[XSG] report a warning on usage of required (#32274)

only for non valuenodes

- fixes #32272

Author: StephaneDelcroix

src/Controls/src/SourceGen/AnalyzerReleases.Unshipped.md

@@ -14,3 +14,4 @@ MAUIX2001 | XamlInflation | Error | Descriptors
 MAUIX2002 | XamlInflation | Error | Descriptors
 MAUIX2003 | XamlInflation | Error | Descriptors
 MAUIX2004 | XamlInflation | Error | Descriptors
+MAUIX2005 | XamlInflation | Warning | Descriptors

src/Controls/src/SourceGen/Descriptors.cs

@@ -186,6 +186,14 @@ public static class Descriptors
 			defaultSeverity: DiagnosticSeverity.Error,
 			isEnabledByDefault: true);
 
+			public static DiagnosticDescriptor RequiredProperty = new DiagnosticDescriptor(
+			id: "MAUIX2005",
+			title: new LocalizableResourceString(nameof(MauiGResources.RequiredPropertyTitle), MauiGResources.ResourceManager, typeof(MauiGResources)),
+			messageFormat: new LocalizableResourceString(nameof(MauiGResources.RequiredPropertyMessage), MauiGResources.ResourceManager, typeof(MauiGResources)),
+			category: "XamlInflation",
+			defaultSeverity: DiagnosticSeverity.Warning,
+			isEnabledByDefault: true);
+
 		// public static BuildExceptionCode TypeResolution = new BuildExceptionCode("XC", 0000, nameof(TypeResolution), "");
 		// public static BuildExceptionCode PropertyResolution = new BuildExceptionCode("XC", 0001, nameof(PropertyResolution), "");
 		// public static BuildExceptionCode MissingEventHandler = new BuildExceptionCode("XC", 0002, nameof(MissingEventHandler), "");

src/Controls/src/SourceGen/MauiGResources.resx

@@ -189,12 +189,18 @@
   </data>
   <data name="DuplicateKeyInRD" xml:space="preserve">
     <value>duplicate key in resource dictionary</value>
-    <comment>
-</comment>
   </data>
   <data name="ConversionFailedTitle" xml:space="preserve">
     <value>Conversion Failed</value>
     <comment>
 </comment>
   </data>
+  <data name="RequiredPropertyTitle" xml:space="preserve">
+    <value>Use of 'required'</value>
+    <comment>/</comment>
+  </data>
+  <data name="RequiredPropertyMessage" xml:space="preserve">
+    <value>{0} has the 'required' keyword. Support for this in XAML is limited at the moment, avoid using it. We're still doing a best effort to provide a value.</value>
+    <comment>0 is a property identifier</comment>
+  </data>
 </root>

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

@@ -224,6 +224,7 @@ public static void CreateValue(ElementNode node, IndentedTextWriter writer, IDic
 					propValue = vn.ConvertTo(pType, pConverter, writer, Context);
 				else if (propNode is ElementNode en)
 				{
+					Context.ReportDiagnostic(Diagnostic.Create(Descriptors.RequiredProperty, LocationCreate(Context.ProjectItem.RelativePath!, node, type.Name), $"'{type.ToFQDisplayString()}.{propXmlName.LocalName}'"));
 					en.TryProvideValue(writer, Context);
 					propValue = variables[en].ValueAccessor;
 				}
@@ -346,4 +347,4 @@ static string ValueForLanguagePrimitive(ITypeSymbol type, ElementNode node, Sour
 
 		return NodeSGExtensions.ValueForLanguagePrimitive(valueString, toType: type, context, node);
 	}
-}
+}

src/Controls/src/SourceGen/xlf/MauiGResources.Designer.cs

@@ -6,7 +6,7 @@
     <AssemblyName>Microsoft.Maui.Controls.Xaml.UnitTests</AssemblyName>
     <WarningLevel>4</WarningLevel>
     <NoWarn>$(NoWarn);0672;0219;0414;CS0436;CS0618</NoWarn>
-    <WarningsNotAsErrors>$(WarningsNotAsErrors);XC0618;XC0022;XC0023;XC0025;XC0045;MAUID1000</WarningsNotAsErrors>
+    <WarningsNotAsErrors>$(WarningsNotAsErrors);XC0618;XC0022;XC0023;XC0025;XC0045;MAUID1000;MAUIX2005</WarningsNotAsErrors>
     <IsPackable>false</IsPackable>
     <DisableMSBuildAssemblyCopyCheck>true</DisableMSBuildAssemblyCopyCheck>
     <MauiEnableXamlCBindingWithSourceCompilation>true</MauiEnableXamlCBindingWithSourceCompilation>

src/Controls/tests/Xaml.UnitTests/Controls.Xaml.UnitTests.csproj

@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using NUnit.Framework;
 
 using static Microsoft.Maui.Controls.Xaml.UnitTests.MockSourceGenerator;
@@ -52,7 +53,7 @@ public override string ToString()
 """)
 					.RunMauiSourceGenerator(typeof(Required));
 
-				Assert.That(result.Diagnostics, Is.Empty, "No diagnostics expected");
+				Assert.That(result.Diagnostics.Length, Is.EqualTo(1), "warning expected");
 			}
 
 			var layout = new Required(inflator);
@@ -76,8 +77,6 @@ public class RequiredRandomSelector : DataTemplateSelector
 public class RequiredPerson
 {
 	public required string Name { get; set; }
-
-
 	public override string ToString()
 		=> Name;
 }