ARSC with multiple packages

[IgorEisberg]

So, I started researching on how resources.arsc with multiple packages are built.
Hopefully, we'll be able to add support for it in Apktool 3.x in the near future.

So far, I found 2 entirely different cases:

• Multiple packages of the same name: Typically found in framework-res.apk. Since duplicate package names aren't allowed when building normal apps, the only way to generate something like that is by defining staged aliases. The types and resources in the synthetic packages are generated from <staging-public-group-final> tags of a public-final.xml file. In Apktool's output, public-final.xml is in fact public.xml. As for public-staged.xml, it doesn't seem to persist into ARSC.
  https://cs.android.com/android/platform/superproject/main/+/main:frameworks/base/tools/aapt2/cmd/Link_test.cpp;l=473?q=staging-public-group-final
• Multiple packages of different names: Typically found in various apps. Those seem to be a result of merging a base app with static libraries (?) it depends on (basically like compiling a static binary vs. a binary with dynamic dependencies), although I'm not sure how to reproduce that...

Discussion is welcome. Will keep updating when I find something new.