Modern Code Review (MCR) tools are still inadequate to meet the expectations of developers. The objective of this paper is to investigate the approaches and tools that are needed by developers to perform MCR activities. To that end, we empirically elicited a taxonomy of MCR change types, starting from a taxonomy from previous work, and extended it by (i) analyzing MCR changes of ten open-source projects from both a qualitative and quantitative point of view; and (ii) surveying developers to further extend the taxonomy. Our results demonstrate that developers perform several activities during MCR and suggest that and that additional types of MCR feedback need to be performed by MCR reviewers. The involved developers provided also insights on the data to analyze and the techniques to employ for building recommender systems able to automate the MCR activities characterized in our taxonomy.
Moreover, they provided inputs on the relevance and completeness of the defined MCR change taxonomy. We believe that this work complements previous studies on MCR and provides important insights and directions for the design and implementation of tools for MCR.