XAML Hot Reload: Improve incremental generation and coverage

src/Controls/src/SourceGen/InitializeComponentCodeWriter.cs

@@ -106,7 +106,7 @@ PrePost newblock() =>
 				var methodName = genSwitch ? "InitializeComponentSourceGen" : "InitializeComponent";
 				codeWriter.WriteLine($"private partial void {methodName}()");
 				root!.XmlType.TryResolveTypeSymbol(null, compilation, xmlnsCache, typeCache, out var baseType);
-				var sgcontext = new SourceGenContext(codeWriter, compilation, sourceProductionContext, xmlnsCache, typeCache, rootType!, baseType, xamlItem.ProjectItem);
+				var sgcontext = new SourceGenContext(codeWriter, compilation, sourceProductionContext, xmlnsCache, typeCache, rootType!, baseType, xamlItem.ProjectItem, sourceProductionContext.ReportDiagnostic);
 
 				// Compute stable node IDs before Visit() mutates the tree (markup expansion etc.)
 				// Use cached effective IDs (from state) if available, to stay consistent with UC patches.

src/Controls/src/SourceGen/SetPropertyHelpers.cs

@@ -229,7 +229,8 @@ public static void AddLazyResourceToResourceDictionary(IndentedTextWriter writer
 				context.TypeCache, 
 				context.RootType, 
 				null, 
-				context.ProjectItem)
+				context.ProjectItem,
+				context.ReportDiagnostic)
 			{
 				ParentContext = context
 			};

src/Controls/src/SourceGen/SourceGenContext.cs

@@ -9,17 +9,21 @@
 
 namespace Microsoft.Maui.Controls.SourceGen;
 
-class SourceGenContext(IndentedTextWriter writer, Compilation compilation, SourceProductionContext sourceProductionContext, AssemblyAttributes assemblyCaches, IDictionary<XmlType, INamedTypeSymbol> typeCache, ITypeSymbol rootType, ITypeSymbol? baseType, ProjectItem projectItem)
+class SourceGenContext(IndentedTextWriter writer, Compilation compilation, SourceProductionContext sourceProductionContext, AssemblyAttributes assemblyCaches, IDictionary<XmlType, INamedTypeSymbol> typeCache, ITypeSymbol rootType, ITypeSymbol? baseType, ProjectItem projectItem, Action<Diagnostic> diagnosticReporter)
 {
-	internal static SourceGenContext CreateNewForTests() => new SourceGenContext(
+	static readonly Action<Diagnostic> s_noOpDiagnosticReporter = static _ => { };
+	List<Diagnostic>? _bufferedDiagnostics;
+
+	internal static SourceGenContext CreateNewForTests(Action<Diagnostic>? diagnosticReporter = null) => new SourceGenContext(
 		null!,
 		null!,
 		default,
 		null!,
 		new Dictionary<XmlType, INamedTypeSymbol>(),
 		null!,
 		null,
-		null!);
+		null!,
+		diagnosticReporter ?? s_noOpDiagnosticReporter);
 
