fix(jest-worker): failed assertion with circular value hangs the test run

CHANGELOG.md

@@ -34,6 +34,7 @@
   - [**BREAKING**] Changes `testPathPattern` configuration option to `testPathPatterns`, which now takes a list of patterns instead of the regex.
   - [**BREAKING**] `--testPathPattern` is now `--testPathPatterns`
 - `[jest-reporters, jest-runner]` Unhandled errors without stack get correctly logged to console ([#14619](https://github.com/facebook/jest/pull/14619))
+- [jest-worker] Properly handle a circular reference error when worker tries to send an assertion fails where either the expected or actual value is circular ([#14675](https://github.com/jestjs/jest/pull/14675))
 
 ### Performance
 

packages/jest-worker/src/workers/__tests__/WorkerEdgeCases.test.ts

@@ -20,7 +20,12 @@ import ThreadsWorker from '../NodeThreadsWorker';
 jest.setTimeout(10_000);
 
 const root = join('../../');
-const filesToBuild = ['workers/processChild', 'workers/threadChild', 'types'];
+const filesToBuild = [
+  'workers/processChild',
+  'workers/threadChild',
+  'workers/withoutCircularRefs',
+  'types',
+];
 const writeDestination = join(__dirname, '__temp__');
 const processChildWorkerPath = join(
   writeDestination,

packages/jest-worker/src/workers/__tests__/processChild.test.ts

@@ -41,6 +41,12 @@ beforeEach(() => {
       mockCount++;
 
       return {
+        fooCircularResult() {
+          const circular = {self: undefined as unknown};
+          circular.self = circular;
+          return {error: circular};
+        },
+
         fooPromiseThrows() {
           return new Promise((_resolve, reject) => {
             setTimeout(() => reject(mockError), 5);
@@ -338,6 +344,33 @@ it('returns results when it gets resolved if function is asynchronous', async ()
   expect(spyProcessSend).toHaveBeenCalledTimes(2);
 });
 
+it('returns results with circular references', () => {
+  process.emit(
+    'message',
+    [
+      CHILD_MESSAGE_INITIALIZE,
+      true, // Not really used here, but for type purity.
+      './my-fancy-worker',
+    ],
+    null,
+  );
+
+  process.emit(
+    'message',
+    [
+      CHILD_MESSAGE_CALL,
+      true, // Not really used here, but for type purity.
+      'fooCircularResult',
+      [],
+    ],
+    null,
+  );
+
+  expect(spyProcessSend.mock.calls[0][0][1]).toEqual({
+    error: {self: expect.anything()},
+  });
+});
+
 it('calls the main module if the method call is "default"', () => {
   process.emit(
     'message',

packages/jest-worker/src/workers/__tests__/withoutCircularRefs.test.ts

@@ -0,0 +1,33 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {withoutCircularRefs} from '../withoutCircularRefs';
+
+it('test simple values', () => {
+  expect(withoutCircularRefs(undefined)).toBeUndefined();
+  expect(withoutCircularRefs(null)).toBeNull();
+  expect(withoutCircularRefs(0)).toBe(0);
+  expect(withoutCircularRefs('12')).toBe('12');
+  expect(withoutCircularRefs(true)).toBe(true);
+  expect(withoutCircularRefs([1])).toEqual([1]);
+  expect(withoutCircularRefs({a: 1, b: {c: 2}})).toEqual({a: 1, b: {c: 2}});
+});
+
+it('test circular values', () => {
+  const circular = {self: undefined as any};
+  circular.self = circular;
+
+  expect(withoutCircularRefs(circular)).toEqual({self: '[Circular]'});
+
+  expect(withoutCircularRefs([{a: circular, b: null}])).toEqual([
+    {a: {self: '[Circular]'}, b: null},
+  ]);
+
+  expect(withoutCircularRefs({a: {b: circular}, c: undefined})).toEqual({
+    a: {b: {self: '[Circular]'}, c: undefined},
+  });
+});

packages/jest-worker/src/workers/messageParent.ts

@@ -7,6 +7,7 @@
 
 import {isMainThread, parentPort} from 'worker_threads';
 import {PARENT_MESSAGE_CUSTOM} from '../types';
+import {withoutCircularRefs} from './withoutCircularRefs';
 
 export default function messageParent(
   message: unknown,
@@ -15,7 +16,21 @@ export default function messageParent(
   if (!isMainThread && parentPort != null) {
     parentPort.postMessage([PARENT_MESSAGE_CUSTOM, message]);
   } else if (typeof parentProcess.send === 'function') {
-    parentProcess.send([PARENT_MESSAGE_CUSTOM, message]);
+    try {
+      parentProcess.send([PARENT_MESSAGE_CUSTOM, message]);
+    } catch (e: any) {
+      if (/circular structure/.test(e?.message)) {
+        // We can safely send a message to the parent process again
+        // because previous sending was halted by "TypeError: Converting circular structure to JSON".
+        // But this time the message will be cleared from circular references.
+        parentProcess.send([
+          PARENT_MESSAGE_CUSTOM,
+          withoutCircularRefs(message),
+        ]);
+      } else {
+        throw e;
+      }
+    }
   } else {
     throw new Error('"messageParent" can only be used inside a worker');
   }

packages/jest-worker/src/workers/processChild.ts

@@ -21,6 +21,7 @@ import {
   PARENT_MESSAGE_SETUP_ERROR,
   type ParentMessageMemUsage,
 } from '../types';
+import {withoutCircularRefs} from './withoutCircularRefs';
 
 type UnknownFunction = (...args: Array<unknown>) => unknown | Promise<unknown>;
 
@@ -97,7 +98,18 @@ function reportSuccess(result: unknown) {
     throw new Error('Child can only be used on a forked process');
   }
 
-  process.send([PARENT_MESSAGE_OK, result]);
+  try {
+    process.send([PARENT_MESSAGE_OK, result]);
+  } catch (e: any) {
+    // We can safely send a message to the parent process again
+    // because previous sending was halted by "TypeError: Converting circular structure to JSON".
+    // But this time the message will be cleared from circular references.
+    if (e && /circular structure/.test(e?.message)) {
+      process.send([PARENT_MESSAGE_OK, withoutCircularRefs(result)]);
+    } else {
+      throw e;
+    }
+  }
 }
 
 function reportClientError(error: Error) {

packages/jest-worker/src/workers/withoutCircularRefs.ts

@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+export function withoutCircularRefs(obj: unknown): unknown {
+  const cache = new WeakSet();
+  function copy(obj: unknown) {
+    if (typeof obj !== 'object' || obj === null) {
+      return obj;
+    }
+    if (cache.has(obj)) {
+      return '[Circular]';
+    }
+    cache.add(obj);
+    const copyObj: any = Array.isArray(obj) ? [] : {};
+    for (const key in obj) {
+      if (Object.prototype.hasOwnProperty.call(obj, key)) {
+        copyObj[key] = copy((obj as any)[key]);
+      }
+    }
+    return copyObj;
+  }
+  return copy(obj);
+}