Towards Reusing Hints from Past Fixes: An Exploratory Study on Thousands of Real Samples

Researchers have recently proposed various automatic program repair (APR) approaches that reuse past fixes to fix new bugs. However, some fundamental questions, such as how new fixes overlap with old fixes, have not been investigated. Intuitively, the overlap between old and new fixes decides how APR approaches can construct new fixes with old ones. Based on this intuition, we systematically designed six overlap metrics, and performed an empirical study on 5,735 bug fixes to investigate the usefulness of past fixes when composing new fixes. For each bug fix, we created delta dependency graphs (i.e., program dependency graphs for code changes), and identified how bug fixes overlapped with each other in terms of the content, code structure, and identifier names of fixes. Our results show that if an APR approach composes new fixes by fully or partially reusing the content of past fixes, only 2.1% and 3.2% new fixes can be created from single or multiple past fixes in the same project, compared with 0.9% and 1.2% fixes created from past fixes across projects. However, if an APR approach composes new fixes by fully or partially reusing the code structure of past fixes, up to 41.3% and 29.7% new fixes can be created.