 	public SourceProductionContext SourceProductionContext => sourceProductionContext;
 	public IndentedTextWriter Writer => writer;
@@ -34,6 +38,12 @@ class SourceGenContext(IndentedTextWriter writer, Compilation compilation, Sourc
 	public IDictionary<INode, ILocalValue> Variables { get; } = new Dictionary<INode, ILocalValue>();
 	public void ReportDiagnostic(Diagnostic diagnostic)
 	{
+		if (ParentContext is not null)
+		{
+			ParentContext.ReportDiagnostic(diagnostic);
+			return;
+		}
+
 		// Check if this diagnostic should be suppressed based on NoWarn
 		var noWarn = ProjectItem?.NoWarn;
 		if (!string.IsNullOrEmpty(noWarn))
@@ -51,8 +61,42 @@ public void ReportDiagnostic(Diagnostic diagnostic)
 				}
 			}
 		}
-		sourceProductionContext.ReportDiagnostic(diagnostic);
+
+		if (_bufferedDiagnostics is not null)
+		{
+			_bufferedDiagnostics.Add(diagnostic);
+			return;
+		}
+
+		ReportDiagnosticCore(diagnostic);
 	}
+
+	internal int BufferedDiagnosticCount => _bufferedDiagnostics?.Count ?? 0;
+
+	internal void BeginDiagnosticBuffering()
+	{
+		if (_bufferedDiagnostics is not null)
+			throw new InvalidOperationException("Diagnostic buffering is already active.");
+
+		_bufferedDiagnostics = [];
+	}
+
+	internal void FlushBufferedDiagnostics()
+	{
+		if (_bufferedDiagnostics is null)
+			throw new InvalidOperationException("Diagnostic buffering is not active.");
+
+		var diagnostics = _bufferedDiagnostics;
+		_bufferedDiagnostics = null;
+		foreach (var diagnostic in diagnostics)
+			ReportDiagnosticCore(diagnostic);
+	}
+
+	internal void DiscardBufferedDiagnostics() => _bufferedDiagnostics = null;
+
+	void ReportDiagnosticCore(Diagnostic diagnostic)
+		=> diagnosticReporter(diagnostic);
+
 	public IDictionary<INode, ILocalValue> ServiceProviders { get; } = new Dictionary<INode, ILocalValue>();
 	public IDictionary<INode, (ILocalValue namescope, IDictionary<string, ILocalValue> namesInScope)> Scopes = new Dictionary<INode, (ILocalValue, IDictionary<string, ILocalValue>)>();
 	public SourceGenContext? ParentContext { get; set; }

src/Controls/src/SourceGen/UpdateComponentCodeWriter.cs

@@ -312,7 +312,8 @@ static void EmitChildListChange(
 				bool hasAdded = false;
 				for (int i = 0; i < change.NewChildren.Count; i++)
 				{
-					if (change.NewChildren[i].Kind == ChildChangeKind.Added) { hasAdded = true; break; }
+					if (change.NewChildren[i].Kind == ChildChangeKind.Added)
+					{ hasAdded = true; break; }
 				}
 				bool pureReorder = !hasAdded && change.RemovedNodeIds.Count == 0;
 
