[XSG] Generate unwrapping for compiled bindings with conditional access to non-nullable value types (#32402)

* Add test

* Generate unwrapping to return non-nullable value types

* Apply suggestion from @StephaneDelcroix

* Apply suggestion from @StephaneDelcroix

---------

Co-authored-by: Stephane Delcroix <[email protected]>

Author: simonrozsival

src/Controls/src/SourceGen/CompiledBindingMarkup.cs

@@ -84,7 +84,7 @@ public bool TryCompileBinding(ITypeSymbol sourceType, bool isTemplateBinding, ou
 				static global::Microsoft.Maui.Controls.BindingBase {{methodName}}({{extensionTypeName}} extension)
 				{
 					return Create(
-						getter: {{GenerateGetterLambda(binding.Path)}},
+						getter: {{GenerateGetterLambda(binding, targetNullValueExpression: isTemplateBinding ? null : "extension.TargetNullValue")}},
 						extension.Mode,
 						extension.Converter,
 						extension.ConverterParameter,
@@ -278,17 +278,32 @@ bool TryParsePath(
 		return true;
 	}
 
-	string GenerateGetterLambda(EquatableArray<IPathPart> bindingPath)
+	string GenerateGetterLambda(BindingInvocationDescription binding, string? targetNullValueExpression)
 	{
 		string expression = "source";
 		bool forceConditionalAccessToNextPart = false;
+		bool hasConditionalAccess = false;
 
-		foreach (var part in bindingPath)
+		foreach (var part in binding.Path)
 		{
 			// Note: AccessExpressionBuilder will happily call unsafe accessors and it expects them to be available.
 			// By calling BindingCodeWriter.GenerateBindingMethod(...), we are ensuring that the unsafe accessors are available.
 			expression = AccessExpressionBuilder.ExtendExpression(expression, MaybeWrapInConditionalAccess(part, forceConditionalAccessToNextPart));
 			forceConditionalAccessToNextPart = part is Cast;
+			hasConditionalAccess |= forceConditionalAccessToNextPart || part is ConditionalAccess;
+		}
+
+		if (hasConditionalAccess && binding.PropertyType is { IsValueType: true, IsNullable: false })
+		{
+			// for non-nullable value types with conditional access in the path, we need to unwrap the getter result
+			// with fallback to either the target null value or default
+			if (targetNullValueExpression is not null)
+			{
+				var nullablePropertyType = binding.PropertyType with { IsNullable = true };
+				expression = $"{expression} ?? {targetNullValueExpression} as {nullablePropertyType}";
+			}
+
+			expression = $"{expression} ?? default";
 		}
 
 		return $"static source => {expression}";

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

@@ -181,6 +181,181 @@ static bool ShouldUseSetter(global::Microsoft.Maui.Controls.BindingMode mode)
 	}
 }
 
+""";
+
+		var (result, generated) = RunGenerator(xaml, code);
+		Assert.False(result.Diagnostics.Any());
+		Assert.Equal(expected, generated, ignoreLineEndingDifferences: true);
+	}
+
+	[Fact]
+	public void CorrectlyDetectsNullableTypes()
+	{
+		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"
+    Title="{Binding Product.Size}"/>
+""";
+
+		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 int Size { 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, 5);
+		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
+#line 8 "{{testXamlFilePath}}"
+		bindingExtension.Path = "Product.Size";
+#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, 5);
+		__root.SetBinding(global::Microsoft.Maui.Controls.Page.TitleProperty, bindingBase);
+		static global::Microsoft.Maui.Controls.BindingBase CreateTypedBindingFrom_bindingExtension(global::Microsoft.Maui.Controls.Xaml.BindingExtension extension)
+{
+	return Create(
+		getter: static source => source.Product?.Size ?? extension.TargetNullValue as int? ?? default,
+		extension.Mode,
+		extension.Converter,
+		extension.ConverterParameter,
+		extension.StringFormat,
+		extension.Source,
+		extension.FallbackValue,
+		extension.TargetNullValue);
+
+	[global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Maui.Controls.BindingSourceGen, Version=10.0.0.0, Culture=neutral, PublicKeyToken=null", "10.0.0.0")]
+	static global::Microsoft.Maui.Controls.BindingBase Create(
+		global::System.Func<global::Test.TestPage, int> 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::Test.TestPage, int>? setter = null;
+		if (ShouldUseSetter(mode))
+		{
+				setter = static (source, value) =>
+				{
+					if (source.Product is {} p0)
+					{
+						p0.Size = value;
+					}
+				};
+		}
+		
+		var binding = new global::Microsoft.Maui.Controls.Internals.TypedBinding<global::Test.TestPage, int>(
+			getter: source => (getter(source), 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, "Size"),
+			})
+		{
+			Mode = mode,
+			Converter = converter,
+			ConverterParameter = converterParameter,
+			StringFormat = stringFormat,
+			Source = source,
+			FallbackValue = fallbackValue,
+			TargetNullValue = targetNullValue
+		};
+		
+		return binding;
+	}
+
+
+	[global::System.Runtime.CompilerServices.MethodImpl(global::System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
+	static bool ShouldUseSetter(global::Microsoft.Maui.Controls.BindingMode mode)
+		=> mode == global::Microsoft.Maui.Controls.BindingMode.OneWayToSource
+			|| mode == global::Microsoft.Maui.Controls.BindingMode.TwoWay
+			|| mode == global::Microsoft.Maui.Controls.BindingMode.Default;
+}
+		
+	}
+}
+
 """;
 
 		var (result, generated) = RunGenerator(xaml, code);