Add AsyncVoidReturningRelayCommandMethodAnalyzer

Author: Sergio0694

src/CommunityToolkit.Mvvm.SourceGenerators/AnalyzerReleases.Shipped.md

@@ -66,3 +66,4 @@ Rule ID | Category | Severity | Notes
 --------|----------|----------|-------
 MVVMTK0037 | CommunityToolkit.Mvvm.SourceGenerators.ObservablePropertyGenerator | Error | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0037
 MVVMTK0038 | CommunityToolkit.Mvvm.SourceGenerators.RelayCommandGenerator | Error | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0038
+MVVMTK0039 | CommunityToolkit.Mvvm.SourceGenerators.RelayCommandGenerator | Warning | See https://aka.ms/mvvmtoolkit/errors/mvvmtk0039

src/CommunityToolkit.Mvvm.SourceGenerators/CommunityToolkit.Mvvm.SourceGenerators.projitems

@@ -39,6 +39,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)ComponentModel\ObservableValidatorValidateAllPropertiesGenerator.Execute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ComponentModel\TransitiveMembersGenerator.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ComponentModel\TransitiveMembersGenerator.Execute.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\AsyncVoidReturningRelayCommandMethodAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\InvalidClassLevelNotifyDataErrorInfoAttributeAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\InvalidClassLevelNotifyPropertyChangedRecipientsAttributeAnalyzer.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Diagnostics\Analyzers\ClassUsingAttributeInsteadOfInheritanceAnalyzer.cs" />

src/CommunityToolkit.Mvvm.SourceGenerators/Diagnostics/Analyzers/AsyncVoidReturningRelayCommandMethodAnalyzer.cs

@@ -0,0 +1,59 @@
+// 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.Collections.Immutable;
+using System.Linq;
+using CommunityToolkit.Mvvm.SourceGenerators.Extensions;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using static CommunityToolkit.Mvvm.SourceGenerators.Diagnostics.DiagnosticDescriptors;
+
+namespace CommunityToolkit.Mvvm.SourceGenerators;
+
+/// <summary>
+/// A diagnostic analyzer that generates a warning when using <c>[RelayCommand]</c> over an <see langword="async"/> <see cref="void"/> method.
+/// </summary>
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public sealed class AsyncVoidReturningRelayCommandMethodAnalyzer : DiagnosticAnalyzer
+{
+    /// <inheritdoc/>
+    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } = ImmutableArray.Create(AsyncVoidReturningRelayCommandMethod);
+
+    /// <inheritdoc/>
+    public override void Initialize(AnalysisContext context)
+    {
+        context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.Analyze | GeneratedCodeAnalysisFlags.ReportDiagnostics);
+        context.EnableConcurrentExecution();
+
+        context.RegisterCompilationStartAction(static context =>
+        {
+            // Get the symbol for [RelayCommand]
+            if (context.Compilation.GetTypeByMetadataName("CommunityToolkit.Mvvm.Input.RelayCommandAttribute") is not INamedTypeSymbol relayCommandSymbol)
+            {
+                return;
+            }
+
+            context.RegisterSymbolAction(context =>
+            {
+                // We're only looking for async void methods
+                if (context.Symbol is not IMethodSymbol { IsAsync: true, ReturnsVoid: true } methodSymbol)
+                {
+                    return;
+                }
+
+                // We only care about methods annotated with [RelayCommand]
+                if (!methodSymbol.HasAttributeWithType(relayCommandSymbol))
+                {
+                    return;
+                }
+
+                // Warn on async void methods using [RelayCommand] (they should return a Task instead)
+                context.ReportDiagnostic(Diagnostic.Create(
+                    AsyncVoidReturningRelayCommandMethod,
+                    context.Symbol.Locations.FirstOrDefault(),
+                    context.Symbol));
+            }, SymbolKind.Method);
+        });
+    }
+}

src/CommunityToolkit.Mvvm.SourceGenerators/Diagnostics/DiagnosticDescriptors.cs

@@ -637,4 +637,20 @@ internal static class DiagnosticDescriptors
         isEnabledByDefault: true,
         description: "All attributes targeting the generated field or property for a method annotated with [RelayCommand] must be using valid expressions.",
         helpLinkUri: "https://aka.ms/mvvmtoolkit/errors/mvvmtk0038");
+
+    /// <summary>
+    /// Gets a <see cref="DiagnosticDescriptor"/> indicating when a method with <c>[RelayCommand]</c> is async void.
+    /// <para>
+    /// Format: <c>"The method {0} annotated with [RelayCommand] is async void (make sure to return a Task type instead)"</c>.
+    /// </para>
+    /// </summary>
+    public static readonly DiagnosticDescriptor AsyncVoidReturningRelayCommandMethod = new DiagnosticDescriptor(
+        id: "MVVMTK0039",
+        title: "Async void returning method annotated with RelayCommand",
+        messageFormat: "The method {0} annotated with [RelayCommand] is async void (make sure to return a Task type instead)",
+        category: typeof(RelayCommandGenerator).FullName,
+        defaultSeverity: DiagnosticSeverity.Warning,
+        isEnabledByDefault: true,
+        description: "All asynchronous methods annotated with [RelayCommand] should return a Task type, to benefit from the additional support provided by AsyncRelayCommand and AsyncRelayCommand<T>.",
+        helpLinkUri: "https://aka.ms/mvvmtoolkit/errors/mvvmtk0039");
 }