feat(browser): Warn on duplicate browserTracingIntegration

.size-limit.js

@@ -40,7 +40,7 @@ module.exports = [
     path: 'packages/browser/build/npm/esm/index.js',
     import: createImport('init', 'browserTracingIntegration'),
     gzip: true,
-    limit: '38 KB',
+    limit: '39 KB',
   },
   {
     name: '@sentry/browser (incl. Tracing, Replay)',

dev-packages/browser-integration-tests/suites/tracing/browserTracingIntegration/multiple-integrations/init.js

@@ -0,0 +1,9 @@
+import * as Sentry from '@sentry/browser';
+
+window.Sentry = Sentry;
+
+Sentry.init({
+  dsn: 'https://[email protected]/1337',
+  integrations: [Sentry.browserTracingIntegration(), Sentry.browserTracingIntegration()],
+  tracesSampleRate: 1,
+});

dev-packages/browser-integration-tests/suites/tracing/browserTracingIntegration/multiple-integrations/test.ts

@@ -0,0 +1,22 @@
+import { expect } from '@playwright/test';
+
+import { sentryTest } from '../../../../utils/fixtures';
+import { shouldSkipTracingTest } from '../../../../utils/helpers';
+
+sentryTest('warns if multiple integrations are used', async ({ getLocalTestUrl, page }) => {
+  if (shouldSkipTracingTest()) {
+    sentryTest.skip();
+  }
+
+  const msgs: string[] = [];
+
+  page.on('console', msg => {
+    msgs.push(msg.text());
+  });
+
+  const url = await getLocalTestUrl({ testDir: __dirname });
+
+  await page.goto(url);
+
+  expect(msgs).toEqual(['Multiple browserTracingIntegration instances are not supported.']);
+});

packages/browser/src/tracing/browserTracingIntegration.ts

@@ -10,6 +10,7 @@ import {
   startTrackingWebVitals,
 } from '@sentry-internal/browser-utils';
 import type { Client, IntegrationFn, Span, StartSpanOptions, TransactionSource, WebFetchHeaders } from '@sentry/core';
+import { consoleSandbox } from '@sentry/core';
 import {
   GLOBAL_OBJ,
   SEMANTIC_ATTRIBUTE_SENTRY_IDLE_SPAN_FINISH_REASON,
@@ -217,6 +218,8 @@ const DEFAULT_BROWSER_TRACING_OPTIONS: BrowserTracingOptions = {
   ...defaultRequestInstrumentationOptions,
 };
 
+let _hasBeenInitialized = false;
+
 /**
  * The Browser Tracing integration automatically instruments browser pageload/navigation
  * actions as transactions, and captures requests, metrics and errors as spans.
@@ -227,6 +230,15 @@ const DEFAULT_BROWSER_TRACING_OPTIONS: BrowserTracingOptions = {
  * We explicitly export the proper type here, as this has to be extended in some cases.
  */
 export const browserTracingIntegration = ((_options: Partial<BrowserTracingOptions> = {}) => {
+  if (_hasBeenInitialized) {
+    consoleSandbox(() => {
+      // eslint-disable-next-line no-console
+      console.warn('Multiple browserTracingIntegration instances are not supported.');
+    });
+  }
+
+  _hasBeenInitialized = true;
+
   /**
    * This is just a small wrapper that makes `document` optional.
    * We want to be extra-safe and always check that this exists, to ensure weird environments do not blow up.