ProjectReference to file-based app.cs in .NET 10 - possible? What syntax?

[rmunn]

While converting an Aspire project to use a single-file AppHost.cs, I ran into an issue. Previously my testing project had a ProjectReference to ../AspireOrchestration/AspireOrchestration.csproj and that .csproj project was where my AppHost.cs file lived. (The testing project did a simple smoke test that launched the AppHost and ensured that all three of its resources, backend, frontend, and db, reported themselves healthy).

Once I converted AppHost.cs to a single-project file using #:sdk [email protected] and #:package [email protected] and so on, the ProjectReference in my testing project failed, and I could no longer run the following line:

var appHost = await DistributedApplicationTestingBuilder.CreateAsync<Projects.AspireOrchestration>(cancellationToken);

because Projects.AspireOrchestration was no longer found. (I had not moved the location of AppHost.cs, so it was still in the AspireOrchestration folder, but it no longer had a .csproj file).

Is there a syntax (either existing or planned for a future .NET release) for ProjectReferences to a file-based app? Or is the only answer to bring back the .csproj file if you want to have a ProjectReference to it?