From a874ba972bfa4c9c3103f6ba6de6381c1edb0603 Mon Sep 17 00:00:00 2001
From: Igor Unanua <igor.unanua@datadoghq.com>
Date: Thu, 2 Jan 2025 11:39:24 +0100
Subject: [PATCH] ignore noop spans

---
 packages/dd-trace/src/priority_sampler.js       |  6 ++++--
 packages/dd-trace/test/priority_sampler.spec.js | 10 ++++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/packages/dd-trace/src/priority_sampler.js b/packages/dd-trace/src/priority_sampler.js
index 3a89f71f664..7497f1f919c 100644
--- a/packages/dd-trace/src/priority_sampler.js
+++ b/packages/dd-trace/src/priority_sampler.js
@@ -120,13 +120,15 @@ class PrioritySampler {
     if (!span || !this.validate(samplingPriority)) return
 
     const context = this._getContext(span)
+    const root = context._trace.started[0]
+
+    if (!root) return // noop span
 
     context._sampling.priority = samplingPriority
     context._sampling.mechanism = mechanism
 
-    const root = context._trace.started[0]
-
     log.trace(span, samplingPriority, mechanism)
+
     this._addDecisionMaker(root)
   }
 
diff --git a/packages/dd-trace/test/priority_sampler.spec.js b/packages/dd-trace/test/priority_sampler.spec.js
index 88c134a5758..2c1a2e273bd 100644
--- a/packages/dd-trace/test/priority_sampler.spec.js
+++ b/packages/dd-trace/test/priority_sampler.spec.js
@@ -490,6 +490,16 @@ describe('PrioritySampler', () => {
       expect(context._sampling.mechanism).to.equal(SAMPLING_MECHANISM_APPSEC)
       expect(context._trace.tags[DECISION_MAKER_KEY]).to.equal('-0')
     })
+
+    it('should ignore noop spans', () => {
+      context._trace.started[0] = undefined // noop
+
+      prioritySampler.setPriority(span, USER_KEEP, SAMPLING_MECHANISM_APPSEC)
+
+      expect(context._sampling.priority).to.undefined
+      expect(context._sampling.mechanism).to.undefined
+      expect(context._trace.tags[DECISION_MAKER_KEY]).to.undefined
+    })
   })
 
   describe('keepTrace', () => {