Found conflicts between different versions of "System.Runtime.CompilerServices.Unsafe" that could not be resolved

Question

This may seem as one of many similar questions, but I could not find the solution in other questions.

I will jump straight to the binary log:

And here is the respective subtree under the ResolveAssemblyReference task:

There was a conflict between "System.Runtime.CompilerServices.Unsafe, Version=4.0.4.1, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" and "System.Runtime.CompilerServices.Unsafe, Version=4.0.6.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a".
    "System.Runtime.CompilerServices.Unsafe, Version = 4.0.4.1, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" was chosen because it was primary and "System.Runtime.CompilerServices.Unsafe, Version=4.0.6.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" was not.
    References which depend on "System.Runtime.CompilerServices.Unsafe, Version = 4.0.4.1, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" [C:\Users\mkharitonov\.nuget\packages\system.runtime.compilerservices.unsafe\4.5.2\ref\netstandard2.0\System.Runtime.CompilerServices.Unsafe.dll].
    C:\Users\mkharitonov\.nuget\packages\system.runtime.compilerservices.unsafe\4.5.2\ref\netstandard2.0\System.Runtime.CompilerServices.Unsafe.dll
          Project file item includes which caused reference "C:\Users\mkharitonov\.nuget\packages\system.runtime.compilerservices.unsafe\4.5.2\ref\netstandard2.0\System.Runtime.CompilerServices.Unsafe.dll".
            C:\Users\mkharitonov\.nuget\packages\system.runtime.compilerservices.unsafe\4.5.2\ref\netstandard2.0\System.Runtime.CompilerServices.Unsafe.dll
        C:\Users\mkharitonov\.nuget\packages\microsoft.extensions.primitives\2.0.0\lib\netstandard2.0\Microsoft.Extensions.Primitives.dll
          Project file item includes which caused reference "C:\Users\mkharitonov\.nuget\packages\microsoft.extensions.primitives\2.0.0\lib\netstandard2.0\Microsoft.Extensions.Primitives.dll".
            C:\Users\mkharitonov\.nuget\packages\microsoft.extensions.primitives\2.0.0\lib\netstandard2.0\Microsoft.Extensions.Primitives.dll
            C:\Users\mkharitonov\.nuget\packages\microsoft.extensions.caching.abstractions\2.0.0\lib\netstandard2.0\Microsoft.Extensions.Caching.Abstractions.dll
            xyz.Common
            C:\xyz\tip\bin.link\xyz.Web.Framework.dll
            C:\xyz\tip\bin.link\xyz.Web.Platform.dll
            AccrualEngine
            DataProcessor
            xyz.BusinessAPI.Core
            xyz.DataManager
            DataSvc
            xyz.Data
            xyz.HtmlPlatform
            xyz.BusinessAPI
            DeviceServices
            GrossPayEngineDataProvider
            MultiApprovalProcessor
            Payroll.Core.Data
            PunchStatusReconciliationEngine
            RateEngine2
            RateEngineDataProviderServer
            RuleEngine
            RuleEngineDataProvider
            RuleEngineHelper
            SharpTop.Common.Security.MemberSession
            SharpTop.DB.DL
            WorkTimeCalculationEngine
            C:\Users\mkharitonov\.nuget\packages\microsoft.extensions.caching.memory\2.0.0\lib\netstandard2.0\Microsoft.Extensions.Caching.Memory.dll
            C:\Users\mkharitonov\.nuget\packages\microsoft.extensions.options\2.0.0\lib\netstandard2.0\Microsoft.Extensions.Options.dll
        C:\Users\mkharitonov\.nuget\packages\system.memory\4.5.3\lib\netstandard2.0\System.Memory.dll
          Project file item includes which caused reference "C:\Users\mkharitonov\.nuget\packages\system.memory\4.5.3\lib\netstandard2.0\System.Memory.dll".
            C:\Users\mkharitonov\.nuget\packages\system.memory\4.5.3\lib\netstandard2.0\System.Memory.dll
            C:\Users\mkharitonov\.nuget\packages\system.diagnostics.diagnosticsource\4.6.0\lib\net46\System.Diagnostics.DiagnosticSource.dll
            C:\Users\mkharitonov\.nuget\packages\microsoft.applicationinsights\2.10.0\lib\net46\Microsoft.ApplicationInsights.dll
            C:\Users\mkharitonov\.nuget\packages\xyz.engine.core.common\1.0.20260.1\lib\netstandard2.0\xyz.Engine.Core.Common.dll
            xyz.Common
            C:\xyz\tip\bin.link\xyz.Web.Framework.dll
            C:\xyz\tip\bin.link\xyz.Web.Platform.dll
            AccrualEngine
            DataProcessor
            xyz.BusinessAPI.Core
            xyz.DataManager
            DataSvc
            xyz.Data
            xyz.HtmlPlatform
            xyz.BusinessAPI
            DeviceServices
            GrossPayEngineDataProvider
            MultiApprovalProcessor
            Payroll.Core.Data
            PunchStatusReconciliationEngine
            RateEngine2
            RateEngineDataProviderServer
            RuleEngine
            RuleEngineDataProvider
            RuleEngineHelper
            SharpTop.Common.Security.MemberSession
            SharpTop.DB.DL
            WorkTimeCalculationEngine
        C:\xyz\tip\Tools\MSBuild\..\..\bin.link\System.Threading.Tasks.Extensions.dll
          Project file item includes which caused reference "C:\xyz\tip\Tools\MSBuild\..\..\bin.link\System.Threading.Tasks.Extensions.dll".
            GrossPayEngineDataProvider
        C:\xyz\tip\Tools\MSBuild\..\..\bin.link\Pipelines.Sockets.Unofficial.dll
          Project file item includes which caused reference "C:\xyz\tip\Tools\MSBuild\..\..\bin.link\Pipelines.Sockets.Unofficial.dll".
            GrossPayEngineDataProvider
    References which depend on "System.Runtime.CompilerServices.Unsafe, Version = 4.0.6.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" [C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Current\Bin\System.Runtime.CompilerServices.Unsafe.dll].

