feat(jest-cli, jest-config, @jest/core, jest-haste-map, @jest/reporters, jest-runner, jest-runtime, @jest/types): add workerThreads configuration option

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Features
 
+- `[jest-cli, jest-config, @jest/core, jest-haste-map, @jest/reporters, jest-runner, jest-runtime, @jest/types]` Add `workerThreads` configuration option to allow using [worker threads](https://nodejs.org/dist/latest/docs/api/worker_threads.html) for parallelization ([#13939](https://github.com/facebook/jest/pull/13939))
 - `[jest-worker]` Add `start` method to worker farms ([#13937](https://github.com/facebook/jest/pull/13937))
 
 ### Fixes

docs/CLI.md

@@ -506,3 +506,13 @@ In most CI environments, this is automatically handled for you.
 ### `--watchman`
 
 Whether to use [`watchman`](https://facebook.github.io/watchman/) for file crawling. Defaults to `true`. Disable using `--no-watchman`.
+
+### `--workerThreads`
+
+Whether to use [worker threads](https://nodejs.org/dist/latest/docs/api/worker_threads.html) for parallelization. [Child processes](https://nodejs.org/dist/latest/docs/api/child_process.html) are used by default.
+
+:::caution
+
+This is **experimental feature**. See the [`workerThreads` configuration option](Configuration.md#workerthreads) for more details.
+
+:::

