An Empirical Study on Obsolete Issue Reports

Issue reports record valuable maintenance details. Developers write issue numbers into code comprehension and researchers mine knowledge from issue reports to assist various programming tasks. Although issue reports are useful, some of them can be obsolete, in that their corresponding commits are overwritten or rolled back, with the evolution of software. The obsolete issue reports can invalidate their references and descriptions, and can have far-reaching impacts on the approaches built on them. To explore their impacts, we conduct the first empirical study to analyze obsolete issue reports.To measure how an issue report becomes obsolete, we define an obsolete ratio of an issue report as its deleted lines over all its modified lines. To support our analysis, we build a tool, ICLINKER, that builds the links between an issue report and its commits, and calculates the obsolete ratio for each issue report. In our study, we analyze 70,180 commits and 46,257 issue reports that are collected from 5 Apache projects. We explore two research questions, which concern the distributions of obsolete issue reports and the obsolete references in code comments. Our findings to these research questions enrich the knowledge on obsolete issue reports, and some are even counterintuitive. For example, we find that obsolete issue reports are mixed with other issue reports. Even when recent issue reports are obsolete, some old issue reports keep up-to-date.