Experimentally configure module formats for test files

Fixes #2345.

Co-authored-by: Mark Wubben <mark@novemberborn.net>

ava.config.js

@@ -1,4 +1,9 @@
+const skipTests = [];
+if (process.versions.node < '12.14.0') {
+	skipTests.push('!test/configurable-module-format/module.js');
+}
+
 export default {
-	files: ['test/**', '!test/**/{fixtures,helpers}/**'],
+	files: ['test/**', '!test/**/{fixtures,helpers}/**', ...skipTests],
 	ignoredByWatcher: ['{coverage,docs,media,test-d,test-tap}/**']
 };

docs/06-configuration.md

@@ -52,7 +52,7 @@ Arguments passed to the CLI will always take precedence over the CLI options con
 - `tap`: if `true`, enables the [TAP reporter](./05-command-line.md#tap-reporter)
 - `verbose`: if `true`, enables verbose output
 - `snapshotDir`: specifies a fixed location for storing snapshot files. Use this if your snapshots are ending up in the wrong location
-- `extensions`: extensions of test files. Setting this overrides the default `["cjs", "mjs", "js"]` value, so make sure to include those extensions in the list
+- `extensions`: extensions of test files. Setting this overrides the default `["cjs", "mjs", "js"]` value, so make sure to include those extensions in the list. [Experimentally you can configure how files are loaded](#configuring-module-formats)
 - `require`: extra modules to require before tests are run. Modules are required in the [worker processes](./01-writing-tests.md#process-isolation)
 - `timeout`: Timeouts in AVA behave differently than in other test frameworks. AVA resets a timer after each test, forcing tests to quit if no new test results were received within the specified timeout. This can be used to handle stalled tests. See our [timeout documentation](./07-test-timeouts.md) for more options.
 - `nodeArguments`: Configure Node.js arguments used to launch worker processes.
@@ -213,6 +213,27 @@ export default {
 };
 ```
 
+### Configuring module formats
+
+Node.js can only load non-standard extension as ES Modules when using [experimental loaders](https://nodejs.org/docs/latest/api/esm.html#esm_experimental_loaders). To use this you'll also have to configure AVA to `import()` your test file.
+
+This is still an experimental feature. You can opt in to it by enabling the `configurableModuleFormat` experiment. Afterwards, you'll be able to specify per-extension module formats using an object form.
+
+As with the array form, you need to explicitly list `js`, `cjs`, and `mjs` extensions. These **must** be set using the `true` value; other extensions are configurable using either `'commonjs'` or `'module'`:
+
+`ava.config.js`:
+```js
+export default {
+	nonSemVerExperiments: {
+		configurableModuleFormat: true
+	},
+	extensions: {
+		js: true,
+		ts: 'module'
+	}
+};
+```
+
 ## Node arguments
 
 The `nodeArguments` configuration may be used to specify additional arguments for launching worker processes. These are combined with `--node-arguments` passed on the CLI and any arguments passed to the `node` binary when starting AVA.

lib/cli.js

@@ -284,6 +284,7 @@ exports.run = async () => { // eslint-disable-line complexity
 	const TapReporter = require('./reporters/tap');
 	const Watcher = require('./watcher');
 	const normalizeExtensions = require('./extensions');
+	const normalizeModuleTypes = require('./module-types');
 	const {normalizeGlobs, normalizePattern} = require('./globs');
 	const normalizeNodeArguments = require('./node-arguments');
 	const validateEnvironmentVariables = require('./environment-variables');
@@ -301,12 +302,6 @@ exports.run = async () => { // eslint-disable-line complexity
 
 	const {type: defaultModuleType = 'commonjs'} = pkg || {};
 
-	const moduleTypes = {
-		cjs: 'commonjs',
-		mjs: 'module',
-		js: defaultModuleType
-	};
-
 	const providers = [];
 	if (Reflect.has(conf, 'babel')) {
 		try {
@@ -348,6 +343,13 @@ exports.run = async () => { // eslint-disable-line complexity
 		exit(error.message);
 	}
 
+	let moduleTypes;
+	try {
+		moduleTypes = normalizeModuleTypes(conf.extensions, defaultModuleType, experiments);
+	} catch (error) {
+		exit(error.message);
+	}
+
 	let globs;
 	try {
 		globs = normalizeGlobs({files: conf.files, ignoredByWatcher: conf.ignoredByWatcher, extensions, providers});

lib/extensions.js

@@ -2,8 +2,11 @@ module.exports = (configuredExtensions, providers = []) => {
 	// Combine all extensions possible for testing. Remove duplicate extensions.
