Throw explicit errors for common moduleFileExtension failures (#7160)

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<!-- Please remember to update CHANGELOG.md in the root of the project if you have not done so. -->

## Summary

Inspired by #7158, I finally decided to throw a better error in the cases where people have custom `moduleFileExtension` resulting in more or less obscure errors.

I've tackled 2 different issues here (in separate commits, happy to split them up into separate PRs if you want).

1. If you require a file without the file extension, we try to look for files matching _with_ a file extension and list them out. Also tell the user to either include file extension in the `require` or update `moduleFileExtension`.
2. If `js` is missing from `moduleFileExtension`, jest is unable to inject into the runtime. I decided to throw an explicit configuration error rather than fixing `jest-jasmine`'s `require`, as we'd also need all of our dependencies to do the same (e.g. `source-map` throws if we do `moduleFileExtension: []` now).

Fixes #4025.

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## Test plan
Integration tests added

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CHANGELOG.md

@@ -12,6 +12,7 @@
 - `[jest-haste-map]` [**BREAKING**] Remove support for `@providesModule` ([#6104](https://github.com/facebook/jest/pull/6104))
 - `[pretty-format]` Support HTMLCollection and NodeList in DOMCollection plugin ([#7125](https://github.com/facebook/jest/pull/7125))
 - `[jest-runtime]` Pass the normalized configuration to script transformers ([#7148](https://github.com/facebook/jest/pull/7148))
+- `[jest-runtime]` If `require` fails without a file extension, print all files that match with one ([#7160](https://github.com/facebook/jest/pull/7160))
 
 ### Fixes
 
@@ -37,6 +38,7 @@
 - `[jest-cli]` Fix unhandled error when a bad revision is provided to `changedSince` ([#7115](https://github.com/facebook/jest/pull/7115))
 - `[jest-config]` Moved dynamically assigned `cwd` from `jest-cli` to default configuration in `jest-config` ([#7146](https://github.com/facebook/jest/pull/7146))
 - `[jest-config]` Fix `getMaxWorkers` on termux ([#7154](https://github.com/facebook/jest/pull/7154))
+- `[jest-runtime]` Throw an explicit error if `js` is missing from `moduleFileExtensions` ([#7160](https://github.com/facebook/jest/pull/7160))
 
 ### Chore & Maintenance
 

e2e/__tests__/__snapshots__/resolve_no_file_extensions.test.js.snap

@@ -0,0 +1,38 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`show error message when no js moduleFileExtensions 1`] = `
+"● Validation Error:
+
+  moduleFileExtensions must include 'js':
+  but instead received:
+    [\\"jsx\\"]
+  Please change your configuration to include 'js'.
+
+  Configuration Documentation:
+  https://jestjs.io/docs/configuration.html
+
+"
+`;
+
+exports[`show error message with matching files 1`] = `
+"FAIL __tests__/test.js
+  ● Test suite failed to run
+
+    Cannot find module './some-json-file' from 'index.js'
+
+    However, Jest was able to find:
+    	'./some-json-file.json'
+
+    You might want to include a file extension in your import, or update your 'moduleFileExtensions', which is currently ['js'].
+
+    See https://jestjs.io/docs/en/configuration#modulefileextensions-array-string
+
+    > 1 | module.exports = require('./some-json-file');
+        |                  ^
+      2 | 
+
+      at packages/jest-resolve/build/index.js:221:17
+      at index.js:1:18
+
+"
+`;

e2e/__tests__/resolve_no_file_extensions.test.js

@@ -0,0 +1,53 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. 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.
+ *
+ * @flow
+ */
+'use strict';
+
+import path from 'path';
+import runJest from '../runJest';
+import {cleanup, extractSummary, writeFiles} from '../Utils';
+
+const DIR = path.resolve(__dirname, '../resolve_no_extensions-no-js');
+
+beforeEach(() => cleanup(DIR));
+afterAll(() => cleanup(DIR));
+
+test('show error message with matching files', () => {
+  const {status, stderr} = runJest('resolve_no_extensions');
+  const {rest} = extractSummary(stderr);
+
+  expect(status).toBe(1);
+  expect(rest).toMatchSnapshot();
+});
+
+test('show error message when no js moduleFileExtensions', () => {
+  writeFiles(DIR, {
+    'index.jsx': `
+      module.exports ={found: true};
+    `,
+    'package.json': `
+      {
+        "jest": {
+          "moduleFileExtensions": ["jsx"]
+        }
+      }
+    `,
+    'test.jsx': `
+      const m = require('../');
+
+      test('some test', () => {
+        expect(m.found).toBe(true);
+      });
+    `,
+  });
+
+  const {status, stderr} = runJest('resolve_no_extensions-no-js');
+
+  expect(status).toBe(1);
+  expect(stderr).toMatchSnapshot();
+});

