Resource lookups fail on Windows when merging xaml in Debug

[kazo0]

When running the Windows sample app in Debug locally, there is a crash with the message saying that it cannot locate the resource MaterialBackgroundBrush.

This is caused by the organization of the ResourceDictionaries when the Xaml Merge target is run and generates for Hot Reload.

By default in Debug, the property BatchMergeGenerateForHotReload is true so it results in a generated xaml file like this:

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006">
    <ResourceDictionary.MergedDictionaries>
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/Button.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/CalendarDatePicker.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/CalendarView.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/CheckBox.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/ComboBox.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/CommandBar.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/DatePicker.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/FloatingActionButton.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/Flyout.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/HyperlinkButton.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/InfoBar.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/ListView.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/NavigationView/NavigationView_MUX.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/PasswordBox.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/ProgressBar.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/ProgressRing.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/RadioButton.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/RatingControl.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/Ripple.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/Slider.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/TextBlock.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/TextBox.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/TimePicker.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/ToggleButton.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/ToggleSwitch.Base.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/ToggleSwitch.Mobile.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/ToggleSwitch.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Controls/v1/_Resources.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Application/Common/AnimationConstants.xaml" />
        <ResourceDictionary Source="ms-appx:///Uno.Material.WinUI/Styles/Application/Common/TextBoxVariables.xaml" />
    </ResourceDictionary.MergedDictionaries>
</ResourceDictionary>

Which will result in a failure

Setting BatchMergeGenerateForHotReload to false or running in release generates something like this instead:

<ResourceDictionary xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d not_win android ios not_ios xamarin mobile wasm skia contract4NotPresent contract7NotPresent macos lottie_not_win uwp winui" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:win="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:um="using:Uno.Material" xmlns:ut="using:Uno.Themes" xmlns:not_win="http://uno.ui/not_win" xmlns:uno="using:Uno.UI.Xaml.Controls" xmlns:android="http://uno.ui/android" xmlns:ios="http://uno.ui/ios" xmlns:not_ios="http://uno.ui/not_ios" xmlns:xamarin="http://uno.ui/xamarin" xmlns:mobile="http://uno.ui/mobile" xmlns:toolkit="using:Uno.UI.Toolkit" xmlns:uuc="using:Uno.UI.Controls" xmlns:wasm="http://uno.ui/wasm" xmlns:controls="using:Microsoft.UI.Xaml.Controls" xmlns:media="using:Microsoft.UI.Xaml.Media" xmlns:primitives="using:Microsoft.UI.Xaml.Controls.Primitives" xmlns:skia="http://uno.ui/skia" xmlns:contract4Present="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:contract4NotPresent="http://schemas.microsoft.com/winfx/2006/xaml/presentation?IsApiContractNotPresent(Windows.Foundation.UniversalApiContract,4)" xmlns:contract7Present="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:contract7NotPresent="http://schemas.microsoft.com/winfx/2006/xaml/presentation?IsApiContractNotPresent(Windows.Foundation.UniversalApiContract,7)" xmlns:not_macos="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:macos="http://uno.ui/macos" xmlns:lottie_not_win="#using:Microsoft.Toolkit.Uwp.UI.Lottie;CommunityToolkit.WinUI.Lottie" xmlns:lottie_win="using:Microsoft.Toolkit.Uwp.UI.Lottie" xmlns:uwp="http://uno.ui/uwp" xmlns:winui="http://uno.ui/winui" xmlns:not_android="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:uuvc="using:Uno.UI.Views.Controls" xmlns:not_mobile="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
  <ResourceDictionary.MergedDictionaries>
    <not_win:ResourceDictionary>
      <lottie_not_win:LottieVisualSource x:Key="MaterialDeterminateAnimation_Uno" uwp:UriSource="embedded://Uno.Material/Uno.Material.Assets.MaterialDeterminate.json" winui:UriSource="embedded://Uno.Material.WinUI/Uno.Material.WinUI.Assets.MaterialDeterminate.json" />
      <lottie_not_win:LottieVisualSource x:Key="MaterialIndeterminateAnimation_Uno" uwp:UriSource="embedded://Uno.Material/Uno.Material.Assets.MaterialIndeterminate.json" winui:UriSource="embedded://Uno.Material.WinUI/Uno.Material.WinUI.Assets.MaterialIndeterminate.json" />
    </not_win:ResourceDictionary>
    <um:MaterialFonts />
    <um:MaterialColorsV1 />
  </ResourceDictionary.MergedDictionaries>
  <ResourceDictionary.ThemeDictionaries>
    <ResourceDictionary x:Key="Light">
      <Color x:Key="ButtonFabLowFabBackgroundColor">#9F9F9F</Color>
      <StaticResource x:Key="MaterialMUXNavigationViewDefaultPaneBackground" ResourceKey="SystemChromeMediumColor" />
      <StaticResource x:Key="MaterialMUXNavigationViewExpandedPaneBackground" ResourceKey="SystemChromeMediumColor" />
      <StaticResource x:Key="MaterialMUXNavigationViewTopPaneBackground" ResourceKey="SystemChromeMediumHighColor" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackground" ResourceKey="SystemControlTransparentBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackgroundPointerOver" ResourceKey="SystemControlHighlightListLowBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackgroundPressed" ResourceKey="SystemControlHighlightListMediumBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackgroundDisabled" ResourceKey="SystemControlTransparentBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackgroundChecked" ResourceKey="SystemControlTransparentBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackgroundCheckedPointerOver" ResourceKey="SystemControlHighlightListLowBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackgroundCheckedPressed" ResourceKey="SystemControlHighlightListMediumBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackgroundCheckedDisabled" ResourceKey="SystemControlTransparentBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackgroundSelected" ResourceKey="SystemControlTransparentBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackgroundSelectedPointerOver" ResourceKey="SystemControlHighlightListLowBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackgroundSelectedPressed" ResourceKey="SystemControlHighlightListMediumBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemBackgroundSelectedDisabled" ResourceKey="SystemControlTransparentBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemForeground" ResourceKey="SystemControlForegroundBaseHighBrush" />
      <StaticResource x:Key="MaterialMUXNavigationViewItemForegroundPointerOver" ResourceKey="SystemControlHighlightAltBaseHighBrush" />

And with that merged xaml we do not see a crash