fix: add require.main when using isolateModules

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - `[jest-runner, jest-runtime]` fix: `require.main` undefined with `createRequire()` ([#10610](https://github.com/facebook/jest/pull/10610))
 - `[jest-runtime]` add missing `module.path` property ([#10615](https://github.com/facebook/jest/pull/10615))
+- `[jest-runtime]` fix: add `mainModule` instance variable to runtime ([#10621](https://github.com/facebook/jest/pull/10621))
 - `[jest-validate]` Show suggestion only when unrecognized cli param is longer than 1 character ([#10604](https://github.com/facebook/jest/pull/10604))
 - `[jest-validate]` Validate `testURL` as CLI option ([#10595](https://github.com/facebook/jest/pull/10595))
 

e2e/__tests__/requireMainIsolateModules.test.ts

@@ -0,0 +1,14 @@
+/**
+ * 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 runJest from '../runJest';
+
+test('`require.main` on using `jest.isolateModules` should not be undefined', () => {
+  const {exitCode} = runJest('require-main-isolate-modules');
+
+  expect(exitCode).toBe(0);
+});

e2e/require-main-isolate-modules/__tests__/index.test.js

@@ -0,0 +1,13 @@
+/**
+ * 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.
+ */
+let foo;
+
+jest.isolateModules(() => (foo = require('../index')));
+
+test('`require.main` on using `jest.isolateModules` should not be undefined', () => {
+  expect(foo()).toEqual(1);
+});

e2e/require-main-isolate-modules/child.js

@@ -0,0 +1,7 @@
+/**
+ * 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.
+ */
+module.exports = 1;

e2e/require-main-isolate-modules/index.js

@@ -0,0 +1,7 @@
+/**
+ * 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.
+ */
+module.exports = () => require.main.require('../child');

e2e/require-main-isolate-modules/package.json

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

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

@@ -45,6 +45,7 @@ describe('Runtime requireModule', () => {
         'path',
         'parent',
         'paths',
+        'main',
       ]);
     }));
 
@@ -63,6 +64,7 @@ describe('Runtime requireModule', () => {
         'path',
         'parent',
         'paths',
+        'main',
       ]);
     }));
 

packages/jest-runtime/src/index.ts

@@ -150,6 +150,7 @@ class Runtime {
     | null;
   private _internalModuleRegistry: ModuleRegistry;
   private _isCurrentlyExecutingManualMock: string | null;
+  private _mainModule: Module | null;
   private _mockFactories: Map<string, () => unknown>;
   private _mockMetaDataCache: Map<
     string,
@@ -202,6 +203,7 @@ class Runtime {
     this._explicitShouldMock = new Map();
     this._internalModuleRegistry = new Map();
     this._isCurrentlyExecutingManualMock = null;
+    this._mainModule = null;
     this._mockFactories = new Map();
     this._mockRegistry = new Map();
     // during setup, this cannot be null (and it's fine to explode if it is)
@@ -880,6 +882,7 @@ class Runtime {
     this.resetModules();
 
     this._internalModuleRegistry.clear();
+    this._mainModule = null;
     this._mockFactories.clear();
     this._mockMetaDataCache.clear();
     this._shouldMockModuleCache.clear();
@@ -1053,6 +1056,15 @@ class Runtime {
       }),
     ];
 
+    if (!this._mainModule && filename === this._testPath) {
+      this._mainModule = module;
+    }
+
+    Object.defineProperty(module, 'main', {
+      enumerable: true,
+      value: this._mainModule,
+    });
+
     try {
       compiledFunction.call(
         module.exports,