Update the DSC’s sample_rate if a traces_sampler is used

Author: cleptric

src/State/Hub.php

@@ -276,8 +276,14 @@ public function startTransaction(TransactionContext $context, array $customSampl
 
             if ($tracesSampler !== null) {
                 $sampleRate = $tracesSampler($samplingContext);
-
                 $sampleSource = 'config:traces_sampler';
+
+                $dynamicSamplingContext = $context->getMetadata()->getDynamicSamplingContext();
+                if ($dynamicSamplingContext !== null) {
+                    // If a tracesSampler is defined,
+                    // always overwrite the sample_rate in the DSC
+                    $dynamicSamplingContext->set('sample_rate', (string) $sampleRate, true);
+                }
             } else {
                 $parentSampleRate = $context->getMetadata()->getParentSamplingRate();
                 if ($parentSampleRate !== null) {

src/Tracing/DynamicSamplingContext.php

@@ -40,9 +40,9 @@ private function __construct()
      * @param string $key   the list member key
      * @param string $value the list member value
      */
-    public function set(string $key, string $value): self
+    public function set(string $key, string $value, bool $forceOverwrite = false): self
     {
-        if ($this->isFrozen) {
+        if ($this->isFrozen && !$forceOverwrite) {
             return $this;
         }