Emotional expression in open- source: How project function shapes communication

Context: Open-source software (OSS) development is often studied as a decentralized process driven by technical goals. However, mature OSS projects operate under external constraints such as security advisories, release deadlines, and ecosystem dependencies. These pressures shape technical decisions and also communication patterns among contributors, including emotional expression. Objective: This study investigates how emotional expression in OSS projects varies across different types of repositories, evolves over time, and relates to the activity of top contributors. The goal is to assess whether emotional dynamics are shaped more by project function than by technical domain or project size. Methods: We analyzed issue comments from 14 OSS repositories spanning over ten years. A transformer-based classifier was used to detect emotions. Emotional patterns were quantified using a composite Emotional Index, and contextual activity. Contributor roles were assessed using a Contribution Index combining code activity, discussion engagement, and sustained involvement. Analyses were conducted at the repository, temporal, and contributor levels. Results: The four most frequent emotions across all repositories were gratitude, curiosity, confusion, and approval. Emotional patterns tend to cluster by functional role rather than technical domain, with repositories converging toward stable emotional profiles over time. High-impact contributors show distinct expression patterns that reflect their role and stage of engagement. Conclusion: Emotional expression in OSS projects follows recurring patterns linked to project function, contributor roles, and maturity. These findings can help anticipate communication challenges during project evolution and support interaction strategies among contributor groups with differing emotional tendencies.