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How does code style inconsistency affect pull request integration? An exploratory study on 117 GitHub projects

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Abstract

GitHub is a popular code platform that provides infrastructures to facilitate collaborative development. A Pull Request (PR) is one of the key ideas to support collaboration. Developers are encouraged to submit PRs to ask for the integration of their contributions. In practice, not all submitted PRs can be integrated into the codebase by project maintainers. Existing studies have investigated factors affecting PR integration. Nevertheless, the code style of PRs, which is largely considered by project maintainers, has not been deeply studied yet. In this paper, we performed an exploratory analysis on the effect of code style on PR integration in GitHub. We modeled the code style via the inconsistency between a submitted PR and the existing code in its target codebase. Such modeling makes our study not limited by a specific definition of code style. We conducted our experiments on 50,092 closed PRs in 117 Java projects. Our findings show that: (1) There indeed exists code style inconsistency between PRs and the codebase. (2) Several code style criteria on how to use spaces or indents, make comments, and write code lines with a suitable length, tend to show more inconsistency among PRs. (3) A PR that is consistent with the current code style tends to be merged into the codebase more easily. (4) A PR that violates the current code style is likely to take more time to get closed. Our study shows evidence to developers about how to deliver better contributions to facilitate efficient collaboration.

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Notes

  1. http://github.com

  2. http://github.com/features

  3. In GitHub, a “repository” denotes a project in general. In this paper, we use “repository” and “project” interchangeably.

  4. http://github.com/rails/rails

  5. https://github.com/AndlyticsProject/andlytics

  6. http://github.com/AndlyticsProject/andlytics#contributing

  7. http://www.gnu.org/prep/standards_toc.html

  8. http://github.com/google/styleguide

  9. It is common for a project to have a readme file or a contribution file. The readme file broadly describes the project; while the contribution file mainly introduces the tips to contribute to this project.

  10. http://guides.github.com/activities/contributing-to-open-source/#contributing

  11. http://github.com/mongodb/mongo

  12. http://github.com/rubinius/rubinius/pull/3512

  13. http://github.com/querydsl/querydsl

  14. In this study, some motivation examples (i.e., GNU, Goolge, and GitHub) mainly came from manual search of code style related documentation in well-known open source communities or company originated open source projects; while other examples (i.e., mongodb/mongo, rubinius/rubinius, and querydsl/querydsl) were collected by manually checking the documents and commit logs of some randomly selected popular projects on GitHub.

  15. http://githut.info

  16. https://www.githubarchive.org/

  17. https://help.github.com/articles/filtering-issues-and-pull-requests-by-assignees/

  18. http://github.com/filipg/amu_automata_2011

  19. http://checkstyle.sourceforge.net/

  20. Checkstyle is a highly configurable tool of checking code style. The code style by Google and Oracle are supported by the tool. In our experiment, we configured Checkstyle to check whether a piece of code violates 37 code style criteria.

  21. http://github.com/magefree/mage

  22. http://github.com/CUTR-at-USF/OpenTripPlanner-for-Android

  23. http://sourceforge.net

  24. http://bitbucket.org/

  25. http://findbugs.sourceforge.net

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Acknowledgments

The authors would like to greatly thank our lab members, Yufeng Zhao, Yiming Chen, and Mengting Zhou, for crawling GitHub project data for experiments. This work is partly supported by the National Natural Science Foundation of China (Grant No.61690201, 61772014, 61802171, 61872273, 61572375), and the China Scholarship Council Scholarship. Any opinions, findings, and conclusions in this paper are those of the authors only and do not necessarily reflect the views of our sponsors.

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Authors and Affiliations

  1. State Key Laboratory for Novel Software Technology, Nanjing University, Nanjing, China

    Weiqin Zou, Zhenyu Chen & Baowen Xu

  2. School of Computer Science, Wuhan University, Wuhan, China

    Jifeng Xuan & Xiaoyuan Xie

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  1. Weiqin Zou
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Correspondence to Zhenyu Chen.

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Communicated by: Ahmed E. Hassan

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Zou, W., Xuan, J., Xie, X. et al. How does code style inconsistency affect pull request integration? An exploratory study on 117 GitHub projects. Empir Software Eng 24, 3871–3903 (2019). https://doi.org/10.1007/s10664-019-09720-x

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