[XSG] simple support for required

src/Controls/src/SourceGen/Visitors/CreateValuesVisitor.cs

@@ -45,7 +45,7 @@ public void Visit(ElementNode node, INode parentNode)
 		//x:Array
 		if (type.Equals(Context.Compilation.GetTypeByMetadataName("Microsoft.Maui.Controls.Xaml.ArrayExtension"), SymbolEqualityComparer.Default))
 		{
-			//we might want to mive this to a separate method
+			//we might want to move this to a separate method
 			var visitor = new SetPropertiesVisitor(Context);
 			// var children = node.Properties.Values.ToList();
 			// children.AddRange(node.CollectionItems);
@@ -150,7 +150,6 @@ public void Visit(ElementNode node, INode parentNode)
 
 		if (ctor is null && factoryMethod is null)
 		{
-
 			//TODO we might need an extension method for that and cache the result. it happens eveytime we have a Style
 			ctor = type.InstanceConstructors.FirstOrDefault(c
 				=> c.Parameters.Length > 0
@@ -189,9 +188,59 @@ public void Visit(ElementNode node, INode parentNode)
 
 		bool isColor = type.Equals(Context.Compilation.GetTypeByMetadataName("Microsoft.Maui.Graphics.Color"), SymbolEqualityComparer.Default);
 
+		//are there any `required` properties ?
+		var requiredPropAndFields = type.GetMembers()
+									.Where(p => p is IPropertySymbol prop && prop.IsRequired || p is IFieldSymbol field && field.IsRequired)
+									.ToList();
+		List<(string name, ISymbol propOrField, ITypeSymbol propType, string propValue)> requiredPropertiesAndFields = [];
+		if (requiredPropAndFields.Count > 0)
+		{
+			var contentPropertyName = type.GetContentPropertyName(Context);
+			foreach (var req in requiredPropAndFields)
+			{
+				XmlName propXmlName ;
+				INode propNode;
+				if (req.Name == contentPropertyName && node.CollectionItems.Count == 1)
+				{
+					propNode = node.CollectionItems[0];
+					propXmlName = new XmlName("", contentPropertyName);
+				}
+				else if (!node.Properties.TryGetValue(req.Name, out propNode, out propXmlName))
+					Context.ReportDiagnostic(Diagnostic.Create(Descriptors.XamlParserError, LocationCreate(Context.FilePath!, node, req.Name), $"Required field '{req.Name}' not found in {type}"));
+
+				string propValue = "null";
+				var pType = req is IPropertySymbol prop ? prop.Type : ((IFieldSymbol)req).Type;
+				var pConverter = req.GetAttributes().FirstOrDefault(a => a.AttributeClass!.Equals(Context.Compilation.GetTypeByMetadataName("System.ComponentModel.TypeConverterAttribute")!, SymbolEqualityComparer.Default))?.ConstructorArguments[0].Value as ITypeSymbol;
+
+				var visitor = new SetPropertiesVisitor(Context);
+				var children = node.Properties.Values.ToList();
+				children.AddRange(node.CollectionItems);
+				foreach (var cn in children)
+				{
+					if (cn is not ElementNode en)
+						continue;
+					foreach (var n in en.Properties.Values.ToList())
+						n.Accept(visitor, cn);
+					foreach (var n in en.CollectionItems)
+						n.Accept(visitor, cn);
+				}
+				if (propNode is ValueNode vn)
+					propValue = vn.ConvertTo(pType, pConverter, Context);
+				else if (propNode is ElementNode en)
+				{
+					en.TryProvideValue(Context);
+					propValue = Context.Variables[en].Name;
+				}
+
+				requiredPropertiesAndFields.Add((req.Name, req, pType, propValue));
+				if (!node.SkipProperties.Contains(new XmlName("", req.Name)))
+					node.SkipProperties.Add(new XmlName("", req.Name));
+			}
+		}
+
 		if (node.CollectionItems.Count == 1
-			&& node.CollectionItems[0] is ValueNode valueNode
-			&& (isColor || type.IsValueType))
+				&& node.CollectionItems[0] is ValueNode valueNode
+				&& (isColor || type.IsValueType))
 		{ //<Color>HotPink</Color>
 			var variableName = NamingHelpers.CreateUniqueVariableName(Context, type);
 			var valueString = valueNode.ConvertTo(type, Context);
@@ -202,7 +251,6 @@ public void Visit(ElementNode node, INode parentNode)
 			return;
 		}
 		//TODO we could also check if there's a TypeConverter, but we have no test (so no need?) for it
-
 		else if (node.CollectionItems.Count == 1
 				&& node.CollectionItems[0] is ValueNode valueNode1
 				&& implicitOperator != null)
@@ -226,7 +274,17 @@ public void Visit(ElementNode node, INode parentNode)
 		{
 			var variableName = NamingHelpers.CreateUniqueVariableName(Context, type);
 
