perf(jest-runtime): load chalk only once per worker

.gitignore

@@ -27,6 +27,8 @@
 /website/translated_docs
 /website/i18n/*
 
+/benchmarks/*/node_modules/
+
 /reports/*
 
 coverage

CHANGELOG.md

@@ -84,6 +84,8 @@
 
 ### Performance
 
+- `[jest-runtime]` Load `chalk` only once per worker ([#10864](https://github.com/facebook/jest/pull/10864))
+
 ## 26.6.3
 
 ### Fixes

benchmarks/test-file-overhead/.gitignore

@@ -0,0 +1 @@
+[1-9]*.test.js

benchmarks/test-file-overhead/0.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.
+ */
+
+it('is fast', () => {});

benchmarks/test-file-overhead/README.md

@@ -0,0 +1,7 @@
+First, run `./prepare.sh` to generate the benchmark files. On Windows, use a Bash (WSL, Git, Cygwin …) to do this, but you can use CMD for the actual benchmark run if the CMD environment is what you want to benchmark for.
+
+To run the benchmark, use a benchmarking tool such as [hyperfine](https://github.com/sharkdp/hyperfine):
+
+```sh
+hyperfine -w 3 -m 10 ../../jest /tmp/other-jest-clone-to-compare-against/jest
+```

benchmarks/test-file-overhead/package.json

@@ -0,0 +1,5 @@
+{
+  "jest": {
+    "testEnvironment": "node"
+  }
+}

benchmarks/test-file-overhead/prepare.sh

@@ -0,0 +1,4 @@
+#!/usr/bin/env sh
+for i in {1..499}; do
+  cp 0.test.js $i.test.js
+done

benchmarks/test-file-overhead/yarn.lock

@@ -0,0 +1,11 @@
+# This file is generated by running "yarn install" inside your project.
+# Manual changes might be lost - proceed with caution!
+
+__metadata:
+  version: 4
+
+"root-workspace-0b6124@workspace:.":
+  version: 0.0.0-use.local
+  resolution: "root-workspace-0b6124@workspace:."
+  languageName: unknown
+  linkType: soft

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

@@ -32,7 +32,6 @@ describe('Runtime', () => {
         runtime.requireModule(modulePath);
       }).toThrow(new Error('preprocessor must not run.'));
     });
-
     it('loads internal modules without applying transforms', async () => {
       const runtime = await createRuntime(__filename, {
         transform: {'\\.js$': './test_preprocessor'},
@@ -56,7 +55,6 @@ describe('Runtime', () => {
       const exports = runtime.requireModule(modulePath);
       expect(exports).toEqual({foo: 'foo'});
     });
-
     it('loads internal JSON modules without applying transforms', async () => {
       const runtime = await createRuntime(__filename, {
         transform: {'\\.json$': './test_json_preprocessor'},
@@ -68,5 +66,29 @@ describe('Runtime', () => {
       const exports = runtime.requireInternalModule(modulePath);
       expect(exports).toEqual({foo: 'bar'});
     });
+
+    const OPTIMIZED_MODULE_EXAMPLE = 'chalk';
+    it('loads modules normally even if on the optimization list', () =>
+      createRuntime(__filename).then(runtime => {
+        const modulePath = path.resolve(
+          path.dirname(runtime.__mockRootPath),
+          'require-by-name.js',
+        );
+        const requireByName = runtime.requireModule(modulePath);
+        expect(requireByName(OPTIMIZED_MODULE_EXAMPLE)).not.toBe(
+          require(OPTIMIZED_MODULE_EXAMPLE),
+        );
+      }));
+    it('loads internal modules from outside if on the optimization list', () =>
+      createRuntime(__filename).then(runtime => {
+        const modulePath = path.resolve(
+          path.dirname(runtime.__mockRootPath),
+          'require-by-name.js',
+        );
+        const requireByName = runtime.requireInternalModule(modulePath);
+        expect(requireByName(OPTIMIZED_MODULE_EXAMPLE)).toBe(
+          require(OPTIMIZED_MODULE_EXAMPLE),
+        );
+      }));
   });
 });

packages/jest-runtime/src/__tests__/test_root/require-by-name.js

@@ -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.
+ */
+
+'use strict';
+
+module.exports = moduleName => require(moduleName);

packages/jest-runtime/src/index.ts

@@ -95,6 +95,17 @@ const defaultTransformOptions: InternalModuleOptions = {
 type InitialModule = Omit<Module, 'require' | 'parent' | 'paths'>;
 type ModuleRegistry = Map<string, InitialModule | Module>;
 
+// These are modules that we know
+// * are safe to require from the outside (not stateful, not prone to errors passing in instances from different realms), and
+// * take sufficiently long to require to warrant an optimization.
+// When required from the outside, they use the worker's require cache and are thus
+// only loaded once per worker, not once per test file.
+// Use /benchmarks/test-file-overhead to measure the impact.
+// Note that this only applies when they are required in an internal context;
+// users who require one of these modules in their tests will still get the module from inside the VM.
+// Prefer listing a module here only if it is impractical to use the jest-resolve-outside-vm-option where it is required,
+// e.g. because there are many require sites spread across the dependency graph.
+const INTERNAL_MODULE_REQUIRE_OUTSIDE_OPTIMIZED_MODULES = new Set(['chalk']);
 const JEST_RESOLVE_OUTSIDE_VM_OPTION = Symbol.for(
   'jest-resolve-outside-vm-option',
 );
@@ -660,6 +671,12 @@ export default class Runtime {
 
   requireInternalModule<T = unknown>(from: Config.Path, to?: string): T {
     if (to) {
+      const require = (
+        nativeModule.createRequire ?? nativeModule.createRequireFromPath
+      )(from);
+      if (INTERNAL_MODULE_REQUIRE_OUTSIDE_OPTIMIZED_MODULES.has(to)) {
+        return require(to);
+      }
       const outsideJestVmPath = decodePossibleOutsideJestVmPath(to);
       if (outsideJestVmPath) {
         return require(outsideJestVmPath);

scripts/checkCopyrightHeaders.js

@@ -99,15 +99,15 @@ const GENERIC_IGNORED_PATTERNS = [
 const CUSTOM_IGNORED_PATTERNS = [
   '\\.(example|map)$',
   '^examples/.*',
-  '^flow-typed/.*',
   '^packages/expect/src/jasmineUtils\\.ts$',
   '^packages/jest-config/src/vendor/jsonlint\\.js$',
   '^packages/jest-diff/src/cleanupSemantic\\.ts$',
   '^packages/jest-haste-map/src/watchers/common\\.js$',
   '^packages/jest-haste-map/src/watchers/NodeWatcher\\.js$',
   '^packages/jest-haste-map/src/watchers/RecrawlWarning\\.js$',
   '^website/static/css/code-block-buttons\\.css$',
-  '^website/static/js/code-block-buttons\\.js',
+  '^website/static/js/code-block-buttons\\.js$',
+  '^benchmarks/test-file-overhead/prepare\\.sh$',
 ].map(createRegExp);
 
 const IGNORED_PATTERNS = [