Understanding Source Code Differences by Separating Refactoring Effects

Comparing and understanding differences between old and new versions of source code are necessary in various software development situations. However, if refactoring is applied between those versions, then the source code differences are more complicated, and understanding them becomes more difficult. Although many techniques for extracting refactoring effects from the differences have been studied, it is necessary to exclude the extracted refactorings´ effects and reconstruct the differences for meaningful and understandable ones with no refactoring effect. As described in this paper, we propose a novel technique to address this difficulty. Using our technique, we extract the refactoring effects and then apply them to the old version of source code to produce the differences without refactoring effects. We also implemented a support tool that helps separate refactorings automatically. An evaluation of open source software showed that our tool is applicable to all target refactorings. Our technique is therefore useful in real situations. Evaluation testing also demonstrated that the approach reduced the code differences more than 21%, on average, and that developers can understand more changes from the differences using our approach than when using the original one in the same limited time.