Treat ValueTask<TResult> as an asynchronous return type

Fixes #68

Author: sharwell

AsyncUsageAnalyzers/AsyncUsageAnalyzers.Test/AsyncUsageAnalyzers.Test.csproj

@@ -15,6 +15,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.0" />
     <PackageReference Include="Microsoft.CodeAnalysis" Version="1.2.1" />
     <PackageReference Include="xunit" Version="2.3.0-beta3-build3705" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.3.0-beta3-build3705" PrivateAssets="all" />

AsyncUsageAnalyzers/AsyncUsageAnalyzers.Test/Helpers/DiagnosticVerifier.Helper.cs

@@ -122,6 +122,16 @@ protected virtual Solution CreateSolution(ProjectId projectId, string language)
                 .AddMetadataReference(projectId, MetadataReferences.CSharpSymbolsReference)
                 .AddMetadataReference(projectId, MetadataReferences.CodeAnalysisReference);
 
+            if (MetadataReferences.SystemThreadingTasksReference != null)
+            {
+                solution = solution.AddMetadataReference(projectId, MetadataReferences.SystemThreadingTasksReference);
+            }
+
+            if (MetadataReferences.SystemThreadingTasksExtensionsReference != null)
+            {
+                solution = solution.AddMetadataReference(projectId, MetadataReferences.SystemThreadingTasksExtensionsReference);
+            }
+
             var settings = this.GetSettings();
             if (!string.IsNullOrEmpty(settings))
             {

AsyncUsageAnalyzers/AsyncUsageAnalyzers.Test/Helpers/MetadataReferences.cs

@@ -3,8 +3,11 @@
 
 namespace AsyncUsageAnalyzers.Test.Helpers
 {
+    using System;
     using System.Collections.Immutable;
     using System.Linq;
+    using System.Reflection;
+    using System.Threading.Tasks;
     using Microsoft.CodeAnalysis;
     using Microsoft.CodeAnalysis.CSharp;
 
@@ -18,5 +21,32 @@ internal static class MetadataReferences
         internal static readonly MetadataReference SystemCoreReference = MetadataReference.CreateFromFile(typeof(Enumerable).Assembly.Location);
         internal static readonly MetadataReference CSharpSymbolsReference = MetadataReference.CreateFromFile(typeof(CSharpCompilation).Assembly.Location);
         internal static readonly MetadataReference CodeAnalysisReference = MetadataReference.CreateFromFile(typeof(Compilation).Assembly.Location);
+
+        internal static readonly MetadataReference SystemThreadingTasksReference;
+        internal static readonly MetadataReference SystemThreadingTasksExtensionsReference;
+
+        static MetadataReferences()
+        {
+            if (typeof(ValueTask<>).Assembly == typeof(string).Assembly)
+            {
+                // mscorlib contains ValueTask<TResult>, so no need to add a separate reference
+                SystemThreadingTasksReference = null;
+                SystemThreadingTasksExtensionsReference = null;
+            }
+            else
+            {
+                Assembly systemThreadingTasks = AppDomain.CurrentDomain.GetAssemblies().SingleOrDefault(x => x.GetName().Name == "System.Threading.Tasks");
+                if (systemThreadingTasks != null)
+                {
+                    SystemThreadingTasksReference = MetadataReference.CreateFromFile(systemThreadingTasks.Location);
+                }
+
+                Assembly systemThreadingTasksExtensions = typeof(ValueTask<>).Assembly;
+                if (systemThreadingTasksExtensions != null)
+                {
+                    SystemThreadingTasksExtensionsReference = MetadataReference.CreateFromFile(systemThreadingTasksExtensions.Location);
+                }
+            }
+        }
     }
 }

AsyncUsageAnalyzers/AsyncUsageAnalyzers.Test/Naming/AvoidAsyncSuffixUnitTests.cs

@@ -340,6 +340,21 @@ class ClassName
             await this.VerifyCSharpDiagnosticAsync(testCode, EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
         }
 
+        [Fact]
+        public async Task TestReturnValueTaskAsync()
+        {
+            string testCode = @"
+using System.Threading.Tasks;
+class ClassName
+{
+    ValueTask<int> FirstMethod() { return new ValueTask<int>(3); }
+    ValueTask<int> SecondMethodAsync() { return new ValueTask<int>(3); }
+}
+";
+
+            await this.VerifyCSharpDiagnosticAsync(testCode, EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
+
         protected override IEnumerable<DiagnosticAnalyzer> GetCSharpDiagnosticAnalyzers()
         {
             yield return new AvoidAsyncSuffixAnalyzer();

AsyncUsageAnalyzers/AsyncUsageAnalyzers.Test/Naming/UseAsyncSuffixUnitTests.cs

@@ -346,6 +346,32 @@ class ClassName
             await this.VerifyCSharpFixAsync(testCode, fixedCode, cancellationToken: CancellationToken.None).ConfigureAwait(false);
         }
 
+        [Fact]
+        public async Task TestReturnGenericValueTaskAsync()
+        {
+            string testCode = @"
+using System.Threading.Tasks;
+class ClassName
+{
+    ValueTask<int> FirstMethod() { return new ValueTask<int>(3); }
+    ValueTask<int> SecondMethodAsync() { return new ValueTask<int>(3); }
+}
+";
+            string fixedCode = @"
+using System.Threading.Tasks;
+class ClassName
+{
+    ValueTask<int> FirstMethodAsync() { return new ValueTask<int>(3); }
+    ValueTask<int> SecondMethodAsync() { return new ValueTask<int>(3); }
+}
+";
+
+            DiagnosticResult expected = this.CSharpDiagnostic().WithArguments("FirstMethod").WithLocation(5, 20);
+            await this.VerifyCSharpDiagnosticAsync(testCode, expected, CancellationToken.None).ConfigureAwait(false);
+            await this.VerifyCSharpDiagnosticAsync(fixedCode, EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+            await this.VerifyCSharpFixAsync(testCode, fixedCode, cancellationToken: CancellationToken.None).ConfigureAwait(false);
+        }
+
         [Fact]
         public async Task TestPropertyGetterAndSetterTaskAsync()
         {

AsyncUsageAnalyzers/AsyncUsageAnalyzers/Helpers/MethodSymbolExtensions.cs

@@ -25,7 +25,8 @@ public static bool HasAsyncSignature(this IMethodSymbol symbol, bool treatAsyncV
             if (!symbol.IsAsync)
             {
                 // This check conveniently covers Task and Task<T> by ignoring the `1 in Task<T>.
-                if (!string.Equals(nameof(Task), symbol.ReturnType?.Name, StringComparison.Ordinal))
+                if (!string.Equals(nameof(Task), symbol.ReturnType?.Name, StringComparison.Ordinal)
+                    && !string.Equals("ValueTask", symbol.ReturnType?.Name, StringComparison.Ordinal))
                 {
                     return false;
                 }