The life of software features: An exploratory case study of 189 feature requests in Marlin

Features are a widely established notion to organize the functionalities of a software system. For instance, features are used to define variability and commonalities in product lines; feature-driven development is an agile development methodology; and social-coding platforms have explicit support for feature requests. Despite the importance of features, we are not aware of extensive research on their life cycles: how and for what reasons do developers evolve features? As a result, we lack an understanding of how features come to be, how they are evolved, or why they may be removed. To narrow this research gap, we have performed an exploratory case study on the evolution of 189 feature requests of the Marlin 3D-printer firmware. We identified the code introducing a feature and traced all commits touching that code or the feature, resulting in a collection of 1,940 unique commits spanning five years of evolution. We have manually inspected all of these commits to classify their intentions with respect to the features they change, and created process graphs of the features’ life cycles based on these intentions to understand the evolution of features. Our results contribute a first overview and detailed examples of evolving features beyond code metrics, showcasing that features are primarily refactored, exhibit interdependent evolution, and are rarely removed. Serving as a starting point, these contributions can support practitioners in managing features and guide researchers in understanding feature evolution as well as in scoping future studies on this matter.