Alias in ProjectReference does not work for framework-included packages

[aortiz-msft]

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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

[aortiz-msft]

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Issue moved from NuGet/Home#10438

• Please respond to @JonDouglas.

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From @JonDouglas on Friday, January 8, 2021 5:49:15 PM

Hi @weltkante,

Thanks for the report!

Can you please provide us a sample project or reproducible steps to help us debug this further?

Feel free to refer to our section on bug reports for more information on what we're looking for!

[aortiz-msft]

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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 7:25:18 PM

Sure, the reproduction steps are literally just what I said above, adding a PackageReference to a framework package and a corresponding extern alias statement. I'm adding a full example below, changing the SDK to Microsoft.NET.Sdk (i.e. removing the Web) makes things compile but obviously I'm then missing a lot of implicit behavior of the Web SDK, both in implicit package references and project system behavior.

<Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <OutputType>Library</OutputType>
    <TargetFramework>net5.0</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="5.0.0" Aliases="logging" />
  </ItemGroup>
</Project>

extern alias logging;

using System;

namespace PackageAlias
{
    public class Helper
    {
        public void MethodWithLogger(logging::Microsoft.Extensions.Logging.ILogger logger)
        {
        }
    }
}

Program.cs(1,14,1,21): error CS0430: The extern alias 'logging' was not specified in a /reference option
Program.cs(9,47,9,56): error CS0234: The type or namespace name 'Microsoft' does not exist in the namespace 'logging' (are you missing an assembly reference?)

[aortiz-msft]

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Issue moved from NuGet/Home#10438

• Please respond to @JonDouglas.

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From @JonDouglas on Friday, January 8, 2021 8:14:16 PM

@weltkante Thank you kindly! We'll look into this shortly in our next triaging session. Thanks for the clarification on the .csproj items!

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[GeirGrusom]

I've never in my life needed to use extern alias before but when I do of course it's completely broken. The Aliases property has no effect in net48 or net5.0 projects. Visual Studio 16.8.5.

[charabaruk]

I'm now getting tripped up on this too. net5.0 project.

[khayes]

I'm also having this problem. The context is I am making a library that has multiple TFMs.

<Project Sdk="Microsoft.NET.Sdk">
	
  <PropertyGroup>
    <TargetFrameworks>net6.0;net472</TargetFrameworks>
  </PropertyGroup>

  <!-- Conditional PackageReferences are in here with Aliases set -->
</Project>

There is a type I need that exists in the same namespace but different assemblies, so I need an external alias. But this won't work as one of my targets is net472.

[timmydo]

Migrating some code from <Reference> to <ProjectReference> I stumbled across this also.