Unfolding the Rationale for Code Commits

One of the main reasons why developers investigate code history is to search for the rationale for code commits. Existing work found that developers report that rationale is one of the most important aspects to understand code changes and that it can be quite difficult to find. While this finding strongly points out the fact that understanding the rationale for code commits is a serious problem for software engineers, no current research efforts have pursued understanding in detail what specifically developers are searching for when they search for rationale. In other words, while the rationale for code commits is informally defined as, "Why was this code implemented this way?" this question could refer to aspects of the code as disparate as, "Why was it necessary to implement this code?"; "Why is this the way in which it was implemented?"; or "Why was the code implemented at that moment?" Our goal with this study is to improve our understanding of what software developers mean when they talk about the rationale for code commits, i.e., how they "unfold" rationale. We additionally study which components of rationale developers find important, which ones they normally need to find, which ones they consider specifically difficult to find, and which ones they normally record in their own code commits. This new, detailed understanding of the components of the rationale for code commits may serve as inspiration for novel techniques to support developers in seeking and accurately recording rationale.