Fix for Nullable partial OAPH properties

Nullable partial properties with ObservableAsProperty are not updated with null value

Author: ChrisPulman

src/ReactiveUI.SourceGenerator.Tests/OAPH/OAPFromObservableGeneratorTests.FromPartialProperty#TestNs.TestVM.ObservableAsPropertyFromObservable.g.verified.cs

@@ -21,7 +21,7 @@ public partial class TestVM
         /// <inheritdoc cref="_testProperty"/>
         [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
         [global::System.Runtime.Serialization.DataMemberAttribute()]
-        public partial double? TestProperty { get => _testProperty = _testPropertyHelper?.Value ?? _testProperty; }
+        public partial double? TestProperty { get => _testProperty = (_testPropertyHelper == null ? _testProperty : _testPropertyHelper.Value); }
 
         [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
         protected void InitializeOAPH()

src/ReactiveUI.SourceGenerators.Execute/TestClassOAPH_VM.cs

@@ -24,6 +24,9 @@ public partial class TestClassOAPH_VM : ReactiveObject
     private string value = string.Empty;
 #pragma warning restore SX1309 // Field names should begin with underscore
 
+    [Reactive]
+    private string? _testProperty;
+
     /// <summary>
     /// Initializes a new instance of the <see cref="TestClassOAPH_VM"/> class.
     /// </summary>
@@ -34,6 +37,21 @@ public TestClassOAPH_VM()
 
         _observableTestFieldHelper = this.WhenAnyValue(x => x.ReactiveTestField)
             .ToProperty(this, x => x.ObservableTestField);
+
+        _testHelper = this.WhenAnyValue(x => x.TestProperty).ToProperty(this, x => x.Test);
+
+        TestProperty = null;
+        var t0 = Test;
+
+        TestProperty = "Test";
+
+        var t1 = Test;
+
+        TestProperty = null;
+        var t2 = Test;
+
+        TestProperty = "Test2";
+        var t3 = Test;
     }
 
     /// <summary>
@@ -53,4 +71,13 @@ public TestClassOAPH_VM()
     /// </value>
     [Reactive]
     public partial bool ReactiveTestProperty { get; set; }
+
+    /// <summary>
+    /// Gets the test.
+    /// </summary>
+    /// <value>
+    /// The test.
+    /// </value>
+    [ObservableAsProperty]
+    public partial string? Test { get; }
 }

src/ReactiveUI.SourceGenerators.Execute/TestViewModel.cs

@@ -21,6 +21,9 @@ namespace SGReactiveUI.SourceGenerators.Test;
 /// <summary>
 /// TestClass.
 /// </summary>
+/// <seealso cref="ReactiveUI.ReactiveObject" />
+/// <seealso cref="ReactiveUI.IActivatableViewModel" />
+/// <seealso cref="System.IDisposable" />
 /// <seealso cref="ReactiveObject" />
 /// <seealso cref="IActivatableViewModel" />
 /// <seealso cref="IDisposable" />
@@ -218,6 +221,14 @@ public TestViewModel()
     /// </value>
     public static TestViewModel Instance { get; } = new();
 
+    /// <summary>
+    /// Gets the test class oaph vm.
+    /// </summary>
+    /// <value>
+    /// The test class oaph vm.
+    /// </value>
+    public TestClassOAPH_VM TestClassOAPH_VM { get; } = new();
+
     /// <summary>
     /// Gets or sets the partial property test.
     /// </summary>

src/ReactiveUI.SourceGenerators.Roslyn/ObservableAsProperty/ObservableAsPropertyGenerator{FromObservable}.Execute.cs

@@ -307,7 +307,7 @@ private static string GetPropertySyntax(ObservableMethodInfo propertyInfo)
     {
         var propertyAttributes = string.Join("\n        ", AttributeDefinitions.ExcludeFromCodeCoverage.Concat(propertyInfo.ForwardedPropertyAttributes));
         var getterFieldIdentifierName = propertyInfo.GetGeneratedFieldName();
-        var getterArrowExpression = propertyInfo.IsNullableType
+        var getterArrowExpression = propertyInfo.IsNullableType || propertyInfo.IsFromPartialProperty
             ? $"{getterFieldIdentifierName} = ({getterFieldIdentifierName}Helper == null ? {getterFieldIdentifierName} : {getterFieldIdentifierName}Helper.Value)"
             : $"{getterFieldIdentifierName} = {getterFieldIdentifierName}Helper?.Value ?? {getterFieldIdentifierName}";