fix: Defer tracing decision to downstream SDKs when using SDK without performance (#8839)

Author: Luca Forstner

packages/core/src/scope.ts

@@ -636,6 +636,5 @@ function generatePropagationContext(): PropagationContext {
   return {
     traceId: uuid4(),
     spanId: uuid4().substring(16),
-    sampled: false,
   };
 }

packages/hub/test/scope.test.ts

@@ -20,7 +20,7 @@ describe('Scope', () => {
       expect(scope._propagationContext).toEqual({
         traceId: expect.any(String),
         spanId: expect.any(String),
-        sampled: false,
+        sampled: undefined,
         dsc: undefined,
         parentSpanId: undefined,
       });
@@ -442,7 +442,7 @@ describe('Scope', () => {
     expect(scope._propagationContext).toEqual({
       traceId: expect.any(String),
       spanId: expect.any(String),
-      sampled: false,
+      sampled: undefined,
     });
     // @ts-expect-error accessing private property
     expect(scope._propagationContext).not.toEqual(oldPropagationContext);

packages/node/test/integrations/http.test.ts

@@ -208,10 +208,11 @@ describe('tracing', () => {
     const baggageHeader = request.getHeader('baggage') as string;
 
     const parts = sentryTraceHeader.split('-');
-    expect(parts.length).toEqual(3);
+
+    // Should not include sampling decision since we don't wanna influence the tracing decisions downstream
+    expect(parts.length).toEqual(2);
     expect(parts[0]).toEqual(traceId);
     expect(parts[1]).toEqual(expect.any(String));
-    expect(parts[2]).toEqual('0');
 
     expect(baggageHeader).toEqual(
       `sentry-environment=production,sentry-release=1.0.0,sentry-user_segment=segmentA,sentry-public_key=dogsarebadatkeepingsecrets,sentry-trace_id=${traceId}`,

packages/tracing-internal/src/browser/browsertracing.ts

@@ -364,7 +364,7 @@ export class BrowserTracing implements Integration {
         traceId: idleTransaction.traceId,
         spanId: idleTransaction.spanId,
         parentSpanId: idleTransaction.parentSpanId,
-        sampled: !!idleTransaction.sampled,
+        sampled: idleTransaction.sampled,
       });
     }
 

packages/types/src/tracing.ts

@@ -5,7 +5,7 @@ export type TracePropagationTargets = (string | RegExp)[];
 export interface PropagationContext {
   traceId: string;
   spanId: string;
-  sampled: boolean;
+  sampled?: boolean;
   parentSpanId?: string;
   dsc?: DynamicSamplingContext;
 }

packages/utils/src/tracing.ts

@@ -61,7 +61,7 @@ export function tracingContextFromHeaders(
   const propagationContext: PropagationContext = {
     traceId: traceId || uuid4(),
     spanId: uuid4().substring(16),
-    sampled: parentSampled === undefined ? false : parentSampled,
+    sampled: parentSampled,
   };
 
   if (parentSpanId) {