Learning from defect removals

Recent research has tried to identify changes in source code repositories that fix bugs by linking these changes to reports in issue tracking systems. These changes have been traced back to the point in time when they were previously modified as a way of identifying bug introducing changes. But we observe that not all changes linked to bug tracking systems are fixing bugs; some are enhancing the code. Furthermore, not all fixes are applied at the point in the code where the bug was originally introduced. We flesh out these observations with a manual review of several software projects, and use this opportunity to see how many defects are in the scope of static analysis tools.