feat: add support for .mjs config (#9431)

Author: SimenB

CHANGELOG.md

@@ -12,6 +12,7 @@
 - `[jest-config]` [**BREAKING**] Set default display name color based on runner ([#8689](https://github.com/facebook/jest/pull/8689))
 - `[jest-config]` Merge preset globals with project globals ([#9027](https://github.com/facebook/jest/pull/9027))
 - `[jest-config]` Support `.cjs` config files ([#9291](https://github.com/facebook/jest/pull/9291))
+- `[jest-config]` [**BREAKING**] Support `.mjs` config files ([#9431](https://github.com/facebook/jest/pull/9431))
 - `[jest-core]` Support reporters as default exports ([#9161](https://github.com/facebook/jest/pull/9161))
 - `[jest-core]` Support `--findRelatedTests` paths case insensitivity on Windows ([#8900](https://github.com/facebook/jest/issues/8900))
 - `[jest-diff]` Add options for colors and symbols ([#8841](https://github.com/facebook/jest/pull/8841))

babel.config.js

@@ -19,6 +19,22 @@ module.exports = {
       presets: ['@babel/preset-typescript'],
       test: /\.tsx?$/,
     },
+    // we want this file to keep `import()`, so exclude the transform for it
+    {
+      plugins: ['@babel/plugin-syntax-dynamic-import'],
+      presets: [
+        '@babel/preset-typescript',
+        [
+          '@babel/preset-env',
+          {
+            exclude: ['@babel/plugin-proposal-dynamic-import'],
+            shippedProposals: true,
+            targets: {node: 8},
+          },
+        ],
+      ],
+      test: 'packages/jest-config/src/importMjs.ts',
+    },
   ],
   plugins: [
     ['@babel/plugin-transform-modules-commonjs', {allowTopLevelThis: true}],

docs/Configuration.md

@@ -3,7 +3,7 @@ id: configuration
 title: Configuring Jest
 ---
 
-Jest's configuration can be defined in the `package.json` file of your project, or through a `jest.config.js` file or through the `--config <path/to/file.js|cjs|json>` option. If you'd like to use your `package.json` to store Jest's config, the "jest" key should be used on the top level so Jest will know how to find your settings:
+Jest's configuration can be defined in the `package.json` file of your project, or through a `jest.config.js` file or through the `--config <path/to/file.js|cjs|mjs|json>` option. If you'd like to use your `package.json` to store Jest's config, the `"jest"` key should be used on the top level so Jest will know how to find your settings:
 
 ```json
 {

e2e/__tests__/cjsConfigFile.test.ts

@@ -0,0 +1,38 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {onNodeVersions} from '@jest/test-utils';
+import {json as runWithJson} from '../runJest';
+
+test('reads config from cjs file', () => {
+  const {json, exitCode} = runWithJson('esm-config/cjs', ['--show-config'], {
+    skipPkgJsonCheck: true,
+  });
+
+  expect(exitCode).toBe(0);
+  expect(json.configs).toHaveLength(1);
+  expect(json.configs[0].displayName).toEqual({
+    color: 'white',
+    name: 'Config from cjs file',
+  });
+});
+
+// not unflagged for other versions yet. Update this range if that changes
+onNodeVersions('^13.2.0', () => {
+  test('reads config from mjs file', () => {
+    const {json, exitCode} = runWithJson('esm-config/mjs', ['--show-config'], {
+      skipPkgJsonCheck: true,
+    });
+
+    expect(exitCode).toBe(0);
+    expect(json.configs).toHaveLength(1);
+    expect(json.configs[0].displayName).toEqual({
+      color: 'white',
+      name: 'Config from mjs file',
+    });
+  });
+});

e2e/__tests__/esmConfigFile.test.ts

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+test('dummy test', () => {
+  expect(1).toBe(1);
+});

e2e/cjs-config/__tests__/test.js e2e/esm-config/cjs/__tests__/test.js

@@ -0,0 +1,11 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+export default {
