Exploring The Impact Of Code Smells On Fine-Grained Structural Change-Proneness

Code smells are used to describe the bad structures in the source code, which could hinder software maintainability, understandability and changeability. Nowadays, scholars mainly focus on the impact of smell on textual change-proneness. However, in comparison to textual changes, structural changes could better reveal the change nature. In practice, not all code change types are equally important in terms of change risk severity levels, and software developers are more interested in particular changes relevant to their current tasks. Therefore, we investigate the relationship between smells and fine-grained structural change-proneness to solve these issues. Our experiment was conducted on 11 typical open source projects. We first employed Fishers exact test and Mann-Whitney test to explore whether smelly files (affected by at least one smell type) had higher structural change-proneness than other files, and whether files with more smell instances are more likely to undergo structural changes, respectively. Multivariate logistic regression model was built to study the relation between each kind of smell and change-proneness with respect to five change categories. Our results showed that: (1) in most cases, smelly files were more prone to structural changes and files with more smell instances tend to undergo higher structural changes; (2) quite a few smell types were related to structural change-proneness, particularly, Refused Parent Bequest (RPB), Message Chains (MCH), Divergent Change (DIVC), Feature Envy (FE) and Shotgun Surgery (SS) increased structural changes for some change categories. However, when controlling the file size Lines of Code (LOC), significant change-proneness of some smells disappeared or the magnitude of significance decreased more or less.