Address AOT warnings in Exporter.OpenTelemetryProtocol

This addresses the AOT warnings in the last library in this opentelemetry-dotnet.

1. Google.Protobuf v3.19.4 isn't trimming and AOT compatible. We need to upgrade to a newer version. I chose the latest patch in v3.22.x. v3.22.0 was the first version that is AOT compatible.

2. There were 2 places in Exporter.OpenTelemetryProtocol that was using System.Reflection.Emit to set a private field on Protobuf's RepeatedField class in order to return it to a pool. Setting this private field is no longer necessary since v3.22.0 because the Clear method was updated to support this scenario. See protocolbuffers/protobuf@a4fd216

Fix open-telemetry#3429

Directory.Packages.props

@@ -13,7 +13,7 @@
       vulnerability in the NuGet packages that are published from this repository.
   -->
   <ItemGroup>
-    <PackageVersion Include="Google.Protobuf" Version="[3.19.4,4.0)" />
+    <PackageVersion Include="Google.Protobuf" Version="[3.22.5,4.0)" />
     <PackageVersion Include="Grpc" Version="[2.44.0,3.0)" />
     <PackageVersion Include="Grpc.Net.Client" Version="[2.52.0,3.0)" />
     <PackageVersion Include="Microsoft.AspNetCore.Http.Abstractions" Version="[2.1.1,6.0)" />

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/ActivityExtensions.cs

@@ -16,11 +16,8 @@
 
 using System.Collections.Concurrent;
 using System.Diagnostics;
-using System.Reflection;
-using System.Reflection.Emit;
 using System.Runtime.CompilerServices;
 using Google.Protobuf;
-using Google.Protobuf.Collections;
 using OpenTelemetry.Internal;
 using OpenTelemetry.Proto.Collector.Trace.V1;
 using OpenTelemetry.Proto.Common.V1;
@@ -34,7 +31,6 @@ namespace OpenTelemetry.Exporter.OpenTelemetryProtocol.Implementation;
 internal static class ActivityExtensions
 {
     private static readonly ConcurrentBag<ScopeSpans> SpanListPool = new();
-    private static readonly Action<RepeatedField<Span>, int> RepeatedFieldOfSpanSetCountAction = CreateRepeatedFieldOfSpanSetCountAction();
 
     internal static void AddBatch(
         this ExportTraceServiceRequest request,
@@ -84,7 +80,7 @@ internal static void Return(this ExportTraceServiceRequest request)
 
         foreach (var scope in resourceSpans.ScopeSpans)
         {
-            RepeatedFieldOfSpanSetCountAction(scope.Spans, 0);
+            scope.Spans.Clear();
             SpanListPool.Add(scope);
         }
     }
@@ -298,27 +294,6 @@ private static Span.Types.Event ToOtlpEvent(in ActivityEvent activityEvent, SdkL
         return otlpEvent;
     }
 
-    private static Action<RepeatedField<Span>, int> CreateRepeatedFieldOfSpanSetCountAction()
-    {
-        FieldInfo repeatedFieldOfSpanCountField = typeof(RepeatedField<Span>).GetField("count", BindingFlags.NonPublic | BindingFlags.Instance);
-
-        DynamicMethod dynamicMethod = new DynamicMethod(
-            "CreateSetCountAction",
-            null,
-            new[] { typeof(RepeatedField<Span>), typeof(int) },
-            typeof(ActivityExtensions).Module,
-            skipVisibility: true);
-
-        var generator = dynamicMethod.GetILGenerator();
-
-        generator.Emit(OpCodes.Ldarg_0);
-        generator.Emit(OpCodes.Ldarg_1);
-        generator.Emit(OpCodes.Stfld, repeatedFieldOfSpanCountField);
-        generator.Emit(OpCodes.Ret);
-
-        return (Action<RepeatedField<Span>, int>)dynamicMethod.CreateDelegate(typeof(Action<RepeatedField<Span>, int>));
-    }
-
     private struct TagEnumerationState : PeerServiceResolver.IPeerServiceState
     {
         public SdkLimitOptions SdkLimitOptions;

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/MetricItemExtensions.cs

@@ -15,8 +15,6 @@
 // </copyright>
 
 using System.Collections.Concurrent;
-using System.Reflection;
-using System.Reflection.Emit;
 using System.Runtime.CompilerServices;
 using Google.Protobuf;
 using Google.Protobuf.Collections;
@@ -31,7 +29,6 @@ namespace OpenTelemetry.Exporter.OpenTelemetryProtocol.Implementation;
 internal static class MetricItemExtensions
 {
     private static readonly ConcurrentBag<OtlpMetrics.ScopeMetrics> MetricListPool = new();
-    private static readonly Action<RepeatedField<OtlpMetrics.Metric>, int> RepeatedFieldOfMetricSetCountAction = CreateRepeatedFieldOfMetricSetCountAction();
 
     internal static void AddMetrics(
         this OtlpCollector.ExportMetricsServiceRequest request,
@@ -82,7 +79,7 @@ internal static void Return(this OtlpCollector.ExportMetricsServiceRequest reque
 
         foreach (var scope in resourceMetrics.ScopeMetrics)
         {
-            RepeatedFieldOfMetricSetCountAction(scope.Metrics, 0);
+            scope.Metrics.Clear();
             MetricListPool.Add(scope);
         }
     }
@@ -418,25 +415,4 @@ private static OtlpMetrics.Exemplar ToOtlpExemplar(this IExemplar exemplar)
         return otlpExemplar;
     }
     */
-
-    private static Action<RepeatedField<OtlpMetrics.Metric>, int> CreateRepeatedFieldOfMetricSetCountAction()
-    {
-        FieldInfo repeatedFieldOfMetricCountField = typeof(RepeatedField<OtlpMetrics.Metric>).GetField("count", BindingFlags.NonPublic | BindingFlags.Instance);
-
-        DynamicMethod dynamicMethod = new DynamicMethod(
-            "CreateSetCountAction",
-            null,
-            new[] { typeof(RepeatedField<OtlpMetrics.Metric>), typeof(int) },
-            typeof(MetricItemExtensions).Module,
-            skipVisibility: true);
-
-        var generator = dynamicMethod.GetILGenerator();
-
-        generator.Emit(OpCodes.Ldarg_0);
-        generator.Emit(OpCodes.Ldarg_1);
-        generator.Emit(OpCodes.Stfld, repeatedFieldOfMetricCountField);
-        generator.Emit(OpCodes.Ret);
-
-        return (Action<RepeatedField<OtlpMetrics.Metric>, int>)dynamicMethod.CreateDelegate(typeof(Action<RepeatedField<OtlpMetrics.Metric>, int>));
-    }
 }

test/OpenTelemetry.AotCompatibility.TestApp/OpenTelemetry.AotCompatibility.TestApp.csproj

@@ -17,6 +17,7 @@
     <TrimmerRootAssembly Include="OpenTelemetry.Api" />
     <TrimmerRootAssembly Include="OpenTelemetry.Exporter.Console" />
     <TrimmerRootAssembly Include="OpenTelemetry.Exporter.InMemory" />
+    <TrimmerRootAssembly Include="OpenTelemetry.Exporter.OpenTelemetryProtocol" />
     <TrimmerRootAssembly Include="OpenTelemetry.Exporter.Prometheus.AspNetCore" />
     <TrimmerRootAssembly Include="OpenTelemetry.Exporter.Prometheus.HttpListener" />
     <TrimmerRootAssembly Include="OpenTelemetry.Exporter.Zipkin" />