Understanding Merge Conflicts and Resolutions in Git Rebases

Software merging is an important activity during software development. Merge conflicts may arise and degrade the software quality. Empirical studies on software merging are helpful to understand developers' needs and the challenges of detecting and resolving conflicts. Existing studies collect merges by identifying commits that have more than one parent commit. Different from these explicit merges, rebasing branches is used to merge other changes but rewrites the evolutionary history. Hence, existing studies fail to identify implicit merges performed by rebasing branches. Consequently, the results of these studies may fail to provide comprehensive insights on software merging. In our study, we leverage the recently updated APIs of GitHub to study rebase activities in the pull requests. Our study shows that rebasing is widely used in pull requests. And our results indicate that, to resolve textual conflicts, developers adopt similar strategies shown in existing studies on explicit merges. However, in 34.2% of non-conflict rebase scenarios, developers add new changes during the rebase process. And this indicates that there are some new challenges of validating rebases. Our results provide useful insights for improving the state-of-the-art techniques on resolving conflicts and validating rebases.