Why Do We Break APIs? First Answers from Developers

Breaking contracts have a major impact on API clients. Despite this fact, recent studies show that libraries are often backward incompatible and that the rate of breaking changes increase over time. However, the specific reasons that motivate library developers to break contracts with their clients are still unclear. In this paper, we describe a qualitative study with library developers and real instance of API breaking changes. Our goal is to (i) elicit the reasons why developers introduce breaking changes; and (ii) check if they are aware about the risks of such changes. Our survey with the top contributors of popular Java libraries contributes to reveal a list of five reasons why developers break API contracts. Moreover, it also shows that most of developers are aware of these risks and, in some cases, adopt strategies to mitigate them. We conclude by prospecting a future study to strengthen our current findings. With this study, we expect to contribute on delineating tools to better assess the risks and impacts of API breaking changes.