+  displayName: 'Config from mjs file',
+  testEnvironment: 'node',
+};

e2e/cjs-config/jest.config.cjs e2e/esm-config/cjs/jest.config.cjs

@@ -0,0 +1,3 @@
+{
+  "jest": {}
+}

e2e/cjs-config/package.json e2e/esm-config/cjs/package.json

@@ -36,6 +36,15 @@ Object {
 }
 `;
 
+exports[`init has-jest-config-file-mjs ask the user whether to override config or not user answered with "Yes" 1`] = `
+Object {
+  "initial": true,
+  "message": "It seems that you already have a jest configuration, do you want to override it?",
+  "name": "continue",
+  "type": "confirm",
+}
+`;
+
 exports[`init project with package.json and no jest config all questions answered with answer: "No" should return the default configuration (an empty config) 1`] = `
 "// For a detailed explanation regarding each configuration property, visit:
 // https://jestjs.io/docs/en/configuration.html

e2e/esm-config/mjs/__tests__/test.js

@@ -0,0 +1,8 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+export default {};

e2e/esm-config/mjs/jest.config.mjs

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

e2e/esm-config/mjs/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "type_module",
+  "scripts": {
+    "test": "different-test-runner"
+  },
+  "type": "module"
+}

packages/jest-cli/src/init/__tests__/__snapshots__/init.test.js.snap

@@ -9,8 +9,11 @@
 import * as fs from 'fs';
 import * as path from 'path';
 import prompts from 'prompts';
+import {constants} from 'jest-config';
 import init from '../';
-import {JEST_CONFIG_EXT_ORDER} from '../constants';
+import {onNodeVersions} from '@jest/test-utils';
+
+const {JEST_CONFIG_EXT_ORDER} = constants;
 
 jest.mock('prompts');
 jest.mock('../../../../jest-config/build/getCacheDirectory', () => () =>
@@ -52,6 +55,22 @@ describe('init', () => {
 
         expect(evaluatedConfig).toEqual({});
       });
+
+      onNodeVersions('^13.2.0', () => {
+        it('should generate empty config with mjs extension', async () => {
+          prompts.mockReturnValueOnce({});
+
+          await init(resolveFromFixture('type_module'));
+
+          const writtenJestConfigFilename = fs.writeFileSync.mock.calls[0][0];
+          const writtenJestConfig = fs.writeFileSync.mock.calls[0][1];
+
+          expect(writtenJestConfigFilename.endsWith('.mjs')).toBe(true);
+
+          expect(typeof writtenJestConfig).toBe('string');
+          expect(writtenJestConfig.split('\n')[3]).toBe('export default {');
+        });
+      });
     });
 
     describe('some questions answered with answer: "Yes"', () => {

packages/jest-cli/src/init/__tests__/fixtures/has_jest_config_file_mjs/jest.config.mjs

@@ -31,7 +31,10 @@ const stringifyOption = (
   );
 };
 
-const generateConfigFile = (results: Record<string, unknown>): string => {
+const generateConfigFile = (
+  results: Record<string, unknown>,
+  generateEsm = false,
+): string => {
   const {coverage, clearMocks, environment} = results;
 
   const overrides: Record<string, any> = {};
@@ -75,7 +78,7 @@ const generateConfigFile = (results: Record<string, unknown>): string => {
   return (
     '// For a detailed explanation regarding each configuration property, visit:\n' +
     '// https://jestjs.io/docs/en/configuration.html\n\n' +
-    'module.exports = {\n' +
+    (generateEsm ? 'export default {\n' : 'module.exports = {\n') +
     properties.join('\n') +
     '};\n'
   );

packages/jest-cli/src/init/__tests__/fixtures/has_jest_config_file_mjs/package.json

@@ -10,18 +10,20 @@ import * as path from 'path';
 import chalk = require('chalk');
 import prompts = require('prompts');
 import {sync as realpath} from 'realpath-native';
+import {constants} from 'jest-config';
 import defaultQuestions, {testScriptQuestion} from './questions';
