From the Ecosystem: How External Pull Requests Contribute to a Software Library

Third-party libraries are now commonplace when building contemporary software applications. Despite their popular use, most libraries are open source software that often rely on volunteer (usually unpaid and overworked) contributions from outside the core team (external). To understand the role that these contributions play to sustain third-party libraries, we analyze Pull Requests (PRs) submitted from outside the core team of contributors (i.e., External PRs). We analyze 945,291 PRs from the NPM ecosystem to empirically investigate External PR prevalence, acceptance, need for attention, and content. Our findings indicate that External PR are indeed prevalent (75.02% of all received PRs are External PR and 88.87% submitted on average). Interestingly, External PRs are just as likely to be accepted compared to Internal PRs (50% per package). For a package, we find that on average, 26.75% of External PRs submitted are linked to an already existing issue, and require the attention of the core team, with labels such as breaking changes, urgent, and on-hold. In a qualitative analysis, we find that External PRs focus on documentation (44 out of 384 PRs), which is different to adding new features (380 out of 384 PRs) for Bot PRs, and refactoring (34 out of 384 PRs) for Internal PRs. The study confirms that external contributions play a key role in the ecosystem, and reinforces the call for help, especially from single maintainer libraries that serve a massive client user-base.