Writing acceptable patches : an empirical study of open source project patches

Patch quality may affect software maintenance cost. However, there is a lack of understanding why patches are accepted/rejected. To provide empirical evidence of patch acceptance, we (1) present patch review criteria based on our literature survey and manual patch inspection, (2) show the result of a large scale online survey to understand the opinion of both patch reviewers and submitters, (3) propose patch acceptance prediction features based on the patch review criteria which show reasonable performance.Software developers submit patches to handle tens or even hundreds of bugs reported daily. However, not all submitted patches can be directly integrated into the codebase, since they might not pass patch review that is adopted in most software projects. As the result of patch review, incoming patches can be rejected or asked for resubmission after improvement. Both scenarios interrupt the workflow of patch writers and reviewers, increase their workload, and potentially delay the general development process. In this paper, we aim to help developers write acceptable patches to avoid patch rejection and resubmission. To this end, we derive a comprehensive list of patch rejection reasons from a manual inspection of 300 rejected Eclipse and Mozilla patches, a large-scale online survey of Eclipse and Mozilla developers, and the literature. We also investigate which patch-rejection reasons are more decisive and which are difficult to judge from the perspective of patch reviewers. Our findings include 1) suboptimal solution and incomplete fix are the most frequent patch-rejection reasons 2) whether a patch introduces new bugs is very important yet very difficult to judge 3) reviewers reject a large patch not solely because of its size, but mainly because of the underlying reasons that induce its large size, such as the involvement of unnecessary changes 4) reviewers consider certain problems to be much more destructive than patch writers expect, such as the inconsistency of documentation in a patch and 5) bad timing of patch submission and a lack of communication with team members can also result in a negative patch review