 import {MalformedPackageJsonError, NotFoundPackageJsonError} from './errors';
-import {
+import generateConfigFile from './generate_config_file';
+import modifyPackageJson from './modify_package_json';
+import {ProjectPackageJson} from './types';
+
+const {
   JEST_CONFIG_BASE_NAME,
-  JEST_CONFIG_EXT_CJS,
+  JEST_CONFIG_EXT_MJS,
   JEST_CONFIG_EXT_JS,
   JEST_CONFIG_EXT_ORDER,
   PACKAGE_JSON,
-} from './constants';
-import generateConfigFile from './generate_config_file';
-import modifyPackageJson from './modify_package_json';
-import {ProjectPackageJson} from './types';
+} = constants;
 
 type PromptsResults = {
   clearMocks: boolean;
@@ -65,7 +67,7 @@ export default async (rootDir: string = realpath(process.cwd())) => {
       rootDir,
       getConfigFilename(
         projectPackageJson.type === 'module'
-          ? JEST_CONFIG_EXT_CJS
+          ? JEST_CONFIG_EXT_MJS
           : JEST_CONFIG_EXT_JS,
       ),
     );
@@ -131,7 +133,11 @@ export default async (rootDir: string = realpath(process.cwd())) => {
     console.log(`✏️  Modified ${chalk.cyan(projectPackageJsonPath)}`);
   }
 
-  const generatedConfig = generateConfigFile(results);
+  const generatedConfig = generateConfigFile(
+    results,
+    projectPackageJson.type === 'module' ||
+      jestConfigPath.endsWith(JEST_CONFIG_EXT_MJS),
+  );
 
   fs.writeFileSync(jestConfigPath, generatedConfig);
 

packages/jest-cli/src/init/__tests__/fixtures/type_module/package.json

@@ -7,6 +7,8 @@
 
 import {defaults} from '../index';
 
+jest.mock('../importMjs', () => (s: string) => import(s));
+
 test('get configuration defaults', () => {
   expect(defaults).toBeDefined();
 });

packages/jest-cli/src/init/__tests__/init.test.js

@@ -7,16 +7,18 @@
 
 import {readConfig} from '../index';
 
-test('readConfig() throws when an object is passed without a file path', () => {
-  expect(() => {
+jest.mock('../importMjs', () => (s: string) => import(s));
+
+test('readConfig() throws when an object is passed without a file path', async () => {
+  await expect(
     readConfig(
       // @ts-ignore
       null /* argv */,
       {} /* packageRootOrConfig */,
       false /* skipArgvConfigOption */,
       null /* parentConfigPath */,
-    );
-  }).toThrowError(
+    ),
+  ).rejects.toThrowError(
     'Jest: Cannot use configuration as an object without a file path',
   );
 });

packages/jest-cli/src/init/constants.ts

@@ -7,9 +7,11 @@
 
 import {readConfigs} from '../index';
 
-test('readConfigs() throws when called without project paths', () => {
-  expect(() => {
+jest.mock('../importMjs', () => (s: string) => import(s));
+
+test('readConfigs() throws when called without project paths', async () => {
+  await expect(
     // @ts-ignore
-    readConfigs(null /* argv */, [] /* projectPaths */);
-  }).toThrowError('jest: No configuration found for any project.');
+    readConfigs(null /* argv */, [] /* projectPaths */),
+  ).rejects.toThrowError('jest: No configuration found for any project.');
 });

packages/jest-cli/src/init/generate_config_file.ts

@@ -13,10 +13,12 @@ export const DEFAULT_REPORTER_LABEL = 'default';
 export const PACKAGE_JSON = 'package.json';
 export const JEST_CONFIG_BASE_NAME = 'jest.config';
 export const JEST_CONFIG_EXT_CJS = '.cjs';
+export const JEST_CONFIG_EXT_MJS = '.mjs';
 export const JEST_CONFIG_EXT_JS = '.js';
 export const JEST_CONFIG_EXT_JSON = '.json';
 export const JEST_CONFIG_EXT_ORDER = Object.freeze([
   JEST_CONFIG_EXT_JS,
+  JEST_CONFIG_EXT_MJS,
   JEST_CONFIG_EXT_CJS,
   JEST_CONFIG_EXT_JSON,
 ]);

packages/jest-cli/src/init/index.ts

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// this is in a separate file so that node 8 don't explode with a syntax error.
