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A Stable Lossless Syntax Tree for Real-Time Collaborative Programming

Authors Leon Freudenthaler , Karl Michael Göschka

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LIPIcs.ECOOP.2026.5.pdf
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Subject Classification

ACM Subject Classification
  • Software and its engineering → Software maintenance tools
  • Software and its engineering → Collaboration in software development
Keywords
  • real-time collaborative programming
  • tree-based operations
  • structure-aware propagation
  • synchronous collaboration systems

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Abstract

Real-time collaborative programming tools synchronize source code as text, propagating keystrokes or text patches to other collaborators. This propagation of unstructured text often leads to syntactically invalid states, because edits take place by character position rather than by syntactic entity. Consequently, our key idea is to propagate syntactically valid changes only.
This paper contributes a structure-aware synchronization substrate based on two complementary representations and a propagation algorithm: (i) A Lossless Syntax Tree stores source code in structured form while preserving program trivia, like whitespace and comments. This is necessary because collaborators must be able to reconstruct byte-identical source text from propagated (structural) changes; (ii) A Stable Syntax Tree extends this representation with persistent node identifiers to enable robust structural diffing between successive versions; (iii) Our propagation algorithm derives deterministic structural edit scripts for the following operations: insert, delete, move, and update. The algorithm can be used across grammars, because a lightweight per-language specification guides the stable reuse of node identifiers.
The biggest achievement of our approach is to take unstructured text changes and extract structural edit operations that provide syntactically correct source code changes. We formalize our proposed representations, show how diffing extracts structural edits, and how these edit scripts are applied at the collaborator. Particularly complex is the resulting move of subtrees. Our approach minimizes within-parent move noise using a per-parent Longest Increasing Subsequence.
We evaluate our approach using two languages (Java and JavaScript), three file sizes (small/medium/large), and five edit scenarios. Across all scenarios we observe byte-identical collaboration, node identity stability, and deterministic edit scripts. We demonstrate that applying Longest Increasing Subsequence is necessary for canonical minimality under sibling moves. We furthermore demonstrate that tree diffing cost is structure-sensitive: per-node cost increases with sibling fanout rather than depth. 95th percentile (p95) of end-to-end latencies meet the ≤ 1 second delay budget for small and medium files in both languages. Large Java is near 1 second (p95 ≈ 1.22 seconds) while JavaScript exceeds the 2 seconds hard-cap (p95 ≈ 2.86 seconds). Overall, our approach provides a deterministic, language-portable substrate for structure-aware real-time collaborative programming that separates structural propagation from unstructured keystrokes to preserve code correctness and developer intent.

Cite As Get BibTex

Leon Freudenthaler and Karl Michael Göschka. A Stable Lossless Syntax Tree for Real-Time Collaborative Programming. In 40th European Conference on Object-Oriented Programming (ECOOP 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 372, pp. 5:1-5:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026) https://doi.org/10.4230/LIPIcs.ECOOP.2026.5

Author Details

Leon Freudenthaler
  • Department of Informatics, Hochschule Campus Wien, Austria
  • TU Wien, Austria
Karl Michael Göschka
  • Institute of Information Systems Engineering, TU Wien, Austria
  • UAS Technikum Wien, Austria

