[XAML] Incremental XAML Hot Reload (source-generated patch chains)

src/Controls/samples/Controls.Sample.Sandbox/MainPage.xaml

@@ -1,3 +1,157 @@
-<ContentPage x:Class="Maui.Controls.Sample.MainPage"
-             xmlns:local="clr-namespace:Maui.Controls.Sample">
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.MainPage"
+             xmlns:local="clr-namespace:Maui.Controls.Sample"
+             Title="XAML Incremental Hot Reload Sandbox"
+             BackgroundColor="White">
+
+    <ScrollView Padding="20">
+        <VerticalStackLayout Spacing="15">
+
+            <!-- Header -->
+            <Label Text="🔥 Incremental Hot Reload Sandbox"
+                   FontSize="24"
+                   FontAttributes="Bold"
+                   HorizontalOptions="Center"
+                   TextColor="DarkSlateBlue" />
+
+            <Label Text="Edit this XAML while the app is running to test incremental hot reload. Property changes (text, colors, sizes) should apply without a full page reload."
+                   FontSize="14"
+                   TextColor="Gray"
+                   HorizontalOptions="Center"
+                   HorizontalTextAlignment="Center" />
+
+            <BoxView HeightRequest="1" Color="LightGray" />
+
+            <!-- Section 1: Simple property changes -->
+            <Label Text="1. Simple Properties"
+                   FontSize="18"
+                   FontAttributes="Bold"
+                   TextColor="DarkSlateBlue" />
+
+            <Label x:Name="TestLabel"
+                   Text="Try changing this text!"
+                   FontSize="20"
+                   TextColor="CornflowerBlue"
+                   HorizontalOptions="Center" />
+
+            <Button x:Name="TestButton"
+                    Text="Button — change my text or color"
+                    BackgroundColor="MediumSlateBlue"
+                    TextColor="White"
+                    FontSize="16"
+                    CornerRadius="10"
+                    Padding="15,10"
+                    HorizontalOptions="Center"
+                    Clicked="OnTestButtonClicked" />
+
+            <Label x:Name="ClickCountLabel"
+                   Text="Clicks: 0"
+                   FontSize="14"
+                   TextColor="Gray"
+                   HorizontalOptions="Center" />
+
+            <BoxView HeightRequest="1" Color="LightGray" />
+
+            <!-- Section 2: Numeric properties -->
+            <Label Text="2. Numeric Properties"
+                   FontSize="18"
+                   FontAttributes="Bold"
+                   TextColor="DarkSlateBlue" />
+
+            <BoxView x:Name="ColorBox"
+                     HeightRequest="60"
+                     WidthRequest="200"
+                     CornerRadius="12"
+                     Color="Coral"
+                     HorizontalOptions="Center" />
+
+            <ProgressBar x:Name="TestProgress"
+                         Progress="0.65"
+                         ProgressColor="MediumSlateBlue"
+                         HorizontalOptions="Fill" />
+
+            <BoxView HeightRequest="1" Color="LightGray" />
+
+            <!-- Section 3: Layout with children -->
+            <Label Text="3. Layout Children"
+                   FontSize="18"
+                   FontAttributes="Bold"
+                   TextColor="DarkSlateBlue" />
+
+            <HorizontalStackLayout x:Name="ChipContainer"
+                                    Spacing="8"
+                                    HorizontalOptions="Center">
+                <Border BackgroundColor="LightCoral" StrokeShape="RoundRectangle 15" Stroke="Transparent" Padding="10,5">
+                    <Label Text="Chip A" TextColor="White" FontSize="12" />
+                </Border>
+                <Border BackgroundColor="CornflowerBlue" StrokeShape="RoundRectangle 15" Stroke="Transparent" Padding="10,5">
