Fix CS8603 error for nullable reference types in SourceGen binding paths

src/Controls/src/SourceGen/CompiledBindingMarkup.cs

@@ -407,19 +407,17 @@ bool TryParsePath(
 			}
 		}
 
-		if (isNullable)
+		propertyType = previousPartType;
+
+		// Apply nullable annotation if any part of the path introduces nullability
+		// For reference types, mark as nullable so the TypedBinding signature is correct
+		// For value types, we don't mark as nullable here because GenerateGetterExpression
+		// will add ?? default fallback for non-nullable value types with conditional access
+		if (isNullable && !propertyType.IsValueType)
 		{
-			if (propertyType.IsValueType)
-			{
-				propertyType = _context.Compilation.GetSpecialType(SpecialType.System_Nullable_T).Construct(propertyType);
-			}
-			else
-			{
-				propertyType = propertyType.WithNullableAnnotation(NullableAnnotation.Annotated);
-			}
+			propertyType = propertyType.WithNullableAnnotation(NullableAnnotation.Annotated);
 		}
 
-		propertyType = previousPartType;
 		bindingPath = new EquatableArray<IPathPart>(bindingPathParts.ToArray());
 		return true;
 	}

src/Controls/tests/BindingSourceGen.UnitTests/IntegrationTests.cs

@@ -2303,6 +2303,147 @@ internal static partial class GeneratedBindingInterceptors
 			""",
 			result.GeneratedFiles["Path-To-Program.cs-GeneratedBindingInterceptors-14-11.g.cs"]);
 	}
+
+	[Fact]
+	public void GenerateBindingWithNullableObjectAndNullableReferenceTypeProperty_SetBinding()
+	{
+		var source = """
+		using Microsoft.Maui.Controls;
+		var label = new Label();
+		label.SetBinding(Label.TextProperty, static (Foo f) => f.NullableObject?.StringProperty);
+
+		class Foo
+		{
+			public Bar? NullableObject { get; set; }
+		}
+
+		class Bar
+		{
+			public string StringProperty { get; set; } = "";
+		}
+		""";
+
+		var result = SourceGenHelpers.Run(source);
+		Assert.NotNull(result.Binding);
+
+		var id = Math.Abs(result.Binding.SimpleLocation!.GetHashCode());
+
+		// The key assertion: no CS8603 errors should be present
+		AssertExtensions.AssertNoDiagnostics(result);
+		AssertExtensions.CodeIsEqual(
+			$$"""
+			//------------------------------------------------------------------------------
+			// <auto-generated>
+			//     This code was generated by a .NET MAUI source generator.
+			//
+			//     Changes to this file may cause incorrect behavior and will be lost if
+			//     the code is regenerated.
+			// </auto-generated>
+			//------------------------------------------------------------------------------
+			#nullable enable
+
+			namespace System.Runtime.CompilerServices
+			{
+			    using System;
+			    using System.Diagnostics;
+
+			    {{BindingCodeWriter.GeneratedCodeAttribute}}
+			    [Conditional("DEBUG")]
+			    [AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
+			    file sealed class InterceptsLocationAttribute : Attribute
+			    {
+			        public InterceptsLocationAttribute(int version, string data)
+			        {
+			            _ = version;
+			            _ = data;
+			        }
+			    }
+			}
+
+			namespace Microsoft.Maui.Controls.Generated
+			{
+			    internal static partial class GeneratedBindingInterceptors
+			    {
+
+			        {{BindingCodeWriter.GeneratedCodeAttribute}}
+			        [global::System.Runtime.CompilerServices.InterceptsLocationAttribute({{result.Binding.InterceptableLocation!.Version}}, @"{{result.Binding.InterceptableLocation!.Data}}")]
+			        public static void SetBinding{{id}}(
+			            this global::Microsoft.Maui.Controls.BindableObject bindableObject,
+			            global::Microsoft.Maui.Controls.BindableProperty bindableProperty,
+			            global::System.Func<global::Foo, string?> getter,
+			            global::Microsoft.Maui.Controls.BindingMode mode = global::Microsoft.Maui.Controls.BindingMode.Default,
+			            global::Microsoft.Maui.Controls.IValueConverter? converter = null,
+			            object? converterParameter = null,
+			            string? stringFormat = null,
+			            object? source = null,
+			            object? fallbackValue = null,
+			            object? targetNullValue = null)
+			        {
+			            global::System.Action<global::Foo, string?>? setter = null;
+			            if (ShouldUseSetter(mode, bindableProperty))
+			            {
+			                setter = static (source, value) =>
+			                {
+			                    if (value is null)
+			                    {
+			                        return;
+			                    }
+			                    if (source.NullableObject is {} p0)
+			                    {
+			                        p0.StringProperty = value;
+			                    }
+			                };
+			            }
+
+			            var binding = new global::Microsoft.Maui.Controls.Internals.TypedBinding<global::Foo, string?>(
+			                getter: source => (getter(source), true),
+			                setter,
+			                handlers: new global::System.Tuple<global::System.Func<global::Foo, object?>, string>[]
+			                {
+			                    new(static source => source, "NullableObject"),
+			                    new(static source => source.NullableObject, "StringProperty"),
+			                })
+			                {
+			                	Mode = mode,
+			                	Converter = converter,
+			                	ConverterParameter = converterParameter,
+			                	StringFormat = stringFormat,
+			                	Source = source,
+			                	FallbackValue = fallbackValue,
+			                	TargetNullValue = targetNullValue,
+			                };
+			            bindableObject.SetBinding(bindableProperty, binding);
+			        }
+			    }
+			}
+			""",
+			result.GeneratedFiles["Path-To-Program.cs-GeneratedBindingInterceptors-3-7.g.cs"]);
+	}
+
+	[Fact]
+	public void GenerateBindingWithNullableObjectAndNullableReferenceTypeProperty_Create()
+	{
+		var source = """
+		using Microsoft.Maui.Controls;
+		var binding = Binding.Create(static (Foo f) => f.NullableObject?.StringProperty);
+
+		class Foo
+		{
+			public Bar? NullableObject { get; set; }
+		}
+
+		class Bar
+		{
+			public string StringProperty { get; set; } = "";
+		}
+		""";
+
+		var result = SourceGenHelpers.Run(source);
+		Assert.NotNull(result.Binding);
+
+		// The key assertion: no CS8603 errors should be present
+		AssertExtensions.AssertNoDiagnostics(result);
+	}
 }
 
