Patches as better bug reports

Tools and analyses that find bugs in software are becoming increasingly prevalent. However, even after the potential false alarms raised by such tools are dealt with, many real reported errors may go unfixed. In such cases the programmers have judged the benefit of fixing the bug to be less than the time cost of understanding and fixing it.The true utility of a bug-finding tool lies not in the number of bugs it finds but in the number of bugs it causes to be fixed.Analyses that find safety-policy violations typically give error reports as annotated backtraces or counterexamples. We propose that bug reports additionally contain a specially-constructed patch describing an example way in which the program could be modified to avoid the reported policy violation. Programmers viewing the analysis output can use such patches as guides, starting points, or as an additional way of understanding what went wrong.We present an algorithm for automatically constructing such patches given model-checking and policy information typically already produced by most such analyses. We are not aware of any previous automatic techniques for generating patches in response to safety policy violations. Our patches can suggest additional code not present in the original program, and can thus help to explain bugs related to missing program elements. In addition, our patches do not introduce any new violations of the given safety policy.To evaluate our method we performed a software engineering experiment, applying our algorithm to over 70 bug reports produced by two off-the-shelf bug-finding tools running on large Java programs. Bug reports also accompanied by patches were three times as likely to be addressed as standard bug reports.This work represents an early step toward developing new ways to report bugs and to make it easier for programmers to fix them. Even a minor increase in our ability to fix bugs would be a great increase for the quality of software.