Question: Can I declare a conditional XAML static resource?

I have a app with conditional ThemeShadow, it works fine with 1903+ however on 1803 it crashes. It complaints that there is a XAML parsing error.

<MainPage
    x:Class="App.Views.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:winui="using:Microsoft.UI.Xaml.Controls"
    xmlns:windows10Version1903="http://schemas.microsoft.com/winfx/2006/xaml/presentation?IsApiContractPresent(Windows.Foundation.UniversalApiContract, 8)"
    Style="{StaticResource PageStyle}"
    mc:Ignorable="d">
    <MainPage.Resources>
        <windows10Version1903:ThemeShadow x:Name="SharedShadow" />
    </MainPage.Resources>

Is there a workaround? Or am I doing something wrong?

[evelynwu-msft]

@robloo As one of the maintainers of the XamlCompiler toolchain (specifically, the parser), I suspect I share many of your frustrations. At the moment we are focused entirely on shipping WinUI 3.0 (which, unfortunately, is not likely to fundamentally change how we process XAML markup) but modernizing the architecture of XamlCompiler is very much something we want to tackle in the future; we have several ideas about how to go about doing this but they do have to be balanced with other competing priorities.

[robloo]

There are several issues related to conditional XAML, #2556 is definitely in the same category of issues.

@StephenLPeters It’s become clear over the years that the XAML compiler is kind-of a mess. Is there any work or plans towards re-writing this? I heard rumors that Xamarin.Forms, UWP and WPF could all share the same XAML infrastructure. Even trying to rename .xaml to .winui is a result of some bad architecture here.