Enhance require feature

* Allow loading of ES modules
* Automatically invoke the default export (if any) and await the result
* Pass arguments from the config to the default export (relies on "advanced" IPC for child processes)
* Document that local files are loaded through the providers (e.g. `@ava/typescript`)

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

docs/06-configuration.md

@@ -55,7 +55,7 @@ Arguments passed to the CLI will always take precedence over the CLI options con
 - `verbose`: if `true`, enables verbose output (though there currently non-verbose output is not supported)
 - `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. [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#test-isolation)
+- `require`: [extra modules to load before test files](#requiring-extra-modules)
 - `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.
 - `sortTestFiles`: A comparator function to sort test files with. Available only when using a `ava.config.*` file. See an example use case [here](recipes/splitting-tests-ci.md).
@@ -84,14 +84,14 @@ The default export can either be a plain object or a factory function which retu
 
 ```js
 export default {
-	require: ['./_my-test-helper']
+	require: ['./_my-test-helper.js']
 };
 ```
 
 ```js
 export default function factory() {
 	return {
-		require: ['./_my-test-helper']
+		require: ['./_my-test-helper.js']
 	};
 };
 ```
@@ -120,14 +120,14 @@ The module export can either be a plain object or a factory function which retur
 
 ```js
 module.exports = {
-	require: ['./_my-test-helper']
+	require: ['./_my-test-helper.js']
 };
 ```
 
 ```js
 module.exports = () => {
 	return {
-		require: ['./_my-test-helper']
+		require: ['./_my-test-helper.js']
 	};
 };
 ```
@@ -154,14 +154,14 @@ The default export can either be a plain object or a factory function which retu
 
 ```js
 export default {
-	require: ['./_my-test-helper']
+	require: ['./_my-test-helper.js']
 };
 ```
 
 ```js
 export default function factory() {
 	return {
-		require: ['./_my-test-helper']
+		require: ['./_my-test-helper.js']
 	};
 };
 ```
@@ -258,6 +258,79 @@ export default {
 };
 ```
 
+## Requiring extra modules
+
+Use the `require` configuration to load extra modules before test files are loaded. Relative paths are resolved against the project directory and can be loaded through `@ava/typescript`. Otherwise, modules are loaded from within the `node_modules` directory inside the project.
+
+You may specify a single value, or an array of values:
+
+`ava.config.js`:
+```js
+export default {
+	require: './_my-test-helper.js'
+}
+```
+```js
+export default {
+	require: ['./_my-test-helper.js']
+}
+```
+
+If the module exports a function, it is called and awaited:
+
+`_my-test-helper.js`:
+```js
+export default function () {
+	// Additional setup
+}
+```
+
+`_my-test-helper.cjs`:
+```js
+module.exports = function () {
+	// Additional setup
+}
+```
+
+In CJS files, a `default` export is also supported:
+
+```js
+exports.default = function () {
+	// Never called
+}
+```
+
+You can provide arguments:
+
+`ava.config.js`:
+```js
+export default {
+	require: [
+		['./_my-test-helper.js', 'my', 'arguments']
+	]
+}
+```
+
+`_my-test-helper.js`:
+```js
+export default function (first, second) { // 'my', 'arguments'
+	// Additional setup
+}
+```
+
+Arguments are copied using the [structured clone algorithm](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm). This means `Map` values survive, but a `Buffer` will come out as a `Uint8Array`.
+
+You can load dependencies installed in your project:
+
+`ava.config.js`:
+```js
+export default {
+	require: '@babel/register'
+}
+```
+
+These may also export a function which is then invoked, and can receive arguments.
