Semantics-assisted code review: An efficient tool chain and a user study

Code changes are often reviewed before they are deployed. Popular source control systems aid code review by presenting textual differences between old and new versions of the code, leaving developers with the difficult task of determining whether the differences actually produced the desired behavior. Fortunately, we can mine such information from code repositories. We propose aiding code review with inter-version semantic differential analysis. During review of a new commit, a developer is presented with summaries of both code differences and behavioral differences, which are expressed as diffs of likely invariants extracted by running the system's test cases. As a result, developers can more easily determine that the code changes produced the desired effect. We created an invariant-mining tool chain, Getty, to support our concept of semantically-assisted code review. To validate our approach, 1) we applied Getty to the commits of 6 popular open source projects, 2) we assessed the performance and cost of running Getty in different configurations, and 3) we performed a comparative user study with 18 developers. Our results demonstrate that semantically-assisted code review is feasible, effective, and that real programmers can leverage it to improve the quality of their reviews.