Fix converter resource removal: register custom types in IC

IC only registered value-type resources (Color, String) in
RegisterResourceKeys, not custom types (converters). When a converter
was removed from XAML during HR, GetResourceKeys didn't include it,
so Resources.Remove was never called — the converter stayed in the
dictionary.

Fix: IC now also registers custom types that have a public
parameterless constructor, matching the UC's BuildResourceValueExpression
logic.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: StephaneDelcroix

src/Controls/src/SourceGen/InitializeComponentCodeWriter.cs

@@ -189,10 +189,22 @@ PrePost newblock() =>
 								if (elem.Properties.TryGetValue(xKeyName, out var keyNode)
 									&& keyNode is ValueNode kv && kv.Value is string keyStr)
 								{
-									// Only register keys for value-type resources we can encode (Color, String, etc.)
-									// Skip custom types (converters, etc.) that IC creates via new()
+									// Register keys for resources we can encode in UC:
+									// Value-type resources have a single ValueNode child (Color, String, etc.)
 									if (elem.CollectionItems.Count == 1 && elem.CollectionItems[0] is ValueNode)
+									{
 										resourceKeys.Add(keyStr);
+									}
+									// Custom types (converters, etc.) with a public parameterless constructor
+									else if (elem.CollectionItems.Count == 0 || elem.CollectionItems.All(c => c is not ValueNode))
+									{
+										if (elem.XmlType.TryResolveTypeSymbol(null, compilation, xmlnsCache, typeCache, out var resTypeSymbol)
+											&& resTypeSymbol != null
+											&& resTypeSymbol.InstanceConstructors.Any(c => c.Parameters.Length == 0 && c.DeclaredAccessibility == Microsoft.CodeAnalysis.Accessibility.Public))
+										{
+											resourceKeys.Add(keyStr);
+										}
+									}
 								}
 							}
 						}

src/Controls/tests/SourceGen.UnitTests/XamlIncrementalHotReloadPipelineTests.cs

@@ -1377,6 +1377,60 @@ public class StatusColorConverter : Microsoft.Maui.Controls.IValueConverter
 		Assert.Contains("new global::TestApp.StatusColorConverter()", uc, StringComparison.Ordinal);
 	}
 
+	[Fact]
+	public void ConverterResourceRemoved_UCEmitsRemove()
+	{
+		// Removing a converter resource should emit Resources.Remove("key") in UC.
+		XamlHotReloadState.Reset();
+
+		const string stubs = """
+			namespace TestApp
+			{
+				public class StatusColorConverter : Microsoft.Maui.Controls.IValueConverter
+				{
+					public object? Convert(object? value, System.Type targetType, object? parameter, System.Globalization.CultureInfo culture) => null;
+					public object? ConvertBack(object? value, System.Type targetType, object? parameter, System.Globalization.CultureInfo culture) => null;
+				}
+			}
+			""";
+
+		const string xamlV1 = """
+			<?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:TestApp"
+			             x:Class="TestApp.MainPage">
+			    <ContentPage.Resources>
+			        <Color x:Key="AccentColor">DarkBlue</Color>
+			        <local:StatusColorConverter x:Key="StatusConverter" />
+			    </ContentPage.Resources>
+			    <Label Text="Hello" />
+			</ContentPage>
+			""";
+		const string xamlV2 = """
+			<?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:TestApp"
+			             x:Class="TestApp.MainPage">
+			    <ContentPage.Resources>
+			        <Color x:Key="AccentColor">DarkBlue</Color>
+			    </ContentPage.Resources>
+			    <Label Text="Hello" />
+			</ContentPage>
+			""";
+
+		var (_, run2) = TwoRunsWithSource(xamlV1, xamlV2, stubs);
+		var uc = FindUCSource(run2, "uc.xsg");
+
+		Assert.NotNull(uc);
+		Assert.Contains("__version = 1", uc, StringComparison.Ordinal);
+		// UC must remove the converter from the dictionary
+		Assert.Contains("Resources.Remove", uc, StringComparison.Ordinal);
+		// The converter key should no longer be registered
+		Assert.DoesNotContain("\"StatusConverter\"", uc.Substring(uc.IndexOf("RegisterResourceKeys")), StringComparison.Ordinal);
+	}
+
 	[Fact]
 	public void ConverterSwap_UCCompilesCleanly()
 	{