feat: Add support for loading config from ESM modules (#7)

Fixes #6

.taprc

@@ -1,4 +1,5 @@
 {
 	"test-ignore": "helpers",
-	"check-coverage": true
+	"esm": false,
+	"nyc-arg": "--nycrc-path=nyc-settings.js"
 }

index.js

@@ -2,18 +2,35 @@
 
 const fs = require('fs');
 const path = require('path');
+const {promisify} = require('util');
 const camelcase = require('camelcase');
 const findUp = require('find-up');
 const resolveFrom = require('resolve-from');
 
+const readFile = promisify(fs.readFile);
+
 const standardConfigFiles = [
 	'.nycrc',
 	'.nycrc.json',
 	'.nycrc.yml',
 	'.nycrc.yaml',
-	'nyc.config.js'
+	'nyc.config.js',
+	'nyc.config.cjs',
+	'nyc.config.mjs'
 ];
 
+async function moduleLoader(file) {
+	try {
+		return require(file);
+	} catch (error) {
+		if (error.code !== 'ERR_REQUIRE_ESM') {
+			throw error;
+		}
+
+		return require('./load-esm')(file);
+	}
+}
+
 function camelcasedConfig(config) {
 	const results = {};
 	for (const [field, value] of Object.entries(config)) {
@@ -23,13 +40,13 @@ function camelcasedConfig(config) {
 	return results;
 }
 
-function findPackage(options) {
+async function findPackage(options) {
 	const cwd = options.cwd || process.env.NYC_CWD || process.cwd();
-	const pkgPath = findUp.sync('package.json', {cwd});
+	const pkgPath = await findUp('package.json', {cwd});
 	if (pkgPath) {
 		return {
 			cwd: path.dirname(pkgPath),
-			pkgConfig: JSON.parse(fs.readFileSync(pkgPath, 'utf8')).nyc || {}
+			pkgConfig: JSON.parse(await readFile(pkgPath, 'utf8')).nyc || {}
 		};
 	}
 
@@ -39,38 +56,37 @@ function findPackage(options) {
 	};
 }
 
-function actualLoad(configFile) {
+async function actualLoad(configFile) {
 	if (!configFile) {
 		return {};
 	}
 
 	const configExt = path.extname(configFile).toLowerCase();
 	switch (configExt) {
 		case '.js':
+		case '.mjs':
+			return moduleLoader(configFile);
+		case '.cjs':
 			return require(configFile);
 		case '.yml':
 		case '.yaml':
-			return require('js-yaml').load(
-				fs.readFileSync(configFile, 'utf8')
-			);
+			return require('js-yaml').load(await readFile(configFile, 'utf8'));
 		default:
-			return JSON.parse(
-				fs.readFileSync(configFile, 'utf8')
-			);
+			return JSON.parse(await readFile(configFile, 'utf8'));
 	}
 }
 
-function applyExtends(config, filename, loopCheck = new Set()) {
+async function applyExtends(config, filename, loopCheck = new Set()) {
 	config = camelcasedConfig(config);
-	if (Object.prototype.hasOwnProperty.call(config, 'extends')) {
+	if ('extends' in config) {
 		const extConfigs = [].concat(config.extends);
 		if (extConfigs.some(e => typeof e !== 'string')) {
 			throw new TypeError(`${filename} contains an invalid 'extends' option`);
 		}
 
 		delete config.extends;
 		const filePath = path.dirname(filename);
-		return extConfigs.reduce((config, extConfig) => {
+		for (const extConfig of extConfigs) {
 			const configFile = resolveFrom.silent(filePath, extConfig) ||
 				resolveFrom.silent(filePath, './' + extConfig);
 			if (!configFile) {
@@ -82,27 +98,28 @@ function applyExtends(config, filename, loopCheck = new Set()) {
 			}
 
 			loopCheck.add(configFile);
-			return {
-				...config,
-				...applyExtends(actualLoad(configFile), configFile, loopCheck)
-			};
-		}, config);
+			Object.assign(
+				config,
+				// eslint-disable-next-line no-await-in-loop
+				await applyExtends(await actualLoad(configFile), configFile, loopCheck)
+			);
+		}
 	}
 
 	return config;
 }
 
-function loadNycConfig(options = {}) {
-	const {cwd, pkgConfig} = findPackage(options);
+async function loadNycConfig(options = {}) {
+	const {cwd, pkgConfig} = await findPackage(options);
 	const configFiles = [].concat(options.nycrcPath || standardConfigFiles);
-	const configFile = findUp.sync(configFiles, {cwd});
+	const configFile = await findUp(configFiles, {cwd});
 	if (options.nycrcPath && !configFile) {
 		throw new Error(`Requested configuration file ${options.nycrcPath} not found`);
 	}
 
