I created two aar-libraries: com.example:test1:1.0.0 and com.example:test2:1.0.0. I added these libs to my main app and after build Android-Studio throws error:
Duplicate class com.example.utils.a found in modules classes.jar (com.example:test1:1.0.0) and classes.jar (com.example:test2:1.0.0)
I find out that this error happens because both libraries have classes in same package (com.example.utils) and after obfuscation R8 creates classes (a.class) with same full name (I saw this in classes.jar of aar). If I disable R8 in properties of my libs this error has gone.
'a' is not library class: after obfuscation all library classe names remain unchanged and a.class was added in package additionaly by R8. I read R8 documentation and found nothing about this problem. Are there any ways to solve this issue without ranaming the package in one of my libs?
When creating two libraries it is best practice to use two different namespaces, as otherwise there will be the possibility of duplicate classes even without using R8 when "accidentally" a class with the same name is added to both. So in your case use com.example.test1 and com.example.test2.
Depending on you use case, it might also be a better option to not apply R8 to the libraries, but only apply R8 to the final app including the two libraries. Shrinking libraries are mainly to make distribution size smaller, and rename internals to avoid library users (accidentally or knowingly) depend on internals which might change between library versions.
When shrinking libraries you also want to consider the option -keeppackagenames to make sure that all renamed classes stay within the package of the library. Otherwise you might end up with class e.g. a.a.a.a.class in multiple libraries.
If this issue happens for libraries that you don't have control over tools like shadow can be used to relocate.