Identifying Supplementary Bug-fix Commits

Real-world bugs and the bug-fix activities are essential in many fields such as bug prediction and automatic program repair. Identifying bug-fix commits from version histories has received much recent attention. Linking commits to bug reports and analyzing the commits individually are common practice. However, considering the one-to-many relationship between the bug report and the bug-fix commits, analyzing commits individually will miss the relevance between commits, since several commits might fix the same bug together. In addition, some supplementary bug-fix commits which supplement or correct the identified bug-fix commit may be neglected. For empirical studies on bug-fix commits, it is important to study all the relevant commits as a whole, otherwise we will fail to understand the complete real bug-fix activities. In this paper, we investigate the relevance between bug-fix commits that are linked to the same bug-fix pull request, and utilize machine learning techniques to determine supplementary bug-fix commits for an identified bug-fix commit. Experimental results show that there indeed exist supplementary bug-fix commits (i.e., 19.8% on average) that are neglected when analyzing commits individually. The performance of our tool SupBCFinder is much better than that of using a sliding window of one hour and that of analyzing the local change. Moreover, inspired by our learning-based approach and extracted features, we propose one effective heuristic as an alternative for the cases when there are not enough pull requests for training.