fix(jest-haste-map): Make watchman existence check lazy+async

CHANGELOG.md

@@ -74,6 +74,7 @@
 - `[jest-environment-node]` Add `structuredClone` to globals ([#12631](https://github.com/facebook/jest/pull/12631))
 - `[@jest/expect-utils]` [**BREAKING**] Fix false positives when looking for `undefined` prop ([#8923](https://github.com/facebook/jest/pull/8923))
 - `[jest-haste-map]` Don't use partial results if file crawl errors ([#12420](https://github.com/facebook/jest/pull/12420))
+- `[jest-haste-map]` Make watchman existence check lazy+async ([#12675](https://github.com/facebook/jest/pull/12675))
 - `[jest-jasmine2, jest-types]` [**BREAKING**] Move all `jasmine` specific types from `@jest/types` to its own package ([#12125](https://github.com/facebook/jest/pull/12125))
 - `[jest-jasmine2]` Do not set `duration` to `0` for skipped tests ([#12518](https://github.com/facebook/jest/pull/12518))
 - `[jest-matcher-utils]` Pass maxWidth to `pretty-format` to avoid printing every element in arrays by default ([#12402](https://github.com/facebook/jest/pull/12402))

packages/jest-haste-map/src/__tests__/index.test.js

@@ -13,9 +13,11 @@ function mockHashContents(contents) {
   return crypto.createHash('sha1').update(contents).digest('hex');
 }
 
-jest.mock('child_process', () => ({
-  // If this does not throw, we'll use the (mocked) watchman crawler
-  execSync() {},
+const mockIsWatchmanInstalled = jest.fn().mockResolvedValue(true);
+
+jest.mock('../lib/isWatchmanInstalled', () => ({
+  __esModule: true,
+  default: mockIsWatchmanInstalled,
 }));
 
 jest.mock('jest-worker', () => ({
@@ -612,6 +614,8 @@ describe('HasteMap', () => {
         });
       });
 
+      mockIsWatchmanInstalled.mockClear();
+
       const hasteMap = await HasteMap.create({
         ...defaultConfig,
         computeSha1: true,
@@ -621,6 +625,10 @@ describe('HasteMap', () => {
 
       const data = (await hasteMap.build()).__hasteMapForTest;
 
+      expect(mockIsWatchmanInstalled).toHaveBeenCalledTimes(
+        useWatchman ? 1 : 0,
+      );
+
       expect(data.files).toEqual(
         createMap({
           [path.join('fruits', 'Banana.js')]: [

packages/jest-haste-map/src/index.ts

@@ -7,7 +7,6 @@
 
 /* eslint-disable local/ban-types-eventually */
 
-import {execSync} from 'child_process';
 import {createHash} from 'crypto';
 import {EventEmitter} from 'events';
 import {tmpdir} from 'os';
@@ -26,6 +25,7 @@ import {watchmanCrawl} from './crawlers/watchman';
 import getMockName from './getMockName';
 import * as fastPath from './lib/fast_path';
 import getPlatformExtension from './lib/getPlatformExtension';
+import isWatchmanInstalled from './lib/isWatchmanInstalled';
 import normalizePathSep from './lib/normalizePathSep';
 import type {
   ChangeEvent,
@@ -124,14 +124,6 @@ const VCS_DIRECTORIES = ['.git', '.hg']
   .map(vcs => escapePathForRegex(path.sep + vcs + path.sep))
   .join('|');
 
-const canUseWatchman = ((): boolean => {
-  try {
-    execSync('watchman --version', {stdio: ['ignore']});
-    return true;
-  } catch {}
-  return false;
-})();
-
 function invariant(condition: unknown, message?: string): asserts condition {
   if (!condition) {
     throw new Error(message);
@@ -221,6 +213,7 @@ export default class HasteMap extends EventEmitter {
   private _cachePath: string;
   private _changeInterval?: ReturnType<typeof setInterval>;
   private _console: Console;
+  private _isWatchmanInstalledPromise: Promise<boolean> | null = null;
   private _options: InternalOptions;
   private _watchers: Array<Watcher>;
   private _worker: WorkerInterface | null;
@@ -763,11 +756,10 @@ export default class HasteMap extends EventEmitter {
     return this._worker;
   }
 
