Alias in ProjectReference does not work for framework-included packages

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Issue moved from NuGet/Home#10438

• Please respond to @weltkante.

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From @weltkante on Friday, January 8, 2021 4:19:41 PM

Details about Problem

In #4989 alias support for PackageReference was added, but when I try to create an alias to a framework-provided package this does not appear to work.

In particular, in a .NET 5 web application I add

<PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="5.0.0" Aliases="logging" />

but extern alias logging; does not compile:

error CS0430: Der externe Alias "logging" wurde nicht in einer /reference-Option angegeben.

If I instead do it in a console application it indeed does work.

Using VS 2019 Update 9 Preview 2

[tdhatcher]

This looks like a related issue. https://github.com/dotnet/msbuild/issues/4943

Problem Only the extern alias of the first occurrence of NuGet PackageReference is recognized v12. v11 results in compilation error CS0430

Reproduce Steps

1. csproj

<ItemGroup>
    <PackageReference Include="Newtonsoft.Json" Version="12.0.3" Aliases="v12" />
    <PackageReference Include="Newtonsoft.Json" Version="11.0.2" Aliases="v11" />
</ItemGroup>

1. Program.cs (C# 11 / NET 7)

extern alias v12;
extern alias v11;

using Json12 = v12::Newtonsoft.Json;
using Json11 = v11::Newtonsoft.Json;

Json12.JsonConvert.SerializeObject(new { message = "Hello, world!" });
Json11.JsonConvert.SerializeObject(new { message = "Hello, world!" });

I even stumped ChatGPT with this one, it seemed so confident that it should be working and that I was doing something wrong.

[CodeOptimist]

Still busted, my project is net472.