Towards the Analysis and Completion of Syntactic Structure Ellipsis for Inline Comments

The ellipsis of the syntactic structure is a common phenomenon in ordinary textual documents. Existing studies have found that despite syntactic ellipsis could help avoid repetition of normative documents, it could also, for example, lead to ambiguity and hamper the understandability of document contents. As a fundamental component of software, code comments are generally written by developers in a non-structured way just like normative documents. This naturally inspires us to explore whether syntactic ellipsis is also a common phenomenon in code comments and what potential negative effects would such ellipsis have on software tasks such as code/comments comprehension activities. Such explorations, in our opinion, are expected to facilitate the research on code comments and comments-related software tasks. To this end, we conduct the first large-scale study to explore the syntactic structure ellipsis problem of code comments, with a focus on Java inline comments. Specifically, we construct a data set of 1,000 Java projects with 1,307,457 inline comments and associated codes. Based on this data set, we first study the prevalence of syntactic structure ellipsis in inline comments. We find that syntactic structure ellipsis is quite common in inline comments where 83.6% comments have structure ellipsis (such as subject/predicate omissions). Then, we investigate the effects of syntactic structure ellipsis on code/comment understanding activities. As a result, we find that there indeed exists a negative relationship between them, with a medium effect size. Based on these findings, we further propose neural network based approaches to complete the ellipsis parts for the inline comments. With our approach, we could achieve: 1) a medium improvement in assisting code/comment understanding activities, and 2) a substantial improvement of 11.3% in comment-assisted code abbreviation extension task.