 

src/Controls/tests/SourceGen.UnitTests/InitializeComponent/CompiledBindings.cs

@@ -299,4 +299,193 @@ static IEnumerable<string> SplitCode(string code)
 				.Select(static line => line.Trim())
 				.Where(static line => !string.IsNullOrWhiteSpace(line));
 	}
+
+	[Fact]
+	public void CorrectlyDetectsNullableReferenceTypes()
+	{
+		var xaml =
+"""
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage
+	xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+	xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+	xmlns:test="clr-namespace:Test"
+	x:Class="Test.TestPage"
+	x:DataType="test:TestPage">
+	<Entry Text="{Binding Product.Name}"/>
+</ContentPage>
+""";
+
+		var code =
+"""
+#nullable enable
+using System;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+
+namespace Test;
+
+[XamlProcessing(XamlInflator.SourceGen)]
+public partial class TestPage : ContentPage
+{
+	public Product? Product { get; set; } = null;
+
+	public TestPage()
+	{
+		InitializeComponent();
+	}
+}
+
+public class Product
+{
+	public string Name { get; set; } = "";
+}
+""";
+		var testXamlFilePath = Path.Combine(Environment.CurrentDirectory, "Test.xaml");
+		var expected = $$"""
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by a .NET MAUI source generator.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+#nullable enable
+
+namespace Test;
+
+[global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Maui.Controls.SourceGen, Version=10.0.0.0, Culture=neutral, PublicKeyToken=null", "10.0.0.0")]
+public partial class TestPage
+{
+	private partial void InitializeComponent()
+	{
+		// Fallback to Runtime inflation if the page was updated by HotReload
+		static string? getPathForType(global::System.Type type)
+		{
+			var assembly = type.Assembly;
+			foreach (var xria in global::System.Reflection.CustomAttributeExtensions.GetCustomAttributes<global::Microsoft.Maui.Controls.Xaml.XamlResourceIdAttribute>(assembly))
+			{
+				if (xria.Type == type)
+					return xria.Path;
+			}
+			return null;
+		}
+
+		var rlr = global::Microsoft.Maui.Controls.Internals.ResourceLoader.ResourceProvider2?.Invoke(new global::Microsoft.Maui.Controls.Internals.ResourceLoader.ResourceLoadingQuery
+		{
+			AssemblyName = typeof(global::Test.TestPage).Assembly.GetName(),
+			ResourcePath = getPathForType(typeof(global::Test.TestPage)),
+			Instance = this,
+		});
+
+		if (rlr?.ResourceContent != null)
+		{
+			this.InitializeComponentRuntime();
+			return;
+		}
+
+		var bindingExtension = new global::Microsoft.Maui.Controls.Xaml.BindingExtension();
+		global::Microsoft.Maui.VisualDiagnostics.RegisterSourceInfo(bindingExtension!, new global::System.Uri(@"Test.xaml;assembly=SourceGeneratorDriver.Generated", global::System.UriKind.Relative), 8, 9);
+		var entry = new global::Microsoft.Maui.Controls.Entry();
+		global::Microsoft.Maui.VisualDiagnostics.RegisterSourceInfo(entry!, new global::System.Uri(@"Test.xaml;assembly=SourceGeneratorDriver.Generated", global::System.UriKind.Relative), 8, 3);
+		var __root = this;
+		global::Microsoft.Maui.VisualDiagnostics.RegisterSourceInfo(__root!, new global::System.Uri(@"Test.xaml;assembly=SourceGeneratorDriver.Generated", global::System.UriKind.Relative), 2, 2);
+#if !_MAUIXAML_SG_NAMESCOPE_DISABLE