Supplementary Materials

References

  1. Dan Abramov and Andrew Clark. React fiber architecture. https://github.com/acdlite/react-fiber-architecture, 2017. Accessed: 2025-10-03.
  2. Paulo Sérgio Almeida, Ali Shoker, and Carlos Baquero. Delta state replicated data types. Journal of Parallel and Distributed Computing, 111:162-173, 2018. URL: https://doi.org/10.1016/J.JPDC.2017.08.003.
  3. Guilherme Cavalcanti, Paulo Borba, Leonardo dos Anjos, and Jonatas Clementino. Semistructured merge with language-specific syntactic separators. In Proceedings of the 39th IEEE/ACM International Conference on Automated Software Engineering, pages 1032-1043, 2024. URL: https://doi.org/10.1145/3691620.3695483.
  4. Sudarshan S Chawathe, Anand Rajaraman, Hector Garcia-Molina, and Jennifer Widom. Change detection in hierarchically structured information. Acm Sigmod Record, 25(2):493-504, 1996. URL: https://doi.org/10.1145/233269.233366.
  5. Kattiana Constantino, Shurui Zhou, Mauricio Souza, Eduardo Figueiredo, and Christian Kästner. Understanding collaborative software development: An interview study. In Proceedings of the 15th international conference on global software engineering, pages 55-65, 2020. Google Scholar
  6. React Contributors. React documentation. https://react.dev/, 2025. Accessed: 2025-10-28.
  7. Mark Day. What synchronous groupware needs: Notification services. In Proceedings. The Sixth Workshop on Hot Topics in Operating Systems (Cat. No. 97TB100133), pages 118-122. IEEE, 1997. URL: https://doi.org/10.1109/HOTOS.1997.595193.
  8. Jinhao Dong, Jun Sun, Yun Lin, Yedi Zhang, Murong Ma, Jin Song Dong, and Dan Hao. Revisiting the conflict-resolving problem from a semantic perspective. In Proceedings of the 39th IEEE/ACM International Conference on Automated Software Engineering, pages 141-152, 2024. URL: https://doi.org/10.1145/3691620.3694993.
  9. Falleri et. al. Gumtree tree-sitter parser. https://github.com/GumTreeDiff/tree-sitter-parser, 2026. Accessed 2026-02-04.
  10. Jean-Remy Falleri and Matias Martinez. Fine-grained, accurate and scalable source differencing. In Proceedings of the IEEE/ACM 46th International Conference on Software Engineering, pages 1-12, 2024. Google Scholar
  11. Jean-Rémy Falleri, Floréal Morandat, Xavier Blanc, Matias Martinez, and Martin Monperrus. Fine-grained and accurate source code differencing. In Proceedings of the 29th ACM/IEEE International Conference on Automated Software Engineering, ASE '14, pages 313-324, New York, NY, USA, 2014. Association for Computing Machinery. URL: https://doi.org/10.1145/2642937.2642982.
  12. Hongfei Fan. Any-time collaborative programming environment and supporting techniques. PhD thesis, Nanyang Technological University, Singapore, 2013. URL: https://doi.org/10.32657/10356/54902.
  13. Hongfei Fan, Kun Li, Xiangzhen Li, Tianyou Song, Wenzhe Zhang, Yang Shi, and Bowen Du. Covscode: a novel real-time collaborative programming environment for lightweight ide. Applied Sciences, 9(21):4642, 2019. Google Scholar
  14. Hongfei Fan and Chengzheng Sun. Achieving integrated consistency maintenance and awareness in real-time collaborative programming environments: The coeclipse approach. In Proceedings of the 2012 IEEE 16th International Conference on Computer Supported Cooperative Work in Design (CSCWD), pages 94-101. IEEE, 2012. URL: https://doi.org/10.1109/CSCWD.2012.6221803.
  15. Beat Fluri, Michael Würsch, Martin Pinzger, and Harald Gall. A retrospective of changedistiller: Tree differencing for fine-grained source code change extraction. IEEE Transactions on Software Engineering, 2025. Google Scholar
  16. Leon Freudenthaler. Supplemental material: Rcp using lst and sst, April 2026. URL: https://doi.org/10.6084/m9.figshare.31368775.
  17. Leon Freudenthaler, Bernhard Taufner, and Karl M. Göschka. From characters to structure: Rethinking real-time collaborative programming models. In Proceedings of the IEEE/ACM International Conference on Automated Software Engineering (ASE), 2025. Google Scholar