@@ -567,9 +568,218 @@ static void EmitNewElementProperties(
 				TryEmitMarkupNodeChange(codeWriter, syntheticDiff, typeSymbol, varName, isRoot: false,
 					compilation, xmlnsCache, typeCache, rootType, sourceProductionContext, projectItem);
 			}
+			else if (kvp.Value is ElementNode or ListNode)
+			{
+				if (!TryEmitNewElementComplexProperty(
+					codeWriter,
+					element,
+					kvp.Value,
+					varName,
+					typeSymbol,
+					compilation,
+					xmlnsCache,
+					typeCache,
+					rootType,
+					sourceProductionContext,
+					projectItem))
+				{
+					codeWriter.WriteLine($"// Complex property '{kvp.Key.LocalName}' ({kvp.Value.GetType().Name}) — skipped (not yet supported)");
+				}
+			}
+		}
+	}
+
+	/// <summary>
+	/// Emits an element-valued property while constructing a new element. This deliberately uses
+	/// the InitializeComponent visitor pipeline; mutations on existing elements continue through
+	/// <see cref="EmitPropertyChange"/> and retain their narrower supported surface.
+	/// </summary>
+	static bool TryEmitNewElementComplexProperty(
+		IndentedTextWriter codeWriter,
+		ElementNode element,
+		INode propertyNode,
+		string varName,
+		INamedTypeSymbol typeSymbol,
+		Compilation compilation,
+		AssemblyAttributes xmlnsCache,
+		IDictionary<XmlType, INamedTypeSymbol> typeCache,
+		INamedTypeSymbol rootType,
+		SourceProductionContext sourceProductionContext,
+		ProjectItem? projectItem)
+	{
+		// This speculative path does not run SetResourcesVisitor, so accepting resources here
+		// would emit an incomplete subtree.
+		if (ContainsInlineResources(propertyNode))
+			return false;
+
+		var preflightDiagnosticContext = CreateConversionContext(
+			compilation,
+			sourceProductionContext,
+			xmlnsCache,
+			typeCache,
+			rootType,
+			projectItem);
+		preflightDiagnosticContext.BeginDiagnosticBuffering();
+		bool containsStaticResource;
+		try
+		{
+			containsStaticResource = ContainsStaticResourceReference(propertyNode, markup => ExpandMarkupForUC(
+				markup,
+				compilation,
+				xmlnsCache,
+				typeCache,
+				rootType,
+				sourceProductionContext,
+				projectItem,
+				preflightDiagnosticContext.ReportDiagnostic));
+		}
+		finally
+		{
+			preflightDiagnosticContext.DiscardBufferedDiagnostics();
+		}
+
+		if (containsStaticResource)
+			return false;
+
+		using var captureStringWriter = new StringWriter(CultureInfo.InvariantCulture);
+		using var captureWriter = new IndentedTextWriter(captureStringWriter, "\t") { NewLine = NewLine };
+		var context = CreateConversionContext(
+			compilation,
+			sourceProductionContext,
+			xmlnsCache,
+			typeCache,
+			rootType,
+			projectItem,
+			captureWriter);
+		context.Variables[element] = new DirectValue(typeSymbol, varName);
+		context.BeginDiagnosticBuffering();
+
+		try
+		{
+			propertyNode.Accept(new CreateValuesVisitor(context), element);
+			propertyNode.Accept(new SetPropertiesVisitor(context, stopOnResourceDictionary: true), element);
+		}
+		catch (InvalidOperationException)
+		{
+			context.DiscardBufferedDiagnostics();
+			return false;
+		}
+
+		captureWriter.Flush();
+		var capturedCode = captureStringWriter.ToString();
+		if (string.IsNullOrWhiteSpace(capturedCode))
+		{
+			context.DiscardBufferedDiagnostics();
+			return false;
+		}
+
+		codeWriter.WriteLine("{");
+		codeWriter.Indent++;
+		foreach (var line in capturedCode.Split(new[] { "\r\n", "\n" }, StringSplitOptions.None))
+		{
+			if (!string.IsNullOrEmpty(line))
+				codeWriter.WriteLine(line);
+		}
+
+		foreach (var localMethod in context.LocalMethods)
+		{
+			codeWriter.WriteLine();
+			foreach (var line in localMethod.Split(new[] { "\r\n", "\n" }, StringSplitOptions.None))
+			{
+				if (string.IsNullOrWhiteSpace(line))
+					codeWriter.InnerWriter.WriteLine();
+				else
+					codeWriter.WriteLine(line);
+			}
 		}
+
+		codeWriter.Indent--;
+		codeWriter.WriteLine("}");
+		context.FlushBufferedDiagnostics();
+		return true;
+	}
+
+	static bool ContainsInlineResources(INode node)
+	{
+		if (node is ElementNode element)
+		{
+			if (element.XmlType.Name == "ResourceDictionary")
+				return true;
+
+			foreach (var property in element.Properties)
+			{
+				if (property.Key.LocalName == "Resources"
+					|| property.Key.LocalName.EndsWith(".Resources", StringComparison.Ordinal)
+					|| ContainsInlineResources(property.Value))
+				{
+					return true;
+				}
+			}
+
+			foreach (var child in element.CollectionItems)
+			{
+				if (ContainsInlineResources(child))
+					return true;
+			}
+
+			return false;
+		}
+
+		if (node is ListNode list)
+		{
+			foreach (var child in list.CollectionItems)
+			{
+				if (ContainsInlineResources(child))
+					return true;
+			}
+		}
+
+		return false;
 	}
 
+	static bool ContainsStaticResourceReference(INode node, Func<MarkupNode, INode?> expandMarkup)
+	{
+		if (node is MarkupNode markup)
+		{
+			var expanded = expandMarkup(markup);
+			return expanded is not null && ContainsStaticResourceReference(expanded, expandMarkup);
+		}
+
+		if (node is ElementNode element)
+		{
+			if (IsStaticResourceExtension(element.XmlType.Name))
+				return true;
+
+			foreach (var property in element.Properties.Values)
+			{
+				if (ContainsStaticResourceReference(property, expandMarkup))
+					return true;
+			}
+
+			foreach (var child in element.CollectionItems)
+			{
+				if (ContainsStaticResourceReference(child, expandMarkup))
+					return true;
+			}
+
+			return false;
+		}
+
+		if (node is ListNode list)
+		{
+			foreach (var child in list.CollectionItems)
+			{
+				if (ContainsStaticResourceReference(child, expandMarkup))
+					return true;
+			}
+		}
+
+		return false;
+	}
+
+	static bool IsStaticResourceExtension(string typeName) =>
+		typeName is "StaticResource" or "StaticResourceExtension";
+
 	/// <summary>
 	/// Recursively creates children for a newly created element, handling both
 	/// Layout containers (Children.Add) and Content containers (Content property).
@@ -1163,7 +1373,8 @@ static void TryEmitAttachedPropertyChange(
 					break;
 				}
 			}
-			if (getter != null) break;
+			if (getter != null)
+				break;
 			current = current.BaseType!;
 		}
 