+		global::Microsoft.Maui.Controls.Internals.INameScope iNameScope = global::Microsoft.Maui.Controls.Internals.NameScope.GetNameScope(__root) ?? new global::Microsoft.Maui.Controls.Internals.NameScope();
+#endif
+#if !_MAUIXAML_SG_NAMESCOPE_DISABLE
+		global::Microsoft.Maui.Controls.Internals.NameScope.SetNameScope(__root, iNameScope);
+#endif
+#if !_MAUIXAML_SG_NAMESCOPE_DISABLE
+		entry.transientNamescope = iNameScope;
+#endif
+#line 8 "{{testXamlFilePath}}"
+		bindingExtension.Path = "Product.Name";
+#line default
+		var bindingBase = CreateTypedBindingFrom_bindingExtension(bindingExtension);
+		if (global::Microsoft.Maui.VisualDiagnostics.GetSourceInfo(bindingBase!) == null)
+			global::Microsoft.Maui.VisualDiagnostics.RegisterSourceInfo(bindingBase!, new global::System.Uri(@"Test.xaml;assembly=SourceGeneratorDriver.Generated", global::System.UriKind.Relative), 8, 9);
+		entry.SetBinding(global::Microsoft.Maui.Controls.Entry.TextProperty, bindingBase);
+#line 8 "{{testXamlFilePath}}"
+		__root.SetValue(global::Microsoft.Maui.Controls.ContentPage.ContentProperty, entry);
+#line default
+		static global::Microsoft.Maui.Controls.BindingBase CreateTypedBindingFrom_bindingExtension(global::Microsoft.Maui.Controls.Xaml.BindingExtension extension)
+		{
+			global::System.Action<global::Test.TestPage, string?>? setter = static (source, value) =>
+			{
+				if (source.Product is {} p0)
+				{
+					p0.Name = value;
+				}
+			};
+
+			return new global::Microsoft.Maui.Controls.Internals.TypedBinding<global::Test.TestPage, string?>(
+				getter: source => (source.Product?.Name, true),
+				setter,
+				handlers: new global::System.Tuple<global::System.Func<global::Test.TestPage, object?>, string>[]
+				{
+					new(static source => source, "Product"),
+					new(static source => source.Product, "Name"),
+				});
+		}
+	}
+}
+
+""";
+
+		var (result, generated) = RunGenerator(xaml, code);
+		Assert.False(result.Diagnostics.Any());
+		CodeIsEqual(expected, generated ?? string.Empty);
+	}
+
+	[Fact]
+	public void CorrectlyDetectsNullableReferenceTypesWithNonNullableTarget()
+	{
+		// This test reproduces the CS8603 error scenario
+		var xaml =
+"""
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage
+	xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+	xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+	xmlns:test="clr-namespace:Test"
+	x:Class="Test.TestPage"
+	x:DataType="test:TestPage">
+	<Entry Text="{Binding Product.Name}"/>
+</ContentPage>
+""";
+
+		var code =
+"""
+#nullable enable
+using System;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+
+namespace Test;
+
+[XamlProcessing(XamlInflator.SourceGen)]
+public partial class TestPage : ContentPage
+{
+	public Product? Product { get; set; } = null;
+
+	public TestPage()
+	{
+		InitializeComponent();
+	}
+}
+
+public class Product
+{
+	public string Name { get; set; } = "";  // Non-nullable string
+}
+""";
+		var (result, generated) = RunGenerator(xaml, code);
+
+		// Check that no CS8603 errors are present - even with non-nullable target property,
+		// the generated getter should handle the nullable path correctly
+		Assert.False(result.Diagnostics.Any(d => d.Id == "CS8603"));
+		Assert.False(result.Diagnostics.Any(d => d.Severity == Microsoft.CodeAnalysis.DiagnosticSeverity.Error));
+	}
 }