feat(runtime): populate require.cache (#9841)

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Features
 
+- `[jest-runtime]` Populate `require.cache` ([#9841](https://github.com/facebook/jest/pull/9841))
+
 ### Fixes
 
 ### Chore & Maintenance

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

@@ -0,0 +1,41 @@
+/**
+ * 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';
+
+let createRuntime;
+
+describe('Runtime require.cache', () => {
+  beforeEach(() => {
+    createRuntime = require('createRuntime');
+  });
+
+  it('require.cache returns loaded module list as native Nodejs require does', () =>
+    createRuntime(__filename).then(runtime => {
+      const regularModule = runtime.requireModule(
+        runtime.__mockRootPath,
+        'RegularModule',
+      ).module;
+
+      expect(regularModule.require.cache[regularModule.id]).toBe(regularModule);
+    }));
+
+  it('require.cache is tolerant readonly', () =>
+    createRuntime(__filename).then(runtime => {
+      const regularModule = runtime.requireModule(
+        runtime.__mockRootPath,
+        'RegularModule',
+      ).module;
+
+      delete regularModule.require.cache[regularModule.id];
+      expect(regularModule.require.cache[regularModule.id]).toBe(regularModule);
+
+      regularModule.require.cache[regularModule.id] = 'something';
+      expect(regularModule.require.cache[regularModule.id]).toBe(regularModule);
+    }));
+});

packages/jest-runtime/src/index.ts

@@ -80,6 +80,8 @@ type ResolveOptions = Parameters<typeof require.resolve>[1];
 type BooleanObject = Record<string, boolean>;
 type CacheFS = {[path: string]: string};
 
+type RequireCache = {[key: string]: Module};
+
 namespace Runtime {
   export type Context = JestContext;
   // ditch this export when moving to esm - for now we need it for to avoid faulty type elision
@@ -1270,11 +1272,25 @@ class Runtime {
           this,
           from.filename,
         )) as LocalModuleRequire;
-    moduleRequire.cache = Object.create(null);
     moduleRequire.extensions = Object.create(null);
     moduleRequire.requireActual = this.requireActual.bind(this, from.filename);
     moduleRequire.requireMock = this.requireMock.bind(this, from.filename);
     moduleRequire.resolve = resolve;
+    moduleRequire.cache = (() => {
+      const notPermittedMethod = () => {
+        console.warn('`require.cache` modification is not permitted');
+        return true;
+      };
+      return new Proxy<RequireCache>(Object.create(null), {
+        defineProperty: notPermittedMethod,
+        deleteProperty: notPermittedMethod,
+        get: (_target, key) =>
+          typeof key === 'string' ? this._moduleRegistry.get(key) : undefined,
+        has: (_target, key) =>
+          typeof key === 'string' && this._moduleRegistry.has(key),
+        set: notPermittedMethod,
+      });
+    })();
 
     Object.defineProperty(moduleRequire, 'main', {
       enumerable: true,