ref(core): Ensure non-recording root spans have frozen DSC (#14964)

Otherwise, parts of the DSC will be missing - we try to make it as
complete as we can.

Since the span cannot be updated anyhow (e.g. the name cannot be
changed), we can safely freeze this at this time.

Extracted out of
#14955

packages/core/src/tracing/idleSpan.ts

@@ -1,5 +1,5 @@
 import { getClient, getCurrentScope } from '../currentScopes';
-import type { Span, StartSpanOptions } from '../types-hoist';
+import type { DynamicSamplingContext, Span, StartSpanOptions } from '../types-hoist';
 
 import { DEBUG_BUILD } from '../debug-build';
 import { SEMANTIC_ATTRIBUTE_SENTRY_IDLE_SPAN_FINISH_REASON } from '../semanticAttributes';
@@ -14,6 +14,7 @@ import {
   spanTimeInputToSeconds,
   spanToJSON,
 } from '../utils/spanUtils';
+import { freezeDscOnSpan, getDynamicSamplingContextFromSpan } from './dynamicSamplingContext';
 import { SentryNonRecordingSpan } from './sentryNonRecordingSpan';
 import { SPAN_STATUS_ERROR } from './spanstatus';
 import { startInactiveSpan } from './trace';
@@ -109,7 +110,16 @@ export function startIdleSpan(startSpanOptions: StartSpanOptions, options: Parti
   const client = getClient();
 
   if (!client || !hasTracingEnabled()) {
-    return new SentryNonRecordingSpan();
+    const span = new SentryNonRecordingSpan();
+
+    const dsc = {
+      sample_rate: '0',
+      sampled: 'false',
+      ...getDynamicSamplingContextFromSpan(span),
+    } satisfies Partial<DynamicSamplingContext>;
+    freezeDscOnSpan(span, dsc);
+
+    return span;
   }
 
   const scope = getCurrentScope();

packages/core/src/tracing/trace.ts

@@ -2,7 +2,14 @@
 
 import type { AsyncContextStrategy } from '../asyncContext/types';
 import { getMainCarrier } from '../carrier';
-import type { ClientOptions, SentrySpanArguments, Span, SpanTimeInput, StartSpanOptions } from '../types-hoist';
+import type {
+  ClientOptions,
+  DynamicSamplingContext,
+  SentrySpanArguments,
+  Span,
+  SpanTimeInput,
+  StartSpanOptions,
+} from '../types-hoist';
 
 import { getClient, getCurrentScope, getIsolationScope, withScope } from '../currentScopes';
 
@@ -284,7 +291,21 @@ function createChildOrRootSpan({
   scope: Scope;
 }): Span {
   if (!hasTracingEnabled()) {
-    return new SentryNonRecordingSpan();
+    const span = new SentryNonRecordingSpan();
+
+    // If this is a root span, we ensure to freeze a DSC
+    // So we can have at least partial data here
+    if (forceTransaction || !parentSpan) {
+      const dsc = {
+        sampled: 'false',
+        sample_rate: '0',
+        transaction: spanArguments.name,
+        ...getDynamicSamplingContextFromSpan(span),
+      } satisfies Partial<DynamicSamplingContext>;
+      freezeDscOnSpan(span, dsc);
+    }
+
+    return span;
   }
 
   const isolationScope = getIsolationScope();

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

@@ -7,6 +7,7 @@ import {
   getActiveSpan,
   getClient,
   getCurrentScope,
+  getDynamicSamplingContextFromSpan,
   getGlobalScope,
   getIsolationScope,
   setCurrentClient,
@@ -60,6 +61,14 @@ describe('startIdleSpan', () => {
     const idleSpan = startIdleSpan({ name: 'foo' });
     expect(idleSpan).toBeDefined();
     expect(idleSpan).toBeInstanceOf(SentryNonRecordingSpan);
+    // DSC is still correctly set on the span
+    expect(getDynamicSamplingContextFromSpan(idleSpan)).toEqual({
+      environment: 'production',
+      public_key: '123',
+      sample_rate: '0',
+      sampled: 'false',
+      trace_id: expect.stringMatching(/[a-f0-9]{32}/),
+    });
 
     // not set as active span, though
     expect(getActiveSpan()).toBe(undefined);

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

@@ -15,6 +15,7 @@ import { getAsyncContextStrategy } from '../../../src/asyncContext';
 import {
   SentrySpan,
   continueTrace,
+  getDynamicSamplingContextFromSpan,
   registerSpanErrorInstrumentation,
   startInactiveSpan,
   startSpan,
@@ -217,6 +218,13 @@ describe('startSpan', () => {
 
     expect(span).toBeDefined();
     expect(span).toBeInstanceOf(SentryNonRecordingSpan);
+    expect(getDynamicSamplingContextFromSpan(span)).toEqual({
+      environment: 'production',
+      sample_rate: '0',
+      sampled: 'false',
+      trace_id: expect.stringMatching(/[a-f0-9]{32}/),
+      transaction: 'GET users/[id]',
+    });
   });
 
   it('creates & finishes span', async () => {
@@ -633,6 +641,13 @@ describe('startSpanManual', () => {
 
     expect(span).toBeDefined();
     expect(span).toBeInstanceOf(SentryNonRecordingSpan);
+    expect(getDynamicSamplingContextFromSpan(span)).toEqual({
+      environment: 'production',
+      sample_rate: '0',
+      sampled: 'false',
+      trace_id: expect.stringMatching(/[a-f0-9]{32}/),
+      transaction: 'GET users/[id]',
+    });
   });
 
   it('creates & finishes span', async () => {
@@ -971,6 +986,13 @@ describe('startInactiveSpan', () => {
 
     expect(span).toBeDefined();
     expect(span).toBeInstanceOf(SentryNonRecordingSpan);
+    expect(getDynamicSamplingContextFromSpan(span)).toEqual({
+      environment: 'production',
+      sample_rate: '0',
+      sampled: 'false',
+      trace_id: expect.stringMatching(/[a-f0-9]{32}/),
+      transaction: 'GET users/[id]',
+    });
   });
 
   it('creates & finishes span', async () => {