Add support for nullable return types in ReactiveCommand

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;
 
@@ -452,4 +453,15 @@ 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 argumentType = methodParameters.ToImmutable().SingleOrDefault()?.Type;
+        var argumentTypeString = argumentType?.GetFullyQualifiedNameWithNullabilityAnnotations();
+
+        token.ThrowIfCancellationRequested();
+
         return new(
             targetInfo,
             symbol.Name,
             realReturnType.GetFullyQualifiedNameWithNullabilityAnnotations(),
-            methodParameters.ToImmutable().SingleOrDefault()?.Type.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat),
+            argumentTypeString,
             isTask,
             isReturnTypeVoid,
             isObservable,
@@ -138,7 +142,7 @@ public partial class ReactiveCommandGenerator
     private static string GenerateSource(string containingTypeName, string containingNamespace, string containingClassVisibility, string containingType, CommandInfo[] commands)
     {
         // Get Parent class details from properties.ParentInfo
-        var (parentClassDeclarationsString, closingBrackets) = TargetInfo.GenerateParentClassDeclarations(commands.Select(p => p.TargetInfo.ParentInfo).ToArray());
+        var (parentClassDeclarationsString, closingBrackets) = TargetInfo.GenerateParentClassDeclarations([.. commands.Select(p => p.TargetInfo.ParentInfo)]);
 
         var classes = GenerateClassWithCommands(containingTypeName, containingNamespace, containingClassVisibility, containingType, commands);
 

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

@@ -9,7 +9,6 @@
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Text;
-using ReactiveUI.SourceGenerators.Extensions;
 using ReactiveUI.SourceGenerators.Helpers;
 
 namespace ReactiveUI.SourceGenerators;