refactor(core): Remove beforeSendSpan null return warning

Co-Authored-By: GPT-6 <codex@openai.com>

Author: msonnb

packages/core/src/tracing/spans/beforeSendSpan.ts

@@ -2,7 +2,6 @@ import { DEBUG_BUILD } from '../../debug-build';
 import type { BeforeSendStaticSpanCallback, BeforeSendStreamedSpanCallback } from '../../types/options';
 import type { SpanJSON, StreamedSpanJSON } from '../../types/span';
 import { addNonEnumerableProperty } from '../../utils/object';
-import { consoleSandbox } from '../../utils/debug-logger';
 import { safeCallback } from '../../utils/safeCallback';
 
 /**
@@ -57,7 +56,6 @@ export function isStaticBeforeSendSpanCallback(callback: unknown): callback is B
   return !!callback && typeof callback === 'function' && '_static' in callback && !!callback._static;
 }
 
-let hasShownSpanDropWarning = false;
 /**
  * Apply a user-provided beforeSendSpan callback to a span JSON.
  */
@@ -72,18 +70,5 @@ export function applyBeforeSendSpanCallback<T extends StreamedSpanJSON | SpanJSO
     () => beforeSendSpan(span),
     () => span,
   );
-  if (modifiedSpan) {
-    return modifiedSpan;
-  }
-
-  if (!hasShownSpanDropWarning) {
-    consoleSandbox(() => {
-      // eslint-disable-next-line no-console
-      console.warn(
-        '[Sentry] Returning null from `beforeSendSpan` is disallowed. To drop certain spans, configure the respective integrations directly or use `ignoreSpans`.',
-      );
-    });
-    hasShownSpanDropWarning = true;
-  }
-  return span;
+  return modifiedSpan || span;
 }

packages/core/test/lib/client.test.ts

@@ -1711,51 +1711,6 @@ describe('Client', () => {
       expect(loggerLogSpy).toBeCalledWith('before send for type `transaction` returned `null`, will not send event.');
     });
 
-    test('does not discard span and warn when returning null from `beforeSendSpan', () => {
-      const consoleWarnSpy = vi.spyOn(console, 'warn').mockImplementation(() => undefined);
-
-      // @ts-expect-error - intentionally violating the type signature here
-      const beforeSendSpan = withStaticSpan(vi.fn(() => null));
-
-      const options = getDefaultTestClientOptions({ dsn: PUBLIC_DSN, beforeSendSpan });
-      const client = new TestClient(options);
-
-      const transaction: Event = {
-        transaction: '/dogs/are/great',
-        type: 'transaction',
-        spans: [
-          {
-            description: 'first span',
-            span_id: '9e15bf99fbe4bc80',
-            start_timestamp: 1591603196.637835,
-            trace_id: '86f39e84263a4de99c326acab3bfe3bd',
-            data: {},
-            status: 'ok',
-          },
-          {
-            description: 'second span',
-            span_id: 'aa554c1f506b0783',
-            start_timestamp: 1591603196.637835,
-            trace_id: '86f39e84263a4de99c326acab3bfe3bd',
-            data: {},
-            status: 'ok',
-          },
-        ],
-      };
-      client.captureEvent(transaction);
-
-      expect(beforeSendSpan).toHaveBeenCalledTimes(3);
-      const capturedEvent = TestClient.instance!.event!;
-      expect(capturedEvent.spans).toHaveLength(2);
-      expect(client['_outcomes']).toEqual({});
-
-      expect(consoleWarnSpy).toHaveBeenCalledTimes(1);
-      expect(consoleWarnSpy).toHaveBeenCalledWith(
-        '[Sentry] Returning null from `beforeSendSpan` is disallowed. To drop certain spans, configure the respective integrations directly or use `ignoreSpans`.',
-      );
-      consoleWarnSpy.mockRestore();
-    });
-
     test("doesn't throw if the `beforeSendSpan` callback throws", () => {
       const debugErrorSpy = vi.spyOn(debugLoggerModule.debug, 'error').mockImplementation(() => undefined);
       const error = new Error('beforeSendSpan is broken');

packages/core/test/lib/tracing/spans/captureSpan.test.ts

@@ -507,8 +507,7 @@ describe('captureSpan', () => {
       expect(beforeSendSpan).not.toHaveBeenCalled();
     });
 
-    it('logs a warning if the beforeSendSpan callback returns null', () => {
-      const consoleWarnSpy = vi.spyOn(console, 'warn').mockImplementation(() => undefined);
+    it('keeps the span if the beforeSendSpan callback returns null', () => {
       const beforeSendSpan = vi.fn(() => null as unknown as StreamedSpanJSON);
 
       const client = new TestClient(
@@ -522,16 +521,17 @@ describe('captureSpan', () => {
         }),
       );
 
-      const span = startInactiveSpan({ name: 'my-span', attributes: { 'sentry.op': 'http.client' } });
-      span.end();
-
-      captureSpan(span, client);
+      const span = withScope(scope => {
+        scope.setClient(client);
+        const span = startInactiveSpan({ name: 'my-span', attributes: { 'sentry.op': 'http.client' } });
+        span.end();
+        return span;
+      });
 
-      expect(consoleWarnSpy).toHaveBeenCalledWith(
-        '[Sentry] Returning null from `beforeSendSpan` is disallowed. To drop certain spans, configure the respective integrations directly or use `ignoreSpans`.',
-      );
+      const serialized = captureSpan(span, client);
 
-      consoleWarnSpy.mockRestore();
+      expect(serialized.span_id).toBe(span.spanContext().spanId);
+      expect(serialized.name).toBe('my-span');
     });
 
     it('keeps the span and logs an error if the beforeSendSpan callback throws', () => {