The Design Smells Breaking the Boundary between Android Variants and AOSP

Phone vendors customize their Android variants to enhance system functionalities based on the Android Open Source Project (AOSP). While independent development, Android variants have to periodically evolve with the upstream AOSP and merge code changes from AOSP. Vendors have invested great effort to maintain their variants and resolve merging conflicts. In this paper, we characterize the design smells with recurring patterns that break the design boundary between Android variants and AOSP. These smells are manifested as problematic dependencies across the boundary, hindering Android variants' maintainability and co-evolution with AOSP. We propose the DroidDS for automatically detecting design smells. We collect 22 Android variant versions and 22 corresponding AOSP versions, involving 4 open-source projects and 1 industrial project. Our results demonstrate that: files involved in design smells consume higher maintenance costs than other files; these infected files are not merely the files with large code size, increased complexity, and object-oriented smells; the infected files have been involved in more than half of code conflicts induced by re-applying AOSP's changes to Android variants; a substantial portion of design issues could be mitigable. Practitioners can utilize our DroidDS to pinpoint and prioritize design problems for Android variants. Refactoring these problems will help keep a healthy coupling between diverse variants and AOSP, potentially improving maintainability and reducing conflict risks.