+// Remove this file when we drop support for Node 8
+export default (specifier: string) => import(specifier);

packages/jest-config/src/__tests__/Defaults.test.ts

@@ -20,7 +20,8 @@ export {default as deprecationEntries} from './Deprecated';
 export {replaceRootDirInPath} from './utils';
 export {default as defaults} from './Defaults';
 export {default as descriptions} from './Descriptions';
-import {JEST_CONFIG_EXT_ORDER} from './constants';
+import * as constants from './constants';
+export {constants};
 
 type ReadConfig = {
   configPath: Config.Path | null | undefined;
@@ -29,7 +30,7 @@ type ReadConfig = {
   projectConfig: Config.ProjectConfig;
 };
 
-export function readConfig(
+export async function readConfig(
   argv: Config.Argv,
   packageRootOrConfig: Config.Path | Config.InitialOptions,
   // Whether it needs to look into `--config` arg passed to CLI.
@@ -39,7 +40,7 @@ export function readConfig(
   skipArgvConfigOption?: boolean,
   parentConfigPath?: Config.Path | null,
   projectIndex: number = Infinity,
-): ReadConfig {
+): Promise<ReadConfig> {
   let rawOptions;
   let configPath = null;
 
@@ -74,11 +75,11 @@ export function readConfig(
     // or a path to directory containing `package.json` or `jest.config.js`
   } else if (!skipArgvConfigOption && typeof argv.config == 'string') {
     configPath = resolveConfigPath(argv.config, process.cwd());
-    rawOptions = readConfigFileAndSetRootDir(configPath);
+    rawOptions = await readConfigFileAndSetRootDir(configPath);
   } else {
     // Otherwise just try to find config in the current rootDir.
     configPath = resolveConfigPath(packageRootOrConfig, process.cwd());
-    rawOptions = readConfigFileAndSetRootDir(configPath);
+    rawOptions = await readConfigFileAndSetRootDir(configPath);
   }
 
   const {options, hasDeprecationWarnings} = normalize(
@@ -262,22 +263,22 @@ This usually means that your ${chalk.bold(
 //
 // If no projects are specified, process.cwd() will be used as the default
 // (and only) project.
-export function readConfigs(
+export async function readConfigs(
   argv: Config.Argv,
   projectPaths: Array<Config.Path>,
-): {
+): Promise<{
   globalConfig: Config.GlobalConfig;
   configs: Array<Config.ProjectConfig>;
   hasDeprecationWarnings: boolean;
-} {
+}> {
   let globalConfig;
   let hasDeprecationWarnings;
   let configs: Array<Config.ProjectConfig> = [];
   let projects = projectPaths;
   let configPath: Config.Path | null | undefined;
 
   if (projectPaths.length === 1) {
-    const parsedConfig = readConfig(argv, projects[0]);
+    const parsedConfig = await readConfig(argv, projects[0]);
     configPath = parsedConfig.configPath;
 
     hasDeprecationWarnings = parsedConfig.hasDeprecationWarnings;
@@ -298,33 +299,37 @@ export function readConfigs(
         ? projects[0] === realpath(process.cwd())
         : projects[0] === process.cwd();
 
-    const parsedConfigs = projects
-      .filter(root => {
-        // Ignore globbed files that cannot be `require`d.
-        if (
-          typeof root === 'string' &&
-          fs.existsSync(root) &&
-          !fs.lstatSync(root).isDirectory() &&
-          !JEST_CONFIG_EXT_ORDER.some(ext => root.endsWith(ext))
-        ) {
-          return false;
-        }
+    const parsedConfigs = await Promise.all(
+      projects
+        .filter(root => {
+          // Ignore globbed files that cannot be `require`d.
