What causes merge conflicts?

Abstract

During the software development process, several developers commonly change artifacts in parallel. A merge process can combine parallel changes. In the case of changes that cannot be automatically combined, the developer responsible for the merge must reconcile decisions and resolve conflicts. Some studies are concerned with investigating ways to deal with merge conflicts and measuring the effort that this activity may require. However, the investigation of factors that may reduce the occurrence of conflicts needs more and deeper attention. This paper aims at identifying and analyzing attributes of past merges with and without conflicts to understand what may induce physical conflicts. We analyzed 182,273 merge scenarios from 80 projects written in eight different programming languages to find characteristics that increase the chances of a merge to have a conflict. We found that attributes such as the number of committers, the number of commits, and the number of changed files seem to have the biggest influence in the occurrence of merge conflicts. Moreover, attributes in the branch that is being integrated seem to be more influential than the same attributes in the other branch. Additionally, we discovered positive correlations between the occurrence of conflicts and both the duration of the branch and the intersection of developers.