Debugging the XAML compiler
You can debug the XAML compiler adding at your's csproj AvaloniaXamlIlDebuggerLaunch property like this:
If build the project in Visual Studio you should see a window like this:
on other IDEs, a message will appear in the build output window indicating the PID of the process to attach the debugger to and the elapsed time. If within one minute of starting the build no debugger is attacked to the process, a timeout message will be reported and the build will continue as normal.