Use prototype Roslyn compiler for runtime-async

NuGet.config

@@ -19,6 +19,8 @@
     <add key="dotnet-libraries-transport" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-libraries-transport/nuget/v3/index.json" />
     <add key="dotnet10" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet10/nuget/v3/index.json" />
     <add key="dotnet10-transport" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet10-transport/nuget/v3/index.json" />
+    <!-- Need for prototype Roslyn compiler for runtime-async -->
+    <add key="general-testing" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/general-testing/nuget/v3/index.json" />
   </packageSources>
   <auditSources>
     <clear />

src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.cs

@@ -4,6 +4,7 @@
 using System.Diagnostics;
 using System.Reflection;
 using System.Runtime.InteropServices;
+using System.Runtime.Versioning;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -19,6 +20,7 @@ public static partial class AsyncHelpers
         // It will not capture/restore any local state that is live across it.
         [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
+        [RequiresPreviewFeatures]
         public static void AwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : INotifyCompletion
         {
             ref AsyncHelpers.RuntimeAsyncAwaitState state = ref AsyncHelpers.t_runtimeAsyncAwaitState;
@@ -34,6 +36,7 @@ public static void AwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : INo
         // It will not capture/restore any local state that is live across it.
         [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.Async)]
+        [RequiresPreviewFeatures]
         public static void UnsafeAwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : ICriticalNotifyCompletion
         {
             ref AsyncHelpers.RuntimeAsyncAwaitState state = ref AsyncHelpers.t_runtimeAsyncAwaitState;
@@ -48,6 +51,7 @@ public static void UnsafeAwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter
         [Intrinsic]
         [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
+        [RequiresPreviewFeatures]
         public static T Await<T>(Task<T> task)
         {
             TaskAwaiter<T> awaiter = task.GetAwaiter();
@@ -62,6 +66,7 @@ public static T Await<T>(Task<T> task)
         [Intrinsic]
         [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
+        [RequiresPreviewFeatures]
         public static void Await(Task task)
         {
             TaskAwaiter awaiter = task.GetAwaiter();
@@ -76,6 +81,7 @@ public static void Await(Task task)
         [Intrinsic]
         [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
+        [RequiresPreviewFeatures]
         public static T Await<T>(ValueTask<T> task)
         {
             ValueTaskAwaiter<T> awaiter = task.GetAwaiter();
@@ -90,6 +96,7 @@ public static T Await<T>(ValueTask<T> task)
         [Intrinsic]
         [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
+        [RequiresPreviewFeatures]
         public static void Await(ValueTask task)
         {
             ValueTaskAwaiter awaiter = task.GetAwaiter();
@@ -104,6 +111,7 @@ public static void Await(ValueTask task)
         [Intrinsic]
         [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
+        [RequiresPreviewFeatures]
         public static void Await(ConfiguredTaskAwaitable configuredAwaitable)
         {
             ConfiguredTaskAwaitable.ConfiguredTaskAwaiter awaiter = configuredAwaitable.GetAwaiter();
@@ -118,6 +126,7 @@ public static void Await(ConfiguredTaskAwaitable configuredAwaitable)
         [Intrinsic]
         [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
+        [RequiresPreviewFeatures]
         public static void Await(ConfiguredValueTaskAwaitable configuredAwaitable)
         {
             ConfiguredValueTaskAwaitable.ConfiguredValueTaskAwaiter awaiter = configuredAwaitable.GetAwaiter();
@@ -132,6 +141,7 @@ public static void Await(ConfiguredValueTaskAwaitable configuredAwaitable)
         [Intrinsic]
         [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
+        [RequiresPreviewFeatures]
         public static T Await<T>(ConfiguredTaskAwaitable<T> configuredAwaitable)
         {
             ConfiguredTaskAwaitable<T>.ConfiguredTaskAwaiter awaiter = configuredAwaitable.GetAwaiter();
@@ -146,6 +156,7 @@ public static T Await<T>(ConfiguredTaskAwaitable<T> configuredAwaitable)
         [Intrinsic]
         [BypassReadyToRun]
         [MethodImpl(MethodImplOptions.Async)]
+        [RequiresPreviewFeatures]
         public static T Await<T>(ConfiguredValueTaskAwaitable<T> configuredAwaitable)
         {
             ConfiguredValueTaskAwaitable<T>.ConfiguredValueTaskAwaiter awaiter = configuredAwaitable.GetAwaiter();
@@ -157,15 +168,25 @@ public static T Await<T>(ConfiguredValueTaskAwaitable<T> configuredAwaitable)
             return awaiter.GetResult();
         }
 #else
+        [RequiresPreviewFeatures]
         public static void UnsafeAwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : ICriticalNotifyCompletion { throw new NotImplementedException(); }
+        [RequiresPreviewFeatures]
         public static void AwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : INotifyCompletion { throw new NotImplementedException(); }
+        [RequiresPreviewFeatures]
         public static void Await(System.Threading.Tasks.Task task) { throw new NotImplementedException(); }
+        [RequiresPreviewFeatures]
         public static T Await<T>(System.Threading.Tasks.Task<T> task) { throw new NotImplementedException(); }
+        [RequiresPreviewFeatures]
         public static void Await(System.Threading.Tasks.ValueTask task) { throw new NotImplementedException(); }
+        [RequiresPreviewFeatures]
         public static T Await<T>(System.Threading.Tasks.ValueTask<T> task) { throw new NotImplementedException(); }
+        [RequiresPreviewFeatures]
         public static void Await(System.Runtime.CompilerServices.ConfiguredTaskAwaitable configuredAwaitable) { throw new NotImplementedException(); }
+        [RequiresPreviewFeatures]
         public static void Await(System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable configuredAwaitable) { throw new NotImplementedException(); }
+        [RequiresPreviewFeatures]
         public static T Await<T>(System.Runtime.CompilerServices.ConfiguredTaskAwaitable<T> configuredAwaitable) { throw new NotImplementedException(); }
+        [RequiresPreviewFeatures]
         public static T Await<T>(System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable<T> configuredAwaitable) { throw new NotImplementedException(); }
 #endif
     }