 	const duplicates = new Set();
 	const seen = new Set();
+
+	const normalize = extensions => Array.isArray(extensions) ? extensions : Object.keys(extensions);
+
 	const combine = extensions => {
-		for (const ext of extensions) {
+		for (const ext of normalize(extensions)) {
 			if (seen.has(ext)) {
 				duplicates.add(ext);
 			} else {

lib/load-config.js

@@ -7,7 +7,7 @@ const pkgConf = require('pkg-conf');
 
 const NO_SUCH_FILE = Symbol('no ava.config.js file');
 const MISSING_DEFAULT_EXPORT = Symbol('missing default export');
-const EXPERIMENTS = new Set(['disableSnapshotsInHooks', 'reverseTeardowns']);
+const EXPERIMENTS = new Set(['configurableModuleFormat', 'disableSnapshotsInHooks', 'reverseTeardowns']);
 
 // *Very* rudimentary support for loading ava.config.js files containing an `export default` statement.
 const evaluateJsConfig = configFile => {

lib/module-types.js

@@ -0,0 +1,75 @@
+const requireTrueValue = value => {
+	if (value !== true) {
+		throw new TypeError('When specifying module types, use `true` for ’cjs’, ’mjs’ and ’js’ extensions');
+	}
+};
+
+const normalize = (extension, type, defaultModuleType) => {
+	switch (extension) {
+		case 'cjs':
+			requireTrueValue(type);
+			return 'commonjs';
+		case 'mjs':
+			requireTrueValue(type);
+			return 'module';
+		case 'js':
+			requireTrueValue(type);
+			return defaultModuleType;
+		default:
+			if (type !== 'commonjs' && type !== 'module') {
+				throw new TypeError(`Module type for ’${extension}’ must be ’commonjs’ or ’module’`);
+			}
+
+			return type;
+	}
+};
+
+const deriveFromObject = (extensionsObject, defaultModuleType) => {
+	const moduleTypes = {};
+	for (const [extension, type] of Object.entries(extensionsObject)) {
+		moduleTypes[extension] = normalize(extension, type, defaultModuleType);
+	}
+
+	return moduleTypes;
+};
+
+const deriveFromArray = (extensions, defaultModuleType) => {
+	const moduleTypes = {};
+	for (const extension of extensions) {
+		switch (extension) {
+			case 'cjs':
+				moduleTypes.cjs = 'commonjs';
+				break;
+			case 'mjs':
+				moduleTypes.mjs = 'module';
+				break;
+			case 'js':
+				moduleTypes.js = defaultModuleType;
+				break;
+			default:
+				moduleTypes[extension] = 'commonjs';
+		}
+	}
+
+	return moduleTypes;
+};
+
+module.exports = (configuredExtensions, defaultModuleType, experiments) => {
+	if (configuredExtensions === undefined) {
+		return {
+			cjs: 'commonjs',
+			mjs: 'module',
+			js: defaultModuleType
+		};
+	}
+
+	if (Array.isArray(configuredExtensions)) {
+		return deriveFromArray(configuredExtensions, defaultModuleType);
+	}
+
+	if (!experiments.configurableModuleFormat) {
+		throw new Error('You must enable the `configurableModuleFormat` experiment in order to specify module types');
+	}
+
+	return deriveFromObject(configuredExtensions, defaultModuleType);
+};

test/configurable-module-format/commonjs.js

@@ -0,0 +1,26 @@
+const test = require('@ava/test');
+const exec = require('../helpers/exec');
+
+test('load js and cjs as commonjs (default configuration)', async t => {
+	const result = await exec.fixture(['*.js', '*.cjs']);
+	const files = new Set(result.stats.passed.map(({file}) => file));
+	t.is(files.size, 2);
+	t.true(files.has('test.cjs'));
+	t.true(files.has('test.js'));
+});
+
+test('load js and cjs as commonjs (using an extensions array)', async t => {
