[XSG][BindingSourceGen] Add support for CommunityToolkit.Mvvm ObservablePropertyAttribute

src/Controls/src/BindingSourceGen/BindingSourceGenerator.cs

@@ -210,20 +210,30 @@ private static Result<ITypeSymbol> GetLambdaReturnType(LambdaExpressionSyntax la
 		var lambdaResultType = semanticModel.GetTypeInfo(lambdaBody, t).Type;
 		if (lambdaResultType == null || lambdaResultType is IErrorTypeSymbol)
 		{
-			// Try to infer the type from known patterns (e.g., RelayCommand properties)
+			// Try to infer the type from known patterns (e.g., RelayCommand, ObservableProperty)
 			if (lambdaBody is MemberAccessExpressionSyntax memberAccess)
 			{
 				var memberName = memberAccess.Name.Identifier.Text;
 				var expressionType = semanticModel.GetTypeInfo(memberAccess.Expression).Type;
-
-				if (expressionType != null && 
-				    expressionType.TryGetRelayCommandPropertyType(memberName, semanticModel.Compilation, out var commandType) &&
-				    commandType != null)
+
+				if (expressionType != null)
 				{
-					return Result<ITypeSymbol>.Success(commandType);
+					// Check for RelayCommand-generated properties
+					if (expressionType.TryGetRelayCommandPropertyType(memberName, semanticModel.Compilation, out var commandType) &&
+						commandType != null)
+					{
+						return Result<ITypeSymbol>.Success(commandType);
+					}
+
+					// Check for ObservableProperty-generated properties
+					if (expressionType.TryGetObservablePropertyType(memberName, semanticModel.Compilation, out var propertyType) &&
+						propertyType != null)
+					{
+						return Result<ITypeSymbol>.Success(propertyType);
+					}
 				}
 			}
-			
+
 			return Result<ITypeSymbol>.Failure(DiagnosticsFactory.LambdaResultCannotBeResolved(lambdaBody.GetLocation()));
 		}
 

src/Controls/src/BindingSourceGen/ITypeSymbolExtensions.cs

@@ -67,10 +67,10 @@ public static bool TryGetRelayCommandPropertyType(this ITypeSymbol symbol, strin
 
 		// Extract the method name (property name without "Command" suffix)
 		var methodName = propertyName.Substring(0, propertyName.Length - "Command".Length);
-		
+
 		// Look for a method with the base name - search in the type and base types
 		var methods = GetAllMethods(symbol, methodName);
-		
+
 		foreach (var method in methods)
 		{
 			// Check if the method has the RelayCommand attribute
@@ -93,6 +93,54 @@ public static bool TryGetRelayCommandPropertyType(this ITypeSymbol symbol, strin
 		return false;
 	}
 
+	/// <summary>
+	/// Checks if a property name could be generated by CommunityToolkit.Mvvm's [ObservableProperty] attribute,
+	/// and returns the inferred property type if found.
+	/// </summary>
+	/// <param name="symbol">The type to search</param>
+	/// <param name="propertyName">The name of the property to find</param>
+	/// <param name="compilation">The compilation (can be null)</param>
+	/// <param name="propertyType">The inferred property type if an ObservableProperty field is found</param>
+	/// <returns>True if an ObservableProperty field was found that would generate this property</returns>
+	public static bool TryGetObservablePropertyType(this ITypeSymbol symbol, string propertyName, Compilation? compilation, out ITypeSymbol? propertyType)
+	{
+		propertyType = null;
+
+		if (compilation == null || string.IsNullOrEmpty(propertyName))
+			return false;
+
+		// ObservableProperty generates a PascalCase property from a camelCase, _camelCase, or m_camelCase field
+		// Try common field naming patterns
+		var possibleFieldNames = new[]
+		{
+			char.ToLowerInvariant(propertyName[0]) + propertyName.Substring(1), // name from Name
+			"_" + char.ToLowerInvariant(propertyName[0]) + propertyName.Substring(1), // _name from Name
+			"m_" + char.ToLowerInvariant(propertyName[0]) + propertyName.Substring(1) // m_name from Name
+		};
+
+		// Look for a field with one of the possible names - search in the type and base types
+		foreach (var fieldName in possibleFieldNames)
+		{
+			var fields = GetAllFields(symbol, fieldName);
+
+			foreach (var field in fields)
+			{
+				// Check if the field has the ObservableProperty attribute
+				var hasObservableProperty = field.GetAttributes().Any(attr =>
+					attr.AttributeClass?.Name == "ObservablePropertyAttribute" ||
+					attr.AttributeClass?.ToDisplayString() == "CommunityToolkit.Mvvm.ComponentModel.ObservablePropertyAttribute");
+
+				if (hasObservableProperty)
+				{
+					propertyType = field.Type;
+					return true;
+				}
+			}
+		}
+
+		return false;
+	}
+
 	private static System.Collections.Generic.IEnumerable<IMethodSymbol> GetAllMethods(ITypeSymbol symbol, string name)
 	{
 		// Search in current type
@@ -114,4 +162,17 @@ private static System.Collections.Generic.IEnumerable<IMethodSymbol> GetAllMetho
 			baseType = baseType.BaseType;
 		}
 	}
+
+	private static System.Collections.Generic.IEnumerable<IFieldSymbol> GetAllFields(ITypeSymbol? symbol, string name)
+	{
+		while (symbol != null)
+		{
+			foreach (var member in symbol.GetMembers(name))
+			{
+				if (member is IFieldSymbol field)
+					yield return field;
+			}
+			symbol = symbol.BaseType;
+		}
+	}
 }

src/Controls/src/BindingSourceGen/PathParser.cs

@@ -87,7 +87,7 @@ private bool TryHandleSpecialCases(string memberName, ITypeSymbol expressionType
 		pathPart = null;
 
