[XSG] Fix Style Setters referencing source-generated bindable properties

src/Controls/src/SourceGen/NodeSGExtensions.cs

@@ -599,21 +599,25 @@ public static (IFieldSymbol?, IPropertySymbol?) GetFieldOrBP(ITypeSymbol owner,
 		return (bpFieldSymbol, property);
 	}
 
-	public static IFieldSymbol GetBindableProperty(this ValueNode node, SourceGenContext context)
+	/// <summary>
+	/// Gets the TargetType symbol from a parent node (Style, Trigger, DataTrigger, MultiTrigger).
+	/// Used to resolve bindable properties when only the property name is specified.
+	/// </summary>
+	public static ITypeSymbol? GetTargetTypeSymbol(INode node, SourceGenContext context)
 	{
-		static ITypeSymbol? GetTargetTypeSymbol(INode node, SourceGenContext context)
-		{
-			var ttnode = (node as ElementNode)?.Properties[new XmlName("", "TargetType")];
-			//it's either a value
-			if (ttnode is ValueNode { Value: string tt })
-				return XmlTypeExtensions.GetTypeSymbol(tt, context, node);
-			//or a x:Type that we parsed earlier
-			if (context.Types.TryGetValue(ttnode!, out var typeSymbol))
-				return typeSymbol;
-			//FIXME: report diagnostic on missing TargetType
-			return null;
-		}
+		var ttnode = (node as ElementNode)?.Properties[new XmlName("", "TargetType")];
+		//it's either a value
+		if (ttnode is ValueNode { Value: string tt })
+			return XmlTypeExtensions.GetTypeSymbol(tt, context, node);
+		//or a x:Type that we parsed earlier
+		if (ttnode != null && context.Types.TryGetValue(ttnode, out var typeSymbol))
+			return typeSymbol;
+		//FIXME: report diagnostic on missing TargetType
+		return null;
+	}
 
+	public static IFieldSymbol GetBindableProperty(this ValueNode node, SourceGenContext context)
+	{
 		var parts = ((string)node.Value).Split('.');
 		if (parts.Length == 1)
 		{

src/Controls/src/SourceGen/SetterValueProvider.cs

@@ -43,7 +43,12 @@ public bool TryProvideValue(ElementNode node, IndentedTextWriter writer, SourceG
 		}
 
 		var bpNode = (ValueNode)node.Properties[new XmlName("", "Property")];
-		var bpRef = bpNode.GetBindableProperty(context);
+		IFieldSymbol? bpRef = bpNode.GetBindableProperty(context);
+		if (!TryGetBindablePropertyNameAndType(bpRef, bpNode, context, out var bpName, out var bpType))
+		{
+			value = string.Empty;
+			return false;
+		}
 
 		string targetsetter;
 		if (node.Properties.TryGetValue(new XmlName("", "TargetName"), out var targetNode))
@@ -53,18 +58,32 @@ public bool TryProvideValue(ElementNode node, IndentedTextWriter writer, SourceG
 
 		if (valueNode is ValueNode vn)
 		{
-			value = $"new global::Microsoft.Maui.Controls.Setter {{{targetsetter}Property = {bpRef.ToFQDisplayString()}, Value = {vn.ConvertTo(bpRef, writer, context)}}}";
+			string valueString;
+			if (bpRef != null)
+			{
+				valueString = vn.ConvertTo(bpRef, writer, context);
+			}
+			else if (bpType != null)
+			{
+				valueString = vn.ConvertTo(bpType, null, writer, context);
+			}
+			else
+			{
+				value = string.Empty;
+				return false;
+			}
+			value = $"new global::Microsoft.Maui.Controls.Setter {{{targetsetter}Property = {bpName}, Value = {valueString}}}";
 			return true;
 		}
 		else if (getNodeValue != null)
 		{
-			var lvalue = getNodeValue(valueNode, bpRef.Type);
-			value = $"new global::Microsoft.Maui.Controls.Setter {{{targetsetter}Property = {bpRef.ToFQDisplayString()}, Value = {lvalue.ValueAccessor}}}";
+			var lvalue = getNodeValue(valueNode, bpType ?? context.Compilation.ObjectType);
+			value = $"new global::Microsoft.Maui.Controls.Setter {{{targetsetter}Property = {bpName}, Value = {lvalue.ValueAccessor}}}";
 			return true;
 		}
 		else if (context.Variables.TryGetValue(valueNode, out var variable))
 		{
-			value = $"new global::Microsoft.Maui.Controls.Setter {{{targetsetter}Property = {bpRef.ToFQDisplayString()}, Value = {variable.ValueAccessor}}}";
+			value = $"new global::Microsoft.Maui.Controls.Setter {{{targetsetter}Property = {bpName}, Value = {variable.ValueAccessor}}}";
 			return true;
 		}
 