From which I conclude there are two versions of the System.Runtime.CompilerServices.Unsafe.dll at play:

1. A NuGet package - C:\Users\mkharitonov.nuget\packages\system.runtime.compilerservices.unsafe\4.5.2\ref\netstandard2.0\System.Runtime.CompilerServices.Unsafe.dll
2. C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Current\Bin\System.Runtime.CompilerServices.Unsafe.dll

The binary log goes to a great detail showing which assemblies depend on the NuGet package, but it shows none for the second reference. Which is weird, because then the question is - why the second version is considered in the first place?

The project in question is just a library and hence does not have an app.config file. Also, AutoUnify == true so the ResolveAssemblyReference task should automatically resolve the conflict to the highest version, at least this is my interpretation of the documentation.

So, I am puzzled. I know that the warning is minor and can be ignored, but I want to understand the nature of it. What is causing it if apparently all the dependencies rely on the NuGet package. Or maybe the task does not output certain kind of dependencies and leaves it up to me to investigate what depends on C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Current\Bin\System.Runtime.CompilerServices.Unsafe.dll ?

For the record:

1. the assembly version of the NuGet package is 4.0.4.1 and that of the second version is 4.0.6.0, so should not all resolve to the highest version, i.e. the second version?
2. None of my code makes direct reference to System.Runtime.CompilerServices.Unsafe, so all the dependencies listed by the ResolveAssemblyReference task must be transitive.
3. I tried adding app.config file to the project in question with the binding redirects, even though there supposed to be no need for that due to the presence of the AutoGenerateBindingRedirects property. As I expected - it did not help.

How can I determine what is going on and how to fix it?

Answer 1

I suddenly had the same error on building the solution. I restored a backup and tried a build. That worked again but after copying the updated code snippets the error came back. Updating the Unsafe.dll package, removing the references everywhere, updating Visual Studio etc did not help. It always restored the incorrect library again somehow.

By pure change I discovered the cause. It had to do with a Linq statement. Which looked something like this

MyList.ForEach(x => x.property = x.property.Replace("ABC", MyOtherList.Where(x => x.property == SomeValue).First().name)));

This caused no errors in the Error List. But this line caused the library Unsafe.dll to be added to the project again and again. And failing the build. Changing the second Linq part x to y fixed all the issues.

MyList.ForEach(x => x.property = x.property.Replace("ABC", MyOtherList.Where(y => y.property == SomeValue).First().name)));

Maybe this helps someone else because this simple issue cost me about 3 hours of extra work.

Answer 2

I have an update. On our side there was an entry in one of the app.config redirecting to the 4.0.6.0.

We have never seen the problem, because there was no 4.0.6.0 on the build machine.

But as we've updated Visual Studio to the newest version, msbuild somehow was copying it.

_CopyFilesMarkedCopyLocal:
  The File will be copied from "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Current\Bin\System.Runtime.CompilerServices.Unsafe.dll" in "D:\agent_03\_work\21\s\Release\System.Runtime.CompilerServices.Unsafe.dll".

As soon we deleted the entry on the config file, the file was not copied anymore.

<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="System.Runtime.CompilerServices.Unsafe" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-4.0.6.0" newVersion="4.0.6.0" />
      </dependentAssembly>
</assemblyBinding>

Search for any specific entry on you app.configs. If you can't find it, i'm afraid you need to go through all your nuget dependencies till you find which one needs this specific version.

Cheers, Marco