Add test coverage for Task/ValueTask-returning methods with __arglist

src/coreclr/inc/clrconfigvalues.h

@@ -710,7 +710,7 @@ RETAIL_CONFIG_DWORD_INFO(EXTERNAL_EnableRiscV64Zbb,             W("EnableRiscV64
 #endif
 
 // Runtime-async
-RETAIL_CONFIG_DWORD_INFO(UNSUPPORTED_RuntimeAsync, W("RuntimeAsync"), 0, "Enables runtime async method support")
+RETAIL_CONFIG_DWORD_INFO(UNSUPPORTED_RuntimeAsync, W("RuntimeAsync"), 1, "Enables runtime async method support")
 
 ///
 /// Uncategorized

src/coreclr/vm/methodtablebuilder.cpp

@@ -3301,6 +3301,23 @@ MethodTableBuilder::EnumerateClassMethods()
             }
         }
 
+        // Vararg methods are not allowed to be marked MethodImpl.Async
+        // and even when they return Tasks they are still treated as NormalMethod.
+        if (returnKind != MethodReturnKind::NormalMethod)
+        {
+            if (MetaSig::IsVarArg(Signature(pMemberSignature, cMemberSignature)))
+            {
+                if (IsMiAsync(dwImplFlags))
+                {
+                    BuildMethodTableThrowException(IDS_EE_VARARG_NOT_SUPPORTED);
+                }
+                else
+                {
+                    returnKind = MethodReturnKind::NormalMethod;
+                }
+            }
+        }
+
         //
         // Create a new bmtMDMethod representing this method and add it to the
         // declared method list.

src/tests/async/Directory.Build.targets

@@ -9,10 +9,5 @@
     <DisableProjectBuild Condition="'$(TestBuildMode)' == 'nativeaot' and '$(TargetArchitecture)' == 'arm64'">true</DisableProjectBuild>
   </PropertyGroup>
 
-  <PropertyGroup>
-    <!-- runtime async testing in main repo NYI -->
-    <DisableProjectBuild Condition="'$(TestBuildMode)' != 'nativeaot'">true</DisableProjectBuild>
-  </PropertyGroup>
-
   <Import Project="$([MSBuild]::GetPathOfFileAbove(Directory.Build.targets, $(MSBuildThisFileDirectory)..))" />
 </Project>

src/tests/async/varargs/varargs.cs

@@ -0,0 +1,80 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Runtime.CompilerServices;
+using System.Threading.Tasks;
+using Xunit;
+
+public class Async2Varargs
+{
+    [Fact]
+    public static void TestTaskDirectCall()
+    {
+        TaskWithArglist(42, __arglist(100, 200)).Wait();
+    }
+
+    [Fact]
+    public static void TestTaskAwait()
+    {
+        TestTaskAwaitAsync().Wait();
+    }
+
+    private static async Task TestTaskAwaitAsync()
+    {
+        await TaskWithArglist(42, __arglist(100, 200));
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static Task TaskWithArglist(int fixedArg, __arglist)
+    {
+        Assert.Equal(42, fixedArg);
+
+        ArgIterator args = new ArgIterator(__arglist);
+        Assert.Equal(2, args.GetRemainingCount());
+
+        int arg1 = __refvalue(args.GetNextArg(), int);
+        int arg2 = __refvalue(args.GetNextArg(), int);
+
+        Assert.Equal(100, arg1);
+        Assert.Equal(200, arg2);
+
+        return Task.CompletedTask;
+    }
+
+    [Fact]
+    public static void TestValueTaskDirectCall()
+    {
+        int result = ValueTaskWithArglist(42, __arglist(100, 200)).Result;
+        Assert.Equal(342, result);
+    }
+
+    [Fact]
+    public static void TestValueTaskAwait()
+    {
+        TestValueTaskAwaitAsync().Wait();
+    }
+
+    private static async Task TestValueTaskAwaitAsync()
+    {
+        int result = await ValueTaskWithArglist(42, __arglist(100, 200));
+        Assert.Equal(342, result);
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static ValueTask<int> ValueTaskWithArglist(int fixedArg, __arglist)
+    {
+        Assert.Equal(42, fixedArg);
+
+        ArgIterator args = new ArgIterator(__arglist);
+        Assert.Equal(2, args.GetRemainingCount());
+
+        int arg1 = __refvalue(args.GetNextArg(), int);
+        int arg2 = __refvalue(args.GetNextArg(), int);
+
+        Assert.Equal(100, arg1);
+        Assert.Equal(200, arg2);
+
+        return new ValueTask<int>(fixedArg + arg1 + arg2);
+    }
+}

src/tests/async/varargs/varargs.csproj

@@ -0,0 +1,5 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <ItemGroup>
+    <Compile Include="$(MSBuildProjectName).cs" />
+  </ItemGroup>
+</Project>