ResolveAssemblies task wrongly uses reference assemblies

[marek-safar]

Steps to Reproduce

1. Get and Build repro https://github.com/marcominerva/XamarinAndroidIssue

If you instead the build log you will see that

Using "ResolveAssemblies" task from assembly "/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Build.Tasks.dll".

has few ...ref/netstandard2.0/... references which is wrong as they should never be used as an input to linker or any post compilation processing

This issue is possibly related to #1154

Expected Behavior

No error during execution.

Actual Behavior

[Mono] Assembly Loader probing location: 'System.Memory'.
[monodroid-assembly] Could not load assembly 'System.Memory' during startup registration.

Version Information

Xamarin.Android
Version: 8.1.0.25 (Visual Studio Community)
Android SDK: /Users/marek/Library/Developer/Xamarin/android-sdk-macosx
Supported Android versions:
6.0 (API level 23)
7.1 (API level 25)

SDK Tools Version: 25.2.5
SDK Platform Tools Version: 25.0.5
SDK Build Tools Version: 25.0.3

Log File

/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1500,2): warning : Ignoring /Users/marek/.nuget/packages/system.buffers/4.4.0/ref/netstandard2.0 as it is a Reference Assembly
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1500,2): warning : Ignoring /Users/marek/.nuget/packages/system.memory/4.4.0-preview2-25405-01/ref/netstandard2.0 as it is a Reference Assembly
/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1500,2): warning : Ignoring /Users/marek/.nuget/packages/system.runtime.compilerservices.unsafe/4.4.0/ref/netstandard2.0 as it is a Reference Assembly

VS bug #585873

[GMariakis]

Until this is resolved, has a workaround been identified? Having this issue with System.Memory and System.Runtime.CompilerServices.Unsafe

[dellis1972]

The only thing I can think of is to add a reference to the missing assemblies to the main app. And make sure you reference the lib versions.

[GMariakis]

That does not work. I have tried all the workarounds, such as changing the linker, adding the packages.config, etc. URLs below.

I am trying to use SignalR Core in a Cross Platform Xamarin / Xamarin Forms app using .NET Standard as the code sharing mechanism. Getting the same two skips with the reason that it is a reference Assembly.

/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1500,2): warning : Ignoring /Users/xxxxxx/.nuget/packages/system.memory/4.4.0-preview2-25405-01/ref/netstandard2.0 as it is a Reference Assembly /Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(1500,2): warning : Ignoring /Users/xxxxxx/.nuget/packages/system.runtime.compilerservices.unsafe/4.4.0/ref/netstandard2.0 as it is a Reference Assembly

https://forums.xamarin.com/discussion/113718/android-error-with-signalr-core-could-not-load-assembly-system-memory-during-startup-registration

https://forums.xamarin.com/discussion/100273/deploying-to-android-emulator-error-could-not-load-assembly-system-runtime-compilerservices-unsafe

https://github.com/aspnet/EntityFrameworkCore/issues/8922

[rwasef1830]

Here's a functioning workaround. It's hacky and ugly but works with minimum fuss. Put this in an XML file and <Import> it in your Android csproj file at the end. It works at least for System.Buffers

<!-- Workaround for https://github.com/xamarin/xamarin-android/issues/1162 -->
<Project>
  <Target Name="ReplaceRefAssemblies" AfterTargets="_ResolveAssemblies">
    <ItemGroup>
      <ResolvedAssembliesFixedWindows Include="@(ResolvedAssemblies->Replace('\ref\','\lib\'))" />
      <ResolvedAssembliesFixedUnix Include="@(ResolvedAssemblies->Replace('/ref/','/lib/'))" />
      <ResolvedAssembliesFixed Include="@(ResolvedAssembliesFixedWindows)" Condition="@(ResolvedAssembliesFixedWindows) != @(ResolvedAssemblies)" />
      <ResolvedAssembliesFixed Include="@(ResolvedAssembliesFixedUnix)" Condition="@(ResolvedAssembliesFixedUnix) != @(ResolvedAssemblies)" />
      <ResolvedAssemblies Condition="'@(ResolvedAssembliesFixed->Count())' &gt; 0" Remove="@(ResolvedAssemblies)" />
      <ResolvedAssemblies Include="@(ResolvedAssembliesFixed)" />
    </ItemGroup>
  </Target>
</Project>

Update: Fixed an issue where if there were no ref assemblies in the list, the ResolvedAssemblies would be emptied. Symptoms of that issue: Build failure with cannot find obj\linksrc\SomeAssembly.dll or an assembly not found error. The bug fix was adding a condition to only empty ResolvedAssemblies if ResolvedAssembliesFixed was not empty.

[SvenEV]

I found another workaround: In my case, the NuGet package "System.Runtime.CompilerServices.Unsafe" caused the issue. So I made a copy of the package (*.nupkg file), removed the "ref"-folder from it (which contains the reference assemblies), and installed that modified package into my project.

Now that the package only contains the "real" assembly, there's no way for Mono to accidentally pick the wrong assembly.

[dellis1972]

That is an interesting workaround :) it that might cause some issues though. We are still working through this issue here, hopefully we will find a good soluition.

[GMariakis]

The problem with any of these workarounds, once I get it to build and deploy, the Xamarin Forms won't find and attach property changed notify for any fields. I spent a week trying to figure out why. The only thing I can think of is that there's an internal problem with these pre-release libraries.