An Empirical Study of Overlooked Code Review Comments in OSS Projects

Open source software (OSS) development widely adopts modern code review to identify issues and guarantee code quality. As reported repeatedly, maintainers are under heavy workloads when reviewing code changes. Meanwhile, we notice that some code reviews were overlooked by the authors of the code changes, i.e., neither causing code modification nor being replied to. These code reviews, if requiring responses but not receiving any, might represent a significant inefficiency, risk of overlooking critical issues, and problematic social exchange. Moreover, leaving code reviews publicly unanswered may cause a negative impression on both the corresponding OSS contributors and the OSS projects. Existing literature on code review mainly focuses on the usefulness of code reviews, reviewer recommendations, factors affecting PR acceptance, and review comment generation; the nature of overlooked reviews has not been explored. To this end, we focus on a widely-used modern code review mechanism, i.e., reviewing Pull Request (PR) code before merge, and conduct the first empirical study on 80 Java OSS projects to explore the prevalence, characteristics, rationales, and possible impact of the overlooked code reviews. We find that approximately 7.5% of PRs have at least one review comment being ignored. We further show that pull requests containing no-response comments are significantly associated with longer review lifecycles and lower acceptance rates, indicating measurable negative outcomes beyond their modest prevalence. Then, we categorize these no-response comments through thematic analysis and find two main categories with seven subcategories: Review inquiry and PR management. We also extract four subcategories in Review inquiry, e.g., Give suggestions about code implementation, Point out implementation issues, and Additional task requests. PR management consists of three subcategories, i.e., PR status checks, PR merge conflict notifications, and Reject PR with uncertain reasons. To better understand the existence of no-response comments, we surveyed developers and received 45 responses. We found that the reasons for the existence of no-response comments are diverse, such as prolonged review times and a lack of consensus on opinions. Developers also hold the consensus that ignored reviews will have negative effects on software projects. These findings emphasize the need for attention from both academia and industry to the responses to review comments and optimization of the reminder mechanism.