Staged Tree Matching for Detecting Code Move across Files

ABSTRACTIn software development, developers often need to understand source code differences in their activities. GumTree is a tool that detects tree-based source code differences. GumTree constructs abstract syntax trees from the source code before and after a given change, and then, it identifies inserted/deleted/moved subtrees and updated nodes. Source code differences are detected based on the four kinds of information in GumTree. However, GumTree calculates the difference for each file individually, so that it cannot detect moves of code fragments across files. In this research, we propose (1) to construct a single abstract syntax tree from all source files included in a project and (2) to perform a staged tree matching to detect across-file code moves efficiently and accurately. We have already conducted a pilot experiment on open source projects with our technique. As a result, we were able to detect code moves across files in all the projects, and the number of such code moves was 76,600 in total.