Add support for .cjs files; select but do not yet handle .mjs files

As per #2293, this begins the work to support `.cjs` and `.mjs` files.

* AVA will now select and load `.cjs` test files
* AVA will now select, but refuse to load, `.mjs` test files
* AVA will detect the module `"type"` in `package.json`, and refuse to load `.js` test files if the type is `"module"`
* `.js` config files can now only contain an `export default` statement
* `.cjs` config files are now supported
* `.mjs` config files are now recognized, but AVA refuses to load them
* `--config` files must have a known extension

docs/05-command-line.md

@@ -20,8 +20,9 @@ Positionals:
 Options:
   --version               Show version number                          [boolean]
   --color                 Force color output                           [boolean]
-  --config                JavaScript file for AVA to read its config from,
-                          instead of using package.json or ava.config.js files
+  --config                Specific JavaScript file for AVA to read its config
+                          from, instead of using package.json or ava.config.*
+                          files
   --help                  Show help                                    [boolean]
   --concurrency, -c       Max number of test files running at the same time
                           (Default: CPU cores)                          [number]

docs/06-configuration.md

@@ -4,7 +4,7 @@ Translations: [Français](https://github.com/avajs/ava-docs/blob/master/fr_FR/do
 
 **This documents the upcoming AVA 3 release. See the [AVA 2](https://github.com/avajs/ava/blob/v2.4.0/docs/06-configuration.md) documentation instead.**
 
-All of the [CLI options][CLI] can be configured in the `ava` section of either your `package.json` file, or an `ava.config.js` file. This allows you to modify the default behavior of the `ava` command, so you don't have to repeatedly type the same options on the command prompt.
+All of the [CLI options][CLI] can be configured in the `ava` section of either your `package.json` file, or an `ava.config.*` file. This allows you to modify the default behavior of the `ava` command, so you don't have to repeatedly type the same options on the command prompt.
 
 To ignore files, prefix the pattern with an `!` (exclamation mark).
 
@@ -40,7 +40,7 @@ Arguments passed to the CLI will always take precedence over the CLI options con
 
 ## Options
 
-- `files`: an array of glob patterns to select test files. Files with an underscore prefix are ignored. By default only selects files with `js` extensions, even if the pattern matches other files. Specify `extensions` to allow other file extensions
+- `files`: an array of glob patterns to select test files. Files with an underscore prefix are ignored. By default only selects files with `cjs`, `mjs` & `js` extensions, even if the pattern matches other files. Specify `extensions` to allow other file extensions
 - `ignoredByWatcher`: an array of glob patterns to match files that, even if changed, are ignored by the watcher. See the [watch mode recipe for details](https://github.com/avajs/ava/blob/master/docs/recipes/watch-mode.md)
 - `match`: not typically useful in the `package.json` configuration, but equivalent to [specifying `--match` on the CLI](./05-command-line.md#running-tests-with-matching-titles)
 - `cache`: cache compiled files under `node_modules/.cache/ava`. If `false`, files are cached in a temporary directory instead
@@ -50,34 +50,42 @@ 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 `"js"` value, so make sure to include that extension 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
 - `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.
 
 Note that providing files on the CLI overrides the `files` option.
 
 Provide the `babel` option (and install [`@ava/babel`](https://github.com/avajs/babel) as an additional dependency) to enable Babel compilation.
 
-## Using `ava.config.js`
+## Using `ava.config.*` files
 
-To use an `ava.config.js` file:
+Rather than specifying the configuration in the `package.json` file you can use `ava.config.js` or `ava.config.cjs` files.
 
-1. It must be in the same directory as your `package.json`
+To use these files:
+
+1. They must be in the same directory as your `package.json`
 2. Your `package.json` must not contain an `ava` property (or, if it does, it must be an empty object)
-3. You must use `export default`, though [`require()`](https://nodejs.org/api/modules.html#modules_require_id) is available to load non-ES modules
+3. You must not both have an `ava.config.js` *and* an `ava.config.cjs` file
+
+AVA recognizes `ava.config.mjs` files but refuses to load them.
+
+### `ava.config.js`
 
-The config file must have a default export, using ES modules. It can either be a plain object or a factory function which returns a plain object:
+For `ava.config.js` files you must use `export default`. You cannot use ["module scope"](https://nodejs.org/docs/latest-v12.x/api/modules.html#modules_the_module_scope). You cannot import dependencies.
+
+The default export can either be a plain object or a factory function which returns a plain object:
 
 ```js
 export default {
-	require: ['esm']
+	require: ['./_my-test-helper']
 };
 ```
 
 ```js
 export default function factory() {
 	return {
-		require: ['esm']
+		require: ['./_my-test-helper']
 	};
 };
 ```
@@ -100,34 +108,74 @@ export default ({projectDir}) => {
 
 Note that the final configuration must not be a promise.
 
