WinUI 3 Single Project MSIX crashes when built for x86

[mattleibow]

Describe the bug

I have a single project app that crashes on launch with a BadImageFormatException:

System.BadImageFormatException: 'An attempt was made to load a program with an incorrect format. (0x8007000B)'
This exception was originally thrown at this call stack:
    App1.Program.Main(string[]) in App.g.i.cs

Steps to reproduce the bug

1. Download and extract this project: App1.zip
2. Hit F5 / Run
3. Observe exception
4. Change the <RuntimeIdentifier>win10-x86</RuntimeIdentifier> to be win10-x64
5. Hit F5 / Run
6. Observe NO exception

I created this by making a new WinUI 3 app, converted it to a single project and then make the app be an AnyCPU with a x86 RID.

Expected behavior

No crash - like win10-x64.

Screenshots

NuGet package version

1.0.0

Packaging type

Packaged (MSIX)

Windows version

Windows 11 version 21H2 (22000)

IDE

Visual Studio 2022-preview

Additional context

No response

AzDo bug: https://dev.azure.com/microsoft/OS/_workitems/edit/38094973

[kmgallahan]

Works fine if you use the single project template instead of converting (or rather doing whatever process resulted in the solution you provided):

csproj looks a bit different (note I updated the sdk build tools from the version that appears in the template).

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net6.0-windows10.0.19041.0</TargetFramework>
    <TargetPlatformMinVersion>10.0.17763.0</TargetPlatformMinVersion>
    <RootNamespace>App7</RootNamespace>
    <ApplicationManifest>app.manifest</ApplicationManifest>
    <Platforms>x86</Platforms>
    <RuntimeIdentifiers>win10-x86</RuntimeIdentifiers>
    <PublishProfile>win10-$(Platform).pubxml</PublishProfile>
    <UseWinUI>true</UseWinUI>
    <EnablePreviewMsixTooling>true</EnablePreviewMsixTooling>
  </PropertyGroup>

  <ItemGroup>
    <Content Include="Assets\SplashScreen.scale-200.png" />
    <Content Include="Assets\LockScreenLogo.scale-200.png" />
    <Content Include="Assets\Square150x150Logo.scale-200.png" />
    <Content Include="Assets\Square44x44Logo.scale-200.png" />
    <Content Include="Assets\Square44x44Logo.targetsize-24_altform-unplated.png" />
    <Content Include="Assets\StoreLogo.png" />
    <Content Include="Assets\Wide310x150Logo.scale-200.png" />
  </ItemGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.WindowsAppSDK" Version="1.0.0" />
    <PackageReference Include="Microsoft.Windows.SDK.BuildTools" Version="10.0.22543-preview" />
    <Manifest Include="$(ApplicationManifest)" />
  </ItemGroup>

  <!-- Defining the "Msix" ProjectCapability here allows the Single-project MSIX Packaging
       Tools extension to be activated for this project even if the Windows App SDK Nuget
       package has not yet been restored -->
  <ItemGroup Condition="'$(DisableMsixProjectCapabilityAddedByProject)'!='true' and '$(EnablePreviewMsixTooling)'=='true'">
    <ProjectCapability Include="Msix" />
  </ItemGroup>
</Project>

[mattleibow]

I believe it is because you have included the <Platforms>x86</Platforms> property. Since we are building a multi-targeting project, we cannot use that because all the projects use AnyCPU.

[kmgallahan]

I didn't think you could use anycpu with WinUI:

https://docs.microsoft.com/en-us/windows/apps/windows-app-sdk/stable-channel#other-limitations-and-known-issues

No support for Any CPU build configuration: When adding the Windows App SDK to an existing .NET application or component that supports Any CPU, you must specify the desired architecture: x86, x64 or arm64.

[mattleibow]

You can in most cases (for example if you target x64), but we need to. In a multitargeting world with a single project in .NET Maui, this is basically the only way.

Partially related to this comment:

• AnyCPU support #893
• AnyCPU Class libraries are broken again #1217