntaxObjectRestSpreadPath = require.resolve('@babel/plugin-syntax-object-rest-spread');
+const transformTestFilesPath = require.resolve('@ava/babel-preset-transform-test-files');
+
 function validate(conf) {
 	if (conf === undefined || conf === null) {
 		conf = 'default';
@@ -28,9 +32,6 @@ function validate(conf) {
 	return conf;
 }
 
-const SOURCE = '(AVA) Base Babel config';
-const AVA_DIR = path.join(__dirname, '..');
-
 function verifyExistingOptions(verifierFile, baseConfig, cache, envName) {
 	return new Promise((resolve, reject) => {
 		try {
@@ -108,48 +109,75 @@ function build(projectDir, cacheDir, userOptions, compileEnhancements) {
 	const baseOptions = {
 		babelrc: false,
 		plugins: [],
-		presets: []
+		presets: [
+			stage4Path // Always apply the stage-4 preset.
+		]
 	};
-	if (compileEnhancements) {
-		baseOptions.presets.push(['@ava/transform-test-files', {powerAssert: true}]);
+
+	// By default extend the project's Babel configuration, but allow this to be
+	// disabled in userOptions.
+	if (userOptions === 'default' || userOptions === 'inherit' || userOptions.babelrc !== false) {
+		baseOptions.babelrc = true;
 	}
-	if (userOptions === 'default') {
-		baseOptions.presets.unshift('@ava/stage-4');
+	if (userOptions.extends) {
+		baseOptions.extends = userOptions.extends;
 	}
 
-	// Include object rest spread support for node versions that support it
+	// Include object rest spread support for Node.js 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');
+	if (semver.satisfies(process.versions.node, '>= 8.3.0')) {
+		baseOptions.plugins.push(syntaxObjectRestSpreadPath);
 	}
 
 	const baseConfig = configManager.createConfig({
-		dir: AVA_DIR, // Presets are resolved relative to this directory
+		dir: projectDir,
 		fileType: 'JSON',
 		hash: md5Hex(JSON.stringify(baseOptions)),
 		options: baseOptions,
-		source: SOURCE
+		source: '(AVA) baseConfig'
 	});
 
-	if (userOptions !== 'default') {
-		baseConfig.extend(configManager.createConfig({
+	let intermediateConfig = baseConfig;
+	if (userOptions !== 'default' && userOptions !== 'inherit') {
+		// At this level, babelrc *must* be false.
+		const options = Object.assign({}, userOptions, {babelrc: false});
+		// Any extends option has been applied in baseConfig.
+		delete options.extends;
+		intermediateConfig = configManager.createConfig({
+			dir: projectDir,
+			fileType: 'JSON',
+			hash: md5Hex(JSON.stringify(options)),
+			options,
+			source: path.join(projectDir, 'package.json') + '#ava.babel'
+		});
+		intermediateConfig.extend(baseConfig);
+	}
+
+	let finalConfig = intermediateConfig;
+	if (compileEnhancements) {
+		finalConfig = configManager.createConfig({
 			dir: projectDir,
-			options: userOptions === 'inherit' ?
-				{babelrc: true} :
-				userOptions,
-			source: path.join(projectDir, 'package.json') + '#ava.babel',
-			hash: md5Hex(JSON.stringify(userOptions))
-		}));
+			fileType: 'JSON',
+			hash: '', // This is deterministic, so no actual value necessary.
+			options: {
+				babelrc: false,
+				presets: [
+					[transformTestFilesPath, {powerAssert: true}]
+				]
+			},
+			source: '(AVA) compileEnhancements'
+		});
+		finalConfig.extend(intermediateConfig);
 	}
 
 	const cache = configManager.prepareCache();
-	return verifyExistingOptions(verifierFile, baseConfig, cache, envName)
+	return verifyExistingOptions(verifierFile, finalConfig, cache, envName)
 		.then(cacheKeys => {
 			if (cacheKeys) {
 				return cacheKeys;
 			}
 
