Honor SENTRY_TRACES_SAMPLE_RATE in the diagnostics-channel injection gate

Author: andreiborza

packages/node/src/sdk/diagnosticsChannelInjection.ts

@@ -35,6 +35,8 @@ let cached: DiagnosticsChannelInjection | undefined;
  */
 export function setDiagnosticsChannelInjectionLoader(load: () => DiagnosticsChannelInjection): void {
   loader = load;
+  // Invalidate the memoized result so a newly set loader resolves fresh.
+  cached = undefined;
 }
 
 /** Whether `experimentalUseDiagnosticsChannelInjection()` was called. */

packages/node/src/sdk/index.ts

@@ -16,6 +16,19 @@ import {
 } from './diagnosticsChannelInjection';
 import { initOpenTelemetry } from './initOtel';
 
+/**
+ * Whether span recording is enabled, including the `SENTRY_TRACES_SAMPLE_RATE` env var that node-core
+ * resolves later. `hasSpansEnabled` only inspects the options object, so on init paths that enable
+ * tracing purely through the env var (e.g. the `@sentry/aws-serverless` Lambda auto-init) it would
+ * otherwise report `false` and skip the diagnostics-channel injection swap and hook registration.
+ */
+function hasSpansEnabledIncludingEnv(options: Options): boolean {
+  return (
+    hasSpansEnabled(options) ||
+    (options.tracesSampleRate == null && !options.tracesSampler && !!process.env.SENTRY_TRACES_SAMPLE_RATE)
+  );
+}
+
 /**
  * Get default integrations, excluding performance.
  */
@@ -61,7 +74,7 @@ export function applyDiagnosticsChannelInjectionIntegrations(
   integrations: Integration[],
   options: Options,
 ): Integration[] {
-  if (isDiagnosticsChannelInjectionEnabled() && hasSpansEnabled(options)) {
+  if (isDiagnosticsChannelInjectionEnabled() && hasSpansEnabledIncludingEnv(options)) {
     const diagnosticsChannelInjection = resolveDiagnosticsChannelInjection();
     if (diagnosticsChannelInjection) {
       const replaced = new Set(diagnosticsChannelInjection.replacedOtelIntegrationNames);
@@ -90,9 +103,12 @@ function _init(
   // EXPERIMENTAL: diagnostics-channel injection, opted into via
   // `experimentalUseDiagnosticsChannelInjection()`. Gated on span recording to
   // match the OTel integrations it replaces. With tracing off there are no
-  // channel subscribers, so injecting is pointless work.
+  // channel subscribers, so injecting is pointless work. The env var is included
+  // because node-core resolves `SENTRY_TRACES_SAMPLE_RATE` later, and without it
+  // the auto-init path (pre-built `integrations`) would skip `register()` and
+  // never install the module hooks, silently emitting no spans.
   const diagnosticsChannelInjection =
-    isDiagnosticsChannelInjectionEnabled() && hasSpansEnabled(options)
+    isDiagnosticsChannelInjectionEnabled() && hasSpansEnabledIncludingEnv(options)
       ? resolveDiagnosticsChannelInjection()
       : undefined;
 

packages/node/test/sdk/diagnosticsChannelInjection.test.ts

@@ -114,4 +114,37 @@ describe('diagnostics-channel injection integration swap', () => {
 
     expect(channelNoDefaults.setupOnce).not.toHaveBeenCalled();
   });
+
+  it('swaps integrations and registers hooks when tracing is enabled only via SENTRY_TRACES_SAMPLE_RATE', () => {
+    // The auto-init path (e.g. `@sentry/aws-serverless`) enables tracing through the env var, not the
+    // options object. `hasSpansEnabled(options)` alone reports false there, so the swap and
+    // `register()` must still fire from the env-derived rate or spans silently never emit.
+    const channelEnvMysql = mockIntegration('EnvMysql');
+    const register = vi.fn();
+    setDiagnosticsChannelInjectionLoader(() => ({
+      integrations: [channelEnvMysql],
+      replacedOtelIntegrationNames: ['EnvMysql'],
+      register,
+      detect: vi.fn(),
+    }));
+
+    const otelEnvMysql = mockIntegration('EnvMysql');
+    const http = mockIntegration('EnvHttp');
+
+    vi.stubEnv('SENTRY_TRACES_SAMPLE_RATE', '1');
+    try {
+      init({
+        dsn: PUBLIC_DSN,
+        skipOpenTelemetrySetup: true,
+        defaultIntegrations: [otelEnvMysql, http],
+      });
+    } finally {
+      vi.unstubAllEnvs();
+    }
+
+    expect(otelEnvMysql.setupOnce).not.toHaveBeenCalled();
+    expect(channelEnvMysql.setupOnce).toHaveBeenCalledTimes(1);
+    expect(http.setupOnce).toHaveBeenCalledTimes(1);
+    expect(register).toHaveBeenCalledTimes(1);
+  });
 });