+### `ava.config.cjs`
+
+For `ava.config.cjs` files you must assign `module.exports`. ["Module scope"](https://nodejs.org/docs/latest-v12.x/api/modules.html#modules_the_module_scope) is available. You can `require()` dependencies.
+
+The module export can either be a plain object or a factory function which returns a plain object:
+
+```js
+module.exports = {
+	require: ['./_my-test-helper']
+};
+```
+
+```js
+module.exports = () => {
+	return {
+		require: ['./_my-test-helper']
+	};
+};
+```
+
+The factory function is called with an object containing a `projectDir` property, which you could use to change the returned configuration:
+
+```js
+module.exports = ({projectDir}) => {
+	if (projectDir === '/Users/username/projects/my-project') {
+		return {
+			// Config A
+		};
+	}
+
+	return {
+		// Config B
+	};
+};
+```
+
+Note that the final configuration must not be a promise.
+
 ## Alternative configuration files
 
-The [CLI] lets you specify a specific configuration file, using the `--config` flag. This file is processed just like an `ava.config.js` file would be. When the `--config` flag is set, the provided file will override all configuration from the `package.json` and `ava.config.js` files. The configuration is not merged.
+The [CLI] lets you specify a specific configuration file, using the `--config` flag. This file must have either a `.js` or `.cjs` extension and is processed like an `ava.config.js` or `ava.config.cjs` file would be.
+
+When the `--config` flag is set, the provided file will override all configuration from the `package.json` and `ava.config.js` or `ava.config.cjs` files. The configuration is not merged.
 
 The configuration file *must* be in the same directory as the `package.json` file.
 
 You can use this to customize configuration for a specific test run. For instance, you may want to run unit tests separately from integration tests:
 
-`ava.config.js`:
+`ava.config.cjs`:
 
 ```js
-export default {
+module.exports = {
 	files: ['unit-tests/**/*']
 };
 ```
 
-`integration-tests.config.js`:
+`integration-tests.config.cjs`:
 
 ```js
-import baseConfig from './ava.config.js';
+const baseConfig = require('./ava.config.cjs');
 
-export default {
+module.exports = {
 	...baseConfig,
 	files: ['integration-tests/**/*']
 };
 ```
 
-You can now run your unit tests through `npx ava` and the integration tests through `npx ava --config integration-tests.config.js`.
+You can now run your unit tests through `npx ava` and the integration tests through `npx ava --config integration-tests.config.cjs`.
 
 ## Object printing depth
 

docs/recipes/es-modules.md

@@ -2,17 +2,21 @@
 
 Translations: [Français](https://github.com/avajs/ava-docs/blob/master/fr_FR/docs/recipes/es-modules.md)
 
-As of Node.js 8.5.0, [ES modules](http://2ality.com/2017/09/native-esm-node.html) are natively supported, but behind the `--experimental-modules` command line flag. It works using the `.mjs` file extension. AVA does not currently support the command line option or the new file extension, but you *can* use the [`esm`](https://github.com/standard-things/esm) module to use the new syntax.
+As of Node.js 13, [ECMAScript modules](https://nodejs.org/docs/latest/api/esm.html#esm_introduction) are natively supported in Node.js itself. AVA does not quite support them *yet*, but we're close.
+
+For the time being, AVA *does* select test files with the `.mjs` extension, however it refuses to load them. Similarly the `package.json` `"type": "module"` field is recognized, but if set AVA will refuse to load test files with the `.js` extension.
+
+For now, your best bet is to use the [`esm`](https://github.com/standard-things/esm) package. Make sure to use the `.js` extension and *do not* set `"type": "module"` in `package.json`.
 
 Here's how you get it working with AVA.
 
-First, install [`esm`](https://github.com/standard-things/esm):
+First, install `esm`:
 
 ```
 $ npm install esm
 ```
 
-Configure it in your `package.json` or `ava.config.js` file, and add it to AVA's `"require"` option as well. Make sure to add it as the first item.
+Configure it in your `package.json` or `ava.config.*` file, and add it to AVA's `"require"` option as well. Make sure to add it as the first item.
 