 	const config = {
-		...applyExtends(pkgConfig, path.join(cwd, 'package.json')),
-		...applyExtends(actualLoad(configFile), configFile)
+		...(await applyExtends(pkgConfig, path.join(cwd, 'package.json'))),
+		...(await applyExtends(await actualLoad(configFile), configFile))
 	};
 
 	const arrayFields = ['require', 'extension', 'exclude', 'include'];

load-esm.js

@@ -0,0 +1,10 @@
+'use strict';
+
+module.exports = async filename => {
+	const mod = await import(filename);
+	if ('default' in mod === false) {
+		throw new Error(`${filename} has no default export`);
+	}
+
+	return mod.default;
+};

nyc-settings.js

@@ -0,0 +1,13 @@
+'use strict';
+
+const {hasImport} = require('./test/helpers');
+
+const include = [
+	'index.js'
+];
+
+if (hasImport) {
+	include.push('load-esm.js');
+}
+
+module.exports = {include};

package.json

@@ -23,16 +23,22 @@
 	"homepage": "https://github.com/istanbuljs/load-nyc-config#readme",
 	"dependencies": {
 		"camelcase": "^5.3.1",
-		"find-up": "^4.0.0",
+		"find-up": "^4.1.0",
 		"js-yaml": "^3.13.1",
 		"resolve-from": "^5.0.0"
 	},
 	"devDependencies": {
-		"standard-version": "^6.0.1",
-		"tap": "^14.0.0",
-		"xo": "^0.24.0"
+		"standard-version": "^7.0.0",
+		"tap": "^14.6.5",
+		"xo": "^0.25.3"
 	},
 	"xo": {
-		"ignores": "tap-snapshots/**"
+		"ignores": [
+			"test/fixtures/extends/invalid.*",
+			"tap-snapshots/**"
+		],
+		"rules": {
+			"require-atomic-updates": 0
+		}
 	}
 }

tap-snapshots/test-basic.js-TAP.test.js

@@ -30,6 +30,18 @@ Object {
 }
 `
 
+exports[`test/basic.js TAP esm nyc-config-js-type-module > must match snapshot 1`] = `
+Object {
+  "all": false,
+}
+`
+
+exports[`test/basic.js TAP esm nyc-config-mjs > must match snapshot 1`] = `
+Object {
+  "all": false,
+}
+`
+
 exports[`test/basic.js TAP extends > must match snapshot 1`] = `
 Object {
   "all": false,
@@ -65,6 +77,18 @@ Object {
 }
 `
 
+exports[`test/basic.js TAP nyc-config-async > must match snapshot 1`] = `
+Object {
+  "all": false,
+}
+`
+
+exports[`test/basic.js TAP nyc-config-cjs > must match snapshot 1`] = `
+Object {
+  "all": false,
+}
+`
+
 exports[`test/basic.js TAP nyc-config-js > must match snapshot 1`] = `
 Object {
   "all": false,

tap-snapshots/test-env-nyc-cwd.js-TAP.test.js

@@ -5,7 +5,7 @@
  * Make sure to inspect the output below.  Do not ignore changes!
  */
 'use strict'
-exports[`test/env-nyc-cwd.js TAP > must match snapshot 1`] = `
+exports[`test/env-nyc-cwd.js TAP env-nyc-cwd > must match snapshot 1`] = `
 Object {
   "all": true,
 }

tap-snapshots/test-process-cwd.js-TAP.test.js

@@ -5,7 +5,7 @@
  * Make sure to inspect the output below.  Do not ignore changes!
  */
 'use strict'
-exports[`test/process-cwd.js TAP > must match snapshot 1`] = `
+exports[`test/process-cwd.js TAP process-cwd > must match snapshot 1`] = `
 Object {
   "all": true,
 }

test/basic.js

@@ -1,40 +1,68 @@
 const t = require('tap');
-const {fixturePath, basicTest} = require('./helpers');
+const {fixturePath, basicTest, hasImport, hasESM} = require('./helpers');
 const {loadNycConfig} = require('..');
 
-t.test('options.nycrcPath points to non-existent file', t => {
+t.test('options.nycrcPath points to non-existent file', async t => {
 	const cwd = fixturePath();
 	const nycrcPath = fixturePath('does-not-exist.json');
-	t.throws(() => loadNycConfig({cwd, nycrcPath}));
-	t.end();
+	await t.rejects(loadNycConfig({cwd, nycrcPath}));
 });
 
 t.test('no-config-file', basicTest);
 t.test('nycrc-no-ext', basicTest);
 t.test('nycrc-json', basicTest);
 t.test('nycrc-yml', basicTest);
 t.test('nycrc-yaml', basicTest);
+t.test('nyc-config-cjs', basicTest);
 t.test('nyc-config-js', basicTest);
+t.test('nyc-config-async', basicTest);
 t.test('array-field-fixup', basicTest);
 t.test('camel-decamel', basicTest);
 t.test('extends', basicTest);
 t.test('extends-array-empty', basicTest);
 t.test('extends-array', basicTest);
 
