Reactive: Reactive 4.2.0 nuget package creates assembly reference and breaks unit testing

[mattzink]

After upgrading our projects (.NET Core 3) from Reactive 4.1.6 -> 4.2.0, our xunit tests failed to start with:

[11/10/2019 11:18:15.912 AM Error] Microsoft.VisualStudio.TestPlatform.ObjectModel.TestPlatformException: Testhost process exited with error: Error:
  An assembly specified in the application dependencies manifest (ProjectX.Tests.deps.json) was not found:
    package: 'System.Reactive.Reference', version: '4.2.0.0'
    path: 'System.Reactive.dll'

Unlike all other nuget packages, I noticed in VS that Reactive.dll now shows up in Solution Explorer->Project->Dependencies->Assembly as well as under Packages:

Reverting back to 4.1.6 removes the assembly reference and allows our unit tests to execute once again.

[clairernovotny]

Do you have a small repro project?

Rx.NET has integration tests against the packages with .NET Core 3 on both Linux and Windows:

https://github.com/dotnet/reactive/blob/master/Rx.NET/Integration/LinuxTests/LinuxTests.csproj#L3
https://github.com/dotnet/reactive/blob/master/Rx.NET/Integration/WindowsDesktopTests/WindowsDesktopTests.csproj#L3

[mattzink]

reactive-issue.zip

Unzip and run dotnet test

[tfabian]

Do you have a small repro project?
Rx.NET has integration tests against the packages with .NET Core 3 on both Linux and Windows:
https://github.com/dotnet/reactive/blob/master/Rx.NET/Integration/LinuxTests/LinuxTests.csproj#L3
https://github.com/dotnet/reactive/blob/master/Rx.NET/Integration/WindowsDesktopTests/WindowsDesktopTests.csproj#L3

Hi @onovotny,
I noticed that the integration tests are using 4.2.0-preview.63. The preview version works correctly, but the release version doesn't.
System.Reactive.dll is not present in the output dir.
Strange is that solutions which I created in the past (before version 4.3.1) are working correctly.. I hope that this will help you somehow.

[mattzink]

I have verified that the problem still persists in RX 4.3.2 by modifying my repro that I linked above:

> dotnet test
Test run for C:\Users\mattzink\source\repos\reactive-issue\build\bin\netcoreapp3.0\reactive-issue.tests.dll(.NETCoreApp,Version=v3.0)
Microsoft (R) Test Execution Command Line Tool Version 16.3.0
Copyright (c) Microsoft Corporation.  All rights reserved.

Starting test execution, please wait...

A total of 1 test files matched the specified pattern.
Testhost process exited with error: Error:
  An assembly specified in the application dependencies manifest (reactive-issue.tests.deps.json) was not found:
    package: 'System.Reactive.Reference', version: '4.3.0.0'
    path: 'System.Reactive.dll'
. Please check the diagnostic logs for more information.

Test Run Aborted.

[tfabian]

@mattzink, couldn't be your problem related to this file Directory.Build.props?

[mattzink]

@tfabian It's pretty standard, and we've never had an issues with any other package because of it. Is there something specific in that file that you see a problem with?

[mattzink]

I've narrowed this down to failing only when the "UseCommonOutputDirectory" property is enabled in our Directory.Builds.props file, which is a standard MSBuild property that disables copying transitively referenced files to the output folder.

It appears that the non-standard way that the Reactive package >= v4.2.0 causes a direct assembly reference on projects is incompatible with this standard setting.

Hope this helps someone track down the underlying issue.

[mattzink]

https://github.com/dotnet/reactive/blob/master/Rx.NET/Source/src/System.Reactive/build/System.Reactive.targets is the culprit. Dynamically adding transitive links to static assemblies based on configuration feels like a hack. Perhaps making the Windows specific Rx it's own NuGet package would be a better approach?

[softlion]

also the netstandard version should not have windowsruntime in its dependencies. It causes dependency errors with xamarin ios.

[clairernovotny]

That library has some structs/interfaces that are interop and are part of the .NET Standard. Not much we can do about that but the assembly is on all platforms.

[mattzink]

So is the intended behavior that a netcoreapp3.1 TFM app that runs on Linux should be linked to the .net standard 2.0 rx assembly, even though a .net core 3.0 rx assembly exists in the nuget package?

[clairernovotny]

@mattzink That is correct. The netcore 3.0 output is only intended for WPF/WinForms on .NET Core on Windows. Everything else is expected to use the .net standard 2.0 version. That's what the custom targets do.