Description

When we check for x:DataType and binding context mismatch when a Binding is applied, we compare the x:DataType with an instance of RelativeBindingSource instead of the resolved source object.

As a result, the runtime log contains misleading warnings:

Microsoft.Maui.Controls.Xaml.Diagnostics.BindingDiagnostics: Warning: Mismatch between the specified x:DataType (Microsoft.Maui.Controls.VerticalStackLayout) and the current binding context (Microsoft.Maui.Controls.RelativeBindingSource).

Steps to Reproduce

Starting from dotnet new maui:

1. Enable $(MauiEnableXamlCBindingWithSourceCompilation) in project file:

<PropertyGroup>
    <MauiEnableXamlCBindingWithSourceCompilation>true</MauiEnableXamlCBindingWithSourceCompilation>
</PropertyGroup>

2. Add a binding with relative source and x:DataType to MainPage.xaml:

<VerticalStackLayout Spacing="25">
      <Image
          Source="dotnet_bot.png"
          HeightRequest="{Binding Spacing, x:DataType=VerticalStackLayout, Source={RelativeSource AncestorType={x:Type VerticalStackLayout}}}" />
</VerticalStackLayout>

Link to public reproduction project repository

No response

Version with bug

Nightly / CI build (Please specify exact version)

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

9.0.0-rc.2.24503.2

Affected platforms

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

Affected platform versions

No response

Did you find any workaround?

No response

Relevant log output

No response