src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeFeature.cs

@@ -54,7 +54,15 @@ public static bool IsSupported(string feature)
         {
             return feature switch
             {
-                PortablePdb or CovariantReturnsOfClasses or ByRefFields or ByRefLikeGenerics or UnmanagedSignatureCallingConvention or DefaultImplementationsOfInterfaces or VirtualStaticsInInterfaces or NumericIntPtr => true,
+                PortablePdb or
+                CovariantReturnsOfClasses or
+                ByRefFields or
+                ByRefLikeGenerics or
+                UnmanagedSignatureCallingConvention or
+                DefaultImplementationsOfInterfaces or
+                VirtualStaticsInInterfaces or
+                NumericIntPtr or
+
                 nameof(IsDynamicCodeSupported) => IsDynamicCodeSupported,
                 nameof(IsDynamicCodeCompiled) => IsDynamicCodeCompiled,
                 _ => false,

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -13832,15 +13832,25 @@ public static void RunModuleConstructor(System.ModuleHandle module) { }
     [System.Diagnostics.CodeAnalysis.ExperimentalAttribute("SYSLIB5007", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
     public static partial class AsyncHelpers
     {
+        [System.Runtime.Versioning.RequiresPreviewFeaturesAttribute]
         public static void UnsafeAwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : ICriticalNotifyCompletion { }
+        [System.Runtime.Versioning.RequiresPreviewFeaturesAttribute]
         public static void AwaitAwaiter<TAwaiter>(TAwaiter awaiter) where TAwaiter : INotifyCompletion { }
+        [System.Runtime.Versioning.RequiresPreviewFeaturesAttribute]
         public static void Await(System.Threading.Tasks.Task task) { throw null; }
+        [System.Runtime.Versioning.RequiresPreviewFeaturesAttribute]
         public static T Await<T>(System.Threading.Tasks.Task<T> task) { throw null; }
+        [System.Runtime.Versioning.RequiresPreviewFeaturesAttribute]
         public static void Await(System.Threading.Tasks.ValueTask task) { throw null; }
+        [System.Runtime.Versioning.RequiresPreviewFeaturesAttribute]
         public static T Await<T>(System.Threading.Tasks.ValueTask<T> task) { throw null; }
+        [System.Runtime.Versioning.RequiresPreviewFeaturesAttribute]
         public static void Await(System.Runtime.CompilerServices.ConfiguredTaskAwaitable configuredAwaitable) { throw null; }
+        [System.Runtime.Versioning.RequiresPreviewFeaturesAttribute]
         public static void Await(System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable configuredAwaitable) { throw null; }
+        [System.Runtime.Versioning.RequiresPreviewFeaturesAttribute]
         public static T Await<T>(System.Runtime.CompilerServices.ConfiguredTaskAwaitable<T> configuredAwaitable) { throw null; }
+        [System.Runtime.Versioning.RequiresPreviewFeaturesAttribute]
         public static T Await<T>(System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable<T> configuredAwaitable) { throw null; }
     }
     public sealed partial class RuntimeWrappedException : System.Exception

src/tests/Directory.Build.props

@@ -8,6 +8,11 @@
   <Import Project="$(MSBuildThisFileDirectory)\Common\dir.sdkbuild.props" Condition="'$(UsingMicrosoftNETSdk)' == 'true'"  />
   <Import Project="$(MSBuildThisFileDirectory)\Common\dir.common.props" Condition="'$(UsingMicrosoftNETSdk)' != 'true'"  />
 
