[DRAFT] Behavior of out-of-box PackageReference undefined when FrameworkReference provides same reference

[jzabroski]

Description

I have searched everywhere for documentation that clearly describes what the expected behavior should be in the following scenario and there is none. The lack of a clearly defined behavior is leading to paradoxical discussions regarding the severity of packaging 6.0.0 out-of-box packages that reference out-of-box netstandard2.0 packages, where the severity is judged without considering what the correct behavior is when the out-of-box package is a referenced from a "library project" that uses netstandard2.0 TFM and the "entry point project" uses net6.0 (or any concrete target framework, but the problem is most visible now due to recent changes).

EntryPoint.csproj [net6.0]
 \_ Dependencies
    \_ Projects
       \_ HelperLibrary.csproj [netstandard2.0]
Common.csproj [netstandard2.0]
 \_ Dependencies
    \_ Packages
       \_ Microsft.Extensions.DependencyModel [netstandard2.0, version 6.0.0]
          \_ System.Buffers [netstandard2.0, version 4.5.1]

In this scenario, System.Buffers has been "in-box" as part of the runtime libraries since .NET Core 2.1.

Reproduction Steps

EntryPoint.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <AssemblyTitle>EntryPoint</AssemblyTitle>
    <OutputType>Exe</OutputType>
    <TargetFrameworks>net60</TargetFrameworks>
  </PropertyGroup>

  <PropertyGroup>
    <StartupObject>EntryPoint.Program</StartupObject>
  </PropertyGroup>

  <ItemGroup>
    <ProjectReference Include="..\Common\Common.csproj" />
  </ItemGroup>

</Project>

Program.cs

namespace EntryPoint
{
  public class Program
  {
    public static void Main(string[] args)
    {
       System.Console.Out.WriteLine("Hello, World");
    }
  }
}

Common.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <AssemblyTitle>Common</AssemblyTitle>
    <TargetFrameworks>netstandard2.0</TargetFrameworks>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="System.Buffers" Version="4.5.1" />
  </ItemGroup>

</Project>

Run

dotnet restore EntryPoint.csproj

Known Workarounds

1. Tell people not to use my project from a netstandard2.0 TFM, and that netstandard2.0 is only supposed to be used by net4.8, and proceed to look like a hacky idiot who doesn't know what he is doing packaging open source projects
2. Remove support for netstandard2.0, or segregate netstandard2.0 into a special nuget package with a funny name like MyNugetPackage.Net48 that makes it abundantly clear the package only works right when used by net48 TFM.

[jzabroski]

https://github.com/dotnet/corefx/pull/36550