Error CS0017 raised when trying to build an app with <UseWinUI>true</UseWinUI> set (without GenerateProgramFiles set to false in the project file)

[lauren-ciha]

In my WinUI (3) test app, the .csproj begins like this:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net10.0-windows10.0.26100.0</TargetFramework>
    <TargetPlatformMinVersion>10.0.17763.0</TargetPlatformMinVersion>
    <RootNamespace>WinUITests12</RootNamespace>
    <ApplicationManifest>app.manifest</ApplicationManifest>
    <Platforms>x86;x64;ARM64</Platforms>
    <RuntimeIdentifier Condition="'$(RuntimeIdentifier)' == ''">win-$([System.Runtime.InteropServices.RuntimeInformation]::ProcessArchitecture.ToString().ToLowerInvariant())</RuntimeIdentifier>
    <PublishProfile Condition="Exists('Properties\PublishProfiles\win-$(Platform).pubxml')">win-$(Platform).pubxml</PublishProfile>
    <WinUIDSKReferences>false</WinUIDSKReferences>
    <EnableMsixTooling>true</EnableMsixTooling>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <UseWinUI>true</UseWinUI>
  </PropertyGroup>

When I attempt to build, I get this error:
CS0017: Program has more than one entry point defined. Compile with /main to specify the type that contains the entry point.

From my understanding, this error is occurring because WinUI apps define their own entry point and if GenerateProgramFiles is true, Microsoft.NET.Test.Sdk.Program.cs is auto-generated with its own entry point.

When I set GenerateProgramFiles to false within the project file, the app builds and runs as expected.

However, based on this line in Microsoft.NET.Test.Sdk.targets, I'm wondering if the UseWinUI property is meant to set GenerateProgramFiles to false when GenerateProgramFiles is not set in the project file. If so, it looks like the following line in the same file overrides the previous line and sets GenerateProgramFiles back to true. If UseWinUI is meant to set GenerateProgramFiles to false, I think both evaluations of true and false should include UseWinUI and UseUwpTools.

Am I misunderstanding the UseWinUI property and/or Microsoft.NET.Test.Sdk.targets? I appreciate any insight you can provide.

[nohwnd]

Thanks for the detailed report and for pinpointing the exact lines! I've confirmed the root cause and submitted a fix.

Root cause: The PropertyGroup in Microsoft.NET.Test.Sdk.targets correctly guards GenerateProgramFile=false when UseWinUI=true, but the check happens during static property evaluation. When UseWinUI is set by the Windows App SDK's NuGet package targets (rather than explicitly in the project file), it may be evaluated after Microsoft.NET.Test.Sdk.targets (NuGet sorts Microsoft.* before WindowsAppSDK.* alphabetically). At that point UseWinUI is still empty, so GenerateProgramFile ends up true and the conflicting Program.cs entry point gets injected — hence CS0017.

Fix: The GenerateProgramFile target's own Condition now also checks UseWinUI and UseUwpTools. Target conditions are evaluated at execution time, after all package targets have been imported, so UseWinUI is always set correctly by then.

A PR has been opened for review.

🔍 Triaged by Issue Repro Triage & Auto-Fix 🔍