feat(analyzers): suppress VSTHRD200 on test and hook methods

Directory.Packages.props

@@ -35,6 +35,7 @@
     <PackageVersion Include="Microsoft.CodeAnalysis.SourceGenerators.Testing" Version="1.1.2" />
     <PackageVersion Include="Microsoft.CodeAnalysis.Workspaces.Common" Version="4.7.0" />
     <PackageVersion Include="Microsoft.CSharp" Version="4.7.0" />
+    <PackageVersion Include="Microsoft.VisualStudio.Threading.Analyzers" Version="17.13.61" />
     <PackageVersion Include="Microsoft.EntityFrameworkCore" Version="10.0.8" />
     <PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="10.0.8" />
     <PackageVersion Include="Microsoft.Extensions.Http" Version="10.0.8" />

TUnit.Analyzers.Tests/TUnit.Analyzers.Tests.csproj

@@ -49,6 +49,13 @@
              Link="Shared\AnalyzerTestCompatibility.cs" />
   </ItemGroup>
 
+  <!-- Reference the VSTHRD analyzer assembly (Analyzer="false") so its analyzer types are
+       usable in suppressor tests via WithAnalyzer<>, without running it against this project. -->
+  <ItemGroup>
+    <PackageReference Include="Microsoft.VisualStudio.Threading.Analyzers" PrivateAssets="all" GeneratePathProperty="true" />
+    <Reference Include="$(PkgMicrosoft_VisualStudio_Threading_Analyzers)\analyzers\cs\Microsoft.VisualStudio.Threading.Analyzers.dll" Analyzer="false" />
+  </ItemGroup>
+
   <ItemGroup Condition="'$(TargetFramework)' == 'net8.0'">
     <PackageReference Include="Microsoft.CodeAnalysis.NetAnalyzers" VersionOverride="9.0.0" PrivateAssets="all" GeneratePathProperty="true" />
     <Reference Include="$(PkgMicrosoft_CodeAnalysis_NetAnalyzers)\analyzers\dotnet\cs\Microsoft.CodeAnalysis.NetAnalyzers.dll" Analyzer="false" />

TUnit.Analyzers.Tests/Vsthrd200AsyncSuffixSuppressorTests.cs

@@ -0,0 +1,62 @@
+#if NET8_0_OR_GREATER
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Testing;
+using Microsoft.VisualStudio.Threading.Analyzers;
+
+namespace TUnit.Analyzers.Tests;
+
+public class Vsthrd200AsyncSuffixSuppressorTests
+{
+    private static readonly DiagnosticResult VSTHRD200 = new("VSTHRD200", DiagnosticSeverity.Warning);
+
+    [Test]
+    [Arguments("Test")]
+    [Arguments("Before(Test)")]
+    [Arguments("After(Test)")]
+    [Arguments("BeforeEvery(Test)")]
+    [Arguments("AfterEvery(Test)")]
+    public async Task WarningsOnTestAndHookMethodsAreSuppressed(string attribute) =>
+        await AnalyzerTestHelpers
+            .CreateSuppressorTest<Vsthrd200AsyncSuffixSuppressor>(
+                $$"""
+                using System.Threading.Tasks;
+                using TUnit.Core;
+                using static TUnit.Core.HookType;
+
+                public class MyTests
+                {
+                    [{{attribute}}]
+                    public async Task {|#0:Foo|}()
+                    {
+                        await Task.CompletedTask;
+                    }
+                }
+                """
+            )
+            .WithAnalyzer<VSTHRD200UseAsyncNamingConventionAnalyzer>()
+            .WithSpecificDiagnostics(VSTHRD200)
+            .WithExpectedDiagnosticsResults(VSTHRD200.WithLocation(0).WithIsSuppressed(true))
+            .RunAsync();
+
+    [Test]
+    public async Task WarningsAllowedElsewhere() =>
+        await AnalyzerTestHelpers
+            .CreateSuppressorTest<Vsthrd200AsyncSuffixSuppressor>(
+                """
+                using System.Threading.Tasks;
+
+                public class MyTests
+                {
+                    public async Task {|#0:DoSomething|}()
+                    {
+                        await Task.CompletedTask;
+                    }
+                }
+                """
+            )
+            .WithAnalyzer<VSTHRD200UseAsyncNamingConventionAnalyzer>()
+            .WithSpecificDiagnostics(VSTHRD200)
+            .WithExpectedDiagnosticsResults(VSTHRD200.WithLocation(0).WithIsSuppressed(false))
+            .RunAsync();
+}
+#endif

