Are Developers Fixing Their Own Bugs? Tracing Bug-fixing and Bug-seeding Committers

The process of fixing software bugs plays a key role in the maintenance activities of a soft-
ware project. Ideally, code ownership and responsibility should be enforced among developers
working on the same artifacts, so that those introducing buggy code could also contribute to
its fix. However, especially in FLOSS projects, this mechanism is not clearly understood: in
particular, it is not known whether those contributors fixing a bug are the same introducing and
seeding it in the first place.
This paper aims to study this issue, by analysing the comm-central FLOSS project, which
hosts part of the Thunderbird, SeaMonkey, Lightning extensions and Sunbird projects from
the Mozilla community. The analysis is focused at the level of lines of code and it uses the
information stored in the source code management system.
The results of this study show, at first, that in 80% of the cases, the bug-fixing activity
involves source code modified by at most two developers. It also emerges that the developers
fixing the bug are only responsible for 3.5% of the previous modifications to the lines affected;
this implies that the other developers making changes to those lines could have made that fix.
We conclude by stating that, in most of the cases the bug fixing process in comm-central is not
carried out by the same developers than those who seeded the buggy code.