+          if (
+            typeof root === 'string' &&
+            fs.existsSync(root) &&
+            !fs.lstatSync(root).isDirectory() &&
+            !constants.JEST_CONFIG_EXT_ORDER.some(ext => root.endsWith(ext))
+          ) {
+            return false;
+          }
 
-        return true;
-      })
-      .map((root, projectIndex) => {
-        const projectIsTheOnlyProject =
-          projectIndex === 0 && projects.length === 1;
-        const skipArgvConfigOption = !(projectIsTheOnlyProject && projectIsCwd);
+          return true;
+        })
+        .map((root, projectIndex) => {
+          const projectIsTheOnlyProject =
+            projectIndex === 0 && projects.length === 1;
+          const skipArgvConfigOption = !(
+            projectIsTheOnlyProject && projectIsCwd
+          );
 
-        return readConfig(
-          argv,
-          root,
-          skipArgvConfigOption,
-          configPath,
-          projectIndex,
-        );
-      });
+          return readConfig(
+            argv,
+            root,
+            skipArgvConfigOption,
+            configPath,
+            projectIndex,
+          );
+        }),
+    );
 
     ensureNoDuplicateConfigs(parsedConfigs, projects);
     configs = parsedConfigs.map(({projectConfig}) => projectConfig);

packages/jest-config/src/__tests__/readConfig.test.ts

@@ -10,26 +10,56 @@ import * as fs from 'fs';
 import {Config} from '@jest/types';
 // @ts-ignore: vendored
 import jsonlint from './vendor/jsonlint';
-import {PACKAGE_JSON} from './constants';
+import {
+  JEST_CONFIG_EXT_JSON,
+  JEST_CONFIG_EXT_MJS,
+  PACKAGE_JSON,
+} from './constants';
+import importMjs from './importMjs';
 
 // Read the configuration and set its `rootDir`
 // 1. If it's a `package.json` file, we look into its "jest" property
 // 2. For any other file, we just require it.
-export default (configPath: Config.Path): Config.InitialOptions => {
-  const isJSON = configPath.endsWith('.json');
+export default async function readConfigFileAndSetRootDir(
+  configPath: Config.Path,
+): Promise<Config.InitialOptions> {
+  const isJSON = configPath.endsWith(JEST_CONFIG_EXT_JSON);
+  const isMjs = configPath.endsWith(JEST_CONFIG_EXT_MJS);
   let configObject;
 
-  try {
-    configObject = require(configPath);
-  } catch (error) {
-    if (isJSON) {
-      throw new Error(
-        `Jest: Failed to parse config file ${configPath}\n` +
-          `  ${jsonlint.errors(fs.readFileSync(configPath, 'utf8'))}`,
-      );
-    } else {
+  if (isMjs) {
+    try {
+      const importedConfig = await importMjs(configPath);
+
+      if (!importedConfig.default) {
+        throw new Error(
+          `Jest: Failed to load mjs config file ${configPath} - did you use a default export?`,
+        );
+      }
+
+      configObject = importedConfig.default;
+    } catch (error) {
+      if (error.message === 'Not supported') {
+        throw new Error(
+          `Jest: Your version of Node does not support dynamic import - please enable it or use a .cjs file extension for file ${configPath}`,
+        );
+      }
+
       throw error;
     }
+  } else {
+    try {
+      configObject = require(configPath);
+    } catch (error) {
+      if (isJSON) {
+        throw new Error(
+          `Jest: Failed to parse config file ${configPath}\n` +
+            `  ${jsonlint.errors(fs.readFileSync(configPath, 'utf8'))}`,
+        );
+      } else {
+        throw error;
+      }
+    }
   }
 
   if (configPath.endsWith(PACKAGE_JSON)) {
@@ -53,4 +83,4 @@ export default (configPath: Config.Path): Config.InitialOptions => {
   }
 
   return configObject;
-};
+}

packages/jest-config/src/__tests__/readConfigs.test.ts

