.NET 4.6.1 project cannot reference a .NET Standard 1.4 project - conflicting types

[gulbanana]

Repro: https://github.com/gulbanana/repro-netstandard-httpclient
These two projects were created with VS2017 RC Refresh. Neither contains any meaningful code. netstdlib builds ok, but netfxlib fails:

banana@forsyth MINGW64 /c/code/repro-netstandard-httpclient/netfxlib (master)
$ dotnet build
Microsoft (R) Build Engine version 15.1.458.808
Copyright (C) Microsoft Corporation. All rights reserved.

  netstdlib -> C:\code\repro-netstandard-httpclient\netstdlib\bin\Debug\netstandard1.4\netstdlib.dll
C:\Program Files\dotnet\sdk\1.0.0-preview4-004233\Microsoft.Common.CurrentVersion.targets(1909,5): warning MSB3243: No way to resolve conflict between "System.IO.Compression, Version=4.1.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" and "System.IO.Compression, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089". Choosing "System.IO.Compression, Version=4.1.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" arbitrarily. [C:\code\repro-netstandard-httpclient\netfxlib\netfxlib.csproj]
C:\Program Files\dotnet\sdk\1.0.0-preview4-004233\Microsoft.Common.CurrentVersion.targets(1909,5): warning MSB3243: No way to resolve conflict between "System.Net.Http, Version=4.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" and "System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a". Choosing "System.Net.Http, Version=4.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" arbitrarily. [C:\code\repro-netstandard-httpclient\netfxlib\netfxlib.csproj]
  Consider app.config remapping of assembly "System.IO.Compression, Culture=neutral, PublicKeyToken=b77a5c561934e089" from Version "4.0.0.0" [C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.6.1\System.IO.Compression.dll] to Version "4.1.0.0" [C:\Users\banana\.nuget\packages\system.io.compression\4.1.0\ref\net46\System.IO.Compression.dll] to solve conflict and get rid of warning.
  Consider app.config remapping of assembly "System.Net.Http, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" from Version "4.0.0.0" [C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.6.1\System.Net.Http.dll] to Version "4.1.0.0" [C:\Users\banana\.nuget\packages\system.net.http\4.1.0\ref\net46\System.Net.Http.dll] to solve conflict and get rid of warning.
Class1.cs(9,29): error CS0433: The type 'HttpClient' exists in both 'System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' and 'System.Net.Http, Version=4.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' [C:\code\repro-netstandard-httpclient\netfxlib\netfxlib.csproj]

Warnings are present even if you don't add a line of code to either project, and if you try to use any types from System.IO.Compression or System.Net.Http it's an unfixable compile error.

[qmfrederik]

I'm seeing this issue as well. I tried to do what the build warning instructs me to do - I added an assembly binding redirect for S.IO.Compression & S.N.Http, and added an <Include> for the app.config file in my .csproj file, but still get the warnings (see my config below).

Is there any way we can workaround this by updating the project file? It would as I'm currently blocked by this.

Extract from my csproj file:

<Project Sdk="Microsoft.NET.Sdk" ToolsVersion="15.0">
  <ItemGroup>
...
    <None Include="app.config"/>
  </ItemGroup>
</Project>
...

My app.config file:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-9.0.0.0" newVersion="9.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.IO.Compression"
                          publicKeyToken="b77a5c561934e089"
                          culture="neutral" />
        <bindingRedirect oldVersion="4.0.0.0-4.1.2.0"
                         newVersion="4.1.2.0"/>
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Net.Http"
                          publicKeyToken="b77a5c561934e089"
                          culture="neutral" />
        <bindingRedirect oldVersion="4.0.0.0-4.1.1.0"
                         newVersion="4.1.1.0"/>
      </dependentAssembly>
    </assemblyBinding>
  </runtime>
</configuration>

Thanks!

[qmfrederik]

Perhaps worth adding that Entity Framework Core references NETStandard.Library even on net461 so anyone using Entity Framework Core is affected by this: dotnet/efcore#7078

[gulbanana]

referencing netstandard.lib on desktop needs to be made ok to do, as it will become harder and harder to avoid. unfortunately the status quo is that you must avoid it due to issues such as the webrequest inheritance security thing. i think the exacerbating factors with new csproj are twofold:

1. default assembly refs cause immediate clashes
2. binding redirects are no longer a workaround option

but the fundamental underlying cause is the same. a desktop-safe release of netstandard.library is needed asap - we cannot wait for the 2.0 timeframe!

[dsplaisted]

I haven't yet looked into what's going on here, but this is definitely supposed to work and it's important for it to work.

@gulbanana I haven't heard about the webrequest inheritance security thing, if there isn't already an issue open for that please also open one (probably the dotnet/standard repo would be the right place).

[gulbanana]

There is already an issue with plenty of work being done :) It's at https://github.com/dotnet/corefx/issues/11100

The only reason I mentioned it here is that it's another reason we can't yet safely reference netstandard.library from desktop, and therefore a reason that overriding the default reference set doesn't fully work around this issue.

[qmfrederik]

@gulbanana Just wanted to make sure I understand correctly: what you are saying is that there is another issue which also blocks projects which reference NETStandard.Library working reliably on .NET FX, not that this issue is a duplicate of dotnet/corefx#11100, correct?

By looking at dotnet/corefx#11100, it seems that

1. dotnet/corefx#11100 is a runtime issue, whereas this is a compile time issue
2. There is a workaround for dotnet/corefx#11100 via manually setting the assembly redirects; whereas this issue is about the dotnet build (msbuild/SDK/CLI) somehow not picking up the assembly binding redirects and the compilation to fail.

My understanding is that the workaround for dotnet/corefx#11100 does not apply here and there is no known workaround for this one, effectively preventing compilation of csproj projects which reference NETStandard.Library for the net461 runtime.

Any workaround for this (or pointers to what we can do to provide a fix - happy to create a PR if needed) would be greatly appreciated :)

[dsplaisted]

I think this is the same issue as dotnet/msbuild#1329

[gulbanana]

I think that's a component of the problem, but bear in mind the warning is not spurious - it is correctly indicating that you will not be able to use those types.

[ericstj]

This looks to me like the SDK is missing this code that existed in the previous NuGet targets:
https://github.com/NuGet/NuGet.BuildTasks/blob/cb9b1a1559efac311b84aacc5f605004ad9e8562/src/Microsoft.NuGet.Build.Tasks/Microsoft.NuGet.targets#L216-L218
That is what made this work in NuGet 3.

RAR is getting a simple name reference which resolves to the targeting pack and the NuGet reference then not resolving the conflicts between the two since they are both primary. We do need RAR to fix that moving forward, so you can let dotnet/msbuild#1329 track that fix.