Make Extensions linker friendly.

src/libraries/Common/src/Extensions/ProviderAliasUtilities/ProviderAliasUtilities.cs

@@ -2,28 +2,26 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics;
 using System.Reflection;
 
 namespace Microsoft.Extensions.Logging
 {
     internal static class ProviderAliasUtilities
     {
         private const string AliasAttibuteTypeFullName = "Microsoft.Extensions.Logging.ProviderAliasAttribute";
-        private const string AliasAttibuteAliasProperty = "Alias";
 
         internal static string GetAlias(Type providerType)
         {
-            foreach (object attribute in providerType.GetTypeInfo().GetCustomAttributes(inherit: false))
+            foreach (CustomAttributeData attributeData in CustomAttributeData.GetCustomAttributes(providerType))
             {
-                if (attribute.GetType().FullName == AliasAttibuteTypeFullName)
+                if (attributeData.AttributeType.FullName == AliasAttibuteTypeFullName)
                 {
-                    PropertyInfo valueProperty = attribute
-                        .GetType()
-                        .GetProperty(AliasAttibuteAliasProperty, BindingFlags.Public | BindingFlags.Instance);
-
-                    if (valueProperty != null)
+                    foreach (CustomAttributeTypedArgument arg in attributeData.ConstructorArguments)
                     {
-                        return valueProperty.GetValue(attribute) as string;
+                        Debug.Assert(arg.ArgumentType == typeof(string));
+
+                        return arg.Value?.ToString();
                     }
                 }
             }

src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/Microsoft.Extensions.Hosting.Abstractions.csproj

@@ -1,11 +1,16 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFrameworks>netstandard2.1;netstandard2.0;net461</TargetFrameworks>
     <RootNamespace>Microsoft.Extensions.Hosting</RootNamespace>
     <EnableDefaultItems>true</EnableDefaultItems>
   </PropertyGroup>
 
+  <ItemGroup>
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMembersAttribute.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.DependencyInjection.Abstractions\src\Microsoft.Extensions.DependencyInjection.Abstractions.csproj" />

src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/ServiceCollectionHostedServiceExtensions.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.Hosting;
 
@@ -15,7 +16,7 @@ public static class ServiceCollectionHostedServiceExtensions
         /// <typeparam name="THostedService">An <see cref="IHostedService"/> to register.</typeparam>
         /// <param name="services">The <see cref="IServiceCollection"/> to register with.</param>
         /// <returns>The original <see cref="IServiceCollection"/>.</returns>
-        public static IServiceCollection AddHostedService<THostedService>(this IServiceCollection services)
+        public static IServiceCollection AddHostedService<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] THostedService>(this IServiceCollection services)
             where THostedService : class, IHostedService
         {
             services.TryAddEnumerable(ServiceDescriptor.Singleton<IHostedService, THostedService>());

src/libraries/Microsoft.Extensions.Hosting/tests/TrimmingTests/AddHostedServiceTests.cs

@@ -0,0 +1,34 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using System.Threading;
+using System.Threading.Tasks;
+
+class Program
+{
+    static int Main(string[] args)
+    {
+        IServiceCollection descriptors = new ServiceCollection();
+        descriptors.AddHostedService<MyHost>();
+
+        ServiceProvider provider = descriptors.BuildServiceProvider();
+
+        foreach (IHostedService h in provider.GetServices<IHostedService>())
+        {
+            if (!(h is MyHost))
+            {
+                return -1;
+            }
+        }
+
+        return 100;
+    }
+
+    private class MyHost : IHostedService
+    {
+        public Task StartAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+        public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+    }
+}

src/libraries/Microsoft.Extensions.Hosting/tests/TrimmingTests/Microsoft.Extensions.Hosting.TrimmingTests.proj