docs/Configuration.md

@@ -2375,3 +2375,17 @@ This option allows comments in `package.json`. Include the comment text as the v
   }
 }
 ```
+
+### `workerThreads`
+
+Default: `false`
+
+Whether to use [worker threads](https://nodejs.org/dist/latest/docs/api/worker_threads.html) for parallelization. [Child processes](https://nodejs.org/dist/latest/docs/api/child_process.html) are used by default.
+
+Using worker threads may help to improve [performance](https://github.com/nodejs/node/discussions/44264).
+
+:::caution
+
+This is **experimental feature**. Keep in mind that the worker threads use structured clone instead of `JSON.stringify()` to serialize messages. This means that built-in JavaScript objects as `BigInt`, `Map` or `Set` will get serialized properly. However extra properties set on `Error`, `Map` or `Set` will not be passed on through the serialization step. For more details see the article on [structured clone](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm).
+
+:::

e2e/__tests__/__snapshots__/showConfig.test.ts.snap

@@ -138,7 +138,8 @@ exports[`--showConfig outputs config info and exits 1`] = `
     "useStderr": false,
     "watch": false,
     "watchAll": false,
-    "watchman": true
+    "watchman": true,
+    "workerThreads": false
   },
   "version": "[version]"
 }"

packages/jest-cli/src/args.ts

@@ -709,4 +709,10 @@ export const options: {[key: string]: Options} = {
       '--no-watchman.',
     type: 'boolean',
   },
+  workerThreads: {
+    description:
+      'Whether to use worker threads for parallelization. Child processes ' +
+      'are used by default.',
+    type: 'boolean',
+  },
 };

packages/jest-config/src/Defaults.ts

@@ -88,6 +88,7 @@ const defaultOptions: Config.DefaultOptions = {
   watch: false,
   watchPathIgnorePatterns: [],
   watchman: true,
+  workerThreads: false,
 };
 
 export default defaultOptions;

packages/jest-config/src/ValidConfig.ts

@@ -186,6 +186,7 @@ export const initialOptions: Config.InitialOptions = {
   ],
   watchman: true,
   workerIdleMemoryLimit: multipleValidOptions(0.2, '50%'),
+  workerThreads: true,
 };
 
 export const initialProjectOptions: Config.InitialProjectOptions = {

packages/jest-config/src/index.ts

@@ -140,6 +140,7 @@ const groupOptions = (
     watchPlugins: options.watchPlugins,
     watchman: options.watchman,
     workerIdleMemoryLimit: options.workerIdleMemoryLimit,
+    workerThreads: options.workerThreads,
   }),
   projectConfig: Object.freeze({
     automock: options.automock,

packages/jest-config/src/normalize.ts

@@ -936,6 +936,7 @@ export default async function normalize(
       case 'watch':
       case 'watchAll':
       case 'watchman':
+      case 'workerThreads':
         value = oldOptions[key];
         break;
       case 'workerIdleMemoryLimit':

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

@@ -157,6 +157,7 @@ const buildContextsAndHasteMaps = async (
         resetCache: !config.cache,
         watch: globalConfig.watch || globalConfig.watchAll,
         watchman: globalConfig.watchman,
+        workerThreads: globalConfig.workerThreads,
       });
       hasteMapInstances[index] = hasteMapInstance;
       return createContext(config, await hasteMapInstance.build());

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

@@ -79,6 +79,7 @@ type Options = {
   throwOnModuleCollision?: boolean;
   useWatchman?: boolean;
   watch?: boolean;
+  workerThreads?: boolean;
 };
 
 type InternalOptions = {
@@ -103,6 +104,7 @@ type InternalOptions = {
   throwOnModuleCollision: boolean;
   useWatchman: boolean;
   watch: boolean;
+  workerThreads?: boolean;
 };
 
 type Watcher = {
@@ -267,6 +269,7 @@ class HasteMap extends EventEmitter implements IHasteMap {
       throwOnModuleCollision: !!options.throwOnModuleCollision,
       useWatchman: options.useWatchman ?? true,
       watch: !!options.watch,
+      workerThreads: options.workerThreads,
     };
     this._console = options.console || globalThis.console;
 
@@ -748,6 +751,7 @@ class HasteMap extends EventEmitter implements IHasteMap {
         this._worker = {getSha1, worker};
       } else {
         this._worker = new Worker(require.resolve('./worker'), {
+          enableWorkerThreads: this._options.workerThreads,
           exposedMethods: ['getSha1', 'worker'],
           forkOptions: {serialization: 'json'},
           maxRetries: 3,

packages/jest-reporters/src/CoverageReporter.ts

@@ -147,6 +147,7 @@ export default class CoverageReporter extends BaseReporter {
       worker = require('./CoverageWorker');
     } else {
       worker = new Worker(require.resolve('./CoverageWorker'), {
+        enableWorkerThreads: this._globalConfig.workerThreads,
         exposedMethods: ['worker'],
         forkOptions: {serialization: 'json'},
         maxRetries: 2,

packages/jest-runner/src/index.ts

@@ -105,6 +105,7 @@ export default class TestRunner extends EmittingTestRunner {
     }
 
     const worker = new Worker(require.resolve('./testWorker'), {
+      enableWorkerThreads: this._globalConfig.workerThreads,
       exposedMethods: ['worker'],
       forkOptions: {serialization: 'json', stdio: 'pipe'},
       // The workerIdleMemoryLimit should've been converted to a number during

packages/jest-runtime/src/index.ts

@@ -79,6 +79,7 @@ type HasteMapOptions = {
   resetCache: boolean;
   watch?: boolean;
   watchman: boolean;
+  workerThreads?: boolean;
 };
 
 interface InternalModuleOptions extends Required<CallerTransformOptions> {
@@ -370,6 +371,7 @@ export default class Runtime {
       throwOnModuleCollision: config.haste.throwOnModuleCollision,
       useWatchman: options?.watchman,
       watch: options?.watch,
+      workerThreads: options?.workerThreads,
     });
   }
 

packages/jest-types/src/Config.ts

@@ -206,6 +206,7 @@ export type DefaultOptions = {
   watch: boolean;
   watchPathIgnorePatterns: Array<string>;
   watchman: boolean;
+  workerThreads: boolean;
 };
 
 export type DisplayName = {
@@ -326,6 +327,7 @@ export type InitialOptions = Partial<{
   watchman: boolean;
   watchPlugins: Array<string | [string, Record<string, unknown>]>;
   workerIdleMemoryLimit: number | string;
+  workerThreads: boolean;
 }>;
 
 export type SnapshotUpdateState = 'all' | 'new' | 'none';
@@ -419,6 +421,8 @@ export type GlobalConfig = {
     config: Record<string, unknown>;
   }> | null;
   workerIdleMemoryLimit?: number;
+  // TODO: make non-optional in Jest 30
+  workerThreads?: boolean;
 };
 
 export type ProjectConfig = {
@@ -574,5 +578,6 @@ export type Argv = Arguments<
     watchman: boolean;
     watchPathIgnorePatterns: Array<string>;
     workerIdleMemoryLimit: number | string;
+    workerThreads: boolean;
   }>
 >;