[Bug] CodeBehind source generator breaks when use the `x:TypeArguments`

Description

IF you have a View that uses the x:TypeArguments the Source Generator will generate the generic type wrong.

<xct:Popup xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
           xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
           xmlns:xct="http://xamarin.com/schemas/2020/toolkit"
           xmlns:local="clr-namespace:Xamarin.CommunityToolkit.Sample.Pages.Views.Popups"
           Size="{x:Static local:PopupSize.Medium}"
           x:Class="Xamarin.CommunityToolkit.Sample.Pages.Views.Popups.ReturnResultPopup"
           x:TypeArguments="x:String">

//Generated code
[global::Microsoft.Maui.Controls.Xaml.XamlFilePath("C:\\Users\\Jesus\\source\\repos\\MauiBugRepro\\MauiBugRepro\\ReturnResultPopup.xaml")]
	public partial class ReturnResultPopup : global::Xamarin.CommunityToolkit.UI.Views.Popup`1<global::System.String>

I believe that `1 shouldn’t be there.

Steps to Reproduce

1. Create new maui app add the XCT.MauiCompat nuget
2. Create a Popup View that declares x:TypeArguments
3. Try to build

Expected Behavior

Right C# code generated.

Actual Behavior

Wrong C# code generated.

Basic Information

• Version with issue: 6.0.100-preview.7.1345
• Last known good version: N/A
• IDE: VS 2022 Windows
• Platform Target Frameworks:
  • iOS:
  • Android:
  • UWP:
• Android Support Library Version:
• Nuget Packages: N/A
• Affected Devices: All

Screenshots

Reproduction Link

https://github.com/pictos/MauiBugRepro/tree/GenericPageError

I added the nuget package here this way will be easier to test it.

Workaround

[StephaneDelcroix]

Your unit tests ran against Page

the CodeGen is agnostic the to the types it runs on

[jonpryor]

My guess that the issue is due to cross-assembly type references is wrong. (Reasonable, but wrong.) Assembly references are required, but not themselves the root cause.

The actual problem is around XmlnsDefinitionAttribute support: the “problematic” XAML uses:

<xct:Popup xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
           xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
           xmlns:xct="http://xamarin.com/schemas/2020/toolkit"
           xmlns:local="clr-namespace:MauiApp2304"
           Size="{x:Static local:PopupSize.Medium}"
           x:Class="MauiApp2304.ReturnResultPopup"
           x:TypeArguments="x:String">

In particular, note the xmlns:xct="http://xamarin.com/schemas/2020/toolkit". If I change this to be using:namespace a’la Gh6176.xaml:

<xct:Popup xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
           xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
           xmlns:xct="using:Xamarin.CommunityToolkit.UI.Views"
           xmlns:local="clr-namespace:MauiApp2304"
           Size="{x:Static local:PopupSize.Medium}"
           x:Class="MauiApp2304.ReturnResultPopup"
           x:TypeArguments="x:String">

then the resulting codebehind is valid C#:

public partial class ReturnResultPopup : global::Xamarin.CommunityToolkit.UI.Views.Popup<global::System.String>

After an inordinate amount of hackery to get a new Microsoft.Maui.Controls.SourceGen.dll used by the app build with the following patch applied to dotnet/maui:

diff --git a/src/Controls/src/SourceGen/CodeBehindGenerator.cs b/src/Controls/src/SourceGen/CodeBehindGenerator.cs
index 839f620521..789c87a15f 100644
--- a/src/Controls/src/SourceGen/CodeBehindGenerator.cs
+++ b/src/Controls/src/SourceGen/CodeBehindGenerator.cs
@@ -306,8 +306,8 @@ namespace Microsoft.Maui.Controls.SourceGen
 
 			namedFields = GetNamedFields(root, nsmgr, compilation, caches, cancellationToken);
 			var typeArguments = GetAttributeValue(root, "TypeArguments", XamlParser.X2006Uri, XamlParser.X2009Uri);
-			baseType = GetTypeName(new XmlType(root.NamespaceURI, root.LocalName, typeArguments != null ? TypeArgumentsParser.ParseExpression(typeArguments, nsmgr, null) : null), compilation, caches);
+			baseType = "/* jonp: TryParseXaml */ " + GetTypeName(new XmlType(root.NamespaceURI, root.LocalName, typeArguments != null ? TypeArgumentsParser.ParseExpression(typeArguments, nsmgr, null) : null), compilation, caches);
+			Console.Error.WriteLine ($"# jonp: TryParseXaml: baseType={baseType}");
 
 			// x:ClassModifier attribute
 			var classModifier = GetAttributeValue(root, "ClassModifier", XamlParser.X2006Uri, XamlParser.X2009Uri);
@@ -365,8 +365,8 @@ namespace Microsoft.Maui.Controls.SourceGen
 			string returnType;
 			var ns = GetClrNamespace(xmlType.NamespaceUri);
 			if (ns != null) {
-				returnType = $"{ns}.{xmlType.Name}";
+				Console.Error.WriteLine($"# jonp: GetTypeName: xmlType.Name=`{xmlType.Name}`");
+				returnType = $"/* jonp: GetTypeName */ {ns}.{xmlType.Name}";
 			}
 			else
 			{
@@ -416,9 +416,9 @@ namespace Microsoft.Maui.Controls.SourceGen
 
 					return null;
 				});
+			Console.Error.WriteLine ($"# jonp: GetTypeNameFromCustomNamespace: typeName={typeName}");
 
-			return typeName;
+			return "/* jonp: GetTypeNameFromCustomNamespace */ " + typeName;
 #nullable enable
 		}
 

my resulting source generator output contains:

public partial class ReturnResultPopup : /* jonp: TryParseXaml */ global::/* jonp: GetTypeNameFromCustomNamespace */ Xamarin.CommunityToolkit.UI.Views.Popup`1<global::/* jonp: GetTypeName */ System.String>

suggesting that the “problem” is in: https://github.com/dotnet/maui/blob/ab09cf98bc17f57725e8d088cbf02c3f0723cea3/src/Controls/src/SourceGen/CodeBehindGenerator.cs#L391-L419

Which could be fixed with:

diff --git a/src/Controls/src/SourceGen/CodeBehindGenerator.cs b/src/Controls/src/SourceGen/CodeBehindGenerator.cs
index 097a2d4b89..c06a7a82ab 100644
--- a/src/Controls/src/SourceGen/CodeBehindGenerator.cs
+++ b/src/Controls/src/SourceGen/CodeBehindGenerator.cs
@@ -407,8 +407,14 @@ namespace Microsoft.Maui.Controls.SourceGen
 						if (type.ContainingAssembly.Identity.Name != typeInfo.assemblyName)
 							continue;
 
-						if (IsPublicOrVisibleInternal(type, caches.InternalsVisible))
-							return fullName;
+						if (!IsPublicOrVisibleInternal(type, caches.InternalsVisible))
+							continue;
+						int i = fullName.IndexOf('`');
+						if (i > 0)
+						{
+							fullName = fullName.Substring(0, i);
+						}
+						return fullName;
 					}
 
 					return null;

The Problem: How do I unit test this puppy? To make it work an [assembly: XmlnsDefinition(URL, NAMESPACE)] needs to be used, which does require an external assembly reference. Is there an easy way to set this up?