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))
 

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)
@@ -1053,6 +1055,15 @@ class Runtime {
       }),
     ];
 
+    if (!this._mainModule) {
+      this._mainModule = module;
+    }
+
+    Object.defineProperty(module, 'main', {
+      enumerable: true,
+      value: this._mainModule,
+    });
+
     try {
       compiledFunction.call(
         module.exports,