Add IReactiveObject source generator and tests

Introduces the [IReactiveObject] attribute and a new source generator to implement IReactiveObject for classes that cannot inherit from ReactiveObject. Updates documentation, adds generator logic, supporting models, and unit tests to verify generated code. Also updates helper and project files to support the new generator.

Author: ChrisPulman

README.md

@@ -51,6 +51,7 @@ ReactiveUI Source Generators automatically generate ReactiveUI objects to stream
 - `[ViewModelControlHost("YourNameSpace.CustomControl")]`
 - `[BindableDerivedList]` Generates a derived list from a ReadOnlyObservableCollection backing field
 - `[ReactiveCollection]` Generates property changed notifications on add, remove, new actions on a ObservableCollection backing field
+- `[IReactiveObject]` Generates IReactiveObject implementation for classes not able to inherit from ReactiveObject
 
 #### IViewFor Registration generator
 
@@ -684,6 +685,19 @@ public partial class MyReactiveClass : ReactiveObject
 }
 ```
 
+### ReactiveObject implementation for classes not able to inherit from ReactiveObject
+```csharp
+using ReactiveUI;
+using ReactiveUI.SourceGenerators;
+
+[IReactiveObject]
+public partial class MyReactiveClass
+{
+    [Reactive]
+    private string _myProperty;
+}
+```
+
 ### TODO:
 - Add ObservableAsProperty to generate from a IObservable method with parameters.
 

src/ReactiveUI.SourceGenerator.Tests/REACTIVEOBJ/ReactiveObjectGeneratorTests.FromReactiveObject#ReactiveUI.SourceGenerators.IReactiveObjectAttribute.g.verified.cs

@@ -0,0 +1,19 @@
+//HintName: ReactiveUI.SourceGenerators.IReactiveObjectAttribute.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>
+/// IReactiveObject Attribute.
+/// </summary>
+/// <seealso cref="System.Attribute" />
+[global::System.AttributeUsage(global::System.AttributeTargets.Class, AllowMultiple = false, Inherited = false)]
+internal sealed class IReactiveObjectAttribute : global::System.Attribute;
+#nullable restore
+#pragma warning restore

src/ReactiveUI.SourceGenerator.Tests/REACTIVEOBJ/ReactiveObjectGeneratorTests.FromReactiveObject#TestNs.TestVM.IReactiveObject.g.verified.cs

@@ -0,0 +1,68 @@
+//HintName: TestNs.TestVM.IReactiveObject.g.cs
+// <auto-generated/>
+#pragma warning disable
+#nullable enable
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.ComponentModel;
+using ReactiveUI;
+
+namespace TestNs
+{
+    /// <summary>
+    /// Partial class for the TestVM which contains ReactiveUI IReactiveObject initialization.
+    /// </summary>
+    public partial class TestVM : IReactiveObject
+    {
+        private bool _propertyChangingEventsSubscribed;
+        private bool _propertyChangedEventsSubscribed;
+
+        /// <inheritdoc/>
+        public event PropertyChangingEventHandler? PropertyChanging
+        {
+            add
+            {
+                if (!_propertyChangingEventsSubscribed)
+                {
+                    this.SubscribePropertyChangingEvents();
+                    _propertyChangingEventsSubscribed = true;
+                }
+
+                PropertyChangingHandler += value;
+            }
+            remove => PropertyChangingHandler -= value;
+        }
+
+        /// <inheritdoc/>
+        public event PropertyChangedEventHandler? PropertyChanged
+        {
+            add
+            {
+                if (!_propertyChangedEventsSubscribed)
+                {
+                    this.SubscribePropertyChangedEvents();
+                    _propertyChangedEventsSubscribed = true;
+                }
+
+                PropertyChangedHandler += value;
+            }
+            remove => PropertyChangedHandler -= value;
+        }
+
+        [SuppressMessage("Roslynator", "RCS1159:Use EventHandler<T>", Justification = "Long term design.")]
+        private event PropertyChangingEventHandler? PropertyChangingHandler;
