[.NET6 android] Compilation failed to complete

[lunelake]

Current behavior

I tried to build by referencing Uno class library in Uno .Net 6 project, but the following error occurred.
The class library itself builds well without issue.

2>Exception in thread "main" java.lang.RuntimeException: com.android.tools.r8.CompilationFailedException: Compilation failed to complete, origin: obj\Debug\net6.0-android\lp\129\jl\bin\classes.jar:android/support/customtabs/ICustomTabsCallback$Stub.class
2>	at com.android.tools.r8.internal.Bj.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:98)
2>	at com.android.tools.r8.D8.main(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:4)
2>Caused by: com.android.tools.r8.CompilationFailedException: Compilation failed to complete, origin: obj\Debug\net6.0-android\lp\129\jl\bin\classes.jar:android/support/customtabs/ICustomTabsCallback$Stub.class
2>	at Version.fakeStackEntry(Version_3.3.28.java:0)
2>	at com.android.tools.r8.internal.Bj.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:75)
2>	at com.android.tools.r8.internal.Bj.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:28)
2>	at com.android.tools.r8.internal.Bj.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:27)
2>	at com.android.tools.r8.internal.Bj.b(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:2)
2>	at com.android.tools.r8.D8.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:22)
2>	at com.android.tools.r8.D8.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:17)
2>	at com.android.tools.r8.internal.Bj.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:85)
2>	... 1 more
2>Caused by: com.android.tools.r8.internal.f: Type android.support.customtabs.ICustomTabsCallback$Stub is defined multiple times: obj\Debug\net6.0-android\lp\129\jl\bin\classes.jar:android/support/customtabs/ICustomTabsCallback$Stub.class, obj\Debug\net6.0-android\lp\134\jl\classes.jar:android/support/customtabs/ICustomTabsCallback$Stub.class
2>	at com.android.tools.r8.internal.DT.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:14)
2>	at com.android.tools.r8.internal.DT.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:22)
2>	at com.android.tools.r8.internal.CN.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:33)
2>	at com.android.tools.r8.internal.CN.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:10)
2>	at java.base/java.util.concurrent.ConcurrentHashMap.merge(ConcurrentHashMap.java:2048)
2>	at com.android.tools.r8.internal.CN.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:6)
2>	at com.android.tools.r8.graph.B2$a.e(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:4)
2>	at com.android.tools.r8.dex.b.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:105)
2>	at com.android.tools.r8.dex.b.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:28)
2>	at com.android.tools.r8.D8.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:25)
2>	at com.android.tools.r8.D8.d(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:606)
2>	at com.android.tools.r8.D8.c(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:1)
2>	at com.android.tools.r8.internal.Bj.a(R8_3.3.28_2aaf796388b4e9f6bed752d926eca110512a53a3f09a8d755196089c1cfdf799:24)
2>	... 5 more
2>C:\Program Files\dotnet\packs\Microsoft.Android.Sdk.Windows\32.0.301\tools\Xamarin.Android.D8.targets(79,5): error : java.lang.RuntimeException: com.android.tools.r8.CompilationFailedException: Compilation failed to complete, origin: obj\Debug\net6.0-android\lp\129\jl\bin\classes.jar : android/support/customtabs/ICustomTabsCallback$Stub.class

Expected behavior

Build works without issue

How to reproduce it (as minimally and precisely as possible)

Reference Xamarin.Auth nuget package in class library

Workaround

Remove Xamarin.Auth package from reference

Anything else we need to know?

MAUI had a similar issue.
dotnet/maui#6022

[jeromelaban]

Thanks for the report. Are you able to create a repro project that we can test with?

[lunelake]

I've tried, but the library is not small so it's hard to find out which one is causing the problem right now.
I'll try again and report back if I can create a repro project.

[sgjesse]

I am not familiar with the .NET6 Android build environment, but as the underlying issue is that android.support.customtabs.ICustomTabsCallback$Stub is defined in both obj\Debug\net6.0-android\lp\129\jl\bin\classes.jar and obj\Debug\net6.0-android\lp\134\jl\classes.jar there might be a way to trace back where these two inputs originates from - possible as transitive dependencies of different dependencies.

[lunelake]

The deprecated Xamarin.Auth library was referenced in the .NET Standard project that the Uno class library was referencing.
I didn't expect that the library referenced by .NET Standard (not Uno class library) was causing the issue, so it took me a long time to find it.
I removed that package and the issue was resolved.

Here is a repro project.
Net6AndroidCompilationFailed.zip

[jeromelaban]

Thanks for the update. Indeed, Xamarin libraries cannot be referenced in a netstandard2.0 project in Uno, but they also cannot be referenced in a .NET 6 mobile context either (there are important breaking changes made by Microsoft on both android and mac-related targets).

[lunelake]

I didn't know that. After switching to .net 6 based, the project structure became much cleaner. Although it is still in preview, there may be some issues. Thanks for your help.