[Android] Throws runtime error in mscorlib, expected class System.Runtime.CompilerServices.ValueTaskAwaiter1

[sacOO7]

Description

I am unable to use ably package with a dependency on System.Threading.Channels (the error might also have origin from System.Threading.Tasks.Extensions/System.Runtime.CompilerServices.Unsafe assembly) , throws below runtime exception on MAUI android.

Throws a runtime error while trying to run on android =>

System.TypeLoadException: 'Could not load type of field 'IO.Ably.Realtime.Workflow.RealtimeWorkflow+d__36:<>u__2' (11) due to:
Could not resolve type with token 010000ba from typeref (expected class 'System.Runtime.CompilerServices.ValueTaskAwaiter1' 
in assembly 'mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e')
assembly:mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e type:System.Runtime.CompilerServices.ValueTaskAwaiter1 member:(null)

It works on a regular net6.0 library, MAUI windows machine, and the latest Xamarin Forms.

I tried all options to disable assembly trimming as per
https://learn.microsoft.com/en-us/dotnet/core/deploying/trimming/trimming-options?pivots=dotnet-6-0
but the issue still persists and the app throws an error at runtime.

I strongly feel the issue is related to a missing type in mscorlib same as the one mentioned in dotnet/maui#5078 and dotnet/maui#5142

Steps to Reproduce

1. Clone the project from https://github.com/sac-fork/MauiAppAblyDemo
2. Build and run it on android emulater ( I used default Pixel 5 - API 33 (API 13 - API 33) )
3. Tap on Click me button, it will throw above error.

Link to public reproduction project repository

https://github.com/sac-fork/MauiAppAblyDemo

Version with bug

6.0 / 7.0

Last version that worked well

Unknown/Other

Affected platforms

Android

Affected platform versions

Android API 13 to 33

Did you find any workaround?

No workarounds were found.

Relevant log output

System.TypeLoadException: 'Could not load type of field 'IO.Ably.Realtime.Workflow.RealtimeWorkflow+d__36:<>u__2' (11) due to: Could not resolve type with token 010000ba from typeref (expected class 'System.Runtime.CompilerServices.ValueTaskAwaiter1' in assembly 'mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e') assembly:mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e type:System.Runtime.CompilerServices.ValueTaskAwaiter1 member:(null)

[sacOO7]

@Redth and @XamlTest can we please include fix for this issue as a part of next release?

[Xyncgas]

I can use System.threading.channel as you said, you should reach out to ably too meanwhile check if trimming is what's breaking this if is then you can also have guys at roslyn or ASP.NET take a look for you

[sacOO7]

I am the person from ably responsible for maintaining the ably-package. I don't think there is an issue with the ably-package. Can you clone the project https://github.com/sac-fork/MauiAppAblyDemo and try running it on android? Because it works fine on windows machines but doesn't work properly on android. Also, as mentioned in the description #82193, I have tried all options to disable assembly trimming, but no luck : (.
So, issues surely have to do with mscorlib same as dotnet/maui#5078 and dotnet/maui#5142

[dotnet-issue-labeler]

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.

[sacOO7]

@rachelkang I am not sure why this issue was transferred to dotnet/runtime, but I am skeptical about getting it fixed sooner. ( There are already 8k+ active issues on this repository ) Can you please add this issue to your priority queue ?

[sacOO7]

Any update on this @Redth and @XamlTest ?

CC @rachelkang

[marek-safar]

The problem is very likely down to this dependency 'System.Runtime.CompilerServices.ValueTaskAwaiter1' in assembly 'mscorlib, Version=2.0.5.0. One of your packages is not targeting .NET5+ but original Xamarin only. This should in theory work but it's always tricky combination.

@steveisok could you check why it's failing?

[sacOO7]

@marek-safar can you try this app ->https://github.com/sac-fork/MauiAppAblyDemo?

If you have a workaround to get this working, it will be super useful 🥇

[akoeplinger]

@sacOO7 the short answer is that you need to add a net6.0 target to your nuget package to fix the issue.

