New rule (disabled by default) to detect async void methods

README.md

@@ -169,7 +169,8 @@ If you are already using other analyzers, you can check [which rules are duplica
 |[MA0151](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0151.md)|Usage|DebuggerDisplay must contain valid members|⚠️|✔️|❌|
 |[MA0152](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0152.md)|Performance|Use Unwrap instead of using await twice|ℹ️|✔️|❌|
 |[MA0153](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0153.md)|Design|Do not log symbols decorated with DataClassificationAttribute directly|⚠️|✔️|❌|
-|[MA0154](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0154.md)|Design|Use langword in XML comment|ℹ️|✔️|❌|
+|[MA0154](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0154.md)|Design|Use langword in XML comment|ℹ️|✔️|✔️|
+|[MA0155](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0155.md)|Design|Do not use async void methods|⚠️|❌|❌|
 
 <!-- rules -->
 

docs/README.md

@@ -153,7 +153,8 @@
 |[MA0151](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0151.md)|Usage|DebuggerDisplay must contain valid members|<span title='Warning'>⚠️</span>|✔️|❌|
 |[MA0152](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0152.md)|Performance|Use Unwrap instead of using await twice|<span title='Info'>ℹ️</span>|✔️|❌|
 |[MA0153](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0153.md)|Design|Do not log symbols decorated with DataClassificationAttribute directly|<span title='Warning'>⚠️</span>|✔️|❌|
-|[MA0154](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0154.md)|Design|Use langword in XML comment|<span title='Info'>ℹ️</span>|✔️|❌|
+|[MA0154](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0154.md)|Design|Use langword in XML comment|<span title='Info'>ℹ️</span>|✔️|✔️|
+|[MA0155](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0155.md)|Design|Do not use async void methods|<span title='Warning'>⚠️</span>|❌|❌|
 
 |Id|Suppressed rule|Justification|
 |--|---------------|-------------|
@@ -622,6 +623,9 @@ dotnet_diagnostic.MA0153.severity = warning
 
 # MA0154: Use langword in XML comment
 dotnet_diagnostic.MA0154.severity = suggestion
+
+# MA0155: Do not use async void methods
+dotnet_diagnostic.MA0155.severity = none
 ```
 
 # .editorconfig - all rules disabled
@@ -1085,4 +1089,7 @@ dotnet_diagnostic.MA0153.severity = none
 
 # MA0154: Use langword in XML comment
 dotnet_diagnostic.MA0154.severity = none
+
+# MA0155: Do not use async void methods
+dotnet_diagnostic.MA0155.severity = none
 ```

docs/Rules/MA0155.md

@@ -0,0 +1,15 @@
+# MA0155 - Do not use async void methods
+
+```c#
+// not-compliant
+async void SomeMethod()
+{
+    await Task.Delay(1000);
+}
+
+// ok
+async Task SomeMethod()
+{
+    await Task.Delay(1000);
+}
+```

src/Meziantou.Analyzer/Rules/DoNotUseAsyncVoidAnalyzer.cs

@@ -0,0 +1,38 @@
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace Meziantou.Analyzer.Rules;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public sealed class DoNotUseAsyncVoidAnalyzer : DiagnosticAnalyzer
+{
+    private static readonly DiagnosticDescriptor Rule = new(
+        RuleIdentifiers.DoNotUseAsyncVoid,
+        title: "Do not use async void methods",
+        messageFormat: "Do not use async void methods",
+        RuleCategories.Design,
+        DiagnosticSeverity.Warning,
+        isEnabledByDefault: false,
+        description: "",
+        helpLinkUri: RuleIdentifiers.GetHelpUri(RuleIdentifiers.DoNotUseAsyncVoid));
+
+    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(Rule);
+
+    public override void Initialize(AnalysisContext context)
+    {
+        context.EnableConcurrentExecution();
+        context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+
+        context.RegisterSymbolAction(AnalyzeSymbol, SymbolKind.Method);
+    }
+
+    private static void AnalyzeSymbol(SymbolAnalysisContext context)
+    {
+        var symbol = (IMethodSymbol)context.Symbol;
+        if (symbol is { ReturnsVoid: true, IsAsync: true })
+        {
+            context.ReportDiagnostic(Rule, symbol);
+        }
+    }
+}

tests/Meziantou.Analyzer.Test/Rules/DoNotUseAsyncVoidAnalyzerTests.cs

@@ -0,0 +1,55 @@
+using System.Threading.Tasks;
+using Meziantou.Analyzer.Rules;
+using TestHelper;
+using Xunit;
+
+namespace Meziantou.Analyzer.Test.Rules;
+public sealed class DoNotUseAsyncVoidAnalyzerTests
+{
+    private static ProjectBuilder CreateProjectBuilder()
+    {
+        return new ProjectBuilder()
+            .WithAnalyzer<DoNotUseAsyncVoidAnalyzer>()
+            .WithTargetFramework(TargetFramework.Net8_0);
+    }
+
+    [Fact]
+    public async Task Method_Void()
+    {
+        await CreateProjectBuilder()
+              .WithSourceCode("""
+                  class Sample
+                  {
+                      void A() => throw null;
+                  }
+                  """)
+              .ValidateAsync();
+    }
+
+    [Fact]
+    public async Task Method_AsyncVoid()
+    {
+        await CreateProjectBuilder()
+              .WithSourceCode("""
+                  class Sample
+                  {
+                      async void [|A|]() => throw null;
+                  }
+                  """)
+              .ValidateAsync();
+    }
+
+    [Fact]
+    public async Task Method_AsyncTask()
+    {
+        await CreateProjectBuilder()
+              .WithSourceCode("""
+                  class Sample
+                  {
+                      async System.Threading.Tasks.Task A() => throw null;
+                  }
+                  """)
+              .ValidateAsync();
+    }
+
+}