I'm certain there's probably a bunch of things going on here that I don't understand well enough, so forgive me if this is a stupid question or if there's obvious details missing.
I have a Visual Studio 2015 solution that I've upgraded from .NET 4.5.1 to .NET 4.7.1. The solution consists of a website (not web app) project, and several libraries. The libraries don't really have any dependencies (except eachother) and while they are targeting .NET 4.7.1, they don't use, need, or reference .NETStandard.Library.
When I compile one of the libraries in particular, it keeps copying a bunch of .NET 4.7.1 facade dlls into the website bin folder. Unfortunately, the website is a Kentico 11 application, and it keeps trying to load the System.IO.Compression.ZipFile facade, and chokes on it because it's a reference assembly, not a real assembly.
If I delete the .dll, everything runs fine... but I don't want to delete it every time or add a post-build event to delete it. That's just silly.
Can anyone help me understand what's going on here, and how to clean it up?
Kentico 11 can only target up to .NET 4.7 so in an attempt to fully support your .NET 4.7.1 libraries I believe it is copying in those additional facade DLLs. This is based on the .NET 4.7.1 release announcement, specifically this section:
BCL – .NET Standard 2.0 Support
.NET Framework 4.7.1 has built-in support for .NET Standard 2.0. .NET Framework 4.7.1 adds about 200 missing APIs that were part of .NET Standard 2.0 but not actually implemented by .NET Framework 4.6.1, 4.6.2 or 4.7. You can refer to details on .NET Standard on .NET Standard Microsoft docs.
Applications that target .NET Framework 4.6.1 through 4.7 must deploy additional .NET Standard 2.0 support files in order to consume .NET Standard 2.0 libraries. This situation occurred because the .NET Standard 2.0 spec was finalized after .NET Framework 4.6.1 was released. .NET Framework 4.7.1 is the first .NET Framework release after .NET Standard 2.0, enabling us to provide comprehensive .NET Standard 2.0 support.
https://blogs.msdn.microsoft.com/dotnet/2017/10/17/announcing-the-net-framework-4-7-1/
Reference that led me to this conclusion: https://github.com/Particular/NServiceBus/issues/5047#issuecomment-339096350
Update:
I was unable to reproduce your issue in Visual Studio 2017 Version 15.6.2.
I installed a Kentico 11 website project targeting .NET 4.7. I then created a library project that targeted .NET 4.7.1. I added some dummy code to the project to make use of Sysetem.IO.Compression and System.Net.Http namespaces. I added a reference to the project from Kentico and ran a build. No facade DLLs where copied to the bin folder.
This post indicates the issue was fixed in Visual Studio version 15.6 https://github.com/dotnet/sdk/issues/1647#issuecomment-364999962