 		// Check for RelayCommand-generated properties
-		if (expressionType.TryGetRelayCommandPropertyType(memberName, _context.SemanticModel.Compilation, out var commandType) 
+		if (expressionType.TryGetRelayCommandPropertyType(memberName, _context.SemanticModel.Compilation, out var commandType)
 			&& commandType != null)
 		{
 			var memberType = commandType.CreateTypeDescription(_enabledNullable);
@@ -105,6 +105,25 @@ private bool TryHandleSpecialCases(string memberName, ITypeSymbol expressionType
 			return true;
 		}
 
+		// Check for ObservableProperty-generated properties
+		if (expressionType.TryGetObservablePropertyType(memberName, _context.SemanticModel.Compilation, out var propertyType)
+			&& propertyType != null)
+		{
+			var memberType = propertyType.CreateTypeDescription(_enabledNullable);
+			var containingType = expressionType.CreateTypeDescription(_enabledNullable);
+
+			pathPart = new MemberAccess(
+				MemberName: memberName,
+				IsValueType: !propertyType.IsReferenceType,
+				ContainingType: containingType,
+				MemberType: memberType,
+				Kind: AccessorKind.Property,
+				IsGetterInaccessible: false, // Assume generated property is accessible
+				IsSetterInaccessible: false); // ObservableProperty properties have setters
+
+			return true;
+		}
+
 		return false;
 	}
 

src/Controls/src/SourceGen/ITypeSymbolExtensions.cs

@@ -2,10 +2,9 @@
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
-
 using Microsoft.CodeAnalysis;
-using Microsoft.Maui.Controls.Xaml;
 using Microsoft.Maui.Controls.BindingSourceGen;
+using Microsoft.Maui.Controls.Xaml;
 
 namespace Microsoft.Maui.Controls.SourceGen;
 
@@ -85,15 +84,15 @@ public static IEnumerable<IPropertySymbol> GetAllProperties(this ITypeSymbol sym
 		=> symbol.GetAllMembers(name, context).OfType<IPropertySymbol>();
 
 	/// <summary>
-	/// Tries to get a property by name, and if not found, checks if it could be inferred from a RelayCommand method.
+	/// Tries to get a property by name, and if not found, checks if it could be inferred from a RelayCommand method or ObservableProperty field.
 	/// Returns the property type if found or inferred.
 	/// </summary>
 	/// <param name="symbol">The type to search</param>
 	/// <param name="propertyName">The name of the property to find</param>
 	/// <param name="context">The source generation context</param>
-	/// <param name="property">The found property symbol (null if inferred from RelayCommand)</param>
-	/// <param name="propertyType">The property type (either from the property or inferred from RelayCommand)</param>
-	/// <returns>True if property exists or can be inferred from RelayCommand</returns>
+	/// <param name="property">The found property symbol (null if inferred from RelayCommand or ObservableProperty)</param>
+	/// <param name="propertyType">The property type (either from the property or inferred from RelayCommand/ObservableProperty)</param>
+	/// <returns>True if property exists or can be inferred from RelayCommand or ObservableProperty</returns>
 	public static bool TryGetProperty(
 		this ITypeSymbol symbol,
 		string propertyName,
@@ -103,7 +102,7 @@ public static bool TryGetProperty(
 	{
 		property = symbol.GetAllProperties(propertyName, context)
 			.FirstOrDefault(p => p.GetMethod != null && !p.GetMethod.IsStatic);
-		
+
 		if (property != null)
 		{
 			propertyType = property.Type;
@@ -117,6 +116,13 @@ public static bool TryGetProperty(
 			return true;
 		}
 
+		// If property not found, check if it could be an ObservableProperty-generated property
+		// Call the BindingSourceGen extension method directly
+		if (symbol.TryGetObservablePropertyType(propertyName, context?.Compilation, out propertyType))
+		{
+			return true;
+		}
+
 		propertyType = null;
 		return false;
 	}