TUnit.Analyzers/Extensions/MethodExtensions.cs

@@ -6,12 +6,38 @@ namespace TUnit.Analyzers.Extensions;
 
 public static class MethodExtensions
 {
+    /// <summary>
+    /// Returns true if the method is decorated with the exact <c>TUnit.Core.TestAttribute</c>.
+    /// </summary>
+    /// <remarks>
+    /// This is an exact-match check — it does not match subclasses of <c>BaseTestAttribute</c>
+    /// (e.g. <c>[DynamicTestBuilder]</c>). Use <see cref="HasTestAttribute"/> for the broader,
+    /// inheritance-aware check.
+    /// </remarks>
     public static bool IsTestMethod(this IMethodSymbol methodSymbol, Compilation compilation)
     {
         var testAttribute = compilation.GetTypeByMetadataName("TUnit.Core.TestAttribute")!;
         return methodSymbol.GetAttributes().Any(x => SymbolEqualityComparer.Default.Equals(x.AttributeClass, testAttribute));
     }
 
+    /// <summary>
+    /// Returns true if the method is decorated with any attribute deriving from
+    /// <c>TUnit.Core.BaseTestAttribute</c> (e.g. <c>[Test]</c> or <c>[DynamicTestBuilder]</c>).
+    /// </summary>
+    public static bool HasTestAttribute(this IMethodSymbol methodSymbol, Compilation compilation)
+    {
+        var baseTestAttribute = compilation.GetTypeByMetadataName("TUnit.Core.BaseTestAttribute");
+
+        if (baseTestAttribute is null)
+        {
+            return false;
+        }
+
+        return methodSymbol.GetAttributes().Any(attribute =>
+            attribute.AttributeClass?.GetSelfAndBaseTypes()
+                .Contains(baseTestAttribute, SymbolEqualityComparer.Default) == true);
+    }
+
     public static bool IsHookMethod(this IMethodSymbol methodSymbol, Compilation compilation, [NotNullWhen(true)] out INamedTypeSymbol? type, [NotNullWhen(true)] out HookLevel? hookLevel, [NotNullWhen(true)] out HookType? hookType)
     {
         return IsStandardHookMethod(methodSymbol, compilation, out type, out hookLevel, out hookType) || IsEveryHookMethod(methodSymbol, compilation, out type, out hookLevel, out hookType);

TUnit.Analyzers/Vsthrd200AsyncSuffixSuppressor.cs

@@ -0,0 +1,56 @@
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using TUnit.Analyzers.Extensions;
+
+namespace TUnit.Analyzers;
+
+/// <summary>
+/// Suppresses VSTHRD200 ("Use 'Async' suffix for async methods") on TUnit test
+/// methods and hook methods, which intentionally do not follow the Async naming convention.
+/// </summary>
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public class Vsthrd200AsyncSuffixSuppressor : DiagnosticSuppressor
+{
+    public override void ReportSuppressions(SuppressionAnalysisContext context)
+    {
+        foreach (var diagnostic in context.ReportedDiagnostics)
+        {
+            if (diagnostic.Location.SourceTree?.GetRoot().FindNode(diagnostic.Location.SourceSpan) is not { } node)
+            {
+                continue;
+            }
+
+            var semanticModel = context.GetSemanticModel(diagnostic.Location.SourceTree);
+
+            if (semanticModel.GetDeclaredSymbol(node) is not IMethodSymbol methodSymbol)
+            {
+                continue;
+            }
+
+            // IsHookMethod covers all hook levels (Before/After/BeforeEvery/AfterEvery) intentionally —
+            // no hook method requires the 'Async' suffix regardless of scope. (This is deliberately
+            // broader than MarkMethodStaticSuppressor, which only narrows CA1822 to Test-level hooks.)
+            if (methodSymbol.HasTestAttribute(context.Compilation)
+                || methodSymbol.IsHookMethod(context.Compilation, out _, out _, out _))
+            {
+                Suppress(context, diagnostic);
+            }
+        }
+    }
+
+    // This suppressor only ever handles VSTHRD200, so reference the single descriptor directly
+    // rather than scanning SupportedSuppressions on every reported diagnostic.
+    private void Suppress(SuppressionAnalysisContext context, Diagnostic diagnostic)
+        => context.ReportSuppression(Suppression.Create(SupportedSuppressions[0], diagnostic));
+
+    public override ImmutableArray<SuppressionDescriptor> SupportedSuppressions { get; } =
+        ImmutableArray.Create(CreateDescriptor("VSTHRD200"));
+
+    private static SuppressionDescriptor CreateDescriptor(string id)
+        => new(
+            id: $"{id}Suppression",
+            suppressedDiagnosticId: id,
+            justification: "TUnit test and hook methods do not require the 'Async' suffix."
+        );
+}