Add GlobalPropagators API and have instrumentation default to it

src/OpenTelemetry.Api/Context/Propagation/NoOpTextMapPropagator.cs

@@ -0,0 +1,37 @@
+// <copyright file="Propagators.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+using System;
+using System.Collections.Generic;
+
+namespace OpenTelemetry.Context.Propagation
+{
+    internal class NoOpTextMapPropagator : TextMapPropagator
+    {
+        private static PropagationContext defaultPropagationContext = default;
+
+        public override ISet<string> Fields => null;
+
+        public override PropagationContext Extract<T>(PropagationContext context, T carrier, Func<T, string, IEnumerable<string>> getter)
+        {
+            return defaultPropagationContext;
+        }
+
+        public override void Inject<T>(PropagationContext context, T carrier, Action<T, string, string> setter)
+        {
+        }
+    }
+}

src/OpenTelemetry.Api/Context/Propagation/Propagators.cs

@@ -0,0 +1,34 @@
+// <copyright file="Propagators.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+namespace OpenTelemetry.Context.Propagation
+{
+    /// <summary>
+    /// Propagators allow setting the global default Propagators.
+    /// </summary>
+    public static class Propagators
+    {
+        /// <summary>
+        /// Gets or sets the Default TextMapPropagator to be used.
+        /// </summary>
+        public static TextMapPropagator DefaultTextMapPropagator { get; set; } = new NoOpTextMapPropagator();
+
+        internal static void Reset()
+        {
+            DefaultTextMapPropagator = new NoOpTextMapPropagator();
+        }
+    }
+}

src/OpenTelemetry.Instrumentation.AspNet/AspNetInstrumentationOptions.cs

@@ -27,13 +27,10 @@ namespace OpenTelemetry.Instrumentation.AspNet
     public class AspNetInstrumentationOptions
     {
         /// <summary>
-        /// Gets or sets <see cref="TextMapPropagator"/> for context propagation. Default value: <see cref="CompositeTextMapPropagator"/> with <see cref="TraceContextPropagator"/> &amp; <see cref="BaggagePropagator"/>.
+        /// Gets or sets <see cref="TextMapPropagator"/> for context propagation.
+        /// By default, <see cref="Propagators.DefaultTextMapPropagator" /> will be used.
         /// </summary>
-        public TextMapPropagator Propagator { get; set; } = new CompositeTextMapPropagator(new TextMapPropagator[]
-        {
-            new TraceContextPropagator(),
-            new BaggagePropagator(),
-        });
+        public TextMapPropagator Propagator { get; set; } = Propagators.DefaultTextMapPropagator;
 
         /// <summary>
         /// Gets or sets a Filter function to filter instrumentation for requests on a per request basis.

src/OpenTelemetry.Instrumentation.AspNetCore/AspNetCoreInstrumentationOptions.cs

@@ -27,13 +27,10 @@ namespace OpenTelemetry.Instrumentation.AspNetCore
     public class AspNetCoreInstrumentationOptions
     {
         /// <summary>
-        /// Gets or sets <see cref="TextMapPropagator"/> for context propagation. Default value: <see cref="CompositeTextMapPropagator"/> with <see cref="TraceContextPropagator"/> &amp; <see cref="BaggagePropagator"/>.
+        /// Gets or sets <see cref="TextMapPropagator"/> for context propagation.
+        /// By default, <see cref="Propagators.DefaultTextMapPropagator" /> will be used.
         /// </summary>
-        public TextMapPropagator Propagator { get; set; } = new CompositeTextMapPropagator(new TextMapPropagator[]
-        {
-            new TraceContextPropagator(),
-            new BaggagePropagator(),
-        });
+        public TextMapPropagator Propagator { get; set; } = Propagators.DefaultTextMapPropagator;
 
         /// <summary>
         /// Gets or sets a Filter function to filter instrumentation for requests on a per request basis.

src/OpenTelemetry.Instrumentation.Http/HttpClientInstrumentationOptions.cs

@@ -35,13 +35,10 @@ public class HttpClientInstrumentationOptions
         public bool SetHttpFlavor { get; set; }
 
