take the responsibility of checking the config away from process tags class

Author: vandonr

tracer/src/Datadog.Trace/Agent/MessagePack/SpanMessagePackFormatter.cs

@@ -605,7 +605,7 @@ private int WriteTags(ref byte[] bytes, int offset, in SpanModel model, ITagProc
             }
 
             // Process tags will be sent only once per trace
-            if (model.IsFirstSpanInChunk)
+            if (model.IsFirstSpanInChunk && model.TraceChunk.ShouldPropagateProcessTags)
             {
                 var processTags = ProcessTags.SerializedTags;
                 var processTagsRawBytes = MessagePackStringCache.GetProcessTagsBytes(processTags);

tracer/src/Datadog.Trace/Agent/MessagePack/TraceChunkModel.cs

@@ -63,6 +63,8 @@ internal readonly struct TraceChunkModel
 
     public readonly ImmutableAzureAppServiceSettings? AzureAppServiceSettings = null;
 
+    public readonly bool ShouldPropagateProcessTags = true;
+
     public readonly bool IsApmEnabled = true;
 
     /// <summary>
@@ -108,6 +110,7 @@ private TraceChunkModel(in ArraySegment<Span> spans, TraceContext? traceContext,
                 {
                     IsRunningInAzureAppService = settings.IsRunningInAzureAppService;
                     AzureAppServiceSettings = settings.AzureAppServiceMetadata;
+                    ShouldPropagateProcessTags = settings.PropagateProcessTags;
                     IsApmEnabled = settings.ApmTracingEnabled;
                 }
 

tracer/src/Datadog.Trace/ProcessTags.cs

@@ -31,12 +31,6 @@ private static Dictionary<string, string> LoadBaseTags()
     {
         var tags = new Dictionary<string, string>();
 
-        if (!Tracer.Instance.Settings.PropagateProcessTags)
-        {
-            // do not collect anything when disabled
-            return tags;
-        }
-
         var entrypointFullName = Assembly.GetEntryAssembly()?.EntryPoint?.DeclaringType?.FullName;
         if (!string.IsNullOrEmpty(entrypointFullName))
         {
@@ -71,9 +65,4 @@ private static string NormalizeTagValue(string tagValue)
         // which we don't want because we use it as a key/value separator.
         return TraceUtil.NormalizeTag(tagValue).Replace(oldChar: ':', newChar: '_');
     }
-
-    internal static void ResetForTests()
-    {
-        _lazySerializedTags = new Lazy<string>(GetSerializedTags);
-    }
 }

tracer/test/Datadog.Trace.Tests/ProcessTagsTests.cs

@@ -3,40 +3,21 @@
 // This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2017 Datadog, Inc.
 // </copyright>
 
-using System.Collections.Generic;
 using System.Linq;
-using Datadog.Trace.Configuration;
 using FluentAssertions;
 using Xunit;
 
 namespace Datadog.Trace.Tests;
 
 public class ProcessTagsTests
 {
-    public ProcessTagsTests()
-    {
-        ProcessTags.ResetForTests();
-    }
-
-    [Fact]
-    public void EmptyIfDisabled()
-    {
-        Tracer.Configure(TracerSettings.Create(new Dictionary<string, object>()));
-
-        ProcessTags.SerializedTags.Should().BeEmpty();
-    }
-
     [Fact]
     public void TagsPresentWhenEnabled()
     {
-        Tracer.Configure(TracerSettings.Create(new Dictionary<string, object>
-        {
-            [ConfigurationKeys.PropagateProcessTags] = "true"
-        }));
-
         var tags = ProcessTags.SerializedTags;
 
         tags.Should().ContainAll(ProcessTags.EntrypointName, ProcessTags.EntrypointBasedir, ProcessTags.EntrypointWorkdir);
+
         tags.Split(',').Should().BeInAscendingOrder();
 
         // assert on the format, which is key:values in a string, comma separated.