-t.test('extends failures', t => {
-	const errorConfigs = ['looper1.json', 'invalid.json', 'missing.json'];
+t.test('extends failures', async t => {
 	const cwd = fixturePath('extends');
-	errorConfigs.map(f => fixturePath('extends', f)).forEach(nycrcPath => {
-		t.throws(() => loadNycConfig({cwd, nycrcPath}));
+	const files = {
+		'looper1.json': /Circular extended configurations/,
+		'invalid.json': /contains an invalid 'extends' option/,
+		'invalid.js': /Unexpected identifier/,
+		'invalid.cjs': /Unexpected identifier/,
+		'missing.json': /Could not resolve configuration file/
+	};
+	if (hasImport && await hasESM()) {
+		files['invalid.mjs'] = /has no default export/;
+	}
+
+	const tests = Object.entries(files).map(([file, error]) => {
+		return t.rejects(loadNycConfig({
+			cwd,
+			nycrcPath: fixturePath('extends', file)
+		}), error, file);
 	});
-	t.end();
+
+	await Promise.all(tests);
 });
 
-t.test('no package.json', t => {
+t.test('no package.json', async t => {
 	const cwd = '/';
 	const nycrcPath = fixturePath('nycrc-no-ext', '.nycrc');
 
-	t.matchSnapshot(loadNycConfig({cwd}), 'no config');
-	t.matchSnapshot(loadNycConfig({cwd, nycrcPath}), 'explicit .nycrc');
-	t.end();
+	t.matchSnapshot(await loadNycConfig({cwd}), 'no config');
+	t.matchSnapshot(await loadNycConfig({cwd, nycrcPath}), 'explicit .nycrc');
 });
+
+if (hasImport) {
+	t.test('esm', async t => {
+		if (await hasESM()) {
+			if (process.versions.node.split('.')[0] >= 12) {
+				await t.test('nyc-config-js-type-module', basicTest);
+			}
+
+			await t.test('nyc-config-mjs', basicTest);
+		} else {
+			t.pass('we have import but it doesn\'t support ES modules');
+		}
+	});
+}

test/env-nyc-cwd.js

@@ -2,10 +2,11 @@ const t = require('tap');
 const {fixturePath} = require('./helpers');
 const {loadNycConfig} = require('..');
 
-const saved = process.env.NYC_CWD;
-process.env.NYC_CWD = fixturePath('no-config-file');
+t.test('env-nyc-cwd', async t => {
+	const saved = process.env.NYC_CWD;
+	process.env.NYC_CWD = fixturePath('no-config-file');
 
-t.matchSnapshot(loadNycConfig());
-t.end();
+	t.matchSnapshot(await loadNycConfig());
 
-process.env.NYC_CWD = saved;
+	process.env.NYC_CWD = saved;
+});

test/fixtures/extends/invalid.cjs

@@ -0,0 +1 @@
+syntax error!

test/fixtures/extends/invalid.js

@@ -0,0 +1 @@
+syntax error!

test/fixtures/extends/invalid.mjs

@@ -0,0 +1,2 @@
+// This is not supported, config must be provided in the default export.
+export const all = true;

test/fixtures/nyc-config-async/nyc.config.js

@@ -0,0 +1,12 @@
+'use strict';
+
+const {promisify} = require('util');
+
+const delay = promisify(setTimeout);
+
+async function loadConfig() {
+	await delay(10);
+	return {all: false};
+}
+
+module.exports = loadConfig();

test/fixtures/nyc-config-async/package.json

@@ -0,0 +1,5 @@
+{
+	"nyc": {
+		"all": true
+	}
+}

test/fixtures/nyc-config-cjs/nyc.config.cjs

@@ -0,0 +1,3 @@
+'use strict';
+
+module.exports = {all: false};

test/fixtures/nyc-config-cjs/package.json

@@ -0,0 +1,2 @@
+{
+}

test/fixtures/nyc-config-js-type-module/nyc.config.js

@@ -0,0 +1,3 @@
+export default {
+	all: false
+};

test/fixtures/nyc-config-js-type-module/package.json

@@ -0,0 +1,6 @@
+{
+	"type": "module",
+	"nyc": {
+		"all": true
+	}
+}