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.

Multiple programming tasks require synchronous collaboration between developers, giving rise to real-time collaborative programming tools that enable simultaneous editing of shared source code. However, most existing tools operate at the text level, propagating every keystroke–including syntactically invalid ones–without considering program structure. This results in excessive communication overhead, frequent propagation of build-breaking states, and poor synchronization. A major consequence is noticeable lag, especially under unstable network conditions, as collaborators are overwhelmed with unnecessary updates that disrupt their workflow and degrade the shared coding experience. In this paper, we introduce a novel structure-aware propagation model that transmits only syntactically valid code changes. For evaluation we implemented our tool as an IntelliJ plugin and evaluate it against three industry-standard tools–VS Code Live Share, Code With Me, and Replit–across eight representative programming scenarios. Our results show that it significantly lowers the number and size of propagated messages while maintaining consistent, buildable program states. Our findings demonstrate the potential of structure-aware propagation as a foundation for the next generation of real-time collaborative programming environments.

This dissertation investigates near-synchronous collaboration in programming environments by means of Conflict-free Replicated Data Types (CRDTs). While screen sharing and video conferencing offer basic features for collaborative programming, IDE-embedded collaboration tools provide precise tracking of source code changes and developer control. CRDTs enable decentralized collaboration, eliminating central server dependencies. However, existing CRDTs fail to preserve user intent and handle complex formats, leading to inefficiencies. Using a Design Science Research approach, this dissertation addresses four key research areas: (1) Identifying the limitations of existing CRDT algorithms in preserving user intent for programming files, (2) Optimizing CRDT implementations for programming collaboration requirements, (3) Determining the appropriate granularity for replicated data types in programming environments, (4) Exploring supervised imitation learning to enhance system capabilities in merging conflicts. This work aims to improve collaborative programming tools, ensuring higher consistency, efficiency, and user satisfaction.