From e4af5305a01dff23e692036265d927b30173f368 Mon Sep 17 00:00:00 2001
From: Chris Pulman <chris.pulman@yahoo.com>
Date: Mon, 12 Aug 2024 00:24:27 +0100
Subject: [PATCH] Feature Allow Default value on OAPH generator

---
 README.md                                             | 10 +++++++++-
 .../TestViewModel.cs                                  |  5 +++--
 .../CodeAnalyzers/PropertyToReactiveFieldAnalyzer.cs  | 11 ++++++++---
 .../Diagnostics/DiagnosticDescriptors.cs              |  2 +-
 .../ObservableAsPropertyGenerator.Execute.cs          |  2 +-
 5 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/README.md b/README.md
index b4e6cc7..0c5fb3a 100644
--- a/README.md
+++ b/README.md
@@ -81,7 +81,15 @@ using ReactiveUI.SourceGenerators;
 public partial class MyReactiveClass : ReactiveObject
 {
     [ObservableAsProperty]
-    private string _myProperty;
+    private string _myProperty = "Default Value";
+
+    public MyReactiveClass()
+    {
+        _myPrpertyHelper = MyPropertyObservable()
+            .ToProperty(this, x => x.MyProperty);
+    }
+
+    IObservable<string> MyPropertyObservable() => Observable.Return("Test Value");
 }
 ```
 
diff --git a/src/ReactiveUI.SourceGenerators.Execute/TestViewModel.cs b/src/ReactiveUI.SourceGenerators.Execute/TestViewModel.cs
index 1f34edb..d65e054 100644
--- a/src/ReactiveUI.SourceGenerators.Execute/TestViewModel.cs
+++ b/src/ReactiveUI.SourceGenerators.Execute/TestViewModel.cs
@@ -21,7 +21,7 @@ public partial class TestViewModel : ReactiveObject
     [JsonInclude]
     [DataMember]
     [ObservableAsProperty]
-    private double _test2Property;
+    private double _test2Property = 1.1d;
 
     [JsonInclude]
     [Reactive]
@@ -53,10 +53,11 @@ public TestViewModel()
         Test6ArgOnlyCommand?.Execute("Hello World").Subscribe();
         Test7ObservableCommand?.Execute().Subscribe();
 
+        Console.Out.WriteLine($"Test2Property default Value: {Test2Property}");
         _test2PropertyHelper = Test8ObservableCommand!.ToProperty(this, x => x.Test2Property);
 
         Test8ObservableCommand?.Execute(100).Subscribe(Console.Out.WriteLine);
-        Console.Out.WriteLine($"Test2Property Value: {Test2}");
+        Console.Out.WriteLine($"Test2Property Value: {Test2Property}");
         Console.Out.WriteLine($"Test2Property underlying Value: {_test2Property}");
 
         Test9AsyncCommand?.ThrownExceptions.Subscribe(Console.Out.WriteLine);
diff --git a/src/ReactiveUI.SourceGenerators/CodeAnalyzers/PropertyToReactiveFieldAnalyzer.cs b/src/ReactiveUI.SourceGenerators/CodeAnalyzers/PropertyToReactiveFieldAnalyzer.cs
index a17b9a8..c6fb054 100644
--- a/src/ReactiveUI.SourceGenerators/CodeAnalyzers/PropertyToReactiveFieldAnalyzer.cs
+++ b/src/ReactiveUI.SourceGenerators/CodeAnalyzers/PropertyToReactiveFieldAnalyzer.cs
@@ -34,9 +34,14 @@ public class PropertyToReactiveFieldAnalyzer : DiagnosticAnalyzer
         /// <param name="context">The context.</param>
         public override void Initialize(AnalysisContext context)
         {
-            context?.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
-            context?.EnableConcurrentExecution();
-            context?.RegisterSyntaxNodeAction(AnalyzeNode, SyntaxKind.PropertyDeclaration);
+            if (context is null)
+            {
+                throw new System.ArgumentNullException(nameof(context));
+            }
+
+            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+            context.EnableConcurrentExecution();
+            context.RegisterSyntaxNodeAction(AnalyzeNode, SyntaxKind.PropertyDeclaration);
         }
 
         private void AnalyzeNode(SyntaxNodeAnalysisContext context)
diff --git a/src/ReactiveUI.SourceGenerators/Diagnostics/DiagnosticDescriptors.cs b/src/ReactiveUI.SourceGenerators/Diagnostics/DiagnosticDescriptors.cs
index 5a5ec5f..a9172da 100644
--- a/src/ReactiveUI.SourceGenerators/Diagnostics/DiagnosticDescriptors.cs
+++ b/src/ReactiveUI.SourceGenerators/Diagnostics/DiagnosticDescriptors.cs
@@ -137,7 +137,7 @@ internal static class DiagnosticDescriptors
         category: typeof(ReactiveCommandGenerator).FullName,
         defaultSeverity: DiagnosticSeverity.Error,
         isEnabledByDefault: true,
-        description: "All asynchronous methods annotated with [ReactiveCommand] should return a Task type, to benefit from the additional support provided by ReactiveCommand and ReactiveCommand<T>.",
+        description: "All asynchronous methods annotated with [ReactiveCommand] should return a Task type, to benefit from the additional support provided by ReactiveCommand.FromTask.",
         helpLinkUri: "https://www.reactiveui.net/errors/RXUISG0008");
 
     /// <summary>
diff --git a/src/ReactiveUI.SourceGenerators/ObservableAsProperty/ObservableAsPropertyGenerator.Execute.cs b/src/ReactiveUI.SourceGenerators/ObservableAsProperty/ObservableAsPropertyGenerator.Execute.cs
index c4ea3fb..89505ff 100644
--- a/src/ReactiveUI.SourceGenerators/ObservableAsProperty/ObservableAsPropertyGenerator.Execute.cs
+++ b/src/ReactiveUI.SourceGenerators/ObservableAsProperty/ObservableAsPropertyGenerator.Execute.cs
@@ -64,7 +64,7 @@ internal static ImmutableArray<MemberDeclarationSyntax> GetPropertySyntax(Proper
                 getterFieldIdentifierName = propertyInfo.FieldName;
             }
 
-            var getterArrowExpression = ArrowExpressionClause(ParseExpression($"{getterFieldIdentifierName} = {getterFieldIdentifierName + "Helper"}.Value"));
+            var getterArrowExpression = ArrowExpressionClause(ParseExpression($"{getterFieldIdentifierName} = ({getterFieldIdentifierName}Helper?.Value ?? {getterFieldIdentifierName})"));
 
             // Prepare the forwarded attributes, if any
             var forwardedAttributes =