@@ -0,0 +1,13 @@
+<Project DefaultTargets="Build">
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.props))" />
+
+  <PropertyGroup>
+    <AdditionalProjectReferences>Microsoft.Extensions.Hosting.Abstractions;Microsoft.Extensions.DependencyInjection</AdditionalProjectReferences>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <TestConsoleAppSourceFiles Include="AddHostedServiceTests.cs" />
+  </ItemGroup>
+
+  <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.targets))" />
+</Project>

src/libraries/Microsoft.Extensions.Http/Microsoft.Extensions.Http.sln

@@ -13,10 +13,10 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Http",
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Http", "src\Microsoft.Extensions.Http.csproj", "{A50C941B-09D7-4AB4-85AF-D02E6F96885A}"
 EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Http.Tests", "tests\Microsoft.Extensions.Http.Tests.csproj", "{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7}"
-EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TestUtilities", "..\Common\tests\TestUtilities\TestUtilities.csproj", "{92E18BB1-B630-4B03-9B05-47F31D1BF94A}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Extensions.Http.Tests", "tests\Microsoft.Extensions.Http.Tests\Microsoft.Extensions.Http.Tests.csproj", "{7DADD323-891C-4EA7-8906-6BC4009FA083}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -31,23 +31,23 @@ Global
 		{A50C941B-09D7-4AB4-85AF-D02E6F96885A}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{A50C941B-09D7-4AB4-85AF-D02E6F96885A}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{A50C941B-09D7-4AB4-85AF-D02E6F96885A}.Release|Any CPU.Build.0 = Release|Any CPU
-		{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7}.Release|Any CPU.Build.0 = Release|Any CPU
 		{92E18BB1-B630-4B03-9B05-47F31D1BF94A}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{92E18BB1-B630-4B03-9B05-47F31D1BF94A}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{92E18BB1-B630-4B03-9B05-47F31D1BF94A}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{92E18BB1-B630-4B03-9B05-47F31D1BF94A}.Release|Any CPU.Build.0 = Release|Any CPU
+		{7DADD323-891C-4EA7-8906-6BC4009FA083}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{7DADD323-891C-4EA7-8906-6BC4009FA083}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{7DADD323-891C-4EA7-8906-6BC4009FA083}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{7DADD323-891C-4EA7-8906-6BC4009FA083}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{183E40F1-33A4-461D-AADF-4CF59FB93CCA} = {B51DC955-13A6-41ED-A6C7-DDAB98911513}
 		{A50C941B-09D7-4AB4-85AF-D02E6F96885A} = {0517D0EB-1ED7-420A-A7D7-9A167C102ED2}
-		{C9FE0B1E-35F6-4AFE-A9A6-DA6C1B88C1E7} = {9DE482AA-076A-4EB1-821F-EE2A4A230B4A}
 		{92E18BB1-B630-4B03-9B05-47F31D1BF94A} = {9DE482AA-076A-4EB1-821F-EE2A4A230B4A}
+		{7DADD323-891C-4EA7-8906-6BC4009FA083} = {9DE482AA-076A-4EB1-821F-EE2A4A230B4A}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {F300086C-E02A-417C-8659-59AA5139E68A}

src/libraries/Microsoft.Extensions.Http/src/DefaultTypedHttpClientFactory.cs

@@ -2,13 +2,15 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Net.Http;
 using System.Threading;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace Microsoft.Extensions.Http
 {
-    internal class DefaultTypedHttpClientFactory<TClient> : ITypedHttpClientFactory<TClient>
+    internal class DefaultTypedHttpClientFactory<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient> :
+        ITypedHttpClientFactory<TClient>
     {
         private readonly Cache _cache;
         private readonly IServiceProvider _services;

src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientBuilderExtensions.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Net.Http;
 using System.Threading;
@@ -316,7 +317,8 @@ public static IHttpClientBuilder ConfigureHttpMessageHandlerBuilder(this IHttpCl
         /// scope bound to the message handler, which is managed independently.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddTypedClient<TClient>(this IHttpClientBuilder builder)
+        public static IHttpClientBuilder AddTypedClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IHttpClientBuilder builder)
             where TClient : class
         {
             if (builder == null)
@@ -327,7 +329,8 @@ public static IHttpClientBuilder AddTypedClient<TClient>(this IHttpClientBuilder
             return AddTypedClientCore<TClient>(builder, validateSingleType: false);
         }
 
