Add debug-only guards for type

Author: andrewlock

tracer/src/Datadog.Trace/Activity/Helpers/ActivityEnumerationHelper.cs

@@ -16,6 +16,10 @@ internal static class ActivityEnumerationHelper
 {
     private static AllocationFreeEnumerator<IEnumerable<KeyValuePair<string, object?>>, KeyValuePair<string, object?>, OtelTagsEnumerationState>.AllocationFreeForEachDelegate? _tagObjectsEnumerator;
     private static AllocationFreeEnumerator<IEnumerable<KeyValuePair<string, string?>>, KeyValuePair<string, string?>, OtelTagsEnumerationState>.AllocationFreeForEachDelegate? _tagsEnumerator;
+#if DEBUG
+    private static Type? _tagObjectsType;
+    private static Type? _tagType;
+#endif
 
     /// <summary>
     /// Returns an enumerator than can be used to iterate the provided <see cref="IActivity5.TagObjects"/>, without allocating.
@@ -26,27 +30,47 @@ internal static class ActivityEnumerationHelper
     public static AllocationFreeEnumerator<IEnumerable<KeyValuePair<string, object?>>, KeyValuePair<string, object?>, OtelTagsEnumerationState>.AllocationFreeForEachDelegate GetTagObjectsEnumerator<T>(T activity5)
         where T : IActivity5
     {
+#if DEBUG
+        // Tag type used to call this method should never change
+        if (Volatile.Read(ref _tagObjectsType) is { } expectedType)
+        {
+            System.Diagnostics.Debug.Assert(expectedType == activity5.TagObjects.GetType(), "Must always call this method with the same type of TagObjects");
+        }
+#endif
         return Volatile.Read(ref _tagObjectsEnumerator) ?? BuildDelegate(activity5);
 
         static AllocationFreeEnumerator<IEnumerable<KeyValuePair<string, object?>>, KeyValuePair<string, object?>, OtelTagsEnumerationState>.AllocationFreeForEachDelegate BuildDelegate(T activity5)
         {
             var forEach = AllocationFreeEnumerator<IEnumerable<KeyValuePair<string, object?>>, KeyValuePair<string, object?>, OtelTagsEnumerationState>
                .BuildAllocationFreeForEachDelegate(activity5.TagObjects.GetType());
 
+#if DEBUG
+            Volatile.Write(ref _tagObjectsType, activity5.TagObjects.GetType());
+#endif
             return Interlocked.CompareExchange(ref _tagObjectsEnumerator, forEach, null) ?? forEach;
         }
     }
 
     public static AllocationFreeEnumerator<IEnumerable<KeyValuePair<string, string?>>, KeyValuePair<string, string?>, OtelTagsEnumerationState>.AllocationFreeForEachDelegate GetTagsEnumerator<T>(T activity)
         where T : IActivity
     {
+#if DEBUG
+        // Tag type used to call this method should never change
+        if (Volatile.Read(ref _tagType) is { } expectedType)
+        {
+            System.Diagnostics.Debug.Assert(expectedType == activity.Tags.GetType(), "Must always call this method with the same type of TagObjects");
+        }
+#endif
         return Volatile.Read(ref _tagsEnumerator) ?? BuildDelegate(activity);
 
         static AllocationFreeEnumerator<IEnumerable<KeyValuePair<string, string?>>, KeyValuePair<string, string?>, OtelTagsEnumerationState>.AllocationFreeForEachDelegate BuildDelegate(T activity)
         {
             var forEach = AllocationFreeEnumerator<IEnumerable<KeyValuePair<string, string?>>, KeyValuePair<string, string?>, OtelTagsEnumerationState>
                .BuildAllocationFreeForEachDelegate(activity.Tags.GetType());
 
+#if DEBUG
+            Volatile.Write(ref _tagType, activity.Tags.GetType());
+#endif
             return Interlocked.CompareExchange(ref _tagsEnumerator, forEach, null) ?? forEach;
         }
     }