feat(am): Introduce startTransaction

CHANGELOG.md

@@ -17,6 +17,7 @@
 - [apm] fix: Improve bundle size by moving span status to @sentry/apm #2589
 - [apm] feat: No longer discard transactions instead mark them deadline exceeded #2588
 - [apm] feat: Introduce `Sentry.startTransaction` and `Transaction.startChild` #2600
+- [apm] feat: Transactions no longer go through `beforeSend` #2600
 
 ## 5.15.5
 

packages/core/src/baseclient.ts

@@ -392,9 +392,11 @@ export abstract class BaseClient<B extends Backend, O extends Options> implement
       return SyncPromise.reject('SDK not enabled, will not send event.');
     }
 
+    const isTransaction = event.type === 'transaction';
     // 1.0 === 100% events are sent
     // 0.0 === 0% events are sent
-    if (typeof sampleRate === 'number' && Math.random() > sampleRate) {
+    // Sampling for transaction happens somewhere else
+    if (!isTransaction && typeof sampleRate === 'number' && Math.random() > sampleRate) {
       return SyncPromise.reject('This event has been sampled, will not send event.');
     }
 
@@ -409,7 +411,8 @@ export abstract class BaseClient<B extends Backend, O extends Options> implement
           let finalEvent: Event | null = prepared;
 
           const isInternalException = hint && hint.data && (hint.data as { [key: string]: any }).__sentry__ === true;
-          if (isInternalException || !beforeSend) {
+          // We skip beforeSend in case of transactions
+          if (isInternalException || !beforeSend || isTransaction) {
             this._getBackend().sendEvent(finalEvent);
             resolve(finalEvent);
             return;