+
+        [SuppressMessage("Roslynator", "RCS1159:Use EventHandler<T>", Justification = "Long term design.")]
+        private event PropertyChangedEventHandler? PropertyChangedHandler;
+
+        /// <inheritdoc/>
+        void IReactiveObject.RaisePropertyChanging(PropertyChangingEventArgs args) =>
+            PropertyChangingHandler?.Invoke(this, args);
+
+        /// <inheritdoc/>
+        void IReactiveObject.RaisePropertyChanged(PropertyChangedEventArgs args) =>
+            PropertyChangedHandler?.Invoke(this, args);
+    }
+}
+#nullable restore
+#pragma warning restore

src/ReactiveUI.SourceGenerator.Tests/ReactiveUI.SourceGenerators.Tests.csproj

@@ -40,6 +40,7 @@
     <Folder Include="OAPH\" />
     <Folder Include="REACTIVECMD\" />
     <Folder Include="REACTIVE\" />
+    <Folder Include="REACTIVEOBJ\" />
     <Folder Include="REACTIVECOLL\" />
   </ItemGroup>
 

src/ReactiveUI.SourceGenerator.Tests/TestHelper.cs

@@ -87,6 +87,7 @@ public string VerifiedFilePath()
             nameof(ViewModelControlHostGenerator) => "CONTROLHOST",
             nameof(BindableDerivedListGenerator) => "DERIVEDLIST",
             nameof(ReactiveCollectionGenerator) => "REACTIVECOLL",
+            nameof(ReactiveObjectGenerator) => "REACTIVEOBJ",
             _ => name,
         };
     }

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

@@ -0,0 +1,41 @@
+// Copyright (c) 2025 ReactiveUI and contributors. All rights reserved.
+// Licensed to the ReactiveUI and contributors under one or more agreements.
+// 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 ReactiveUI.SourceGenerators;
+
+namespace ReactiveUI.SourceGenerator.Tests;
+
+/// <summary>
+/// Unit tests for the Reactive generator.
+/// </summary>
+[TestFixture]
+public class ReactiveObjectGeneratorTests : TestBase<ReactiveObjectGenerator>
+{
+    /// <summary>
+    /// Froms the reactive object.
+    /// </summary>
+    /// <returns>A task to monitor the async.</returns>
+    [Test]
+    public Task FromReactiveObject()
+    {
+        // Arrange: Setup the source code that matches the generator input expectations.
+        const string sourceCode = """
+                using System;
+                using ReactiveUI.SourceGenerators;
+                using System.Reactive.Linq;
+                namespace TestNs;
+
+                [IReactiveObject]
+                public partial class TestVM
+                {
+                    [Reactive]
+                    private int _test1 = 10;
+                }
+            """;
+
+        // Act: Initialize the helper and run the generator. Assert: Verify the generated code.
+        return TestHelper.TestPass(sourceCode);
+    }
+}

src/ReactiveUI.SourceGenerators.Execute/Person.cs

@@ -4,7 +4,6 @@
 // See the LICENSE file in the project root for full license information.
 
 using System.Diagnostics.CodeAnalysis;
-using ReactiveUI;
 using ReactiveUI.SourceGenerators;
 
 namespace SGReactiveUI.SourceGenerators.Test;
@@ -14,7 +13,8 @@ namespace SGReactiveUI.SourceGenerators.Test;
 /// </summary>
 /// <seealso cref="ReactiveUI.ReactiveObject" />
 [ExcludeFromCodeCoverage]
-public partial class Person : ReactiveObject
+[IReactiveObject]
+public partial class Person
 {
     /// <summary>
     /// Gets or sets a value indicating whether this <see cref="Person"/> is deleted.
@@ -23,5 +23,5 @@ public partial class Person : ReactiveObject
     ///   <c>true</c> if deleted; otherwise, <c>false</c>.
     /// </value>
     [Reactive]
-    public bool Deleted { get; set; }
+    public partial bool Deleted { get; set; }
 }

src/ReactiveUI.SourceGenerators.Roslyn/AttributeDefinitions.cs

@@ -77,6 +77,8 @@ internal enum SplatRegistrationType
         #pragma warning restore
         """;
 
+    public const string ReactiveObjectAttributeType = "ReactiveUI.SourceGenerators.IReactiveObjectAttribute";
