Add support for nullable return types in ReactiveCommand

Introduces new unit tests and verified source for ReactiveCommand methods with nullable parameter and return types. Updates generator logic to handle nullable types correctly. Adds usage of nested classes with nullable types in test and example view models, and updates project references accordingly.

Author: ChrisPulman

src/ReactiveUI.SourceGenerator.Tests/REACTIVECMD/ReactiveCMDGeneratorTests.FromReactiveCommandWithNullableTypeAndNullableReturnType#ReactiveUI.SourceGenerators.ReactiveCommandAttribute.g.verified.cs

@@ -0,0 +1,44 @@
+//HintName: ReactiveUI.SourceGenerators.ReactiveCommandAttribute.g.cs
+// Copyright (c) 2025 .NET Foundation and Contributors. All rights reserved.
+// 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 full license information.
+
+// <auto-generated/>
+#pragma warning disable
+#nullable enable
+namespace ReactiveUI.SourceGenerators;
+
+/// <summary>
+/// ReativeCommandAttribute.
+/// </summary>
+/// <seealso cref="Attribute" />
+[global::System.AttributeUsage(global::System.AttributeTargets.Method, AllowMultiple = false, Inherited = false)]
+internal sealed class ReactiveCommandAttribute : global::System.Attribute
+{
+    /// <summary>
+    /// Gets the can execute method or property.
+    /// </summary>
+    /// <value>
+    /// The name of the CanExecute Observable of bool.
+    /// </value>
+    public string? CanExecute { get; init; }
+    
+    /// <summary>
+    /// Gets the output scheduler.
+    /// </summary>
+    /// <value>
+    /// The output scheduler.
+    /// </value>
+    public string? OutputScheduler { get; init; }
+
+    /// <summary>
+    /// Gets the AccessModifier of the ReactiveCommand property.
+    /// </summary>
+    /// <value>
+    /// The AccessModifier of the property.
+    /// </value>
+    public PropertyAccessModifier AccessModifier { get; init; }
+}
+#nullable restore
+#pragma warning restore

src/ReactiveUI.SourceGenerator.Tests/UnitTests/ReactiveCMDGeneratorTests.cs

@@ -238,4 +238,31 @@ public partial class TestVM : ReactiveObject
         """;
         return TestHelper.TestPass(sourceCode);
     }
+
+    /// <summary>
+    /// Froms the type of the reactive command with nullable type and nullable return.
+    /// </summary>
+    /// <returns>A task to monitor the async.</returns>
+    [Test]
+    public Task FromReactiveCommandWithNullableTypeAndNullableReturnType()
+    {
+        const string sourceCode = """
+            using System;
+            using ReactiveUI;
+            using ReactiveUI.SourceGenerators;
+            namespace TestNs;
+
+            public class NullableInput
+            {
+                public string? Name { get; set; }
+            }
+
+            public partial class TestVM : ReactiveObject
+            {
+                [ReactiveCommand]
+                private NullableInput? Test1(NullableInput? input) => input;
+            }
+        """;
+        return TestHelper.TestPass(sourceCode);
+    }
 }

src/ReactiveUI.SourceGenerators.Execute.Nested3/Class1.cs

@@ -6,6 +6,7 @@
 using System.Diagnostics.CodeAnalysis;
 using ReactiveUI;
 using ReactiveUI.SourceGenerators;
+using SGReactiveUI.SourceGenerators.Execute.Nested2;
 
 namespace SGReactiveUI.SourceGenerators.Execute.Nested3;
 
@@ -17,4 +18,23 @@ public partial class Class1 : ReactiveObject
 {
     [Reactive]
     private string? _property1;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="Class1"/> class.
+    /// </summary>
+    public Class1()
+    {
+        SetPropertyCommand.Execute(new Nested1.Class1 { Property1 = "Initial Value" }).Subscribe();
+    }
+
+    [ReactiveCommand]
+    private SGReactiveUI.SourceGenerators.Execute.Nested2.Class1? SetProperty(Nested1.Class1? class1)
+    {
+        if (class1 == null)
+        {
+            return null;
+        }
+
+        return new() { Property1 = class1.Property1 };
+    }
 }

src/ReactiveUI.SourceGenerators.Execute/ReactiveUI.SourceGenerators.Execute.csproj

@@ -20,6 +20,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\ReactiveUI.SourceGenerators.Analyzers.CodeFixes\ReactiveUI.SourceGenerators.Analyzers.CodeFixes.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
+    <ProjectReference Include="..\ReactiveUI.SourceGenerators.Execute.Nested3\ReactiveUI.SourceGenerators.Execute.Nested3.csproj" />
     <ProjectReference Include="..\ReactiveUI.SourceGenerators.Roslyn4120\ReactiveUI.SourceGenerators.Roslyn4120.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
   </ItemGroup>
 </Project>

src/ReactiveUI.SourceGenerators.Execute/TestViewModel.cs

@@ -16,6 +16,7 @@
 using DynamicData;
 using ReactiveUI;
 using ReactiveUI.SourceGenerators;
+using SGReactiveUI.SourceGenerators.Execute.Nested3;
 
 namespace SGReactiveUI.SourceGenerators.Test;
 
@@ -88,6 +89,7 @@ public partial class TestViewModel : ReactiveObject, IActivatableViewModel, IDis
     [SetsRequiredMembers]
     public TestViewModel()
     {
+        var c = new Class1();
         var itv = new InternalTestViewModel { PublicRequiredPartialPropertyTest = true };
         MustBeSet = "Test";
         this.WhenActivated(disposables =>
@@ -452,4 +454,15 @@ protected virtual void Dispose(bool disposing)
     [ReactiveCommand]
     private Task<System.Collections.IEnumerable> GetData(CancellationToken ct) =>
         Task.FromResult<System.Collections.IEnumerable>(Array.Empty<System.Collections.IEnumerable>());
+
+    [ReactiveCommand]
+    private Execute.Nested2.Class1? SetProperty(Execute.Nested1.Class1? class1)
+    {
+        if (class1 == null)
+        {
+            return null;
+        }
+
+        return new() { Property1 = class1.Property1 };
+    }
 }

src/ReactiveUI.SourceGenerators.Roslyn/ReactiveCommand/ReactiveCommandGenerator.Execute.cs

@@ -3,7 +3,7 @@
 // The ReactiveUI and contributors licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for full license information.
 
-using System.Collections.Generic;
+using System;
 using System.Collections.Immutable;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
@@ -15,7 +15,6 @@
 using ReactiveUI.SourceGenerators.Helpers;
 using ReactiveUI.SourceGenerators.Input.Models;
 using ReactiveUI.SourceGenerators.Models;
-using static ReactiveUI.SourceGenerators.Diagnostics.DiagnosticDescriptors;
 
 namespace ReactiveUI.SourceGenerators;
 
@@ -120,11 +119,16 @@ public partial class ReactiveCommandGenerator
 
         token.ThrowIfCancellationRequested();
 
+        var methodReturnType = methodParameters.ToImmutable().SingleOrDefault()?.Type;
+        var methodParametersstring = methodReturnType?.GetFullyQualifiedNameWithNullabilityAnnotations();
+
+        token.ThrowIfCancellationRequested();
+
         return new(
             targetInfo,
             symbol.Name,
             realReturnType.GetFullyQualifiedNameWithNullabilityAnnotations(),
-            methodParameters.ToImmutable().SingleOrDefault()?.Type.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat),
+            methodParametersstring,
             isTask,
             isReturnTypeVoid,
             isObservable,