Change projects to target netcoreapp3.0

[natemcmaster]

As a part of only supporting .NET Core, we can change most projects to target netcoreapp3.0 instead of netstandard2.0.
This change applies to test projects, which no longer need to cross-target .NET Framework.

See aspnet/Announcements#324

Remaining feature areas (I likely missed a few here, keep adding them ~Chris):

• Html
• Razor - make sure to ping @rynowak on this one. We're splitting code here into a new repo soon.
• Http - (Chris) - With exceptions Change projects to target netcoreapp3.0 #3754 (comment)
• Hosting (Chris)
• DataProtection (Chris)
• HttpSysServer (Chris)
• Kestrel (Chris)
• BasicMiddleware (Chris)
• IISIntegration (Justin)
• Antiforgery (Chris)
• StaticFiles (Chris)
• ResponseCaching (Chris)
• Middleware (Chris)

[natemcmaster]

I want to emphasize the "most" part of the original post. Some libraries, like the SignalR .NET client, must continue to target .NET Standard when the library is intended for use on other .NET runtimes like Xamarin and UWP. This decision is being made on a case-by-base basis. We should finish going through our list of assemblies and post the decisions to clarify exactly which assemblies should change to netcoreapp3.0-only.

[bdominguez]

What about WPF applications that host asp net core? It will no longer be possible to do this.

[khellang]

What about WPF applications that host asp net core?

Just port it over to .NET Core? 😉 https://blogs.msdn.microsoft.com/dotnet/2018/10/04/update-on-net-core-3-0-and-net-framework-4-8/

[natemcmaster]

@khellang is correct, WPF and AspNetCore can be used together. A WPF app will be able to set TargetFramework to netcoreapp3.0 and also have a FrameworkReference to Microsoft.AspNetCore.App.

[benaadams]

What about WPF applications that host asp net core? It will no longer be possible to do this.

And if you don't want to port your WPF to .NET Core (though you should 😉) you can keep using ASP.NET Core 2.1 #3753 (comment)

In order to give customers a reasonable stepping stone on their path to migrating applications to ASP.NET Core on .NET Core, we are going to extend support and servicing for ASP.NET Core 2.1.x on .NET Framework to match the current support policy for the other package-based ASP.NET frameworks, e.g. MVC 5.x, Web API 2.x, SignalR 2.x. This effectively means the ASP.NET Core 2.1.x related packages (final detailed list TBD) will be supported indefinitely, beyond the 3 year LTS period for the .NET Core 2.1 train overall.