  18. Akira Fujimoto, Yoshiki Higo, and Shinji Kusumoto. Towards accurate file tracking based on ast differences. In 2021 28th Asia-Pacific Software Engineering Conference (APSEC), pages 553-558. IEEE, 2021. URL: https://doi.org/10.1109/APSEC53868.2021.00067.
  19. Harald C Gall, Beat Fluri, and Martin Pinzger. Change analysis with evolizer and changedistiller. IEEE software, 26(1):26-33, 2009. URL: https://doi.org/10.1109/MS.2009.6.
  20. Felix Grund, Shaiful Alam Chowdhury, Nick C Bradley, Braxton Hall, and Reid Holmes. Codeshovel: Constructing method-level source code histories. In 2021 IEEE/ACM 43rd International Conference on Software Engineering (ICSE), pages 1510-1522. IEEE, 2021. URL: https://doi.org/10.1109/ICSE43902.2021.00135.
  21. JetBrains. Code with me, 2025. Accessed: 2025-10-27. URL: https://plugins.jetbrains.com/plugin/14896-code-with-me.
  22. Martin Kleppmann, Dominic P Mulligan, Victor BF Gomes, and Alastair R Beresford. A highly-available move operation for replicated trees. IEEE Transactions on Parallel and Distributed Systems, 33(7):1711-1724, 2021. URL: https://doi.org/10.1109/TPDS.2021.3118603.
  23. Stanislav Levin and Amiram Yehudai. Collaborative real time coding or how to avoid the dreaded merge. arXiv preprint arXiv:1504.06741, 2015. URL: https://arxiv.org/abs/1504.06741.
  24. Eric Lippert. Persistence, façades and roslyn’s red-green trees. Accessed: 2025-10-03. URL: https://ericlippert.com/2012/06/08/red-green-trees/.
  25. Geoffrey Litt, Sarah Lim, Martin Kleppmann, and Peter Van Hardenberg. Peritext: A crdt for collaborative rich text editing. Proceedings of the ACM on Human-Computer Interaction, 6(CSCW2):1-36, 2022. URL: https://doi.org/10.1145/3555644.
  26. Yifan Ma, Batu Qi, Wenhua Xu, Mingjie Wang, Bowen Du, and Hongfei Fan. Integrating real-time and non-real-time collaborative programming: Workflow, techniques, and prototypes. Proceedings of the ACM on Human-computer Interaction, 7(GROUP):1-19, 2023. URL: https://doi.org/10.1145/3567563.
  27. Max Brunsfeld et. al. Tree-sitter is a parser generator tool and an incremental parsing library, 2024. Accessed: 2024-10-25. URL: https://github.com/tree-sitter/tree-sitter.
  28. Microsoft. Visual studio live share, 2025. Accessed: 2025-10-27. URL: https://marketplace.visualstudio.com/items?itemName=MS-vsliveshare.vsliveshare.
  29. Robert B Miller. Response time in man-computer conversational transactions. In Proceedings of the December 9-11, 1968, fall joint computer conference, part I, pages 267-277, 1968. URL: https://doi.org/10.1145/1476589.1476628.
  30. Aäron Munsters, Angel Luis Scull Pupo, and Jens Nicolay. Coast: A conflict-free replicated abstract syntax tree. In 17th International Conference on Software Technologies, volume 1 of Proceedings of the 17th International Conference on Software Technologies - ICSOFT, pages 187-196. Scitepress, July 2022. URL: https://doi.org/10.5220/0011278800003266.
  31. .NET Foundation, Microsoft, and contributors. The .net compiler platform (roslyn). Accessed: 2025-10-26; MIT license. URL: https://github.com/dotnet/roslyn.
  32. Jakob Nielsen. Usability engineering. Morgan Kaufmann, 1994. Google Scholar
  33. Cyrus Omar, Ian Voysey, Michael Hilton, Joshua Sunshine, Claire Le Goues, Jonathan Aldrich, and Matthew A Hammer. Toward semantic foundations for program editors. arXiv preprint arXiv:1703.08694, 2017. URL: https://arxiv.org/abs/1703.08694.
  34. Mateusz Pawlik and Nikolaus Augsten. Tree edit distance: Robust and memory-efficient. Information Systems, 56:157-173, 2016. URL: https://doi.org/10.1016/J.IS.2015.08.004.
  35. Replit. Replit - The collaborative browser-based IDE. https://replit.com/, 2025. Accessed: 2025-05-22.
  36. rust-analyzer contributors. Rowan. Accessed: 2025-10-26; Dual-licensed Apache-2.0 or MIT. URL: https://github.com/rust-analyzer/rowan.
