Separate CoreCLR-specific methods into partial struct

src/mscorlib/System.Private.CoreLib.csproj

@@ -491,6 +491,7 @@
     <Compile Include="$(BclSourcesRoot)\System\Threading\Tasks\ConcurrentExclusiveSchedulerPair.cs" />
     <Compile Include="$(BclSourcesRoot)\System\Threading\Tasks\ProducerConsumerQueues.cs" />
     <Compile Include="$(BclSourcesRoot)\System\Threading\Tasks\TPLETWProvider.cs" />
+    <Compile Include="$(BclSourcesRoot)\System\Threading\Tasks\ValueTask.CoreCLR.cs" />
     <Compile Condition="'$(FeatureCominterop)' == 'true'" Include="$(BclSourcesRoot)\System\Threading\Tasks\IAsyncCausalityTracerStatics.cs" />
   </ItemGroup>
   <ItemGroup>

src/mscorlib/shared/System/Threading/Tasks/ValueTask.cs

@@ -49,7 +49,7 @@ namespace System.Threading.Tasks
     /// </remarks>
     [AsyncMethodBuilder(typeof(AsyncValueTaskMethodBuilder<>))]
     [StructLayout(LayoutKind.Auto)]
-    public readonly struct ValueTask<TResult> : IEquatable<ValueTask<TResult>>
+    public readonly partial struct ValueTask<TResult> : IEquatable<ValueTask<TResult>>
     {
         /// <summary>The task to be used if the operation completed asynchronously or if it completed synchronously but non-successfully.</summary>
         internal readonly Task<TResult> _task;
@@ -72,7 +72,7 @@ public ValueTask(Task<TResult> task)
         {
             if (task == null)
             {
-                ThrowHelper.ThrowArgumentNullException(ExceptionArgument.task);
+                ThrowNullTaskException();
             }
 
             _task = task;
@@ -113,7 +113,7 @@ public Task<TResult> AsTask() =>
             // Return the task if we were constructed from one, otherwise manufacture one.  We don't
             // cache the generated task into _task as it would end up changing both equality comparison
             // and the hash code we generate in GetHashCode.
-            _task ?? AsyncTaskMethodBuilder<TResult>.GetTaskForResult(_result);
+            _task ?? GetTaskForResult();
 
         internal Task<TResult> AsTaskExpectNonNull() =>
             // Return the task if we were constructed from one, otherwise manufacture one.
@@ -122,13 +122,13 @@ internal Task<TResult> AsTaskExpectNonNull() =>
             _task ?? GetTaskForResultNoInlining();
 
         [MethodImpl(MethodImplOptions.NoInlining)]
-        private Task<TResult> GetTaskForResultNoInlining() => AsyncTaskMethodBuilder<TResult>.GetTaskForResult(_result);
+        private Task<TResult> GetTaskForResultNoInlining() => GetTaskForResult();
 
         /// <summary>Gets whether the <see cref="ValueTask{TResult}"/> represents a completed operation.</summary>
         public bool IsCompleted => _task == null || _task.IsCompleted;
 
         /// <summary>Gets whether the <see cref="ValueTask{TResult}"/> represents a successfully completed operation.</summary>
-        public bool IsCompletedSuccessfully => _task == null || _task.IsCompletedSuccessfully;
+        public bool IsCompletedSuccessfully => _task == null || IsTaskCompletedSuccessfully;
 
         /// <summary>Gets whether the <see cref="ValueTask{TResult}"/> represents a failed operation.</summary>
         public bool IsFaulted => _task != null && _task.IsFaulted;
@@ -154,7 +154,7 @@ public override string ToString()
         {
             if (_task != null)
             {
-                return _task.IsCompletedSuccessfully && _task.Result != null ?
+                return IsTaskCompletedSuccessfully && _task.Result != null ?
                     _task.Result.ToString() :
                     string.Empty;
             }

src/mscorlib/src/System/Threading/Tasks/ValueTask.CoreCLR.cs

@@ -0,0 +1,17 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Runtime.CompilerServices;
+
+namespace System.Threading.Tasks
+{
+    readonly partial struct ValueTask<TResult>
+    {
+        private static void ThrowNullTaskException() => ThrowHelper.ThrowArgumentNullException(ExceptionArgument.task);
+
+        private bool IsTaskCompletedSuccessfully => _task.IsCompletedSuccessfully;
+
+        private Task<TResult> GetTaskForResult() => AsyncTaskMethodBuilder<TResult>.GetTaskForResult(_result);
+    }
+}