+
 ## 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/api.js

@@ -9,7 +9,6 @@ import commonPathPrefix from 'common-path-prefix';
 import Emittery from 'emittery';
 import ms from 'ms';
 import pMap from 'p-map';
-import resolveCwd from 'resolve-cwd';
 import tempDir from 'temp-dir';
 
 import fork from './fork.js';
@@ -22,15 +21,13 @@ import RunStatus from './run-status.js';
 import scheduler from './scheduler.js';
 import serializeError from './serialize-error.js';
 
-function resolveModules(modules) {
-	return arrify(modules).map(name => {
-		const modulePath = resolveCwd.silent(name);
-
-		if (modulePath === undefined) {
-			throw new Error(`Could not resolve required module ’${name}’`);
+function normalizeRequireOption(require) {
+	return arrify(require).map(name => {
+		if (typeof name === 'string') {
+			return arrify(name);
 		}
 
-		return modulePath;
+		return name;
 	});
 }
 
@@ -81,7 +78,7 @@ export default class Api extends Emittery {
 		super();
 
 		this.options = {match: [], moduleTypes: {}, ...options};
-		this.options.require = resolveModules(this.options.require);
+		this.options.require = normalizeRequireOption(this.options.require);
 
 		this._cacheDir = null;
 		this._interruptHandler = () => {};

lib/fork.js

@@ -53,6 +53,7 @@ const createWorker = (options, execArgv) => {
 			silent: true,
 			env: {NODE_ENV: 'test', ...process.env, ...options.environmentVariables},
 			execArgv: [...execArgv, ...additionalExecArgv],
+			serialization: 'advanced',
 		});
 		postMessage = controlFlow(worker);
 		close = async () => worker.kill();

lib/worker/base.js

@@ -1,9 +1,12 @@
+import {mkdir} from 'node:fs/promises';
 import {createRequire} from 'node:module';
+import {join as joinPath, resolve as resolvePath} from 'node:path';
 import process from 'node:process';
 import {pathToFileURL} from 'node:url';
 import {workerData} from 'node:worker_threads';
 
 import setUpCurrentlyUnhandled from 'currently-unhandled';
+import writeFileAtomic from 'write-file-atomic';
 
 import {set as setChalk} from '../chalk.js';
 import nowAndTimers from '../now-and-timers.cjs';
@@ -174,9 +177,56 @@ const run = async options => {
 		return require(ref);
 	};
 
+	const loadRequiredModule = async ref => {
+		// If the provider can load the module, assume it's a local file and not a
+		// dependency.
+		for (const provider of providers) {
+			if (provider.canLoad(ref)) {
+				return provider.load(ref, {requireFn: require});
+			}
+		}
+
+		// Try to load the module as a file, relative to the project directory.
+		// Match load() behavior.
+		const fullPath = resolvePath(projectDir, ref);
+		try {
+			for (const extension of extensionsToLoadAsModules) {
+				if (fullPath.endsWith(`.${extension}`)) {
+					return await import(pathToFileURL(fullPath)); // eslint-disable-line no-await-in-loop
+				}
+			}
+
+			return require(fullPath);
+		} catch (error) {
+			// If the module could not be found, assume it's not a file but a dependency.
+			if (error.code === 'ERR_MODULE_NOT_FOUND' || error.code === 'MODULE_NOT_FOUND') {
+				return importFromProject(ref);
+			}
+
+			throw error;
+		}
+	};
+
+	let importFromProject = async ref => {
+		// Do not use the cacheDir since it's not guaranteed to be inside node_modules.
