fix(analyzers): scope TUnit0031 async-void rule to tests and hooks (#6190)

TUnit.Analyzers.Tests/AsyncVoidAnalyzerTests.cs

@@ -188,4 +188,86 @@ public void Test()
                     .WithLocation(0)
             );
     }
+
+    [Test]
+    public async Task Async_Void_NonTest_Method_Raises_No_Error()
+    {
+        // An async void method that is not a test or hook (e.g. an event handler)
+        // must not be flagged just because the project references TUnit. See #6190.
+        await Verifier
+            .VerifyAnalyzerAsync(
+                """
+                using System;
+                using System.Threading.Tasks;
+                using TUnit.Core;
+
+                public class MyClass
+                {
+                    public event EventHandler? Ticked;
+
+                    public void Setup()
+                    {
+                        Ticked += OnTicked;
+                    }
+
+                    private async void OnTicked(object? sender, EventArgs e)
+                    {
+                        await Task.Delay(1);
+                    }
+                }
+                """
+            );
+    }
+
+    [Test]
+    public async Task Async_Void_EventHandler_Lambda_In_NonTest_Method_Raises_No_Error()
+    {
+        // An async void lambda subscribed to an event from a non-test method is legitimate.
+        await Verifier
+            .VerifyAnalyzerAsync(
+                """
+                using System;
+                using System.Threading.Tasks;
+                using TUnit.Core;
+
+                public class MyClass
+                {
+                    public event EventHandler? Ticked;
+
+                    public void Setup()
+                    {
+                        Ticked += async (sender, e) =>
+                        {
+                            await Task.Delay(1);
+                        };
+                    }
+                }
+                """
+            );
+    }
+
+    [Test]
+    public async Task Async_Void_Hook_Raises_Error()
+    {
+        await Verifier
+            .VerifyAnalyzerAsync(
+                """
+                using System.Threading.Tasks;
+                using TUnit.Core;
+
+                public class MyClass
+                {
+                    [Before(HookType.Test)]
+                    public async void {|#0:Setup|}()
+                    {
+                        await Task.Delay(1);
+                    }
+                }
+                """,
+
+                Verifier
+                    .Diagnostic(Rules.AsyncVoidMethod)
+                    .WithLocation(0)
+            );
+    }
 }

TUnit.Analyzers/AsyncVoidAnalyzer.cs

@@ -1,8 +1,9 @@
-using System.Collections.Immutable;
+using System.Collections.Immutable;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Diagnostics;
+using TUnit.Analyzers.Extensions;
 
 namespace TUnit.Analyzers;
 
@@ -28,12 +29,22 @@ private void AnalyzeMethod(SymbolAnalysisContext context)
             return;
         }
 
-        if (methodSymbol is { IsAsync: true, ReturnsVoid: true })
+        if (methodSymbol is not { IsAsync: true, ReturnsVoid: true })
         {
-            context.ReportDiagnostic(Diagnostic.Create(Rules.AsyncVoidMethod,
-                methodSymbol.Locations.FirstOrDefault())
-            );
+            return;
+        }
+
+        // Only flag `async void` on TUnit test methods and hooks. Other `async void`
+        // methods (e.g. an event handler for System.Timers.Timer.Elapsed) are legitimate
+        // and must not be flagged just because the project references TUnit. See #6190.
+        if (!IsTestOrHookMethod(methodSymbol, context.Compilation))
+        {
+            return;
         }
+
+        context.ReportDiagnostic(Diagnostic.Create(Rules.AsyncVoidMethod,
+            methodSymbol.Locations.FirstOrDefault())
+        );
     }
 
     private void AnalyzeLambda(SyntaxNodeAnalysisContext context)
@@ -50,11 +61,44 @@ private void AnalyzeLambda(SyntaxNodeAnalysisContext context)
 
         var symbol = context.SemanticModel.GetSymbolInfo(anonymousFunction).Symbol;
 
-        if (symbol is IMethodSymbol { ReturnsVoid: true })
+        if (symbol is not IMethodSymbol { ReturnsVoid: true })
         {
-            context.ReportDiagnostic(Diagnostic.Create(Rules.AsyncVoidMethod,
-                anonymousFunction.GetLocation())
-            );
+            return;
+        }
+
+        // Only flag `async void` lambdas declared inside a TUnit test method or hook,
+        // so legitimate async void event-handler lambdas elsewhere aren't flagged. See #6190.
+        var enclosingMethod = GetEnclosingMethod(symbol);
+
+        if (enclosingMethod is null || !IsTestOrHookMethod(enclosingMethod, context.Compilation))
+        {
+            return;
         }
+
+        context.ReportDiagnostic(Diagnostic.Create(Rules.AsyncVoidMethod,
+            anonymousFunction.GetLocation())
+        );
+    }
+
+    private static bool IsTestOrHookMethod(IMethodSymbol methodSymbol, Compilation compilation)
+    {
+        return methodSymbol.HasTestAttribute(compilation)
+               || methodSymbol.IsHookMethod(compilation, out _, out _, out _);
+    }
+
+    private static IMethodSymbol? GetEnclosingMethod(ISymbol? symbol)
+    {
+        // Walk out of nested lambdas/anonymous methods to the real enclosing method.
+        while (symbol is IMethodSymbol method)
+        {
+            if (method.MethodKind != MethodKind.AnonymousFunction)
+            {
+                return method;
+            }
+
+            symbol = method.ContainingSymbol;
+        }
+
+        return null;
     }
 }