@@ -73,6 +92,58 @@ public bool TryProvideValue(ElementNode node, IndentedTextWriter writer, SourceG
 		return false;
 	}
 
+	/// <summary>
+	/// Gets the bindable property name and type for a Setter's Property attribute.
+	/// Uses the resolved field symbol if available, otherwise uses heuristics for source-generated properties.
+	/// </summary>
+	/// <returns>True if the property could be resolved, false otherwise.</returns>
+	private static bool TryGetBindablePropertyNameAndType(IFieldSymbol? bpRef, ValueNode bpNode, SourceGenContext context, out string bpName, out ITypeSymbol? bpType)
+	{
+		if (bpRef != null)
+		{
+			bpName = bpRef.ToFQDisplayString();
+			bpType = bpRef.GetBPTypeAndConverter(context)?.type;
+			return true;
+		}
+
+		var propertyText = bpNode.Value as string ?? string.Empty;
+		var parts = propertyText.Split('.');
+
+		ITypeSymbol? targetType = null;
+		string propertyName;
+
+		if (parts.Length == 1)
+		{
+			propertyName = parts[0];
+			var parent = bpNode.Parent?.Parent as ElementNode ?? (bpNode.Parent?.Parent as IListNode)?.Parent as ElementNode;
+			if (parent?.XmlType.IsOfAnyType("Trigger", "DataTrigger", "MultiTrigger", "Style") == true)
+				targetType = NodeSGExtensions.GetTargetTypeSymbol(parent, context);
+		}
+		else if (parts.Length == 2)
+		{
+			targetType = XmlTypeExtensions.GetTypeSymbol(parts[0], context, bpNode);
+			propertyName = parts[1];
+		}
+		else
+		{
+			bpName = string.Empty;
+			bpType = null;
+			return false;
+		}
+
+		if (targetType != null && targetType.HasBindablePropertyHeuristic(propertyName, context, out var explicitPropertyName))
+		{
+			var bpFieldName = explicitPropertyName ?? $"{propertyName}Property";
+			bpName = $"{targetType.ToFQDisplayString()}.{bpFieldName}";
+			bpType = targetType.GetAllProperties(propertyName, context).FirstOrDefault()?.Type;
+			return true;
+		}
+
+		bpName = string.Empty;
+		bpType = null;
+		return false;
+	}
+
 	/// <summary>
 	/// Shared helper to get the value node from a Setter element.
 	/// Checks properties first, then collection items.

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

@@ -383,4 +383,70 @@ public class BalanceView : Label
 		Assert.NotNull(generated);
 		Assert.Contains(".Balance = ", generated, StringComparison.Ordinal);
 	}
+
+	[Fact]
+	public void StyleSetter_WithSourceGeneratedBindableProperty_ShouldGenerateInlineSetter()
+	{
+		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:local="clr-namespace:Test"
+	x:Class="Test.TestPage">
+	<ContentPage.Resources>
+		<Style TargetType="local:BalanceView">
+			<Setter Property="Balance" Value="42.5" />
+		</Style>
+	</ContentPage.Resources>
+	<local:BalanceView />
+</ContentPage>
+""";
+
+		var code =
+"""
+using System;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+
+namespace CommunityToolkit.Maui
+{
+	// Simulates an attribute from a third-party library
+	public class BindablePropertyAttribute : Attribute
+	{
+		public string? PropertyName { get; set; }
+	}
+}
+
+namespace Test
+{
+	[XamlProcessing(XamlInflator.SourceGen)]
+	public partial class TestPage : ContentPage
+	{
+		public TestPage()
+		{
+			InitializeComponent();
+		}
+	}
+
+	public class BalanceView : Label
+	{
+		[CommunityToolkit.Maui.BindableProperty]
+		public double Balance { get; set; }
+	}
+}
+""";
+
+		// assertNoCompilationErrors: false because BalanceProperty is expected to be generated by another source generator
+		var (result, generated) = RunGenerator(xaml, code, assertNoCompilationErrors: false);
+
+		// Should NOT have errors
+		var errorDiagnostics = result.Diagnostics.Where(d => d.Severity == Microsoft.CodeAnalysis.DiagnosticSeverity.Error).ToList();
+		Assert.Empty(errorDiagnostics);
+
+		// Should have generated code with the Setter using the heuristically determined BalanceProperty
+		Assert.NotNull(generated);
+		Assert.Contains("Property = global::Test.BalanceView.BalanceProperty", generated, StringComparison.Ordinal);
+	}
 }