-        internal static IHttpClientBuilder AddTypedClientCore<TClient>(this IHttpClientBuilder builder, bool validateSingleType)
+        internal static IHttpClientBuilder AddTypedClientCore<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IHttpClientBuilder builder, bool validateSingleType)
             where TClient : class
         {
             ReserveClient(builder, typeof(TClient), builder.Name, validateSingleType);
@@ -375,7 +378,8 @@ internal static IHttpClientBuilder AddTypedClientCore<TClient>(this IHttpClientB
         /// scope bound to the message handler, which is managed independently.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddTypedClient<TClient, TImplementation>(this IHttpClientBuilder builder)
+        public static IHttpClientBuilder AddTypedClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IHttpClientBuilder builder)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -387,7 +391,8 @@ public static IHttpClientBuilder AddTypedClient<TClient, TImplementation>(this I
             return AddTypedClientCore<TClient, TImplementation>(builder, validateSingleType: false);
         }
 
-        internal static IHttpClientBuilder AddTypedClientCore<TClient, TImplementation>(this IHttpClientBuilder builder, bool validateSingleType)
+        internal static IHttpClientBuilder AddTypedClientCore<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IHttpClientBuilder builder, bool validateSingleType)
             where TClient : class
             where TImplementation : class, TClient
         {

src/libraries/Microsoft.Extensions.Http/src/DependencyInjection/HttpClientFactoryServiceCollectionExtensions.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Net.Http;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.Http;
@@ -198,7 +199,8 @@ public static IHttpClientBuilder AddHttpClient(this IServiceCollection services,
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services)
             where TClient : class
         {
             if (services == null)
@@ -240,7 +242,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -282,7 +285,8 @@ public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IS
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services, string name)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services, string name)
             where TClient : class
         {
             if (services == null)
@@ -332,7 +336,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services, string name)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services, string name)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -376,7 +381,8 @@ public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IS
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services, Action<HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services, Action<HttpClient> configureClient)
             where TClient : class
         {
             if (services == null)
@@ -421,7 +427,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services, Action<IServiceProvider, HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services, Action<IServiceProvider, HttpClient> configureClient)
             where TClient : class
         {
             if (services == null)
@@ -470,7 +477,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services, Action<HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services, Action<HttpClient> configureClient)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -520,7 +528,8 @@ public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IS
         /// <typeparamref name="TClient"/> as the service type.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services, Action<IServiceProvider, HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services, Action<IServiceProvider, HttpClient> configureClient)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -569,7 +578,8 @@ public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IS
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services, string name, Action<HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services, string name, Action<HttpClient> configureClient)
             where TClient : class
         {
             if (services == null)
@@ -621,7 +631,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection services, string name, Action<IServiceProvider, HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TClient>(
+            this IServiceCollection services, string name, Action<IServiceProvider, HttpClient> configureClient)
             where TClient : class
         {
             if (services == null)
@@ -677,7 +688,8 @@ public static IHttpClientBuilder AddHttpClient<TClient>(this IServiceCollection
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services, string name, Action<HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services, string name, Action<HttpClient> configureClient)
             where TClient : class
             where TImplementation : class, TClient
         {
@@ -734,7 +746,8 @@ public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IS
         /// Use <see cref="Options.Options.DefaultName"/> as the name to configure the default client.
         /// </para>
         /// </remarks>
-        public static IHttpClientBuilder AddHttpClient<TClient, TImplementation>(this IServiceCollection services, string name, Action<IServiceProvider, HttpClient> configureClient)
+        public static IHttpClientBuilder AddHttpClient<TClient, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TImplementation>(
+            this IServiceCollection services, string name, Action<IServiceProvider, HttpClient> configureClient)
             where TClient : class
             where TImplementation : class, TClient
         {