log telemetry load failures

src/Build.UnitTests/Telemetry/OpenTelemetryManager_Tests.cs

@@ -2,7 +2,10 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Reflection;
+using Microsoft.Build.Execution;
 using Microsoft.Build.Framework.Telemetry;
 using Microsoft.Build.UnitTests;
 using Shouldly;
@@ -98,6 +101,23 @@ public void Initialize_ShouldNoOp_WhenCalledMultipleTimes()
             state2.ShouldBe(false);
         }
 
+        [Fact]
+        public void TelemetryLoadFailureIsLoggedOnce()
+        {
+            OpenTelemetryManager.Instance.LoadFailureExceptionMessage = new System.IO.FileNotFoundException().ToString();
+            using BuildManager bm = new BuildManager();
+            var deferredMessages = new List<BuildManager.DeferredBuildMessage>();
+            bm.BeginBuild(new BuildParameters(), deferredMessages);
+            deferredMessages.ShouldContain(x => x.Text.Contains("FileNotFound"));
+            bm.EndBuild();
+            bm.BeginBuild(new BuildParameters());
+            bm.EndBuild();
+
+            // should not add message twice
+            int count = deferredMessages.Count(x => x.Text.Contains("FileNotFound"));
+            count.ShouldBe(1);
+        }
+
         /* Helper methods */
 
         /// <summary>

src/Build.UnitTests/Telemetry/Telemetry_Tests.cs

@@ -5,9 +5,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
-#if NET
 using System.Text.Json;
-#endif
 using Microsoft.Build.Execution;
 using Microsoft.Build.Framework;
 using Microsoft.Build.Framework.Telemetry;

src/Build/BackEnd/BuildManager/BuildManager.cs

@@ -459,7 +459,8 @@ private void UpdatePriority(Process p, ProcessPriorityClass priority)
         /// <exception cref="InvalidOperationException">Thrown if a build is already in progress.</exception>
         public void BeginBuild(BuildParameters parameters)
         {
-            OpenTelemetryManager.Instance.Initialize(isStandalone: false);
+            InitializeTelemetry();
+
             if (_previousLowPriority != null)
             {
                 if (parameters.LowPriority != _previousLowPriority)
@@ -723,6 +724,26 @@ void InitializeCaches()
             }
         }
 
+        private void InitializeTelemetry()
+        {
+            OpenTelemetryManager.Instance.Initialize(isStandalone: false);
+            string? failureMessage = OpenTelemetryManager.Instance.LoadFailureExceptionMessage;
+            if (_deferredBuildMessages != null &&
+                failureMessage != null &&
+                _deferredBuildMessages is ICollection<DeferredBuildMessage> deferredBuildMessagesCollection)
+            {
+                deferredBuildMessagesCollection.Add(
+                    new DeferredBuildMessage(
+                        ResourceUtilities.FormatResourceStringIgnoreCodeAndKeyword(
+                            "OpenTelemetryLoadFailed",
+                            failureMessage),
+                    MessageImportance.Low));
+
+                // clean up the message from OpenTelemetryManager to avoid double logging it
+                OpenTelemetryManager.Instance.LoadFailureExceptionMessage = null;
+            }
+        }
+
 #if FEATURE_REPORTFILEACCESSES
         /// <summary>
         /// Configure the build to use I/O tracking for nodes.

src/Build/Resources/Strings.resx

@@ -2392,6 +2392,9 @@ Utilization:          {0} Average Utilization: {1:###.0}</value>
     <value>succeeded: {0}</value>
     <comment>{0} whole number</comment>
   </data>
+  <data name="OpenTelemetryLoadFailed" xml:space="preserve">
+    <value>Loading telemetry libraries failed with exception: {0}.</value>
+  </data>
   <!--
         The Build message bucket is: MSB4000 - MSB4999
 

src/Framework/Telemetry/OpenTelemetryManager.cs

@@ -39,6 +39,8 @@ internal class OpenTelemetryManager
         private IOpenTelemetryCollector? _collector;
 #endif
 
+        public string? LoadFailureExceptionMessage { get; set; }
+
         /// <summary>
         /// Optional activity source for MSBuild or other telemetry usage.
         /// </summary>
@@ -104,6 +106,7 @@ public void Initialize(bool isStandalone)
             {
                 // catch exceptions from loading the OTel SDK or Collector to maintain usability of Microsoft.Build.Framework package in our and downstream tests in VS.
                 _telemetryState = TelemetryState.Unsampled;
+                LoadFailureExceptionMessage = ex.ToString();
                 return;
             }
 #endif