feat(pwt): serialize and expose Error.cause from Worker process (#32833)

docs/src/test-api/class-testinfoerror.md

@@ -4,6 +4,12 @@
 
 Information about an error thrown during test execution.
 
+## property: TestInfoError.cause
+* since: v1.49
+- type: ?<[TestInfoError]>
+
+Error cause. Set when there is a [cause](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause) for the error. Will be `undefined` if there is no cause or if the cause is not an instance of [Error].
+
 ## property: TestInfoError.message
 * since: v1.10
 - type: ?<[string]>

docs/src/test-reporter-api/class-testerror.md

@@ -4,6 +4,12 @@
 
 Information about an error thrown during test execution.
 
+## property: TestError.cause
+* since: v1.49
+- type: ?<[TestError]>
+
+Error cause. Set when there is a [cause](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause) for the error. Will be `undefined` if there is no cause or if the cause is not an instance of [Error].
+
 ## property: TestError.message
 * since: v1.10
 - type: ?<[string]>

packages/playwright/src/reporters/base.ts

@@ -434,15 +434,16 @@ export function formatError(error: TestError, highlightCode: boolean): ErrorDeta
     tokens.push(snippet);
   }
 
-  if (parsedStack && parsedStack.stackLines.length) {
-    tokens.push('');
+  if (parsedStack && parsedStack.stackLines.length)
     tokens.push(colors.dim(parsedStack.stackLines.join('\n')));
-  }
 
   let location = error.location;
   if (parsedStack && !location)
     location = parsedStack.location;
 
+  if (error.cause)
+    tokens.push(colors.dim('[cause]: ') + formatError(error.cause, highlightCode).message);
+
   return {
     location,
     message: tokens.join('\n'),

packages/playwright/src/util.ts

@@ -29,15 +29,17 @@ import type { TestInfoErrorImpl } from './common/ipc';
 const PLAYWRIGHT_TEST_PATH = path.join(__dirname, '..');
 const PLAYWRIGHT_CORE_PATH = path.dirname(require.resolve('playwright-core/package.json'));
 
-export function filterStackTrace(e: Error): { message: string, stack: string } {
+export function filterStackTrace(e: Error): { message: string, stack: string, cause?: ReturnType<typeof filterStackTrace> } {
   const name = e.name ? e.name + ': ' : '';
+  const cause = e.cause instanceof Error ? filterStackTrace(e.cause) : undefined;
   if (process.env.PWDEBUGIMPL)
-    return { message: name + e.message, stack: e.stack || '' };
+    return { message: name + e.message, stack: e.stack || '', cause };
 
   const stackLines = stringifyStackFrames(filteredStackTrace(e.stack?.split('\n') || []));
   return {
     message: name + e.message,
-    stack: `${name}${e.message}${stackLines.map(line => '\n' + line).join('')}`
+    stack: `${name}${e.message}${stackLines.map(line => '\n' + line).join('')}`,
+    cause,
   };
 }
 

packages/playwright/src/worker/testTracing.ts

@@ -224,11 +224,18 @@ export class TestTracing {
     const stack = rawStack ? filteredStackTrace(rawStack) : [];
     this._appendTraceEvent({
       type: 'error',
-      message: error.message || String(error.value),
+      message: this._formatError(error),
       stack,
     });
   }
 
+  _formatError(error: TestInfoErrorImpl) {
+    const parts: string[] = [error.message || String(error.value)];
+    if (error.cause)
+      parts.push('[cause]: ' + this._formatError(error.cause));
+    return parts.join('\n');
+  }
+
   appendStdioToTrace(type: 'stdout' | 'stderr', chunk: string | Buffer) {
     this._appendTraceEvent({
       type,

packages/playwright/types/test.d.ts

@@ -9152,6 +9152,13 @@ export interface TestInfo {
  * Information about an error thrown during test execution.
  */
 export interface TestInfoError {
+  /**
+   * Error cause. Set when there is a
+   * [cause](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause) for the
+   * error. Will be `undefined` if there is no cause or if the cause is not an instance of [Error].
+   */
+  cause?: TestInfoError;
+
   /**
    * Error message. Set when [Error] (or its subclass) has been thrown.
    */

packages/playwright/types/testReporter.d.ts

@@ -554,6 +554,13 @@ export interface TestCase {
  * Information about an error thrown during test execution.
  */
 export interface TestError {
+  /**
+   * Error cause. Set when there is a
+   * [cause](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause) for the
+   * error. Will be `undefined` if there is no cause or if the cause is not an instance of [Error].
+   */
+  cause?: TestError;
+
   /**
    * Error location in the source code.
    */

tests/playwright-test/reporter-base.spec.ts

@@ -118,6 +118,53 @@ for (const useIntermediateMergeReport of [false, true] as const) {
       expect(output).toContain(`a.spec.ts:5:13`);
     });
 
+    test('should print error with a nested cause', async ({ runInlineTest }) => {
+      const result = await runInlineTest({
+        'a.spec.ts': `
+          import { test, expect } from '@playwright/test';
+
+          test('foobar', async ({}) => {
+            try {
+              try {
+                const error = new Error('my-message');
+                error.name = 'SpecialError';
+                throw error;
+              } catch (e) {
+                try {
+                  throw new Error('inner-message', { cause: e });
+                } catch (e) {
+                  throw new Error('outer-message', { cause: e });
+                }
+              }
+            } catch (e) {
+              throw new Error('wrapper-message', { cause: e });
+            }
+          });
+          test.afterAll(() => {
+            expect(test.info().errors.length).toBe(1);
+            expect(test.info().errors[0]).toBe(test.info().error);
+            expect(test.info().error.message).toBe('Error: wrapper-message');
+            expect(test.info().error.cause.message).toBe('Error: outer-message');
+            expect(test.info().error.cause.cause.message).toBe('Error: inner-message');
+            expect(test.info().error.cause.cause.cause.message).toBe('SpecialError: my-message');
+            expect(test.info().error.cause.cause.cause.cause).toBe(undefined);
+            console.log('afterAll executed successfully');
+          })
+        `
+      });
+      expect(result.exitCode).toBe(1);
+      expect(result.failed).toBe(1);
+      const testFile = path.join(result.report.config.rootDir, result.report.suites[0].specs[0].file);
+      expect(result.output).toContain(`${testFile}:18:21`);
+      expect(result.output).toContain(`[cause]: Error: outer-message`);
+      expect(result.output).toContain(`${testFile}:14:25`);
+      expect(result.output).toContain(`[cause]: Error: inner-message`);
+      expect(result.output).toContain(`${testFile}:12:25`);
+      expect(result.output).toContain(`[cause]: SpecialError: my-message`);
+      expect(result.output).toContain(`${testFile}:7:31`);
+      expect(result.output).toContain('afterAll executed successfully');
+    });
+
     test('should print codeframe from a helper', async ({ runInlineTest }) => {
       const result = await runInlineTest({
         'helper.ts': `