Long answer:

.NET (Core) provides a compatibility mechanism for using assemblies which were compiled against the legacy .NET Framework assembly layout (e.g. mscorlib.dll, System.dll etc). The way this works is that we ship a tiny shim mscorlib.dll which is only used to forward the types to their new locations in a different assembly on modern .NET (e.g. System.Private.CoreLib.dll).

However this breaks down in this case since the classic Xamarin.Android frameworks used the classic Mono implementation of .NET Framework and we made a few additions that didn't exist in the original Microsoft .NET Framework implementation, mainly to support .NET Standard 2.1 use cases.

Your nuget package contains these target frameworks:

The net6.0-android target framework has a compatibility fallback path with monoandroid so the build uses the assembly from that folder instead of e.g. the netstandard2.0, since it is considered more compatible.
However that assembly was compiled against a Xamarin.Android-specific mscorlib.dll which contained types like ValueTaskAwaiter<T> and ReadOnlySpan<T> so the assembly expects them to be there. The compatibility shim mscorlib.dll however doesn't have type forwarders for these types (since they didn't exist on the Microsoft .NET Framework implementation) and we get the TypeLoadException.

A quick way to hack it is to go into your local nuget package cache folder <home directory>/.nuget/packages/ably.io/1.2.10/lib/ and remove the monoandroid folder there, then rebuild the app. That will make it pick the netstandard2.0 version instead which works:

But the real solution is to add a proper net6.0 target to your nuget package so that assembly will be picked instead of the monoandroid one.

[sacOO7]

@akoeplinger Thanks for the answer!

I had one final question.
If target for .Net6 is not yet added, why does it show support for .Net 6/ .Net7 under nuget
https://www.nuget.org/packages/ably.io#supportedframeworks-body-tab ?

[sacOO7]

Also, I feel the project should throw a proper error/ warning if the .Net 6 or .Net 7 target is not found in the package.

[akoeplinger]

If target for .Net6 is not yet added, why does it show support for .Net 6/ .Net7 under nuget

See the legend at the bottom of the table, that target is "computed", because we have this compatibility layer so monoandroid or net46 works on modern .NET.

We can't throw an error since this is supposed to work, you're just hitting an edge case where it doesn't. The compatibility layer is best effort which is why we're recommending adding a real net6.0 target.

[sacOO7]

Got it @akoeplinger. I had few small questions coming up.

1. Can we make project choose netstandard 2.0 assembly instead of xamarin-android at compile time through some configuration.
2. How can I add targets for .Net 6 / .Net 7 so it reflects in nuget package, any link to the related doc will be super useful?

[akoeplinger]

1. Can we make project choose netstandard 2.0 assembly instead of xamarin-android at compile time through some configuration.

No, the only option I can think of would be to remove the monoandroid folder from your nuget package so it always picks the netstandard2.0 one, but I assume this won't work because you likely have Android-specific code otherwise the monoandroid target doesn't make sense. There's a longstanding nuget feature request to override the selection which would be helpful here: NuGet/Home#7416

2. How can I add targets for .Net 6 / .Net 7 so it reflects in nuget package, any link to the related doc will be super useful?

That depends on how your nuget package build works today. You'd need to build with the modern .NET SDK and set <TargetFramework>net6.0</TargetFramework> in your csproj file.

[sacOO7]

Great, we will fix this as per your suggestion and will let you know if anything comes up !!!

Thanks again, this is really helpful : )

[sacOO7]

There's a longstanding nuget feature request to override the selection which would be helpful here: NuGet/Home#7416

I think being able to choose the selection would be useful. At the same time, it will be great to enforce users to make them add explicit targets for .Net 6 and .Net 7.

[akoeplinger]

I've also just experimented with adding these missing type forwarders to the mscorlib.dll shim and it fixes the issue as well, i.e. the monoandroid assembly works.

I opened a PR, we'll see if we can maybe backport it to 7.0: #82618

[sacOO7]

@akoeplinger wow, this is amazing : )

When can we expect this to get merged and available after release?

[akoeplinger]

@sacOO7 we merged the backport to the release/7.0 branch and is currently targeted for the 7.0.5 release.

[sacOO7]

Thanks @akoeplinger, this is helpful 👍