x:Bind Pathless Casting (this) references cause source generator error

[hawkerm]

Current behavior

Was using pathless casting in UWP data template to bind to the 'this' object of the data template:

<DataTemplate x:DataType="local:SomeTypeName">
  <local:MyControl MyProperty="{x:Bind (local:SomeTypeName)}"/>
</DataTemplate>

This gave me the following error when trying to run in WASM:

Uno.UI.SourceGenerators.XamlGenerator.XamlCodeGenerator\MainPage_bf38630c1c1d5b8ecc552685d35228f7.cs(914,322,914,324): error CS7000: Unexpected use of an aliased name

Switching out to old-style {Binding} syntax allowed me to compile.

Expected behavior

Should accept the pathless casting syntax for x:Bind.

How to reproduce it (as minimally and precisely as possible)

No response

Workaround

Switch x:Bind pathless cast to Binding if only doing direct. Not sure if there's the same issue for function binding which I'm not sure how you'd work around.

Works on UWP/WinUI

Yes

Environment

Uno.UI / Uno.UI.WebAssembly / Uno.UI.Skia

NuGet package version(s)

4.0.11

Affected platforms

WebAssembly

IDE

Visual Studio 2022

IDE version

17.0.5

Relevant plugins

No response

Anything else we need to know?

No response

[jeromelaban]

Thanks for the report! Would you have the exact type that was bound? We're looking for an exact repro, as previous ones we got were not successful.

[hawkerm]

It's my own type implemented in my project:

public partial class MyClass : ObservableObject
{

With a couple of simple properties (string and custom enum), nothing more.

It is being built using the new MVVM Toolkit source generators (initially V1, now V2), so maybe there's a conflict between the two source generators somehow? (If you're not seeing it with regular types?)

Though I tried switching it to a regular ObservableObject without the partial class and think I'm still getting the same message. So it may not be related.

If I remove the pathless cast to the whole type, and instead use a specific property, then I don't get the error message.

[jeromelaban]

Thanks for the update! Yes it may seem that the parser is not handling this very well.

Note for contributors

This is the location of the parser tests:

uno/src/SourceGenerators/Uno.UI.SourceGenerators.Tests/Given_XBindRewriter.cs

Lines 10 to 31 in bb3f815

	public class Given_XBindRewriter
	{
	[TestMethod]
	// DataTemplates (with context)
	[DataRow("ctx", "MyProperty.A", "ctx.MyProperty.A")]
	[DataRow("ctx", "MyProperty", "ctx.MyProperty")]
	[DataRow("ctx", "MyStaticProperty", "MyStaticProperty")]
	[DataRow("ctx", "MyStaticMethod()", "MyStaticMethod()")]
	[DataRow("ctx", "MyProperty.A.ToLower()", "ctx.MyProperty.A.ToLower()")]
	[DataRow("ctx", "System.String.Format('{0:X8}', a.Value)", "System.String.Format('{0:X8}', ctx.a.Value)")]
	[DataRow("ctx", "Static.MyFunction(42.0)", "Static.MyFunction(42.0)")]
	[DataRow("ctx", "Static.MyFunction(true)", "Static.MyFunction(true)")]
	[DataRow("ctx", "Static.MyFunction(MyProperty)", "Static.MyFunction(ctx.MyProperty)")]
	[DataRow("ctx", "MyNameSpace.Static2.MyProperty", "MyNameSpace.Static2.MyProperty")]
	[DataRow("ctx", "MyNameSpace.Static2.MyEnum.EnumMember", "MyNameSpace.Static2.MyEnum.EnumMember")]
	[DataRow("ctx", "MyNameSpace.Static2.MyProperty.ToArray()", "MyNameSpace.Static2.MyProperty.ToArray()")]
	[DataRow("ctx", "MyNameSpace.Static2.MyFunction(MyProperty)", "MyNameSpace.Static2.MyFunction(ctx.MyProperty)")]
	[DataRow("ctx", "MyFunction(MyProperty)", "ctx.MyFunction(ctx.MyProperty)")]
	[DataRow("ctx", "", "ctx")]
	[DataRow("ctx", "(FontFamily)a.Value", "(FontFamily)ctx.a.Value")]
	[DataRow("ctx", "(global::System.Int32)a.Value", "(global::System.Int32)ctx.a.Value")]

[michael-hawker]

I think this is for any types of parentheses; so not just pathless casting, but for attached properties as well (i.e. uno only looking for function and casting scenarios):

"{x:Bind AdornerCanvas.(labs:FrameworkElementExtensions.ActualWidth), Mode=OneWay}"

Hit above in labs trying to use our helpers in the Toolkit for size binding.

From the official docs, see https://learn.microsoft.com/windows/uwp/xaml-platform/x-bind-markup-extension#attached-properties

Text="{x:Bind Button22.(Grid.Row)}"

xBind markup extension - UWP applications

The xBind markup extension is a high performance alternative to Binding. xBind - new for Windows 10 - runs in less time and less memory than Binding and supports better debugging.