fix(browser): Mark stack trace from captureMessage with attachStacktrace: true as synthetic

.size-limit.js

@@ -147,7 +147,7 @@ module.exports = [
     path: 'packages/svelte/build/esm/index.js',
     import: createImport('init'),
     gzip: true,
-    limit: '24 KB',
+    limit: '24.5 KB',
   },
   // Browser CDN bundles
   {

dev-packages/browser-integration-tests/suites/public-api/captureMessage/simple_message_attachStackTrace/init.js

@@ -0,0 +1,8 @@
+import * as Sentry from '@sentry/browser';
+
+window.Sentry = Sentry;
+
+Sentry.init({
+  dsn: 'https://[email protected]/1337',
+  attachStacktrace: true,
+});

dev-packages/browser-integration-tests/suites/public-api/captureMessage/simple_message_attachStackTrace/subject.js

@@ -0,0 +1 @@
+Sentry.captureMessage('foo');

dev-packages/browser-integration-tests/suites/public-api/captureMessage/simple_message_attachStackTrace/test.ts

@@ -0,0 +1,28 @@
+import { expect } from '@playwright/test';
+import type { Event } from '@sentry/core';
+
+import { sentryTest } from '../../../../utils/fixtures';
+import { getFirstSentryEnvelopeRequest } from '../../../../utils/helpers';
+
+sentryTest(
+  'captures a simple message string with stack trace if `attachStackTrace` is `true`',
+  async ({ getLocalTestUrl, page }) => {
+    const url = await getLocalTestUrl({ testDir: __dirname });
+
+    const eventData = await getFirstSentryEnvelopeRequest<Event>(page, url);
+
+    expect(eventData.message).toBe('foo');
+    expect(eventData.level).toBe('info');
+    expect(eventData.exception?.values?.[0]).toEqual({
+      mechanism: {
+        handled: true,
+        type: 'generic',
+        synthetic: true,
+      },
+      stacktrace: {
+        frames: expect.arrayContaining([expect.any(Object), expect.any(Object)]),
+      },
+      value: 'foo',
+    });
+  },
+);

packages/browser/src/eventbuilder.ts

@@ -347,6 +347,7 @@ function eventFromString(
         values: [{ value: message, stacktrace: { frames } }],
       };
     }
+    addExceptionMechanism(event, { synthetic: true });
   }
 
   if (isParameterizedString(message)) {

packages/browser/test/eventbuilder.test.ts

@@ -5,7 +5,7 @@
 import { afterEach, describe, expect, it, vi } from 'vitest';
 
 import { defaultStackParser } from '../src';
-import { eventFromUnknownInput, extractMessage, extractType } from '../src/eventbuilder';
+import { eventFromMessage, eventFromUnknownInput, extractMessage, extractType } from '../src/eventbuilder';
 
 vi.mock('@sentry/core', async requireActual => {
   return {
@@ -231,3 +231,33 @@ describe('extractName', () => {
     expect(name).toBeUndefined();
   });
 });
+
+describe('eventFromMessage ', () => {
+  it('creates an event from a string message', async () => {
+    const event = await eventFromMessage(defaultStackParser, 'Test message');
+    expect(event).toEqual({
+      level: 'info',
+      message: 'Test message',
+    });
+  });
+
+  it('creates an event with a synthetic stack trace if attachStacktrace is true', async () => {
+    const syntheticException = new Error('Test message');
+    const event = await eventFromMessage(defaultStackParser, 'Test message', 'info', { syntheticException }, true);
+    expect(event.exception?.values?.[0]).toEqual(
+      expect.objectContaining({
+        mechanism: { handled: true, synthetic: true, type: 'generic' },
+        stacktrace: {
+          frames: expect.arrayContaining([expect.any(Object), expect.any(Object)]),
+        },
+        value: 'Test message',
+      }),
+    );
+  });
+
+  it("doesn't add a synthetic stack trace if attachStacktrace is false, even if one is passed-", async () => {
+    const syntheticException = new Error('Test message');
+    const event = await eventFromMessage(defaultStackParser, 'Test message', 'info', { syntheticException }, false);
+    expect(event.exception).toBeUndefined();
+  });
+});