e2e/resolve_no_extensions/__tests__/test.js

@@ -0,0 +1,5 @@
+const m = require('../');
+
+test('some test', () => {
+  expect(m.found).toBe(true);
+});

e2e/resolve_no_extensions/index.js

@@ -0,0 +1 @@
+module.exports = require('./some-json-file');

e2e/resolve_no_extensions/package.json

@@ -0,0 +1,7 @@
+{
+  "jest": {
+    "moduleFileExtensions": [
+      "js"
+    ]
+  }
+}

e2e/resolve_no_extensions/some-json-file.json

@@ -0,0 +1,3 @@
+{
+  "found": true
+}

flow-typed/npm/glob_v7.1.x.js

@@ -0,0 +1,87 @@
+// flow-typed signature: 7c09aef8ac07163d6ef9e3f50c6bc35c
+// flow-typed version: a12a42a747/glob_v7.1.x/flow_>=v0.42.x
+
+declare module "glob" {
+  declare type MinimatchOptions = {|
+    debug?: boolean,
+    nobrace?: boolean,
+    noglobstar?: boolean,
+    dot?: boolean,
+    noext?: boolean,
+    nocase?: boolean,
+    nonull?: boolean,
+    matchBase?: boolean,
+    nocomment?: boolean,
+    nonegate?: boolean,
+    flipNegate?: boolean
+  |};
+
+  declare type Options = {|
+    ...MinimatchOptions,
+    cwd?: string,
+    root?: string,
+    nomount?: boolean,
+    mark?: boolean,
+    nosort?: boolean,
+    stat?: boolean,
+    silent?: boolean,
+    strict?: boolean,
+    cache?: {
+      [path: string]: boolean | "DIR" | "FILE" | $ReadOnlyArray<string>
+    },
+    statCache?: {
+      [path: string]: boolean | { isDirectory(): boolean } | void
+    },
+    symlinks?: { [path: string]: boolean | void },
+    realpathCache?: { [path: string]: string },
+    sync?: boolean,
+    nounique?: boolean,
+    nodir?: boolean,
+    ignore?: string | $ReadOnlyArray<string>,
+    follow?: boolean,
+    realpath?: boolean,
+    absolute?: boolean
+  |};
+
+  /**
+   * Called when an error occurs, or matches are found
+   *   err
+   *   matches: filenames found matching the pattern
+   */
+  declare type CallBack = (err: ?Error, matches: Array<string>) => void;
+
+  declare class Glob extends events$EventEmitter {
+    constructor(pattern: string): this;
+    constructor(pattern: string, callback: CallBack): this;
+    constructor(pattern: string, options: Options, callback: CallBack): this;
+
+    minimatch: {};
+    options: Options;
+    aborted: boolean;
+    cache: {
+      [path: string]: boolean | "DIR" | "FILE" | $ReadOnlyArray<string>
+    };
+    statCache: {
+      [path: string]: boolean | { isDirectory(): boolean } | void
+    };
+    symlinks: { [path: string]: boolean | void };
+    realpathCache: { [path: string]: string };
+    found: Array<string>;
+
+    pause(): void;
+    resume(): void;
+    abort(): void;
+  }
+
+  declare class GlobModule {
+    Glob: Class<Glob>;
+
+    (pattern: string, callback: CallBack): void;
+    (pattern: string, options: Options, callback: CallBack): void;
+
+    hasMagic(pattern: string, options?: Options): boolean;
+    sync(pattern: string, options?: Options): Array<string>;
+  }
+
+  declare module.exports: GlobModule;
+}

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

@@ -260,7 +260,7 @@ describe('SearchSource', () => {
     it('finds tests with similar but custom file extensions', () => {
       const {options: config} = normalize(
         {
-          moduleFileExtensions: ['jsx'],
+          moduleFileExtensions: ['js', 'jsx'],
           name,
           rootDir,
           testMatch,
@@ -271,14 +271,17 @@ describe('SearchSource', () => {
         const relPaths = toPaths(data.tests).map(absPath =>
           path.relative(rootDir, absPath),
         );
-        expect(relPaths).toEqual([path.normalize('__testtests__/test.jsx')]);
+        expect(relPaths.sort()).toEqual([
+          path.normalize('__testtests__/test.js'),
+          path.normalize('__testtests__/test.jsx'),
+        ]);
       });
     });
 
     it('finds tests with totally custom foobar file extensions', () => {
       const {options: config} = normalize(
         {
-          moduleFileExtensions: ['foobar'],
+          moduleFileExtensions: ['js', 'foobar'],
           name,
           rootDir,
           testMatch,
@@ -289,7 +292,10 @@ describe('SearchSource', () => {
         const relPaths = toPaths(data.tests).map(absPath =>
           path.relative(rootDir, absPath),
         );
-        expect(relPaths).toEqual([path.normalize('__testtests__/test.foobar')]);
+        expect(relPaths.sort()).toEqual([
+          path.normalize('__testtests__/test.foobar'),
+          path.normalize('__testtests__/test.js'),
+        ]);
       });
     });
 

