From c2e7613681e12ce70c52aaac951759155b3ad812 Mon Sep 17 00:00:00 2001
From: Lukas Stracke <lukas.stracke@sentry.io>
Date: Mon, 1 Sep 2025 14:38:36 +0200
Subject: [PATCH] fix(browser): ensure name and source are set correctly when
 updating span name in-place in `beforeStartSpan`

---
 .../src/tracing/browserTracingIntegration.ts  |  3 +-
 .../tracing/browserTracingIntegration.test.ts | 39 ++++++++++++++++++-
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/packages/browser/src/tracing/browserTracingIntegration.ts b/packages/browser/src/tracing/browserTracingIntegration.ts
index d2224f141797..cd63678de16f 100644
--- a/packages/browser/src/tracing/browserTracingIntegration.ts
+++ b/packages/browser/src/tracing/browserTracingIntegration.ts
@@ -356,6 +356,7 @@ export const browserTracingIntegration = ((_options: Partial<BrowserTracingOptio
   function _createRouteSpan(client: Client, startSpanOptions: StartSpanOptions, makeActive = true): void {
     const isPageloadTransaction = startSpanOptions.op === 'pageload';
 
+    const initialSpanName = startSpanOptions.name;
     const finalStartSpanOptions: StartSpanOptions = beforeStartSpan
       ? beforeStartSpan(startSpanOptions)
       : startSpanOptions;
@@ -364,7 +365,7 @@ export const browserTracingIntegration = ((_options: Partial<BrowserTracingOptio
 
     // If `finalStartSpanOptions.name` is different than `startSpanOptions.name`
     // it is because `beforeStartSpan` set a custom name. Therefore we set the source to 'custom'.
-    if (startSpanOptions.name !== finalStartSpanOptions.name) {
+    if (initialSpanName !== finalStartSpanOptions.name) {
       attributes[SEMANTIC_ATTRIBUTE_SENTRY_SOURCE] = 'custom';
       finalStartSpanOptions.attributes = attributes;
     }
diff --git a/packages/browser/test/tracing/browserTracingIntegration.test.ts b/packages/browser/test/tracing/browserTracingIntegration.test.ts
index 84aea8b13c9e..6a5d8c3b4894 100644
--- a/packages/browser/test/tracing/browserTracingIntegration.test.ts
+++ b/packages/browser/test/tracing/browserTracingIntegration.test.ts
@@ -446,7 +446,44 @@ describe('browserTracingIntegration', () => {
     setCurrentClient(client);
     client.init();
 
-    startBrowserTracingPageLoadSpan(client, { name: 'test span' });
+    startBrowserTracingPageLoadSpan(client, {
+      name: 'test span',
+      attributes: {
+        [SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]: 'url',
+      },
+    });
+
+    const pageloadSpan = getActiveSpan();
+
+    expect(spanToJSON(pageloadSpan!).description).toBe('changed');
+    expect(spanToJSON(pageloadSpan!).data[SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]).toBe('custom');
+  });
+
+  it('sets source to "custom" if name is changed in-place in beforeStartSpan', () => {
+    const client = new BrowserClient(
+      getDefaultBrowserClientOptions({
+        tracesSampleRate: 0,
+        integrations: [
+          browserTracingIntegration({
+            instrumentPageLoad: false,
+            instrumentNavigation: false,
+            beforeStartSpan: opts => {
+              opts.name = 'changed';
+              return opts;
+            },
+          }),
+        ],
+      }),
+    );
+    setCurrentClient(client);
+    client.init();
+
+    startBrowserTracingPageLoadSpan(client, {
+      name: 'test span',
+      attributes: {
+        [SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]: 'url',
+      },
+    });
 
     const pageloadSpan = getActiveSpan();