-			Writer.WriteLine($"var {variableName} = new {type.ToFQDisplayString()}({string.Join(", ", parameters?.ToMethodParameters(Context) ?? [])});");
+			if (requiredPropAndFields.Any())
+			{
+				Writer.WriteLine($"var {variableName} = new {type.ToFQDisplayString()}({string.Join(", ", parameters?.ToMethodParameters(Context) ?? [])})");
+				using (PrePost.NewBlock(Writer, begin: "{", end: "};"))
+				{
+					foreach (var (name, propOrField, propType, propValue) in requiredPropertiesAndFields)
+						Writer.WriteLine($"{name} = ({propType.ToFQDisplayString()}){propValue},");
+				}
+			}			
+			else
+				Writer.WriteLine($"var {variableName} = new {type.ToFQDisplayString()}({string.Join(", ", parameters?.ToMethodParameters(Context) ?? [])});");
 			Context.Variables[node] = new LocalVariable(type, variableName);
 			node.RegisterSourceInfo(Context, Writer);
 			return;

src/Controls/src/Xaml/XamlNode.cs

@@ -150,6 +150,29 @@ public override void Accept(IXamlNodeVisitor visitor, INode parentNode)
 		};
 	}
 
+	static class XmlNameExtensions
+	{ 
+		public static bool TryGetValue(this Dictionary<XmlName, INode> properties, string name, out INode node, out XmlName xmlName)
+		{
+			xmlName = new XmlName("", name);
+			if (properties.TryGetValue(xmlName, out node))
+				return true;
+
+#if NETSTANDARD2_0
+			var kvp = properties.FirstOrDefault(kvp => kvp.Key.LocalName == name);
+			if (kvp.Key != null)
+			{
+				xmlName = kvp.Key;
+				node = kvp.Value;
+			}
+#else
+			(xmlName, node) = properties.FirstOrDefault(kvp => kvp.Key.LocalName == name);
+#endif
+			return node != null;
+		}
+
+		public static bool TryGetValue(this Dictionary<XmlName, INode> properties, string name, out INode node) => properties.TryGetValue(name, out node, out _);
+	}
 
 	[DebuggerDisplay("{XmlType.Name}")]
 	class ElementNode : BaseNode, IValueNode, IElementNode

src/Controls/tests/Xaml.UnitTests/Required.xaml

@@ -0,0 +1,22 @@
+<?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:Microsoft.Maui.Controls.Xaml.UnitTests"
+             x:Class="Microsoft.Maui.Controls.Xaml.UnitTests.Required"
+             Title="Required">
+    <ContentPage.Resources>
+        <DataTemplate x:Key="template1"><Label/></DataTemplate>
+    </ContentPage.Resources>
+    <local:Required.Selector>
+        <local:RequiredRandomSelector Template1="{StaticResource template1}">
+            <local:RequiredRandomSelector.Template2>
+                <DataTemplate>
+                    <Label Text="Template 2"/>
+                </DataTemplate>
+            </local:RequiredRandomSelector.Template2>                                    
+        </local:RequiredRandomSelector>
+    </local:Required.Selector>
+    <local:Required.Person>
+        <local:RequiredPerson Name="John Doe" />
+    </local:Required.Person>
+</ContentPage>

src/Controls/tests/Xaml.UnitTests/Required.xaml.cs

@@ -0,0 +1,83 @@
+using System;
+using NUnit.Framework;
+
+using static Microsoft.Maui.Controls.Xaml.UnitTests.MockSourceGenerator;
+
+namespace Microsoft.Maui.Controls.Xaml.UnitTests;
+
+public partial class Required : ContentPage
+{
+	public RequiredRandomSelector Selector { get; set; }
+	public RequiredPerson Person { get; set; }
+	public Required() => InitializeComponent();
+
+	class Tests
+	{
+		[Test]
+		public void RequiredFieldsAndPropertiesAreSet([Values] XamlInflator inflator)
+		{
+			if (inflator == XamlInflator.SourceGen)
+			{
+				var result = CreateMauiCompilation()
+					.WithAdditionalSource(
+	"""
+using System;
+using NUnit.Framework;
+
+namespace Microsoft.Maui.Controls.Xaml.UnitTests;
+
+[XamlProcessing(XamlInflator.SourceGen)]
+public partial class Required : ContentPage
+{
+	public RequiredRandomSelector Selector { get; set; }
+	public RequiredPerson Person { get; set; }
+	public Required() => InitializeComponent();
+}
+
+public class RequiredRandomSelector : DataTemplateSelector
+{
+	public /*required*/ Controls.DataTemplate Template1 { get; set; }
+	public required Controls.DataTemplate Template2 { get; set; }
+
+	protected override Controls.DataTemplate OnSelectTemplate(object item, BindableObject container) => new Random().Next(2) == 0 ? Template1 : Template2;
+}
+
+public class RequiredPerson
+{
+	public required string Name { get; set; }
+
+	public override string ToString()
+		=> Name;
+}
+""")
+					.RunMauiSourceGenerator(typeof(Required));
+
+				Assert.That(result.Diagnostics, Is.Empty, "No diagnostics expected");
+			}
+
+			var layout = new Required(inflator);
+			Assert.IsNotNull(layout.Selector);
+			Assert.IsNotNull(layout.Selector.Template1);
+			Assert.IsNotNull(layout.Selector.Template2);
+			Assert.IsNotNull(layout.Person);
+			Assert.IsNotNull(layout.Person.Name);
+		}
+	}
+}
+
+public class RequiredRandomSelector : DataTemplateSelector
+{
+	public /*required*/ Controls.DataTemplate Template1 { get; set; }
+	public required Controls.DataTemplate Template2 { get; set; }
+
+	protected override Controls.DataTemplate OnSelectTemplate(object item, BindableObject container) => new Random().Next(2) == 0 ? Template1 : Template2;
+}
+
+public class RequiredPerson
+{
+	public required string Name { get; set; }
+
+
+	public override string ToString()
+		=> Name;
+}