support importing node core modules

Author: SimenB

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

@@ -2,7 +2,7 @@
 
 exports[`on node ^12.16.0 || >=13.0.0 runs test with native ESM 1`] = `
 Test Suites: 1 passed, 1 total
-Tests:       2 passed, 2 total
+Tests:       3 passed, 3 total
 Snapshots:   0 total
 Time:        <<REPLACED>>
 Ran all test suites.

e2e/native-esm/__tests__/native-esm.test.js

@@ -5,9 +5,13 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+import {readFileSync} from 'fs';
+import {dirname, resolve} from 'path';
+import {fileURLToPath} from 'url';
 import {double} from '../index';
 
 test('should have correct import.meta', () => {
+  expect(typeof require).toBe('undefined');
   expect(typeof jest).toBe('undefined');
   expect(import.meta).toEqual({
     jest: expect.anything(),
@@ -21,3 +25,16 @@ test('should have correct import.meta', () => {
 test('should double stuff', () => {
   expect(double(1)).toBe(2);
 });
+
+test('should support importing node core modules', () => {
+  const dir = dirname(fileURLToPath(import.meta.url));
+  const packageJsonPath = resolve(dir, '../package.json');
+
+  expect(JSON.parse(readFileSync(packageJsonPath, 'utf8'))).toEqual({
+    jest: {
+      testEnvironment: 'node',
+      transform: {},
+    },
+    type: 'module',
+  });
+});

packages/jest-runtime/src/index.ts

@@ -12,6 +12,9 @@ import {
   // @ts-ignore: experimental, not added to the types
   SourceTextModule,
   // @ts-ignore: experimental, not added to the types
+  SyntheticModule,
+  Context as VMContext,
+  // @ts-ignore: experimental, not added to the types
   Module as VMModule,
   compileFunction,
 } from 'vm';
@@ -337,6 +340,12 @@ class Runtime {
 
       invariant(context);
 
+      if (this._resolver.isCoreModule(modulePath)) {
+        const core = await this._importCoreModule(modulePath, context);
+        this._esmoduleRegistry.set(cacheKey, core);
+        return core;
+      }
+
       const transformedFile = this.transformFile(modulePath, {
         isInternalModule: false,
         supportsDynamicImport: true,
@@ -1030,6 +1039,24 @@ class Runtime {
     return require(moduleName);
   }
 
+  private _importCoreModule(moduleName: string, context: VMContext) {
+    const required = this._requireCoreModule(moduleName);
+
+    return new SyntheticModule(
+      ['default', ...Object.keys(required)],
+      function () {
+        // @ts-ignore: TS doesn't know what `this` is
+        this.setExport('default', required);
+        Object.entries(required).forEach(([key, value]) => {
+          // @ts-ignore: TS doesn't know what `this` is
+          this.setExport(key, value);
+        });
+      },
+      // should identifier be `node://${moduleName}`?
+      {context, identifier: moduleName},
+    );
+  }
+
   private _getMockedNativeModule(): typeof nativeModule.Module {
     if (this._moduleImplementation) {
       return this._moduleImplementation;
@@ -1064,13 +1091,20 @@ class Runtime {
     // should we implement the class ourselves?
     class Module extends nativeModule.Module {}
 
+    Object.entries(nativeModule.Module).forEach(([key, value]) => {
+      // @ts-ignore
+      Module[key] = value;
+    });
+
     Module.Module = Module;
 
     if ('createRequire' in nativeModule) {
       Module.createRequire = createRequire;
     }
     if ('createRequireFromPath' in nativeModule) {
-      Module.createRequireFromPath = (filename: string | URL) => {
+      Module.createRequireFromPath = function createRequireFromPath(
+        filename: string | URL,
+      ) {
         if (typeof filename !== 'string') {
           const error = new TypeError(
             `The argument 'filename' must be string. Received '${filename}'.${
@@ -1087,7 +1121,7 @@ class Runtime {
       };
     }
     if ('syncBuiltinESMExports' in nativeModule) {
-      Module.syncBuiltinESMExports = () => {};
+      Module.syncBuiltinESMExports = function syncBuiltinESMExports() {};
     }
 
     this._moduleImplementation = Module;