@@ -49,7 +49,7 @@ export const runCLI = async (
   const outputStream =
     argv.json || argv.useStderr ? process.stderr : process.stdout;
 
-  const {globalConfig, configs, hasDeprecationWarnings} = readConfigs(
+  const {globalConfig, configs, hasDeprecationWarnings} = await readConfigs(
     argv,
     projects,
   );

packages/jest-config/src/constants.ts

@@ -20,7 +20,7 @@ import {VERSION} from '../version';
 import {Context} from '../types';
 import * as args from './args';
 
-export function run(cliArgv?: Config.Argv, cliInfo?: Array<string>) {
+export async function run(cliArgv?: Config.Argv, cliInfo?: Array<string>) {
   const realFs = require('fs');
   const fs = require('graceful-fs');
   fs.gracefulify(realFs);
@@ -62,7 +62,7 @@ export function run(cliArgv?: Config.Argv, cliInfo?: Array<string>) {
     const info = cliInfo ? ', ' + cliInfo.join(', ') : '';
     console.log(`Using Jest Runtime v${VERSION}${info}`);
   }
-  const options = readConfig(argv, root);
+  const options = await readConfig(argv, root);
   const globalConfig = options.globalConfig;
   // Always disable automocking in scripts.
   const config: Config.ProjectConfig = {
@@ -73,26 +73,26 @@ export function run(cliArgv?: Config.Argv, cliInfo?: Array<string>) {
   // Break circular dependency
   const Runtime: any = require('..');
 
-  (Runtime.createContext(config, {
-    maxWorkers: Math.max(cpus().length - 1, 1),
-    watchman: globalConfig.watchman,
-  }) as Promise<Context>)
-    .then(hasteMap => {
-      const Environment: typeof JestEnvironment = require(config.testEnvironment);
-      const environment = new Environment(config);
-      setGlobal(
-        environment.global,
-        'console',
-        new CustomConsole(process.stdout, process.stderr),
-      );
-      setGlobal(environment.global, 'jestProjectConfig', config);
-      setGlobal(environment.global, 'jestGlobalConfig', globalConfig);
-
-      const runtime = new Runtime(config, environment, hasteMap.resolver);
-      runtime.requireModule(filePath);
-    })
-    .catch(e => {
-      console.error(chalk.red(e.stack || e));
-      process.on('exit', () => (process.exitCode = 1));
+  try {
+    const hasteMap: Context = await Runtime.createContext(config, {
+      maxWorkers: Math.max(cpus().length - 1, 1),
+      watchman: globalConfig.watchman,
     });
+
+    const Environment: typeof JestEnvironment = require(config.testEnvironment);
+    const environment = new Environment(config);
+    setGlobal(
+      environment.global,
+      'console',
+      new CustomConsole(process.stdout, process.stderr),
+    );
+    setGlobal(environment.global, 'jestProjectConfig', config);
+    setGlobal(environment.global, 'jestGlobalConfig', globalConfig);
+
+    const runtime = new Runtime(config, environment, hasteMap.resolver);
+    runtime.requireModule(filePath);
+  } catch (e) {
+    console.error(chalk.red(e.stack || e));
+    process.on('exit', () => (process.exitCode = 1));
+  }
 }

packages/jest-config/src/importMjs.ts

@@ -149,7 +149,14 @@ function buildFile(file, silent) {
           Array.isArray(plugin) &&
           plugin[0] === '@babel/plugin-transform-modules-commonjs'
         ) {
-          return [plugin[0], Object.assign({}, plugin[1], {lazy: true})];
+          return [
+            plugin[0],
+            Object.assign({}, plugin[1], {
+              lazy: string =>
+                // we want to lazyload all non-local modules plus `importMjs` - the latter to avoid syntax errors. Set to just `true` when we drop support for node 8
+                !string.startsWith('./') || string === './importMjs',
+            }),
+          ];
         }
 
         return plugin;