+	const result = await exec.fixture(['*.js', '*.cjs', '--config', 'array-extensions.config.js']);
+	const files = new Set(result.stats.passed.map(({file}) => file));
+	t.is(files.size, 2);
+	t.true(files.has('test.cjs'));
+	t.true(files.has('test.js'));
+});
+
+test('load js and cjs as commonjs (using an extensions object)', async t => {
+	const result = await exec.fixture(['*.js', '*.cjs', '--config', 'object-extensions.config.js']);
+	const files = new Set(result.stats.passed.map(({file}) => file));
+	t.is(files.size, 2);
+	t.true(files.has('test.cjs'));
+	t.true(files.has('test.js'));
+});

test/configurable-module-format/custom.js

@@ -0,0 +1,16 @@
+const test = require('@ava/test');
+const exec = require('../helpers/exec');
+
+test('load ts as commonjs (using an extensions array)', async t => {
+	const result = await exec.fixture(['*.ts', '--config', 'array-custom.config.js']);
+	const files = new Set(result.stats.passed.map(({file}) => file));
+	t.is(files.size, 1);
+	t.true(files.has('test.ts'));
+});
+
+test('load ts as commonjs (using an extensions object)', async t => {
+	const result = await exec.fixture(['*.ts', '--config', 'object-custom.config.js']);
+	const files = new Set(result.stats.passed.map(({file}) => file));
+	t.is(files.size, 1);
+	t.true(files.has('test.ts'));
+});

test/configurable-module-format/experimental.js

@@ -0,0 +1,10 @@
+const test = require('@ava/test');
+const exec = require('../helpers/exec');
+
+const stripLeadingFigures = string => string.replace(/^\W+/, '');
+
+test('opt-in is required', async t => {
+	const result = await t.throwsAsync(exec.fixture(['--config', 'not-enabled.config.js']));
+	t.is(result.exitCode, 1);
+	t.snapshot(stripLeadingFigures(result.stderr.trim()));
+});

test/configurable-module-format/fixtures/array-custom.config.js

@@ -0,0 +1,3 @@
+export default {
+	extensions: ['js', 'ts']
+};

test/configurable-module-format/fixtures/array-extensions.config.js

@@ -0,0 +1,3 @@
+export default {
+	extensions: ['js', 'cjs', 'mjs']
+};

test/configurable-module-format/fixtures/bad-custom-type.config.js

@@ -0,0 +1,9 @@
+export default {
+	extensions: {
+		js: true,
+		ts: 'cjs'
+	},
+	nonSemVerExperiments: {
+		configurableModuleFormat: true
+	}
+};

test/configurable-module-format/fixtures/change-cjs-loading.config.js

@@ -0,0 +1,8 @@
+export default {
+	extensions: {
+		cjs: 'module'
+	},
+	nonSemVerExperiments: {
+		configurableModuleFormat: true
+	}
+};

test/configurable-module-format/fixtures/change-js-loading.config.js

@@ -0,0 +1,8 @@
+export default {
+	extensions: {
+		js: 'module'
+	},
+	nonSemVerExperiments: {
+		configurableModuleFormat: true
+	}
+};

test/configurable-module-format/fixtures/change-mjs-loading.config.js

@@ -0,0 +1,8 @@
+export default {
+	extensions: {
+		mjs: 'commonjs'
+	},
+	nonSemVerExperiments: {
+		configurableModuleFormat: true
+	}
+};

test/configurable-module-format/fixtures/not-enabled.config.js

@@ -0,0 +1,7 @@
+export default {
+	extensions: {
+		js: true,
+		cjs: true,
+		mjs: true
+	}
+};

test/configurable-module-format/fixtures/object-custom.config.js

@@ -0,0 +1,9 @@
+export default {
+	extensions: {
+		js: true,
+		ts: 'commonjs'
+	},
+	nonSemVerExperiments: {
+		configurableModuleFormat: true
+	}
+};

test/configurable-module-format/fixtures/object-extensions.config.js

@@ -0,0 +1,10 @@
+export default {
+	extensions: {
+		js: true,
+		cjs: true,