@@ -1264,12 +1475,20 @@ static bool TryEmitMarkupNodeChange(
 		IDictionary<XmlType, INamedTypeSymbol> typeCache,
 		INamedTypeSymbol rootType,
 		SourceProductionContext sourceProductionContext,
-		ProjectItem? projectItem)
+		ProjectItem? projectItem,
+		Action<Diagnostic>? diagnosticReporter = null)
 	{
 		var markupString = markupNode.MarkupString;
 
 		// Build a minimal SourceGenContext for ExpandMarkupsVisitor's parser
-		var ctx = CreateConversionContext(compilation, sourceProductionContext, xmlnsCache, typeCache, rootType, projectItem);
+		var ctx = CreateConversionContext(
+			compilation,
+			sourceProductionContext,
+			xmlnsCache,
+			typeCache,
+			rootType,
+			projectItem,
+			diagnosticReporter: diagnosticReporter);
 
 		// Classification: expression or markup extension?
 		bool TryResolveMarkup(string name)
@@ -1759,12 +1978,14 @@ static SourceGenContext CreateConversionContext(
 		IDictionary<XmlType, INamedTypeSymbol> typeCache,
 		INamedTypeSymbol rootType,
 		ProjectItem? projectItem,
-		IndentedTextWriter? writer = null)
+		IndentedTextWriter? writer = null,
+		Action<Diagnostic>? diagnosticReporter = null)
 	{
 		var pi = projectItem ?? new ProjectItem(EmptyAdditionalText.Instance, EmptyConfigOptions.Instance);
+		diagnosticReporter ??= sourceProductionContext.ReportDiagnostic;
 		return new SourceGenContext(
 			writer ?? new IndentedTextWriter(new StringWriter()),
 			compilation, sourceProductionContext,
-			xmlnsCache, typeCache, rootType, rootType.BaseType, pi);
+			xmlnsCache, typeCache, rootType, rootType.BaseType, pi, diagnosticReporter);
 	}
 }

src/Controls/src/SourceGen/Visitors/SetPropertiesVisitor.cs

@@ -278,7 +278,7 @@ public void Visit(ElementNode node, INode parentNode)
 					Writer.WriteLine($"object {methodName}()");
 					using (PrePost.NewBlock(Writer, begin: "{", end: "}"))
 					{
-						var templateContext = new SourceGenContext(Writer, context.Compilation, context.SourceProductionContext, context.XmlnsCache, context.TypeCache, context.RootType!, null, context.ProjectItem)
+						var templateContext = new SourceGenContext(Writer, context.Compilation, context.SourceProductionContext, context.XmlnsCache, context.TypeCache, context.RootType!, null, context.ProjectItem, context.ReportDiagnostic)
 						{
 							ParentContext = context,
 						};
@@ -298,7 +298,7 @@ public void Visit(ElementNode node, INode parentNode)
 			Writer.WriteLine($"{variable.ValueAccessor}.LoadTemplate = () =>");
 			using (PrePost.NewBlock(Writer, begin: "{", end: "};"))
 			{
-				var templateContext = new SourceGenContext(Writer, context.Compilation, context.SourceProductionContext, context.XmlnsCache, context.TypeCache, context.RootType!, null, context.ProjectItem)
+				var templateContext = new SourceGenContext(Writer, context.Compilation, context.SourceProductionContext, context.XmlnsCache, context.TypeCache, context.RootType!, null, context.ProjectItem, context.ReportDiagnostic)
 				{
 					ParentContext = context,
 				};