-			return resolveOptions(baseConfig, cache, envName, optionsFile, verifierFile);
+			return resolveOptions(finalConfig, cache, envName, optionsFile, verifierFile);
 		})
 		.then(cacheKeys => {
 			const getOptions = require(optionsFile).getOptions;

stage-4.js

@@ -0,0 +1 @@
+module.exports = require('@ava/babel-preset-stage-4');

test/api.js

@@ -841,22 +841,22 @@ function generateTests(prefix, apiCreator) {
 			}, t.threw);
 	});
 
-	test(`${prefix} Default babel config doesn't use .babelrc`, t => {
-		t.plan(2);
+	test(`${prefix} Default babel config uses .babelrc`, t => {
+		t.plan(3);
 
 		const api = apiCreator({
 			projectDir: path.join(__dirname, 'fixture/babelrc')
 		});
 
 		api.on('test-run', runStatus => {
 			runStatus.on('test', data => {
-				t.is(data.title, 'foo');
+				t.ok((data.title === 'foo') || (data.title === 'repeated test: foo'));
 			});
 		});
 
 		return api.run()
 			.then(result => {
-				t.is(result.passCount, 1);
+				t.is(result.passCount, 2);
 			});
 	});
 
@@ -902,6 +902,27 @@ function generateTests(prefix, apiCreator) {
 			});
 	});
 
+	test(`${prefix} babelConfig:{babelrc:false} does not use .babelrc`, t => {
+		t.plan(2);
+
+		const api = apiCreator({
+			babelConfig: {babelrc: false},
+			cacheEnabled: false,
+			projectDir: path.join(__dirname, 'fixture/babelrc')
+		});
+
+		api.on('test-run', runStatus => {
+			runStatus.on('test', data => {
+				t.is(data.title, 'foo');
+			});
+		});
+
+		return api.run()
+			.then(result => {
+				t.is(result.passCount, 1);
+			});
+	});
+
 	test(`${prefix} babelConfig:{babelrc:true, plugins:[...]} merges plugins with .babelrc`, t => {
 		t.plan(3);
 

test/babel-config.js

@@ -86,10 +86,37 @@ test('uses userOptions for babel options when userOptions is an object', t => {
 		.then(result => {
 			const options = result.getOptions();
 			t.false(options.babelrc);
-			t.is(options.plugins[0][0].wrapped, custom);
-			t.is(options.presets[0][0].wrapped, custom);
-			t.is(options.presets[1][0].wrapped, require('@ava/babel-preset-transform-test-files'));
-			t.same(options.presets[1][1], {powerAssert: true});
+			if (options.plugins.length === 1) {
+				t.is(options.plugins[0][0].wrapped, custom);
+			} else {
+				t.is(options.plugins[1][0].wrapped, custom);
+			}
+			t.is(options.presets[0][0].wrapped, require('@ava/babel-preset-stage-4'));
+			t.is(options.presets[1][0].wrapped, custom);
+			t.is(options.presets[2][0].wrapped, require('@ava/babel-preset-transform-test-files'));
+			t.same(options.presets[2][1], {powerAssert: true});
+		});
+});
+
+test('userOptions can disable ava/stage-4', t => {
+	const userOptions = {
+		presets: [['module:ava/stage-4', false]]
+	};
+	const transpileEnhancements = true;
+
+	const projectDir = uniqueTempDir();
+	const cacheDir = path.join(projectDir, 'cache');
+	fs.mkdirSync(projectDir);
+	fs.mkdirSync(path.join(projectDir, 'node_modules'));
+	fs.mkdirSync(path.join(projectDir, 'node_modules', 'ava'));
+	fs.writeFileSync(path.join(projectDir, 'node_modules', 'ava', 'stage-4.js'), `module.exports = require(${JSON.stringify(require.resolve('@ava/babel-preset-stage-4'))})`);
+
+	return babelConfigHelper.build(projectDir, cacheDir, userOptions, transpileEnhancements)
+		.then(result => {
+			const options = result.getOptions();
+			t.false(options.babelrc);
+			t.is(options.presets[0][0].wrapped, require('@ava/babel-preset-stage-4'));
+			t.is(options.presets[0][1], false);
 		});
 });