+		mjs: true
+	},
+	nonSemVerExperiments: {
+		configurableModuleFormat: true
+	}
+};

test/configurable-module-format/fixtures/package.json

@@ -0,0 +1 @@
+{}

test/configurable-module-format/fixtures/test.cjs

@@ -0,0 +1,5 @@
+const test = require('ava');
+
+test('always passing test', t => {
+	t.pass();
+});

test/configurable-module-format/fixtures/test.js

@@ -0,0 +1,5 @@
+const test = require('ava');
+
+test('always passing test', t => {
+	t.pass();
+});

test/configurable-module-format/fixtures/test.mjs

@@ -0,0 +1,5 @@
+import test from 'ava';
+
+test('always passing test', t => {
+	t.pass();
+});

test/configurable-module-format/fixtures/test.ts

@@ -0,0 +1,8 @@
+// eslint-disable-next-line ava/no-ignored-test-files
+const test = require('ava');
+
+test('always passing test', t => {
+	const numberWithTypes = 0;
+
+	t.is(numberWithTypes, 0);
+});

test/configurable-module-format/invalid-configurations.js

@@ -0,0 +1,24 @@
+const test = require('@ava/test');
+const exec = require('../helpers/exec');
+
+const stripLeadingFigures = string => string.replace(/^\W+/, '');
+
+test('cannot configure how js extensions should be loaded', async t => {
+	const result = await t.throwsAsync(exec.fixture(['--config', 'change-js-loading.config.js']));
+	t.snapshot(stripLeadingFigures(result.stderr.trim()));
+});
+
+test('cannot configure how cjs extensions should be loaded', async t => {
+	const result = await t.throwsAsync(exec.fixture(['--config', 'change-cjs-loading.config.js']));
+	t.snapshot(stripLeadingFigures(result.stderr.trim()));
+});
+
+test('cannot configure how mjs extensions should be loaded', async t => {
+	const result = await t.throwsAsync(exec.fixture(['--config', 'change-mjs-loading.config.js']));
+	t.snapshot(stripLeadingFigures(result.stderr.trim()));
+});
+
+test('custom extensions must be either commonjs or module', async t => {
+	const result = await t.throwsAsync(exec.fixture(['--config', 'bad-custom-type.config.js']));
+	t.snapshot(stripLeadingFigures(result.stderr.trim()));
+});

test/configurable-module-format/module.js

@@ -0,0 +1,23 @@
+const test = require('@ava/test');
+const exec = require('../helpers/exec');
+
+test('load mjs as module (default configuration)', async t => {
+	const result = await exec.fixture(['*.mjs']);
+	const files = new Set(result.stats.passed.map(({file}) => file));
+	t.is(files.size, 1);
+	t.true(files.has('test.mjs'));
+});
+
+test('load mjs as module (using an extensions array)', async t => {
+	const result = await exec.fixture(['*.mjs', '--config', 'array-extensions.config.js']);
+	const files = new Set(result.stats.passed.map(({file}) => file));
+	t.is(files.size, 1);
+	t.true(files.has('test.mjs'));
+});
+
+test('load mjs as module (using an extensions object)', async t => {
+	const result = await exec.fixture(['*.mjs', '--config', 'object-extensions.config.js']);
+	const files = new Set(result.stats.passed.map(({file}) => file));
+	t.is(files.size, 1);
+	t.true(files.has('test.mjs'));
+});

test/configurable-module-format/snapshots/experimental.js.md

@@ -0,0 +1,11 @@
+# Snapshot report for `test/configurable-module-format/experimental.js`
+
+The actual snapshot is saved in `experimental.js.snap`.
+
+Generated by [AVA](https://avajs.dev).
+
+## opt-in is required
+
+> Snapshot 1
+
+    'You must enable the `configurableModuleFormat` experiment in order to specify module types'