Current behavior

On Linux, builds can fail with:

MSB3024: Could not copy the file ".../obj/.../apphost" to the destination file ".../bin/.../<AssemblyName>", because the destination is a folder instead of a file.

In our case, a folder named <AssemblyName> is created in output, then apphost tries to copy to the same path (no extension on Linux), causing a folder/file collision.

Why this happens

Two target behaviors combine:

1. Microsoft.Playwright.targets adds content (playwright.ps1, and optionally .playwright/*) to output.

   • ~/.nuget/packages/microsoft.playwright/1.58.0/buildTransitive/Microsoft.Playwright.targets
   • Content Include="$(MSBuildThisFileDirectory)playwright.ps1" (lines ~52-55)

2. Uno rewrites ContentFilesProjectOutputGroupOutput to prefix $(UnoPriInitialPath) (which defaults to $(AssemblyName)).

   • ~/.nuget/packages/uno.winui/6.5.153/buildTransitive/uno.ui.tasks.assets.targets
   • _UnoAddAssetsFilesToCopyLocal lines ~189-207
   • specifically:
     • Link ... $(UnoPriInitialPath)/%(ContentFilesProjectOutputGroupOutput.Link)
     • TargetPath ... $(UnoPriInitialPath)/%(ContentFilesProjectOutputGroupOutput.TargetPath)

This produces e.g. TargetPath=<AssemblyName>/playwright.ps1, which creates the <AssemblyName> directory and then collides with apphost destination <AssemblyName>.

Evidence from diagnostic build

From dotnet build -v:diag:

• TargetPath=MonacoEditorComponentTests/playwright.ps1
• then apphost copy tries destination .../bin/.../MonacoEditorComponentTests
• then MSB3024 folder-vs-file error

Repro (from real project)

Project: MonacoEditorComponent.Tests (net10.0, OutputType=Exe, AssemblyName=MonacoEditorComponentTests) references Uno.WinUI transitively and Microsoft.Playwright.

dotnet build MonacoEditorComponent.Tests/MonacoEditorComponent.Tests.csproj

Fails on Linux with MSB3024 as above.

Notes

• This appears Linux/macOS-specific in practice because apphost has no .exe extension.
• Even with -p:PlaywrightPlatform=none, playwright.ps1 is still added by Playwright and still gets Uno-prefixed, so collision remains.

Expected behavior

Uno asset copy-local prefixing should not create output paths that can collide with apphost destination (or at minimum should avoid prefixing non-Uno package content such as Playwright content files).