  37. Fred B Schneider. Implementing fault-tolerant services using the state machine approach: A tutorial. Acm Computing Surveys (CSUR), 22(4):299-319, 1990. URL: https://doi.org/10.1145/98163.98167.
  38. Fred B Schneider. Replication management using the state-machine approach. Distributed systems, 2:169-198, 1993. Google Scholar
  39. Marc Shapiro, Nuno Preguiça, Carlos Baquero, and Marek Zawirski. Conflict-free replicated data types. In Symposium on Self-Stabilizing Systems, pages 386-400. Springer, 2011. URL: https://doi.org/10.1007/978-3-642-24550-3_29.
  40. Leo Stewen and Martin Kleppmann. Undo and redo support for replicated registers. In Proceedings of the 11th Workshop on Principles and Practice of Consistency for Distributed Data, pages 1-7, 2024. URL: https://doi.org/10.1145/3642976.3653029.
  41. Chengzheng Sun and Clarence Ellis. Operational transformation in real-time group editors: issues, algorithms, and achievements. In Proceedings of the 1998 ACM conference on Computer supported cooperative work, pages 59-68, 1998. URL: https://doi.org/10.1145/289444.289469.
  42. Dan Sun, Fan Ouyang, Yan Li, and Hongyu Chen. Three contrasting pairs’ collaborative programming processes in china’s secondary education. Journal of Educational Computing Research, 59(4):740-762, 2021. Google Scholar
  43. Dan Sun and Fan Xu. Real-time collaborative programming in undergraduate education: A comprehensive empirical analysis of its impact on knowledge, behaviors, and attitudes. Journal of Educational Computing Research, 63(1):33-63, 2025. Google Scholar
  44. Swift project contributors. Swift programming language, 2025. Accessed: 2025-10-26; Apache-2.0 license. URL: https://github.com/swiftlang/swift.
  45. Xin Tan, Xinyue Lv, Jing Jiang, and Li Zhang. Understanding real-time collaborative programming: a study of visual studio live share. ACM Transactions on Software Engineering and Methodology, 33(4):1-28, 2024. URL: https://doi.org/10.1145/3643672.
  46. Matthew Weidner and Martin Kleppmann. The art of the fugue: Minimizing interleaving in collaborative text editing. IEEE Transactions on Parallel and Distributed Systems, 2025. Google Scholar
  47. Jim Whitehead. Collaboration in software engineering: A roadmap. In Future of Software Engineering (FOSE'07), pages 214-225. IEEE, 2007. URL: https://doi.org/10.1109/FOSE.2007.4.
  48. Wenhua Xu, Yifan Ma, Hongguang Zhou, Mingjie Wang, Bowen Du, and Hongfei Fan. A multiple locking group scheme for flexible semantic conflict prevention in real-time collaborative programming. In 2022 IEEE 25th International Conference on Computer Supported Cooperative Work in Design (CSCWD), pages 1432-1437. IEEE, 2022. URL: https://doi.org/10.1109/CSCWD54268.2022.9776068.
  49. Weihai Yu. A string-wise crdt for group editing. In Proceedings of the 2012 ACM International Conference on Supporting Group Work, GROUP '12, pages 141-144, New York, NY, USA, 2012. Association for Computing Machinery. URL: https://doi.org/10.1145/2389176.2389198.
  50. Weihai Yu. Supporting string-wise operations and selective undo for peer-to-peer group editing. In Proceedings of the 2014 ACM International Conference on Supporting Group Work, pages 226-237, 2014. URL: https://doi.org/10.1145/2660398.2660401.
  51. Kaizhong Zhang and Dennis Shasha. Simple fast algorithms for the editing distance between trees and related problems. SIAM journal on computing, 18(6):1245-1262, 1989. URL: https://doi.org/10.1137/0218082.
  52. Hongguang Zhou, Yifan Ma, Wenhua Xu, Mingjie Wang, Bowen Du, and Hongfei Fan. Context-based operation merging in real-time collaborative programming environments. In 2022 IEEE 25th International Conference on Computer Supported Cooperative Work in Design (CSCWD), pages 1426-1431. IEEE, 2022. URL: https://doi.org/10.1109/CSCWD54268.2022.9776234.
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