A Characterization Study of Repeated Bug Fixes

Programmers always fix bugs when maintaining software. Previous studies showed that developers apply repeated bug fixes-similar or identical code changes-to multiple locations. Based on the observation, researchers built tools to identify code locations in need of similar changes, or to suggest similar bug fixes to multiple code fragments. However, some fundamental research questions, such as what are the characteristics of repeated bug fixes, are still unexplored. In this paper, we present a comprehensive empirical study with 341,856 bug fixes from 3 open source projects to investigate repeated fixes in terms of their frequency, edit locations, and semantic meanings. Specifically, we sampled bug reports and retrieved the corresponding fixing patches in version history. Then we chopped patches into smaller fixes (edit fragments). Among all the fixes related to a bug, we identified repeated fixes using clone detection, and put a fix and its repeated ones into one repeated-fix group. With these groups, we characterized the edit locations, and investigated the common bug patterns as well as common fixes.Our study on Eclipse JDT, Mozilla Firefox, and LibreOffice shows that (1) 15-20% of bugs involved repeated fixes; (2) 73-92% of repeated-fix groups were applied purely to code clones; and (3) 39% of manually examined groups focused on bugs relevant to additions or deletions of whole if-structures. These results deepened our understanding of repeated fixes. They enabled us to assess the effectiveness of existing tools, and will further provide insights for future research directions in automatic software maintenance and program repair.