Revisiting ssFix for Better Program Repair

A branch of automated program repair (APR) techniques look at finding and reusing existing code for bug repair. ssFix is one of such techniques that is syntactic search-based: it searches a code database for code fragments that are syntactically similar to the bug context and reuses such retrieved code fragments to produce patches. Using such a syntactic approach, ssFix is relatively lightweight and was shown to outperform many other APR techniques. In this paper, to investigate the true effectiveness of ssFix, we conducted multiple experiments to validate ssFix's built-upon assumption (i.e., to see whether it is often possible to reuse existing code for bug repair) and evaluate its code search and code reuse approaches. Our results show that while the basic idea of ssFix, i.e., reusing existing code for bug repair, is promising, the approaches ssFix uses are not the best and can be significantly improved. We proposed a new repair technique sharpFix which follows ssFix's basic idea but differs in the code search and reuse approaches used. We evaluated sharpFix and ssFix on two bug datasets: Defects4J and Bugs.jar-ELIXIR. The results confirm that sharpFix is an improvement over ssFix. For the Defects4J dataset, sharpFix successfully repaired a total of 36 bugs and outperformed many existing repair techniques in repairing more bugs. For the Bugs.jar-ELIXIR dataset, we compared sharpFix, ssFix, and four other APR techniques, and found that sharpFix has the best repair performance. In essence, the paper shows how effective a syntactic search-based approach can be and what techniques should be used for such an approach.