+  <PropertyGroup>
+    <!-- Override the compiler version with a private build that supports runtime-async -->
+    <MicrosoftNetCompilersToolsetVersion>5.0.0-1.25259.6</MicrosoftNetCompilersToolsetVersion>
+  </PropertyGroup>
+
   <PropertyGroup>
     <RunningOnUnix Condition="('$(RunningOnUnix)' == '') And ('$(MSBuildRuntimeType)' == 'Core') And ('$(OS)'!='Windows_NT')">true</RunningOnUnix>
   </PropertyGroup>

src/tests/async/Directory.Build.props

@@ -7,5 +7,9 @@
     <RunAnalyzers>true</RunAnalyzers>
     <NoWarn>$(NoWarn);xUnit1013</NoWarn>
     <EnableNETAnalyzers>false</EnableNETAnalyzers>
+    <Features>$(Features);runtime-async=on</Features>
   </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="$(MSBuildThisFileDirectory)RuntimeAsyncMethodGenerationAttribute.cs" />
+  </ItemGroup>
 </Project>

src/tests/async/RuntimeAsyncMethodGenerationAttribute.cs

@@ -0,0 +1,6 @@
+namespace System.Runtime.CompilerServices;
+[AttributeUsage(AttributeTargets.Method)]
+public class RuntimeAsyncMethodGenerationAttribute(bool runtimeAsync) : Attribute
+{
+    public bool RuntimeAsync { get; } = runtimeAsync;
+}

src/tests/async/awaitingnotasync/awaitingnotasync.cs

@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
 using System.Threading.Tasks;
 using Xunit;
 
@@ -14,13 +13,15 @@ public static void TestEntryPoint()
         AsyncEntryPoint().Wait();
     }
 
+    [System.Runtime.CompilerServices.RuntimeAsyncMethodGeneration(false)]
     private static async Task<T> GetTask<T>(T arg)
     {
         await Task.Yield();
         return arg;
     }
 
     // TODO: switch every other scenario to use ValueTask
+    [System.Runtime.CompilerServices.RuntimeAsyncMethodGeneration(false)]
     private static async ValueTask<T> GetValueTask<T>(T arg)
     {
         await Task.Yield();
@@ -33,13 +34,13 @@ private static async ValueTask<T> GetValueTask<T>(T arg)
 
     private static T sIdentity<T>(T arg) => arg;
 
-    private static async2 Task AsyncEntryPoint()
+    private static async Task AsyncEntryPoint()
     {
         // static field
         sField = GetTask(5);
         Assert.Equal(5, await sField);
 
-        // property 
+        // property
         Assert.Equal(6, await sProp);
 
         // generic identity

src/tests/async/collectible-alc/collectible-alc.cs

@@ -17,7 +17,7 @@ public static void TestEntryPoint()
         AsyncEntryPoint().Wait();
     }
 
-    private static async2 Task AsyncEntryPoint()
+    private static async Task AsyncEntryPoint()
     {
         WeakReference wr = await CallFooAsyncAndUnload();
 
@@ -31,7 +31,7 @@ private static async2 Task AsyncEntryPoint()
     }
 
     [MethodImpl(MethodImplOptions.NoInlining)]
-    private static async2 Task<WeakReference> CallFooAsyncAndUnload()
+    private static async Task<WeakReference> CallFooAsyncAndUnload()
     {
         TaskCompletionSource tcs = new();
         (Task<string> task, WeakReference wr) = CallFooAsyncInCollectibleALC(tcs.Task);
@@ -63,7 +63,7 @@ private static (Task<string>, WeakReference) CallFooAsyncInCollectibleALC(Task t
     }
 