-  private _crawl(hasteMap: InternalHasteMap) {
+  private async _crawl(hasteMap: InternalHasteMap) {
     const options = this._options;
     const ignore = this._ignore.bind(this);
-    const crawl =
-      canUseWatchman && this._options.useWatchman ? watchmanCrawl : nodeCrawl;
+    const crawl = (await this._shouldUseWatchman()) ? watchmanCrawl : nodeCrawl;
     const crawlerOptions: CrawlerOptions = {
       computeSha1: options.computeSha1,
       data: hasteMap,
@@ -811,7 +803,7 @@ export default class HasteMap extends EventEmitter {
   /**
    * Watch mode
    */
-  private _watch(hasteMap: InternalHasteMap): Promise<void> {
+  private async _watch(hasteMap: InternalHasteMap): Promise<void> {
     if (!this._options.watch) {
       return Promise.resolve();
     }
@@ -822,12 +814,11 @@ export default class HasteMap extends EventEmitter {
     this._options.retainAllFiles = true;
 
     // WatchmanWatcher > FSEventsWatcher > sane.NodeWatcher
-    const Watcher =
-      canUseWatchman && this._options.useWatchman
-        ? WatchmanWatcher
-        : FSEventsWatcher.isSupported()
-        ? FSEventsWatcher
-        : NodeWatcher;
+    const Watcher = (await this._shouldUseWatchman())
+      ? WatchmanWatcher
+      : FSEventsWatcher.isSupported()
+      ? FSEventsWatcher
+      : NodeWatcher;
 
     const extensions = this._options.extensions;
     const ignorePattern = this._options.ignorePattern;
@@ -1110,6 +1101,16 @@ export default class HasteMap extends EventEmitter {
     );
   }
 
+  private async _shouldUseWatchman(): Promise<boolean> {
+    if (!this._options.useWatchman) {
+      return false;
+    }
+    if (!this._isWatchmanInstalledPromise) {
+      this._isWatchmanInstalledPromise = isWatchmanInstalled();
+    }
+    return this._isWatchmanInstalledPromise;
+  }
+
   private _createEmptyMap(): InternalHasteMap {
     return {
       clocks: new Map(),

packages/jest-haste-map/src/lib/__tests__/isWatchmanInstalled.test.js

@@ -0,0 +1,37 @@
+/**
+ * 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 {execFile} from 'child_process';
+import isWatchmanInstalled from '../isWatchmanInstalled';
+
+jest.mock('child_process');
+
+describe('isWatchmanInstalled', () => {
+  beforeEach(() => jest.clearAllMocks());
+
+  it('executes watchman --version and returns true on success', async () => {
+    execFile.mockImplementation((file, args, cb) => {
+      expect(file).toBe('watchman');
+      expect(args).toStrictEqual(['--version']);
+      cb(null, {stdout: 'v123'});
+    });
+    expect(await isWatchmanInstalled()).toBe(true);
+    expect(execFile).toHaveBeenCalledWith(
+      'watchman',
+      ['--version'],
+      expect.any(Function),
+    );
+  });
+
+  it('returns false when execFile fails', async () => {
+    execFile.mockImplementation((file, args, cb) => {
+      cb(new Error());
+    });
+    expect(await isWatchmanInstalled()).toBe(false);
+    expect(execFile).toHaveBeenCalled();
+  });
+});

packages/jest-haste-map/src/lib/isWatchmanInstalled.ts

@@ -0,0 +1,18 @@
+/**
+ * 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 {execFile} from 'child_process';
+import {promisify} from 'util';
+
+export default async function isWatchmanInstalled(): Promise<boolean> {
+  try {
+    await promisify(execFile)('watchman', ['--version']);
+    return true;
+  } catch {
+    return false;
+  }
+}