+
     public static string ReactiveObjectAttribute => $$"""
 // Copyright (c) {{DateTime.Now.Year}} .NET Foundation and Contributors. All rights reserved.
 // Licensed to the .NET Foundation under one or more agreements.
@@ -89,12 +91,12 @@ internal enum SplatRegistrationType
 namespace ReactiveUI.SourceGenerators;
 
 /// <summary>
-/// ReactiveObjectAttribute.
+/// IReactiveObject Attribute.
 /// </summary>
 /// <seealso cref="System.Attribute" />
 [global::System.CodeDom.Compiler.GeneratedCode("ReactiveUI.SourceGenerators.ReactiveObjectGenerator", "{{ReactiveGenerator.GeneratorVersion}}")]
 [global::System.AttributeUsage(global::System.AttributeTargets.Class, AllowMultiple = false, Inherited = false)]
-internal sealed class ReactiveObjectAttribute : global::System.Attribute;
+internal sealed class IReactiveObjectAttribute : global::System.Attribute;
 #nullable restore
 #pragma warning restore
 """;

src/ReactiveUI.SourceGenerators.Roslyn/BindableDerivedList/BindableDerivedListGenerator.cs

@@ -3,8 +3,6 @@
 // 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;
-using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
 using System.Text;

src/ReactiveUI.SourceGenerators.Roslyn/Core/Extensions/FieldSyntaxExtensions.cs

@@ -5,6 +5,7 @@
 
 using System.Globalization;
 using Microsoft.CodeAnalysis;
+using ReactiveUI.SourceGenerators.Helpers;
 
 namespace ReactiveUI.SourceGenerators.Extensions;
 
@@ -124,7 +125,7 @@ internal static bool IsTargetTypeValid(this IFieldSymbol fieldSymbol)
     {
         var isObservableObject = fieldSymbol.ContainingType.InheritsFromFullyQualifiedMetadataName("ReactiveUI.ReactiveObject");
         var isIObservableObject = fieldSymbol.ContainingType.ImplementsFullyQualifiedMetadataName("ReactiveUI.IReactiveObject");
-        var hasObservableObjectAttribute = fieldSymbol.ContainingType.HasOrInheritsAttributeWithFullyQualifiedMetadataName("ReactiveUI.SourceGenerators.ReactiveObjectAttribute");
+        var hasObservableObjectAttribute = fieldSymbol.ContainingType.HasOrInheritsAttributeWithFullyQualifiedMetadataName(AttributeDefinitions.ReactiveObjectAttributeType);
 
         return isIObservableObject || isObservableObject || hasObservableObjectAttribute;
     }
@@ -138,7 +139,7 @@ internal static bool IsTargetTypeValid(this IPropertySymbol propertySymbol)
     {
         var isObservableObject = propertySymbol.ContainingType.InheritsFromFullyQualifiedMetadataName("ReactiveUI.ReactiveObject");
         var isIObservableObject = propertySymbol.ContainingType.ImplementsFullyQualifiedMetadataName("ReactiveUI.IReactiveObject");
-        var hasObservableObjectAttribute = propertySymbol.ContainingType.HasOrInheritsAttributeWithFullyQualifiedMetadataName("ReactiveUI.SourceGenerators.ReactiveObjectAttribute");
+        var hasObservableObjectAttribute = propertySymbol.ContainingType.HasOrInheritsAttributeWithFullyQualifiedMetadataName(AttributeDefinitions.ReactiveObjectAttributeType);
 
         return isIObservableObject || isObservableObject || hasObservableObjectAttribute;
     }
@@ -152,7 +153,7 @@ internal static bool IsTargetTypeValid(this IMethodSymbol methodSymbol)
     {
         var isObservableObject = methodSymbol.ContainingType.InheritsFromFullyQualifiedMetadataName("ReactiveUI.ReactiveObject");
         var isIObservableObject = methodSymbol.ContainingType.ImplementsFullyQualifiedMetadataName("ReactiveUI.IReactiveObject");
-        var hasObservableObjectAttribute = methodSymbol.ContainingType.HasOrInheritsAttributeWithFullyQualifiedMetadataName("ReactiveUI.SourceGenerators.ReactiveObjectAttribute");
+        var hasObservableObjectAttribute = methodSymbol.ContainingType.HasOrInheritsAttributeWithFullyQualifiedMetadataName(AttributeDefinitions.ReactiveObjectAttributeType);
 
         return isIObservableObject || isObservableObject || hasObservableObjectAttribute;
     }