In software development, there are many situations in which developers need to understand given source code changes in detail. Until now, a variety of techniques have been proposed to support understanding source code changes. Tree-based differencing techniques are expected to have better understandability than text-based ones, which are widely used nowadays (e.g., diff in Unix). In this paper, we propose to consider copy-and-paste as a kind of editing action forming tree-based edit script, which is an editing sequence that transforms a tree to another one. Software developers often perform copy- and-paste when they are writing source code. Introducing copy- and-paste action into edit script contributes to not only making simpler (more easily understandable) edit scripts but also making edit scripts closer to developers' actual editing sequences. We conducted experiments on an open dataset. As a result, we confirmed that our technique made edit scripts shorter for 18% of the code changes with a little more computational time. For the other 82% code changes, our technique generated the same edit scripts as an existing technique. We also confirmed that our technique provided more helpful visualizations.

Existing techniques have succeeded to help developers implement new code. However, they are insufficient to help to change existing code. Previous studies have proposed techniques to support bug fixes but other kinds of code changes such as function enhancements and refactorings are not supported by them. In this paper, we propose a novel system that helps developers change existing code. Unlike existing techniques, our system can support any kinds of code changes if similar code changes occurred in the past. Our research is still on very early stage and we have not have any implementation or any prototype yet. This paper introduces our research purpose, an outline of our system, and how our system is different from existing techniques.