+                    <Label Text="Chip B" TextColor="White" FontSize="12" />
+                </Border>
+                <Border BackgroundColor="MediumSeaGreen" StrokeShape="RoundRectangle 15" Stroke="Transparent" Padding="10,5">
+                    <Label Text="Chip C" TextColor="White" FontSize="12" />
+                </Border>
+            </HorizontalStackLayout>
+
+            <Label Text="Try: add/remove/reorder chips above"
+                   FontSize="12"
+                   TextColor="Silver"
+                   HorizontalTextAlignment="Center"
+                   HorizontalOptions="Center" />
+
+            <BoxView HeightRequest="1" Color="LightGray" />
+
+            <!-- Section 4: Grid layout -->
+            <Label Text="4. Grid Layout"
+                   FontSize="18"
+                   FontAttributes="Bold"
+                   TextColor="DarkSlateBlue" />
+
+            <Grid ColumnDefinitions="*,*"
+                  RowDefinitions="Auto,Auto"
+                  ColumnSpacing="10"
+                  RowSpacing="10">
+                <Border BackgroundColor="#F0F4FF" StrokeShape="RoundRectangle 8" Stroke="Transparent" Padding="15">
+                    <VerticalStackLayout Spacing="5">
+                        <Label Text="📊" FontSize="28" HorizontalOptions="Center" />
+                        <Label Text="Card 1" FontAttributes="Bold" HorizontalTextAlignment="Center" />
+                        <Label Text="Change my text" FontSize="12" TextColor="Gray" HorizontalTextAlignment="Center" />
+                    </VerticalStackLayout>
+                </Border>
+                <Border Grid.Column="1" BackgroundColor="#FFF4F0" StrokeShape="RoundRectangle 8" Stroke="Transparent" Padding="15">
+                    <VerticalStackLayout Spacing="5">
+                        <Label Text="🎨" FontSize="28" HorizontalOptions="Center" />
+                        <Label Text="Card 2" FontAttributes="Bold" HorizontalTextAlignment="Center" />
+                        <Label Text="Change my color" FontSize="12" TextColor="Gray" HorizontalTextAlignment="Center" />
+                    </VerticalStackLayout>
+                </Border>
+                <Border Grid.Row="1" BackgroundColor="#F0FFF4" StrokeShape="RoundRectangle 8" Stroke="Transparent" Padding="15">
+                    <VerticalStackLayout Spacing="5">
+                        <Label Text="🚀" FontSize="28" HorizontalOptions="Center" />
+                        <Label Text="Card 3" FontAttributes="Bold" HorizontalTextAlignment="Center" />
+                        <Label Text="Change my emoji" FontSize="12" TextColor="Gray" HorizontalTextAlignment="Center" />
+                    </VerticalStackLayout>
+                </Border>
+                <Border Grid.Row="1" Grid.Column="1" BackgroundColor="#FFF0FF" StrokeShape="RoundRectangle 8" Stroke="Transparent" Padding="15">
+                    <VerticalStackLayout Spacing="5">
+                        <Label Text="⚡" FontSize="28" HorizontalOptions="Center" />
+                        <Label Text="Card 4" FontAttributes="Bold" HorizontalTextAlignment="Center" />
+                        <Label Text="Add more cards!" FontSize="12" TextColor="Gray" HorizontalTextAlignment="Center" />
+                    </VerticalStackLayout>
+                </Border>
+            </Grid>
+
+            <BoxView HeightRequest="1" Color="LightGray" />
+
+            <!-- Section 5: Version info -->
+            <Label x:Name="VersionLabel"
+                   Text="Version info will appear here"
+                   FontSize="12"
+                   TextColor="Silver"
+                   HorizontalOptions="Center"
+                   HorizontalTextAlignment="Center" />
+
+        </VerticalStackLayout>
+    </ScrollView>
+
 </ContentPage>

