Mobile device vendors develop their customized Android OS (termed downstream) based on Google Android (termed upstream) to support new features. During daily independent development, the downstream also periodically merges changes of a new release from the upstream into its development branches, keeping in sync with the upstream. Due to a large number of commits to be merged, heavy code conflicts would be reported if auto-merge operations failed. Prior work has studied conflicts in this scenario. However, it is still unclear about the coupling between the downstream and the upstream (We term this coupling as the dependency facade), as well as how merge conflicts are related to this coupling. To address this issue, we first propose the DepFCD to reveal the dependency facade from three aspects, including interface-level dependencies that indicate a clear design boundary, intrusion-level dependencies which blur the boundary, and dependency constraints imposed by the upstream non-SDK restrictions. We then empirically investigate these three aspects (RQ1, RQ2, RQ3) and merge conflicts (RQ4) on the dependency facade. To support the study, we collect four open-source downstream projects and one industrial project, with 15 downstream and 15 corresponding upstream versions. Our study reveals interesting observations and suggests earlier mitigation of merge conflicts through a well-managed dependency facade. Our study will benefit the research about the coupling between upstream and downstream as well as the downstream maintenance practice.

Architecture anti-patterns violate design principles and negatively impact software internal quality. Both academia and industry have designed methods and tools to detect anti-patterns. However, these tools tend to report a large number of defects, hindering developers from prioritizing true debts. In this work, we take one step further to explore the most problematic files (we define them as root files) in the architecture anti-patterns, which are potential causes leading to the difficulty of software maintenance. Using 45 Python projects as subjects, we investigate root files' maintainability, evolution (i.e., birth, living, and death), and their interactions in different architecture anti-patterns. Our results reveal that, compared with other files in anti-patterns, these root files take only a small proportion but incur heavy maintenance costs. Our study of their evolution and interactions can help developers identify potential causes of anti-patterns. We believe our findings will benefit the practice of design problem fixing.