fix(tracing): ignore baggage sample rate if sentry trace is not present

src/Tracing/Traits/TraceHeaderParserTrait.php

@@ -65,22 +65,21 @@ protected static function parseTraceAndBaggageHeaders(string $sentryTrace, strin
 
         $samplingContext = DynamicSamplingContext::fromHeader($baggage);
 
-        if ($hasSentryTrace && !$samplingContext->hasEntries()) {
+        if ($hasSentryTrace) {
             // The request comes from an old SDK which does not support Dynamic Sampling.
             // Propagate the Dynamic Sampling Context as is, but frozen, even without sentry-* entries.
-            $samplingContext->freeze();
-            $result['dynamicSamplingContext'] = $samplingContext;
-        }
+            if (!$samplingContext->hasEntries()) {
+                $samplingContext->freeze();
+            }
 
-        if ($hasSentryTrace && $samplingContext->hasEntries()) {
             // The baggage header contains Dynamic Sampling Context data from an upstream SDK.
             // Propagate this Dynamic Sampling Context.
             $result['dynamicSamplingContext'] = $samplingContext;
-        }
 
-        // Store the propagated traces sample rate
-        if ($samplingContext->has('sample_rate')) {
-            $result['parentSamplingRate'] = (float) $samplingContext->get('sample_rate');
+            // Store the propagated traces sample rate
+            if ($samplingContext->has('sample_rate')) {
+                $result['parentSamplingRate'] = (float)$samplingContext->get('sample_rate');
+            }
         }
 
         // Store the propagated trace sample rand or generate a new one

tests/State/HubTest.php

@@ -636,6 +636,22 @@ public function testStartTransactionWithTracesSampler(Options $options, Transact
         $this->assertSame($expectedSampled, $transaction->getSampled());
     }
 
+    public function testStartTransactionIgnoresBaggageSampleRateWithoutSentryTrace(): void
+    {
+        $client = $this->createMock(ClientInterface::class);
+        $client->expects($this->once())
+            ->method('getOptions')
+            ->willReturn(new Options([
+                'traces_sample_rate' => 0.0,
+            ]));
+
+        $hub = new Hub($client);
+        $transactionContext = TransactionContext::fromHeaders('', 'sentry-sample_rate=1');
+        $transaction = $hub->startTransaction($transactionContext);
+
+        $this->assertFalse($transaction->getSampled());
+    }
+
     public static function startTransactionDataProvider(): iterable
     {
         yield 'Acceptable float value returned from traces_sampler' => [

tests/Tracing/TransactionContextTest.php

@@ -149,4 +149,11 @@ public function testSampleRandRangeWhenParentNotSampledAndSampleRateProvided():
         $this->assertGreaterThanOrEqual(0.4, $sampleRand);
         $this->assertLessThanOrEqual(0.999999, $sampleRand);
     }
+
+    public function testParentSamplingRateIsIgnoredWithoutSentryTraceHeader(): void
+    {
+        $context = TransactionContext::fromHeaders('', 'sentry-sample_rate=1');
+
+        $this->assertNull($context->getMetadata()->getParentSamplingRate());
+    }
 }