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

Author: jeysal

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 +95,16 @@ 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.
+// 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',
 );
@@ -660,9 +670,12 @@ export default class Runtime {
 
   requireInternalModule<T = unknown>(from: Config.Path, to?: string): T {
     if (to) {
+      if (INTERNAL_MODULE_REQUIRE_OUTSIDE_OPTIMIZED_MODULES.has(to)) {
+        return nativeModule.createRequire(from)(to);
+      }
       const outsideJestVmPath = decodePossibleOutsideJestVmPath(to);
       if (outsideJestVmPath) {
-        return require(outsideJestVmPath);
+        return nativeModule.createRequire(from)(outsideJestVmPath);
       }
     }