         /// <summary>
-        /// Gets or sets <see cref="TextMapPropagator"/> for context propagation. Default value: <see cref="CompositeTextMapPropagator"/> with <see cref="TraceContextPropagator"/> &amp; <see cref="BaggagePropagator"/>.
+        /// Gets or sets <see cref="TextMapPropagator"/> for context propagation.
+        /// By default, <see cref="Propagators.DefaultTextMapPropagator" /> will be used.
         /// </summary>
-        public TextMapPropagator Propagator { get; set; } = new CompositeTextMapPropagator(new TextMapPropagator[]
-        {
-            new TraceContextPropagator(),
-            new BaggagePropagator(),
-        });
+        public TextMapPropagator Propagator { get; set; } = Propagators.DefaultTextMapPropagator;
 
         /// <summary>
         /// Gets or sets a Filter function to filter instrumentation for requests on a per request basis.

src/OpenTelemetry/Logs/OpenTelemetryLoggerProvider.cs

@@ -31,6 +31,13 @@ public class OpenTelemetryLoggerProvider : ILoggerProvider, ISupportExternalScop
         private bool disposed;
         private IExternalScopeProvider scopeProvider;
 
+        static OpenTelemetryLoggerProvider()
+        {
+            // Accessing Sdk class is just to trigger its static ctor,
+            // which sets default Propagators.
+            _ = Sdk.SuppressInstrumentation;
+        }
+
         public OpenTelemetryLoggerProvider(IOptionsMonitor<OpenTelemetryLoggerOptions> options)
             : this(options?.CurrentValue)
         {

src/OpenTelemetry/Sdk.cs

@@ -14,6 +14,7 @@
 // limitations under the License.
 // </copyright>
 
+using OpenTelemetry.Context.Propagation;
 using OpenTelemetry.Metrics;
 using OpenTelemetry.Trace;
 
@@ -24,6 +25,15 @@ namespace OpenTelemetry
     /// </summary>
     public static class Sdk
     {
+        static Sdk()
+        {
+            Propagators.DefaultTextMapPropagator = new CompositeTextMapPropagator(new TextMapPropagator[]
+            {
+                new TraceContextPropagator(),
+                new BaggagePropagator(),
+            });
+        }
+
         /// <summary>
         /// Gets a value indicating whether instrumentation is suppressed (disabled).
         /// </summary>

test/OpenTelemetry.Instrumentation.AspNetCore.Tests/BasicTests.cs

@@ -58,6 +58,21 @@ public void AddAspNetCoreInstrumentation_BadArgs()
             Assert.Throws<ArgumentNullException>(() => builder.AddAspNetCoreInstrumentation());
         }
 
+        [Fact]
+        public void DefaultPropagatorIsFromPropagators()
+        {
+            var options = new AspNetCoreInstrumentationOptions();
+            Assert.Same(Propagators.DefaultTextMapPropagator, options.Propagator);
+        }
+
+        [Fact]
+        public void PropagatorSetDoesNotAffectGlobalPropagators()
+        {
+            var options = new AspNetCoreInstrumentationOptions();
+            options.Propagator = new TraceContextPropagator();
+            Assert.NotSame(Propagators.DefaultTextMapPropagator, options.Propagator);
+        }
+
         [Fact]
         public async Task StatusIsUnsetOn200Response()
         {

test/OpenTelemetry.Tests/Context/PropagatorsTest.cs

@@ -0,0 +1,46 @@
+// <copyright file="PropagatorsTest.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+using System;
+using OpenTelemetry.Context.Propagation;
+using OpenTelemetry.Context.Propagation.Tests;
+using Xunit;
+
+namespace OpenTelemetry.Context.Tests
+{
+    public class PropagatorsTest : IDisposable
+    {
+        [Fact]
+        public static void DefaultTextMapPropagatorIsNoop()
+        {
+            Assert.IsType<NoOpTextMapPropagator>(Propagators.DefaultTextMapPropagator);
+            Assert.Same(Propagators.DefaultTextMapPropagator, Propagators.DefaultTextMapPropagator);
+        }
+
+        [Fact]
+        public static void CanSetPropagator()
+        {
+            var testPropagator = new TestPropagator(string.Empty, string.Empty);
+            Propagators.DefaultTextMapPropagator = testPropagator;
+            Assert.Same(testPropagator, Propagators.DefaultTextMapPropagator);
+        }
+
+        public void Dispose()
+        {
+            Propagators.Reset();
+        }
+    }
+}