+		const avaCacheDir = joinPath(projectDir, 'node_modules', '.cache', 'ava');
+		await mkdir(avaCacheDir, {recursive: true});
+		const stubPath = joinPath(avaCacheDir, 'import-from-project.mjs');
+		await writeFileAtomic(stubPath, 'export const importFromProject = ref => import(ref);\n');
+		({importFromProject} = await import(pathToFileURL(stubPath)));
+		return importFromProject(ref);
+	};
+
 	try {
-		for await (const ref of (options.require || [])) {
-			await load(ref);
+		for await (const [ref, ...args] of (options.require ?? [])) {
+			const loadedModule = await loadRequiredModule(ref);
+
+			if (typeof loadedModule === 'function') { // CJS module
+				await loadedModule(...args);
+			} else if (typeof loadedModule.default === 'function') { // ES module, or exports.default from CJS
+				const {default: fn} = loadedModule;
+				await fn(...args);
+			}
 		}
 
 		// Install dependency tracker after the require configuration has been evaluated

test-tap/api.js

@@ -359,25 +359,6 @@ for (const opt of options) {
 			});
 	});
 
-	test(`Node.js-style --require CLI argument - workerThreads: ${opt.workerThreads}`, async t => {
-		const requirePath = './' + path.relative('.', path.join(__dirname, 'fixture/install-global.cjs')).replace(/\\/g, '/');
-
-		const api = await apiCreator({
-			...opt,
-			require: [requirePath],
-		});
-
-		return api.run({files: [path.join(__dirname, 'fixture/validate-installed-global.cjs')]})
-			.then(runStatus => {
-				t.equal(runStatus.stats.passedTests, 1);
-			});
-	});
-
-	test(`Node.js-style --require CLI argument module not found - workerThreads: ${opt.workerThreads}`, t => {
-		t.rejects(apiCreator({...opt, require: ['foo-bar']}), /^Could not resolve required module ’foo-bar’$/);
-		t.end();
-	});
-
 	test(`caching is enabled by default - workerThreads: ${opt.workerThreads}`, async t => {
 		fs.rmSync(path.join(__dirname, 'fixture/caching/node_modules'), {recursive: true, force: true});
 

test/config-require/fixtures/exports-default/package.json

@@ -0,0 +1,6 @@
+{
+	"type": "module",
+	"ava": {
+		"require": "./required.cjs"
+	}
+}

test/config-require/fixtures/exports-default/required.cjs

@@ -0,0 +1,5 @@
+exports.called = false;
+
+exports.default = function () {
+	exports.called = true;
+};

test/config-require/fixtures/exports-default/test.js

@@ -0,0 +1,7 @@
+import test from 'ava';
+
+import required from './required.cjs';
+
+test('exports.default is called', t => {
+	t.true(required.called);
+});

test/config-require/fixtures/failed-import/package.json

@@ -0,0 +1,6 @@
+{
+	"type": "module",
+	"ava": {
+		"require": "@babel/register"
+	}
+}

test/config-require/fixtures/failed-import/test.js

@@ -0,0 +1,5 @@
+import test from 'ava';
+
+test('should not make it this far', t => {
+	t.fail();
+});

test/config-require/fixtures/non-json/ava.config.js

@@ -0,0 +1,5 @@
+export default {
+	require: [
+		['./required.mjs', new Map([['hello', 'world']])],
+	],
+};

test/config-require/fixtures/non-json/package.json

@@ -0,0 +1,3 @@
+{
+	"type": "module"
+}

test/config-require/fixtures/non-json/required.mjs

@@ -0,0 +1,5 @@
+export let receivedArgs = null; // eslint-disable-line import/no-mutable-exports
+
+export default function (...args) {
+	receivedArgs = args;
+}

test/config-require/fixtures/non-json/test.js

@@ -0,0 +1,7 @@
+import test from 'ava';
+
+import {receivedArgs} from './required.mjs';
+
+test('non-JSON arguments can be provided', t => {
+	t.deepEqual(receivedArgs, [new Map([['hello', 'world']])]);
+});

test/config-require/fixtures/require-dependency/.gitignore

@@ -0,0 +1 @@
+!node_modules/@ava

test/config-require/fixtures/require-dependency/package.json

@@ -0,0 +1,8 @@
+{
+	"type": "module",
+	"ava": {
+		"require": [
+			"@ava/stub"
+		]
+	}
+}

test/config-require/fixtures/require-dependency/test.js

@@ -0,0 +1,6 @@
+import {required} from '@ava/stub';
+import test from 'ava';
+
+test('loads dependencies', t => {
+	t.true(required);
+});

test/config-require/fixtures/single-argument/package.json

@@ -0,0 +1,6 @@
+{
+	"type": "module",
+	"ava": {
+		"require": "./required.js"
+	}
+}

test/config-require/fixtures/single-argument/required.js

@@ -0,0 +1,5 @@
+export let required = false; // eslint-disable-line import/no-mutable-exports
+
+export default function () {
+	required = true;
+}

test/config-require/fixtures/single-argument/test.js

@@ -0,0 +1,7 @@
+import test from 'ava';
+
+import {required} from './required.js';
+
+test('loads when given as a single argument', t => {
+	t.true(required);
+});