WARNING: This is a purposefully BROKEN PROJECT which triggers a bug in Android Studio.
A multi-module Android application with resources and UI in two secondary modules
This project builds correctly and the application runs.
However, Android Studio seems to not be able to generate the R class.
The problem is that multiple android (application and library) modules can share the same package but creating multiple R classes in the same Java package will result in a conflict. On specific occasions, your application may still build and run but the IDE will get confused.
This project was created by starting from the "Navigation Drawer Activity" template, and then moving most of the resources to a module and the whole UI to another module.
This is now an assigned Android Studio issue with priprity P3: https://issuetracker.google.com/issues/151765079
The IDE issue is that it fails to provide a proper diagnostics message for this issue, leaving you in the dark.