x:Static in conjunction with XamlCompilation results in XFC0101 compile time error.

[bakerhillpins]

Description

The following XAML snippet will result in failed compilation on a NOOB application as compiled XAML is the default for MAUI apps. Simply add it as a binding to any property.

<Binding Path="Foo" TargetNullValue="{x:Static Binding.DoNothing}"/>

Specifically the following error code is returned:

Error XFC0101 x:Static: unable to find a public -- or accessible internal -- static field, static property, const or enum value named "DoNothing" in "Binding".

It would appear that string "Binding" is somehow special during type lookup in XAML compilation operations as using another static field from the same namespace Microsoft.Maui.Controls works without error:

<Binding Path="Foo" TargetNullValue="{x:Static Application.AccentColor}"/>

Steps to Reproduce

1. Create a new MAUI app
2. Add the binding that causes error to one of the Image elements in MainPage.xaml

                <Image.AnchorX>
                    <Binding Path="Foo" TargetNullValue="{x:Static Binding.DoNothing}"/>
                </Image.AnchorX>

3. Compile

Link to public reproduction project repository

https://github.com/bakerhillpins/Issues/tree/NetMauiIssue11833

Version with bug

6.0 Release Candidate 2 or older

Last version that worked well

Unknown/Other

Affected platforms

iOS, Android, Windows, macOS, Other (Tizen, Linux, etc. not supported by Microsoft directly)

Affected platform versions

All

Did you find any workaround?

This is a Compiled Bindings issue. There are the following workarounds:

1. Add the [XamlCompilation(XamlCompilationOptions.Skip)] Attribute to the View class in the .xaml.cs file.
2. Create a static field/property that exists in your own namespace, reference that from the binding, and have the field redirect to the Microsoft.Maui.Controls.Binding.DoNothing field.

<Binding Path="Foo" TargetNullValue="{x:Static views:Binding.DoNothing}" />

namespace MyProject.Views
{
    public sealed class Binding
    {
        public static readonly object DoNothing = Microsoft.Maui.Controls.Binding.DoNothing;
    }
}

Relevant log output

No response

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[jsuarezruiz]

cc @StephaneDelcroix

[PureWeen]

related #11740

[mattleibow]

As far as I can tell in the code, Binding.DoNothing is just for cases when using IMultiValueConverter or MultiBinding. XamlC still should not fail, but I am not sure using Binding.DoNothing is what you are looking for. It is used only in multi-bindings.

Also note to future people: even Static (not just x:Static) gives the same error.

[bakerhillpins]

@mattleibow Short story, I'm trying (unsuccessfully) to inject Binding.DoNothing into the FallBackValue/NullTargetValue of the bindings in the MultiBinding.Bindings collection so that my IMultibindingConverter can short circuit the MultiBinding.

Anyway, There's also the bug mentioned above where Binding would start to respect the return values as defined by the IValueConverter docs. Which would be wonderful as any opportunity to terminate unnecessary binding engine operations is a welcome and easy performance gain.

[XamlTest]

Verified this on Visual Studio Enterprise 17.7.0 Preview 1.0. Repro on Windows 11, Android 13.0-API33 and iOS 16.4 with provided Project:
MauiBugz.zip

[StephaneDelcroix]

in XAML, Binding resolves to... BindingExtension 🤦