 **`package.json`:**
 
@@ -29,7 +33,7 @@ Configure it in your `package.json` or `ava.config.js` file, and add it to AVA's
 You can now use native ES modules with AVA:
 
 ```js
-// sum.mjs
+// sum.js
 export default function sum(a, b) {
 	return a + b;
 };
@@ -38,24 +42,9 @@ export default function sum(a, b) {
 ```js
 // test.js
 const test = require('ava');
-const sum = require('./sum.mjs');
+const sum = require('./sum');
 
 test('2 + 2 = 4', t => {
 	t.is(sum(2, 2), 4);
 });
 ```
-
-You need to configure AVA to recognize `.mjs` extensions;
-
-**`package.json`:**
-
-```json
-{
-	"ava": {
-		"extensions": [
-			"js",
-			"mjs"
-		]
-	}
-}
-```

docs/recipes/flow.md

@@ -8,7 +8,7 @@ Until [1.4.1](https://github.com/avajs/ava/releases/tag/v1.4.1) AVA came bundled
 
 This guide assumes you've already set up Flow for your project. Note that AVA's definition as been tested with version 0.95.1.
 
-We recommend you use AVA's [Babel support](https://github.com/avajs/babel) to strip Flow type annotations and declarations. AVA automatically applies your project's Babel configuration, so everything may just work without changes. Alternatively install [`@babel/plugin-transform-flow-strip-types`](https://www.npmjs.com/package/@babel/plugin-transform-flow-strip-types) and customize AVA's configuration in the `package.json` file (or the `ava.config.js` file) as follows.
+We recommend you use AVA's [Babel support](https://github.com/avajs/babel) to strip Flow type annotations and declarations. AVA automatically applies your project's Babel configuration, so everything may just work without changes. Alternatively install [`@babel/plugin-transform-flow-strip-types`](https://www.npmjs.com/package/@babel/plugin-transform-flow-strip-types) and customize AVA's configuration in the `package.json` file (or the `ava.config.*` file) as follows.
 
 **`package.json`:**
 

docs/recipes/react.md

@@ -6,7 +6,7 @@ Translations: [Español](https://github.com/avajs/ava-docs/blob/master/es_ES/doc
 
 When you [enable Babel](https://github.com/avajs/babel), AVA will automatically extend your regular (project-level) Babel configuration. You should be able to use React in your test files without any additional configuration.
 
-However if you want to set it up explicitly, add the preset to the test options in AVA's Babel pipeline by modifying your `package.json` or `ava.config.js` file.
+However if you want to set it up explicitly, add the preset to the test options in AVA's Babel pipeline by modifying your `package.json` or `ava.config.*` file.
 
 **`package.json`:**
 

docs/recipes/watch-mode.md

@@ -47,7 +47,7 @@ And then use:
 $ npm run watch:test
 ```
 
-Finally you could configure AVA to *always* run in watch mode by setting the `watch` key in the [`ava` section of your `package.json`, or `ava.config.js` file][config].
+Finally you could configure AVA to *always* run in watch mode by setting the `watch` key in the [`ava` section of your `package.json`, or `ava.config.*` file][config].
 
 **`package.json`:**
 
@@ -67,17 +67,17 @@ AVA uses [`chokidar`] as the file watcher. Note that even if you see warnings ab
 
 ## Ignoring changes
 
-By default AVA watches for changes to all files, except for those with a `.snap.md` extension, `ava.config.js` and files in [certain directories](https://github.com/novemberborn/ignore-by-default/blob/master/index.js) as provided by the [`ignore-by-default`] package.
+By default AVA watches for changes to all files, except for those with a `.snap.md` extension, `ava.config.*` and files in [certain directories](https://github.com/novemberborn/ignore-by-default/blob/master/index.js) as provided by the [`ignore-by-default`] package.
 
-You can configure additional patterns for files to ignore in the [`ava` section of your `package.json`, or `ava.config.js` file][config], using the `ignoredByWatcher` key.
+You can configure additional patterns for files to ignore in the [`ava` section of your `package.json`, or `ava.config.*` file][config], using the `ignoredByWatcher` key.
 
 If your tests write to disk they may trigger the watcher to rerun your tests. Configuring additional ignore patterns helps avoid this.
 
