Make segment-span deferral enable-only

Author: andreiborza

packages/core/src/tracing/sentrySpan.ts

@@ -68,22 +68,18 @@ const DEFERRED_SEGMENT_SPAN_CAPTURES = new WeakMap<Client, (capture: () => void)
 const CAPTURED_SPANS = new WeakSet<Span>();
 
 /**
- * Opt a client into (or out of) deferring its segment-span transaction capture.
- * Set by the SDK client during setup (e.g. the Node SDK); see {@link DEFERRED_SEGMENT_SPAN_CAPTURES}.
+ * Defer a client's segment-span transaction capture. Set once by the SDK during setup (e.g. the Node
+ * SDK); see {@link DEFERRED_SEGMENT_SPAN_CAPTURES}. Idempotent, and deferral stays on for the client's
+ * lifetime (there is no opt-out: deferral is a set-once-at-setup property, never toggled mid-session).
  *
  * The transaction is otherwise assembled from the live span tree the instant a root span ends, which
  * drops children whose async instrumentation closes them later (a diagnostics-channel `asyncEnd`
- * callback in the same tick, or engine spans replayed on a later tick). A debounced timer — the same
- * one the OpenTelemetry span exporter uses — delays the snapshot just enough for those later span ends
- * to land first. Pending captures are drained synchronously on the client's `flush` hook so
+ * callback in the same tick, or engine spans replayed on a later tick). A debounced timer (the same one
+ * the OpenTelemetry span exporter uses) delays the snapshot just enough for those later span ends to
+ * land first. Pending captures are drained synchronously on the client's `flush` hook so
  * `Sentry.flush()` / `client.close()` cannot resolve before they run.
  */
-export function _INTERNAL_setDeferSegmentSpanCapture(client: Client, defer: boolean): void {
-  if (!defer) {
-    DEFERRED_SEGMENT_SPAN_CAPTURES.delete(client);
-    return;
-  }
-
+export function _INTERNAL_setDeferSegmentSpanCapture(client: Client): void {
   if (DEFERRED_SEGMENT_SPAN_CAPTURES.has(client)) {
     return;
   }

packages/core/test/lib/tracing/sentrySpan.test.ts

@@ -2,7 +2,7 @@ import { describe, expect, it, test, vi } from 'vitest';
 import { getCurrentScope } from '../../../src/currentScopes';
 import { setCurrentClient } from '../../../src/sdk';
 import { SEMANTIC_ATTRIBUTE_SENTRY_SOURCE } from '../../../src/semanticAttributes';
-import { SentrySpan } from '../../../src/tracing/sentrySpan';
+import { _INTERNAL_setDeferSegmentSpanCapture, SentrySpan } from '../../../src/tracing/sentrySpan';
 import { SPAN_STATUS_ERROR } from '../../../src/tracing/spanstatus';
 import { markSpanForOtelSourceInference, spanSourceWasExplicitlySet } from '../../../src/tracing/utils';
 import type { SpanJSON } from '../../../src/types/span';
@@ -132,6 +132,18 @@ describe('SentrySpan', () => {
     });
   });
 
+  describe('_INTERNAL_setDeferSegmentSpanCapture', () => {
+    it('registers the flush listener once and is idempotent on repeated enable', () => {
+      const client = new TestClient(getDefaultTestClientOptions());
+      const onSpy = vi.spyOn(client, 'on');
+
+      _INTERNAL_setDeferSegmentSpanCapture(client);
+      _INTERNAL_setDeferSegmentSpanCapture(client);
+
+      expect(onSpy.mock.calls.filter(([hook]) => hook === 'flush')).toHaveLength(1);
+    });
+  });
+
   describe('end', () => {
     test('simple', () => {
       const span = new SentrySpan({});