Behind Developer Contributions on Conflicting Merge Scenarios.

Context: The success of Open Source Software (OSS) projects typically depends on simultaneous contributions of several developers. These contributions often affect the same changing source files and may lead to merge conflicts when integrated. Previous studies investigated the reduction of conflicting merge scenarios. However, empirical evidence on the involvement of OSS contributors in conflicting merge scenarios is scarce. Objective: We aim to fill this gap with a large-scale quantitative study with the goal of understanding: 1) the extent in which OSS contributors are involved in conflicting merge scenarios; 2) characteristics of these contributors; and 3) characteristics of changing source files. Method: We collect both contributor data and contribution data from 66 popular GitHub projects and analyze data of 2972 distinct contributors who were involved in at least one conflicting merge scenario. We rely on both descriptive and inferential statistics to address our research questions. Results: About 80% of the analyzed contributors are involved in only one or two conflicting merge scenarios. Additionally, 42 out of the 66 projects had its top-one contributor as the one mostly involved in conflicting merge scenarios. Finally, only a small set of changing source files are involved in conflicting merge scenarios. Conclusions: We advocate that training the typically small group of contributors involved in conflicting merge scenarios could significantly reduce the number of merge conflicts.