packages/jest-config/src/__tests__/normalize.test.js

@@ -1273,3 +1273,23 @@ describe('testPathPattern', () => {
     expect(options.onlyChanged).toBe(false);
   });
 });
+
+describe('moduleFileExtensions', () => {
+  it('defaults to something useful', () => {
+    const {options} = normalize({rootDir: '/root'}, {});
+
+    expect(options.moduleFileExtensions).toEqual(['js', 'json', 'jsx', 'node']);
+  });
+
+  it('throws if missing `js`', () => {
+    expect(() =>
+      normalize(
+        {
+          rootDir: '/root/',
+          moduleFileExtensions: ['json', 'jsx'],
+        },
+        {},
+      ),
+    ).toThrowError("moduleFileExtensions must include 'js'");
+  });
+});

packages/jest-config/src/normalize.js

@@ -36,6 +36,7 @@ import DEFAULT_CONFIG from './Defaults';
 import DEPRECATED_CONFIG from './Deprecated';
 import setFromArgv from './setFromArgv';
 import VALID_CONFIG from './ValidConfig';
+
 const ERROR = `${BULLET}Validation Error`;
 const PRESET_EXTENSIONS = ['.json', '.js'];
 const PRESET_NAME = 'jest-preset';
@@ -548,6 +549,32 @@ export default function normalize(options: InitialOptions, argv: Argv) {
       case 'testRegex':
         value = options[key] && replacePathSepForRegex(options[key]);
         break;
+      case 'moduleFileExtensions': {
+        value = options[key];
+
+        // If it's the wrong type, it can throw at a later time
+        if (Array.isArray(value) && !value.includes('js')) {
+          const errorMessage =
+            `  moduleFileExtensions must include 'js':\n` +
+            `  but instead received:\n` +
+            `    ${chalk.bold.red(JSON.stringify(value))}`;
+
+          // If `js` is not included, any dependency Jest itself injects into
+          // the environment, like jasmine or sourcemap-support, will need to
+          // `require` its modules with a file extension. This is not plausible
+          // in the long run, so it's way easier to just fail hard early.
+          // We might consider throwing if `json` is missing as well, as it's a
+          // fair assumption from modules that they can do
+          // `require('some-package/package') without the trailing `.json` as it
+          // works in Node normally.
+          throw createConfigError(
+            errorMessage +
+              "\n  Please change your configuration to include 'js'.",
+          );
+        }
+
+        break;
+      }
       case 'automock':
       case 'bail':
       case 'browser':
@@ -571,7 +598,6 @@ export default function normalize(options: InitialOptions, argv: Argv) {
       case 'listTests':
       case 'logHeapUsage':
       case 'mapCoverage':
-      case 'moduleFileExtensions':
       case 'name':
       case 'noStackTrace':
       case 'notify':

packages/jest-runtime/package.json

@@ -14,6 +14,7 @@
     "convert-source-map": "^1.4.0",
     "exit": "^0.1.2",
     "fast-json-stable-stringify": "^2.0.0",
+    "glob": "^7.1.3",
     "graceful-fs": "^4.1.11",
     "jest-config": "^23.6.0",
     "jest-haste-map": "^23.6.0",

packages/jest-runtime/src/__tests__/__snapshots__/runtime_require_module_no_ext.test.js.snap

@@ -0,0 +1,12 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Runtime requireModule with no extension throws error pointing out file with extension 1`] = `
+"Cannot find module 'RegularModuleWithWrongExt' from 'root.js'
+
+However, Jest was able to find:
+	'./RegularModuleWithWrongExt.txt'
+
+You might want to include a file extension in your import, or update your 'moduleFileExtensions', which is currently ['js', 'json', 'jsx', 'node'].
+
+See https://jestjs.io/docs/en/configuration#modulefileextensions-array-string"
+`;

packages/jest-runtime/src/__tests__/runtime_require_module_no_ext.test.js

@@ -0,0 +1,28 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. 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.
+ *
+ */
+
+'use strict';
+
+let createRuntime;
+
+describe('Runtime requireModule with no extension', () => {
+  beforeEach(() => {
+    createRuntime = require('createRuntime');
+  });
+
+  it('throws error pointing out file with extension', async () => {
+    const runtime = await createRuntime(__filename);
+
+    expect(() =>
+      runtime.requireModuleOrMock(
+        runtime.__mockRootPath,
+        'RegularModuleWithWrongExt',
+      ),
+    ).toThrowErrorMatchingSnapshot();
+  });
+});

packages/jest-runtime/src/__tests__/test_root/RegularModuleWithWrongExt.txt

@@ -0,0 +1 @@
+some file