     // Task[] to work around a compiler bug
-    private static async2 Task<string> FooAsync(Task[] t)
+    private static async Task<string> FooAsync(Task[] t)
     {
         await t[0];
         return "done";

src/tests/async/collectible-alc/collectible-alc.csproj

@@ -3,6 +3,7 @@
     <!-- For collectible ALC -->
     <RequiresProcessIsolation>True</RequiresProcessIsolation>
     <Optimize>True</Optimize>
+    <Features>$(Features);runtime-async</Features>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).cs" />

src/tests/async/cse-array-index-byref/cse-array-index-byref.cs

@@ -16,13 +16,14 @@ public static void TestEntryPoint()
         Assert.Equal(199_990_000, arr[0]);
     }
 
+    [System.Runtime.CompilerServices.RuntimeAsyncMethodGeneration(false)]
     private static async Task AsyncTestEntryPoint(int[] arr, int index)
     {
         await HoistedByref(arr, index);
     }
 
     [MethodImpl(MethodImplOptions.NoInlining)]
-    private static async2 Task<int> HoistedByref(int[] arr, int index)
+    private static async Task<int> HoistedByref(int[] arr, int index)
     {
         for (int i = 0; i < 20000; i++)
         {

src/tests/async/eh-microbench/eh-microbench.cs

@@ -24,6 +24,7 @@ public static int Main()
         return 100;
     }
 
+    [System.Runtime.CompilerServices.RuntimeAsyncMethodGeneration(false)]
     public static async Task AsyncEntry()
     {
         if (!GCSettings.IsServerGC)
@@ -68,6 +69,7 @@ public static async Task AsyncEntry()
         await RunBench(yieldFrequency, depth, finallyRate, throwOrReturn, "ValueTask");
     }
 
+    [System.Runtime.CompilerServices.RuntimeAsyncMethodGeneration(false)]
     private static async Task RunBench(int yieldCount, int depth, int finallyRate, bool throwOrReturn, string type)
     {
 
@@ -104,7 +106,7 @@ public Benchmark(int yieldCount, int depth, int finallyRate, bool throwOrReturn)
             _throwOrReturn = throwOrReturn;
         }
 
-        public async2 Task<long> Run(string type)
+        public async Task<long> Run(string type)
         {
             if (type == "Async2")
                 return await RunAsync2(_depth);
@@ -117,6 +119,7 @@ public async2 Task<long> Run(string type)
             return 0;
         }
 
+        [System.Runtime.CompilerServices.RuntimeAsyncMethodGeneration(false)]
         public async Task<long> RunTask(int depth)
         {
             int liveState1 = depth * 3 + _yieldCount;
@@ -182,6 +185,7 @@ public async Task<long> RunTask(int depth)
             return result;
         }
 
+        [System.Runtime.CompilerServices.RuntimeAsyncMethodGeneration(false)]
         public async ValueTask<long> RunValueTask(int depth)
         {
             int liveState1 = depth * 3 + _yieldCount;
@@ -267,7 +271,7 @@ public class FakeThread
         // This case is used to test the impact of save/restore of the sync and execution context on performance
         // The intent here is to measure what the performance impact of maintaining the current async semantics with
         // the new implementation.
-        public async2 Task<long> RunAsync2WithContextSaveRestore(int depth)
+        public async Task<long> RunAsync2WithContextSaveRestore(int depth)
         {
             FakeThread thread = CurrentThread;
             if (thread == null)
@@ -361,7 +365,7 @@ public async2 Task<long> RunAsync2WithContextSaveRestore(int depth)
             }
         }
 
-        public async2 Task<long> RunAsync2(int depth)
+        public async Task<long> RunAsync2(int depth)
         {
             int liveState1 = depth * 3 + _yieldCount;
             int liveState2 = depth;

src/tests/async/fibonacci-with-yields/fibonacci-with-yields.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Runtime.CompilerServices;
 using System.Threading.Tasks;
 using System.Diagnostics;
 using Xunit;
@@ -22,7 +23,7 @@ public static void Test()
         System.Console.WriteLine("allocated: " + allocated);
     }
 
-    public static async2 Task AsyncEntry()
+    public static async Task AsyncEntry()
     {
         for (int i = 0; i < iterations; i++)
         {
@@ -34,7 +35,7 @@ public static async2 Task AsyncEntry()
         }
     }
 
-    static async2 Task<int> Fib(int i)
+    static async Task<int> Fib(int i)
     {
         if (i <= 1)
         {

src/tests/async/fibonacci-with-yields/fibonacci-with-yields.csproj

@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <Optimize>True</Optimize>
+    <Features>$(Features);runtime-async</Features>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(MSBuildProjectName).cs" />