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

@@ -0,0 +1,160 @@
+using System.Linq;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.Maui.Controls.BindingSourceGen;
+using Xunit;
+
+namespace BindingSourceGen.UnitTests;
+
+public class ObservablePropertyTests
+{
+	// Note: Expression-based bindings work with ObservableProperty through type inference in
+	// GetLambdaReturnType. The generated interceptor code will be correct. In tests,
+	// we'll see compilation errors because the actual generated property doesn't exist
+	// (CommunityToolkit.Mvvm's source generator isn't running in the test environment),
+	// but the interceptor code itself is generated correctly.
+
+	[Fact]
+	public void GenerateBindingToObservablePropertyFromCamelCaseField()
+	{
+		var source = """
+			using Microsoft.Maui.Controls;
+			using System.Collections.ObjectModel;
+
+			namespace CommunityToolkit.Mvvm.ComponentModel
+			{
+				[System.AttributeUsage(System.AttributeTargets.Field)]
+				public class ObservablePropertyAttribute : System.Attribute { }
+			}
+
+			namespace TestApp
+			{
+				public class MyViewModel
+				{
+					[CommunityToolkit.Mvvm.ComponentModel.ObservableProperty]
+					private string? name;
+					// Name property will be generated by CommunityToolkit.Mvvm
+				}
+
+				public class TestCode
+				{
+					public void Test()
+					{
+						var label = new Label();
+						label.SetBinding(Label.TextProperty, static (MyViewModel vm) => vm.Name);
+					}
+				}
+			}
+			""";
+
+		var result = SourceGenHelpers.Run(source);
+
+		// The binding should be generated successfully with ObservableProperty inference
+		Assert.NotNull(result.Binding);
+
+		// Verify the generated interceptor code contains the correct getter and setter references
+		var allGeneratedCode = string.Join("\n\n", result.GeneratedFiles.Values);
+		// Check that the handler contains the property access
+		Assert.Contains("new(static source => source, \"Name\")", allGeneratedCode, System.StringComparison.Ordinal);
+		// Check that setter assigns to .Name
+		Assert.Contains("source.Name = value;", allGeneratedCode, System.StringComparison.Ordinal);
+
+		// Note: There will be compilation errors because Name doesn't actually exist,
+		// but the interceptor code itself is generated correctly. In real usage with
+		// CommunityToolkit.Mvvm, the property would exist and compile successfully.
+	}
+
+	[Fact]
+	public void GenerateBindingToObservablePropertyFromUnderscorePrefixedField()
+	{
+		var source = """
+			using Microsoft.Maui.Controls;
+			using System.Collections.ObjectModel;
+
+			namespace CommunityToolkit.Mvvm.ComponentModel
+			{
+				[System.AttributeUsage(System.AttributeTargets.Field)]
+				public class ObservablePropertyAttribute : System.Attribute { }
+			}
+
+			namespace TestApp
+			{
+				public class MyViewModel
+				{
+					[CommunityToolkit.Mvvm.ComponentModel.ObservableProperty]
+					private string? _title;
+					// Title property will be generated by CommunityToolkit.Mvvm
+				}
+
+				public class TestCode
+				{
+					public void Test()
+					{
+						var label = new Label();
+						label.SetBinding(Label.TextProperty, static (MyViewModel vm) => vm.Title);
+					}
+				}
+			}
+			""";
+
+		var result = SourceGenHelpers.Run(source);
+
+		// The binding should be generated successfully with ObservableProperty inference
+		Assert.NotNull(result.Binding);
+
+		// Verify the generated interceptor code contains the correct getter and setter references
+		var allGeneratedCode = string.Join("\n\n", result.GeneratedFiles.Values);
+		// Check that the handler contains the property access
+		Assert.Contains("new(static source => source, \"Title\")", allGeneratedCode, System.StringComparison.Ordinal);
+		// Check that setter assigns to .Title
+		Assert.Contains("source.Title = value;", allGeneratedCode, System.StringComparison.Ordinal);
+	}
+
+	[Fact]
+	public void GenerateBindingToObservablePropertyCollection()
+	{
+		var source = """
+			using Microsoft.Maui.Controls;
+			using System.Collections.ObjectModel;
+
+			namespace CommunityToolkit.Mvvm.ComponentModel
+			{
+				[System.AttributeUsage(System.AttributeTargets.Field)]
+				public class ObservablePropertyAttribute : System.Attribute { }
+			}
+
+			namespace TestApp
+			{
+				public class Tag { }
+
+				public class MyViewModel
+				{
+					[CommunityToolkit.Mvvm.ComponentModel.ObservableProperty]
+					private ObservableCollection<Tag> _tags = new();
+					// Tags property will be generated by CommunityToolkit.Mvvm
+				}
+
+				public class TestCode
+				{
+					public void Test()
+					{
+						var label = new Label();
+						label.SetBinding(Label.BindingContextProperty, static (MyViewModel vm) => vm.Tags);
+					}
+				}
+			}
+			""";
+
+		var result = SourceGenHelpers.Run(source);
+
+		// The binding should be generated successfully with ObservableProperty inference
+		Assert.NotNull(result.Binding);
+
+		// Verify the generated interceptor code contains the correct getter and setter references
+		var allGeneratedCode = string.Join("\n\n", result.GeneratedFiles.Values);
+		// Check that the handler contains the property access
+		Assert.Contains("new(static source => source, \"Tags\")", allGeneratedCode, System.StringComparison.Ordinal);
+		// Check that setter assigns to .Tags
+		Assert.Contains("source.Tags = value;", allGeneratedCode, System.StringComparison.Ordinal);
+	}
+}