feat(core): Set custom transaction source for event processors (#5722)

This PR updates `BaseClient` class to set a custom transaction source if event processors change the transaction name. It also adds metadata around a transaction name change when this is done.

Author: AbhiPrasad

packages/core/src/baseclient.ts

@@ -33,6 +33,7 @@ import {
   resolvedSyncPromise,
   SentryError,
   SyncPromise,
+  timestampInSeconds,
   truncate,
   uuid4,
 } from '@sentry/utils';
@@ -658,6 +659,26 @@ export abstract class BaseClient<O extends ClientOptions> implements Client<O> {
           this._updateSessionFromEvent(session, processedEvent);
         }
 
+        // None of the Sentry built event processor will update transaction name,
+        // so if the transaction name has been changed by an event processor, we know
+        // it has to come from custom event processor added by a user
+        const transactionInfo = processedEvent.transaction_info;
+        if (isTransaction && transactionInfo && processedEvent.transaction !== event.transaction) {
+          const source = 'custom';
+          processedEvent.transaction_info = {
+            ...transactionInfo,
+            source,
+            changes: [
+              ...transactionInfo.changes,
+              {
+                source,
+                timestamp: timestampInSeconds(),
+                propagations: transactionInfo.propagations,
+              },
+            ],
+          };
+        }
+
         this.sendEvent(processedEvent, hint);
         return processedEvent;
       })

packages/core/test/lib/base.test.ts

@@ -1092,6 +1092,53 @@ describe('BaseClient', () => {
       expect(recordLostEventSpy).toHaveBeenCalledWith('event_processor', 'error');
     });
 
+    test('mutating transaction name with event processors sets transaction name change metadata', () => {
+      const options = getDefaultTestClientOptions({ dsn: PUBLIC_DSN, enableSend: true });
+      const client = new TestClient(options);
+
+      const transaction: Event = {
+        contexts: {
+          trace: {
+            op: 'pageload',
+            span_id: 'a3df84a60c2e4e76',
+            trace_id: '86f39e84263a4de99c326acab3bfe3bd',
+          },
+        },
+        environment: 'production',
+        event_id: '972f45b826a248bba98e990878a177e1',
+        spans: [],
+        start_timestamp: 1591603196.614865,
+        timestamp: 1591603196.728485,
+        transaction: 'initialName',
+        type: 'transaction',
+        transaction_info: {
+          source: 'url',
+          changes: [],
+          propagations: 3,
+        },
+      };
+
+      const scope = new Scope();
+      scope.addEventProcessor(event => {
+        event.transaction = 'updatedName';
+        return event;
+      });
+
+      client.captureEvent(transaction, {}, scope);
+      expect(TestClient.instance!.event!.transaction).toEqual('updatedName');
+      expect(TestClient.instance!.event!.transaction_info).toEqual({
+        source: 'custom',
+        changes: [
+          {
+            propagations: 3,
+            source: 'custom',
+            timestamp: expect.any(Number),
+          },
+        ],
+        propagations: 3,
+      });
+    });
+
     test('eventProcessor sends an event and logs when it crashes', () => {
       expect.assertions(3);