Partitioning composite code changes to facilitate code review

Developers expend significant effort on reviewing source code changes. Hence, the comprehensibility of code changes directly affects development productivity. Our prior study has suggested that composite code changes, which mix multiple development issues together, are typically difficult to review. Unfortunately, our manual inspection of 453 open source code changes reveals a non-trivial occurrence (up to 29%) of such composite changes. In this paper, we propose a heuristic-based approach to automatically partition composite changes, such that each subchange in the partition is more cohesive and self-contained. Our quantitative and qualitative evaluation results are promising in demonstrating the potential benefits of our approach for facilitating code review of composite code changes.