 ## Dependency tracking
 
 AVA tracks which source files your test files depend on. If you change such a dependency only the test file that depends on it will be rerun. AVA will rerun all tests if it cannot determine which test file depends on the changed source file.
 
-Dependency tracking works for required modules. Custom extensions and transpilers are supported, provided you [added them in your `package.json` or `ava.config.js` file][config], and not from inside your test file. Files accessed using the `fs` module are not tracked.
+Dependency tracking works for required modules. Custom extensions and transpilers are supported, provided you [added them in your `package.json` or `ava.config.*` file][config], and not from inside your test file. Files accessed using the `fs` module are not tracked.
 
 ## Watch mode and the `.only` modifier
 

lib/api.js

@@ -42,7 +42,7 @@ class Api extends Emittery {
 	constructor(options) {
 		super();
 
-		this.options = {match: [], ...options};
+		this.options = {match: [], moduleTypes: {}, ...options};
 		this.options.require = resolveModules(this.options.require);
 
 		this._cacheDir = null;

lib/cli.js

@@ -7,6 +7,7 @@ const arrify = require('arrify');
 const yargs = require('yargs');
 const Promise = require('bluebird');
 const isCi = require('is-ci');
+const readPkg = require('read-pkg');
 const loadConfig = require('./load-config');
 
 // Bluebird specific
@@ -113,7 +114,7 @@ exports.run = async () => { // eslint-disable-line complexity
 				type: 'boolean'
 			},
 			config: {
-				description: 'JavaScript file for AVA to read its config from, instead of using package.json or ava.config.js files'
+				description: 'Specific JavaScript file for AVA to read its config from, instead of using package.json or ava.config.* files'
 			}
 		})
 		.command('* [<pattern>...]', 'Run tests', yargs => yargs.options(FLAGS).positional('pattern', {
@@ -254,6 +255,23 @@ exports.run = async () => { // eslint-disable-line complexity
 	const {normalizeGlobs, normalizePatterns} = require('./globs');
 	const validateEnvironmentVariables = require('./environment-variables');
 
+	let pkg;
+	try {
+		pkg = readPkg.sync({cwd: projectDir});
+	} catch (error) {
+		if (error.code !== 'ENOENT') {
+			throw error;
+		}
+	}
+
+	const {type: defaultModuleType = 'commonjs'} = pkg || {};
+
+	const moduleTypes = {
+		cjs: 'commonjs',
+		mjs: 'module',
+		js: defaultModuleType
+	};
+
 	let babelProvider;
 	if (Reflect.has(conf, 'babel')) {
 		try {
@@ -306,6 +324,7 @@ exports.run = async () => { // eslint-disable-line complexity
 		failFast: combined.failFast,
 		failWithoutAssertions: combined.failWithoutAssertions !== false,
 		globs,
+		moduleTypes,
 		environmentVariables,
 		match,
 		parallelRuns,

lib/extensions.js

@@ -24,10 +24,19 @@ module.exports = (configuredExtensions, babelProvider) => {
 		throw new Error(`Unexpected duplicate extensions in options: '${[...duplicates].join('\', \'')}'.`);
 	}
 
-	// Unless the default was used by `babelProvider`, as long as the extensions aren't explicitly set to be the empty
-	// array, set the default.
-	if (!seen.has('js') && configuredExtensions === undefined) {
-		seen.add('js');
+	// Unless the default was used by `babelProvider`, as long as the extensions aren't explicitly set, set the default.
+	if (configuredExtensions === undefined) {
+		if (!seen.has('cjs')) {
+			seen.add('cjs');
+		}
+
+		if (!seen.has('mjs')) {
+			seen.add('mjs');
+		}
+
+		if (!seen.has('js')) {
+			seen.add('js');
+		}
 	}
 
 	return [...seen];

lib/globs.js

@@ -14,7 +14,8 @@ const defaultMicromatchIgnorePatterns = [
 
 const defaultIgnoredByWatcherPatterns = [
 	'**/*.snap.md', // No need to rerun tests when the Markdown files change.
-	'ava.config.js' // Config is not reloaded so avoid rerunning tests when it changes.
+	'ava.config.js', // Config is not reloaded so avoid rerunning tests when it changes.
+	'ava.config.cjs' // Config is not reloaded so avoid rerunning tests when it changes.
 ];
 
 const buildExtensionPattern = extensions => extensions.length === 1 ? extensions[0] : `{${extensions.join(',')}}`;