Build conflicts in the wild

When collaborating, developers often create and change software artifacts without being fully aware of team members' work. While such independence is essential for increasing development productivity, it might also result in conflicts when integrating developers' contributions. To better understand the conflicts revealed by failures when building integrated code, we investigate their frequency and structure and adopted resolution patterns in 451 open-source Java projects. To detect such build conflicts, we select merge scenarios from git repositories, parse their Travis build logs, and check whether the build error messages are related to the merged changes. We find and classify 239 build conflicts and their resolution patterns. Most build conflicts are caused by missing declarations removed or renamed by one developer but referenced by another developer. Conflicts caused by renaming are often resolved by updating the missing reference, whereas removed declarations are often reintroduced. Most fix commits are authored by one of the merge scenario contributors. Based on our catalogue of conflict causes, awareness tools could alert developers about the risk of conflict situations. Program repair tools could benefit from our catalogue of resolution patterns to automatically fix conflicts; we illustrate that with a proof of concept implementation of a tool that fixes conflicts.