Representation of Developer Expertise in Open Source Software

With tens of millions of projects and developers, the OSS ecosystem is both vibrant and intimidating. On one hand, it hosts the source code for the most critical infrastructures and has the most brilliant developers as contributors, while on the other hand, poor quality or even malicious software, and novice developers abound. External contributions are critical to OSS projects, but the chances their contributions are accepted or even considered depend on the trust between maintainers and contributors. Such trust is built over repeated interactions and coding platforms provide signals of project or developer quality via measures of activity (commits), and social relationships (followers/stars) to facilitate trust. These signals, however, do not represent the specific expertise of a developer. We, therefore, aim to address this gap by defining the skill space for APIs, developers, and projects that reflects what developers know (and projects need) more precisely than could be obtained via aggregate activity counts, and more generally than pointing to individual files developers have changed in the past. Specifically, we use the World of Code infrastructure to extract the complete set of APIs in the files changed by all open source developers. We use that data to represent APIs, developers, and projects in the skill space, and evaluate if the alignment measures in the skill space can predict whether or not the developers use new APIs, join new projects, or get their pull requests accepted. We also check if the developers' representation in the skill space aligns with their self-reported expertise. Our results suggest that the proposed embedding in the skill space achieves our aims and may serve not only as a signal to increase trust (and efficiency) of open source ecosystems, but may also allow more detailed investigations of other phenomena related to developer proficiency and learning.