src/Controls/samples/Controls.Sample.Sandbox/MainPage.xaml.cs

@@ -1,9 +1,43 @@
-namespace Maui.Controls.Sample;
+using Microsoft.Maui.Controls.Xaml;
+
+namespace Maui.Controls.Sample;
 
 public partial class MainPage : ContentPage
 {
+	int _clickCount;
+
 	public MainPage()
 	{
 		InitializeComponent();
+		UpdateVersionInfo();
+	}
+
+	void OnTestButtonClicked(object? sender, EventArgs e)
+	{
+		_clickCount++;
+		ClickCountLabel.Text = $"Clicks: {_clickCount}";
+	}
+
+	void UpdateVersionInfo()
+	{
+		// Show whether incremental hot reload infrastructure is active
+		var registryType = typeof(XamlComponentRegistry);
+		var hasRegistry = registryType != null;
+
+		// Check if __version field exists (generated when EnableMauiIncrementalHotReload=true)
+		var versionField = GetType().GetField("__version",
+			System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
+		var hasVersionField = versionField != null;
+		var currentVersion = hasVersionField ? versionField!.GetValue(this) : "N/A";
+
+		// Check if UpdateComponent method exists
+		var ucMethod = GetType().GetMethod("UpdateComponent",
+			System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance,
+			null, Type.EmptyTypes, null);
+		var hasUC = ucMethod != null;
+
+		VersionLabel.Text = $"Registry: {(hasRegistry ? "✅" : "❌")} | " +
+			$"__version field: {(hasVersionField ? "✅" : "❌")} (={currentVersion}) | " +
+			$"UpdateComponent: {(hasUC ? "✅" : "❌")}";
 	}
 }

src/Controls/samples/Controls.Sample.Sandbox/Maui.Controls.Sample.Sandbox.csproj

@@ -16,6 +16,8 @@
     <!-- NOTE: By default the UseMaterial3 flag value is false. If you change the UseMaterial3 flag, you MUST delete the artifacts folder 
        and rebuild the entire codebase using: dotnet build ./Microsoft.Maui.BuildTasks.slnf -->
     <UseMaterial3>false</UseMaterial3>
+    <!-- Enable XAML Incremental Hot Reload via source generator -->
+    <EnableMauiIncrementalHotReload>true</EnableMauiIncrementalHotReload>
   </PropertyGroup>
 
   <PropertyGroup>

src/Controls/src/Build.Tasks/nuget/buildTransitive/netstandard2.0/Microsoft.Maui.Controls.Common.targets

@@ -34,5 +34,7 @@
     <CompilerVisibleProperty Include="EnablePreviewFeatures" />
     <CompilerVisibleProperty Include="MauiXamlLazyRD" />
 		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="LazyRD" />
+    <CompilerVisibleProperty Include="EnableMauiIncrementalHotReload" />
+		<CompilerVisibleItemMetadata Include="AdditionalFiles" MetadataName="EnableIncrementalHotReload" />
 	</ItemGroup>
 </Project>

src/Controls/src/Build.Tasks/nuget/buildTransitive/netstandard2.0/Microsoft.Maui.Controls.targets

@@ -380,6 +380,10 @@
                                       Condition="'$(UseMaterial3)' != ''"
                                       Value="$(UseMaterial3)"
                                       Trim="true" />
+      <RuntimeHostConfigurationOption Include="Microsoft.Maui.RuntimeFeature.IsIncrementalHotReloadEnabled"
+                                      Condition="'$(EnableMauiIncrementalHotReload)' != ''"
+                                      Value="$(EnableMauiIncrementalHotReload)"
+                                      Trim="true" />
     </ItemGroup>
   </Target>
 

src/Controls/src/SourceGen/CSharpExpressionHelpers.cs

@@ -348,12 +348,15 @@ public static (string? prefix, string name) ParseBareIdentifier(string value)
 		"FontImage",
 	};
 
-	static bool IsKnownMarkupExtension(string name)
+	internal static bool IsKnownMarkupExtensionName(string name)
 	{
 		return KnownMarkupExtensions.Contains(name)
 			|| KnownMarkupExtensions.Contains(name + "Extension");
 	}
 
+	// Keep backward compat for existing callers
+	static bool IsKnownMarkupExtension(string name) => IsKnownMarkupExtensionName(name);
+
 	/// <summary>
 	/// Extracts the C# code from an expression value and transforms quotes.
 	/// Single-quoted strings are always transformed to double-quoted strings since C# doesn't support single-quoted strings.