Can't build any xaml islands app with 2.7.0-prerelease.210827001

[champnic]

Originally asked by @asklar here: microsoft/microsoft-ui-xaml#5793

Describe the bug
I upgraded a Win32 C++/WinRT app to WinUI 2.7.0-prerelease.210827001, now I get a cppwinrt error:

Rebuild started...
1>------ Rebuild All started: Project: Playground, Configuration: Debug Win32 ------
1>cppwinrt : error Type 'Microsoft.Web.WebView2.Core.CoreWebView2' could not be found
1> method: CoreWebView2
1> type: Microsoft.UI.Xaml.Controls.IWebView2
1> database: F:\xaml-islands\Playground\packages\Microsoft.UI.Xaml.2.7.0-prerelease.210827001\lib\uap10.0\Microsoft.UI.Xaml.winmd
1>F:\xaml-islands\Playground\packages\Microsoft.Windows.CppWinRT.2.0.210825.3\build\native\Microsoft.Windows.CppWinRT.targets(736,9): error MSB3073: The command ""F:\xaml-islands\Playground\packages\Microsoft.Windows.CppWinRT.2.0.210825.3\build\native\..\..\bin\"cppwinrt @"Debug\Playground.vcxproj.cppwinrt_ref.rsp"" exited with code 1.
1>Done building project "Playground.vcxproj" -- FAILED.
========== Rebuild All: 0 succeeded, 1 failed, 0 skipped ==========

Steps to reproduce the bug
Create C++/WinRT app, reference latest winui nuget, build.

Note this does not require me to use WebView2 in my project - the build error happens even before any of my code gets compiled.

Version Info

NuGet package version: Microsoft.UI.Xaml 2.7.0-prerelease.210827001
latest cppwinrt version: 2.0.210825.3
mux brought in webview2 pkg: 1.0.955-prerelease

This works in a uwp cppwinrt app, but for a regular win32 app, something is not passing the webview2 winmd file to cppwinrt

The problem seems to come from the webview2 pkg.
In \packages\Microsoft.Web.WebView2.1.0.955-prerelease\build\Common.targets, it says:

<ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'UAP'">
  <Reference Include="$(MSBuildThisFileDirectory)..\lib\Microsoft.Web.WebView2.Core.winmd">
    <Implementation>Microsoft.Web.WebView2.Core.dll</Implementation>
  </Reference>
  <ReferenceCopyLocalPaths Include="$(MSBuildThisFileDirectory)..\runtimes\win-$(EffectivePlatform)\native_uap\Microsoft.Web.WebView2.Core.dll" />
  <SDKReference Include="Microsoft.VCLibs.Desktop, Version=14.0"/>
</ItemGroup>

However this won't be evaluated for non-UWP apps like win32 xaml islands apps.

Putting this in the xaml islands project seems to get it building:

  <PropertyGroup>
    <EffectivePlatform>$(Platform)</EffectivePlatform>
    <EffectivePlatform Condition="'$(Platform)' == 'Win32'">x86</EffectivePlatform>
  </PropertyGroup>
  <ItemGroup>
    <Reference Include="packages\Microsoft.Web.WebView2.1.0.955-prerelease\lib\Microsoft.Web.WebView2.Core.winmd">
      <Implementation>Microsoft.Web.WebView2.Core.dll</Implementation>
    </Reference>
    <ReferenceCopyLocalPaths Include="packages\Microsoft.Web.WebView2.1.0.955-prerelease\runtimes\win-$(EffectivePlatform)\native_uap\Microsoft.Web.WebView2.Core.dll" />
  </ItemGroup>

AB#35837927

[champnic]

This should be working in SDK 1.0.1018-prerelease. Thanks!

[joseartrivera]

This is still reproing for me on 1.0.1018-prerelease

[asklar]

This is still reproing for me on 1.0.1018-prerelease

make sure your project sets the property: microsoft/microsoft-ui-xaml#5793 (comment)

(newer versions of the winui package will set this property for you)