Hello, This is my GSoC 2025 proposal for the project "Refactoring in order to reduce Git’s global state". You can view docs version here: https://docs.google.com/document/d/1tJrtWxo1UGKChB3hu5eZ-ljm0FtU_fsv0TnIRwu3EKY/edit?usp=sharing --------- Refactoring in order to reduce git’s state My Information: --------------- Name: Ayush Chandekar Email: ayu.chandekar@xxxxxxxxx Mobile No: (+91) 9372496874 Education: UG Sophomore, IIT Roorkee Github: https://github.com/ayu-ch Blog: https://ayu-ch.github.io About me: --------- I'm Ayush Chandekar, a UG Sophomore studying at Indian Institute of Technology, Roorkee. I like participating in various software development and tech-development endeavors, usually hackathons, CTFs, and projects at SDSLabs. SDSLabs is a student-run technical group that includes passionate developers and designers interested in various fields and involved in multiple software development projects that aim to foster a software development culture on campus. Being a part of this group has exposed me to different software development methodologies, tools and frameworks and helped me become comfortable contributing to an open-source project with multiple contributors. Some open-source contributions I made here are: [1], [2] & [3] I see this project as a meaningful opportunity to deepen my involvement in the Git community and to build a foundation for continued contributions to open source development in the future. Overview: --------- Git currently uses a global object called `the_repository`, which refers to a single instance of `struct repository`. Many internal functions rely on this global object rather than accepting a `struct repository` as an explicit parameter. This design inherently assumes a single active repository, making it difficult to support multi-repository use cases and obstructing the long-term goal of libification of Git. A key architectural limitation is that while `struct repository` encapsulates some repository-specific information, many important environment variables and configuration settings that logically belong to a repository are still stored as global variables, primarily in `environment.c`, not within the `repository` struct. As a result, even if multiple repositories were to exist concurrently, they would still share this global state, leading to incorrect behavior, race conditions, or subtle bugs. This project aims to refactor Git’s environment handling by relocating global variables into more appropriate local contexts, primarily within struct repository and struct repo_settings. However, some global variables may only apply to specific subsystems. In such cases, rather than placing them in struct repository or struct repo_settings, they should be moved into a context that better reflects their scope. This change will not only make the environment state repository-specific but also improve the modularity and maintainability of the codebase. The work involves identifying environment-related global variables, determining the most suitable structure to house them, and updating all affected code paths accordingly. The difficulty of this project is medium, and it is estimated to take 175 to 350 hours. Pre-GSOC: --------- I started exploring Git’s codebase and documentation around the end of January, familiarizing myself with its structure and development practices. I submitted a microproject, which helped me navigate the code and contribution workflow. After selecting the project on refactoring Git’s state, I studied the surrounding code and reviewed past patches ([4], [5], [6], [7], [8] & [9]) to understand the reasoning behind previous changes. To better prepare for the GSoC timeline, I submitted a patch related to the project, to gain hands-on experience with both the implementation details and the submission process. The patch focused on refactoring access to `core.attributesfile`. Through discussions and feedback from the community, I gained a clearer understanding of a key aspect of the project: determining whether certain variables should belong to repo_settings/ repository or be part of a separate subsystem. Junio pointed out in a feedback that not all global variables should be blindly moved into `repo_settings`. Specifically, for `git_attributes_file`, adding it to the repository struct doesn’t make sense. He explained that it’s similar to how index_state is handled, while index_state knows which repository it belongs to, the repository struct only holds a pointer to a single index_state instance and isn’t aware of other instances. Following this approach, instead of placing `git_attributes_file` in the repository struct, we can house it within an attribute set and pass a pointer to that set wherever needed. This practice patch gave me a clearer understanding of the project. Patches: -------- For git: + (Microproject) t6423: fix suppression of Git’s exit code in tests Thread: https://public-inbox.org/git/20250202120926.322417-1-ayu.chandekar@xxxxxxxxx/ Status: Merged into master Commit Hash: 7c1d34fe5d1229362f2c3ecf2d493167a1f555a2 Description: Instead of executing a Git command as the upstream component of a pipe, which can result in the exit status being lost, redirect its output to a file and then process that file in two steps to ensure the exit status is properly preserved. + midx: implement progress reporting for QSORT operation Thread: https://public-inbox.org/git/20250210074623.136599-1-ayu.chandekar@xxxxxxxxx/ Status: Dropped Description: Add progress reporting during the QSORT operation in multi-pack-index verification. While going through the code, I found this TODO, which I thought was interesting however my approach assumed that the qsort() operation processes elements in a structured order, which isn't guaranteed. + Stop depending on `the_repository` for core.attributesfile Thread: https://public-inbox.org/git/20250310151048.69825-1-ayu.chandekar@xxxxxxxxx/ Status: WIP, needs more discussion. Description: This patch refactors access to the `core.attributesfiles` configuration by moving it into the `repo_settings` struct. It eliminates the global variable `git_attributes_file` and updates relevant code paths to pass the `struct repository` as a parameter. For git.github.io: + GSoC-participants: add GSoC 2024 participants to the list #762 Status: Merged into master Description: Adding GSoC 2024 participants will help new contributors understand their journey, making it easier for them to navigate the program and the project. Proposed Plan: -------------- I have been reviewing global variables across the codebase to understand their dependencies and impact. To do this, I examined `config.c` and cross-referenced it with `environment.c` to see how these variables are currently managed. The goal of this project is to eliminate global variables by moving their configurations into their local contexts. The general approach for handling a global variable begins with understanding its purpose. This involves tracing its usage across the codebase and identifying the subsystem it should belong to. If the variable is closely tied to repository-related functionality, it may belong in struct repository or struct repo_settings. Otherwise, it should be placed in a more suitable context based on its scope. Additionally, it's important to review previous attempts or related patches to understand past design decisions and ensure consistency with ongoing efforts. Finally, the global instance is eliminated by relocating the variable into the appropriate context and passing it through the relevant code paths. Example: Handling `is_bare_repository_cfg` The variable `is_bare_repository_cfg` determines whether a repository is bare, meaning it lacks a working directory. Since this property is fundamental to how a repository functions, it should be placed in struct repository. I have also gone through the code paths and analyzed how this variable is initialized. We can initialize it similarly to how hash_algo is set through the repository format. The repository format already contains an `is_bare` field, which we can use to set this variable inside struct repository. However, I still have some questions regarding why the is_bare_repository() function checks for `repo->worktree` and why the `worktree struct` itself has an `is_bare` variable. If a repository is considered bare when !repo->worktree is true, the role of `worktree->is_bare` needs further clarification. I believe that by engaging with the community, my understanding will become clearer. I also went through [4] to see how John Cai's approach was. This is how we can also approach for other global variables. Through multiple iterations, this approach will be refined based on feedback, edge cases, and community input. Timeline: --------- Pre-GSOC: (Until 8 May) - Explore the codebase more, focusing on environment-related code paths. - Document how each global variable is used and how it can be moved to repository settings. - Study Git’s Coding Guidelines and the Pro Git Book to align with best practices. ---------- Community Bonding: (May 8 - June 1) - Engage with mentors to discuss different environment variables, their dependencies, and the best approach for refactoring. - Finalize an implementation plan based on discussions. - Since I will be on summer vacation, I can start coding early and make progress on the project. ---------- Coding Period: (June 2 - August 25) - Identify the appropriate subsystem for each global variable and relocate it into struct repository, struct repo_settings, or other suitable contexts. - Modify function signatures to pass the new contexts explicitly, replacing reliance on global variables. - Continuously submit patches for review and incorporate feedback from mentors and the community. - I plan to write weekly blogs which will document what I did in the whole week. ---------- Final Week: (August 25 - September 1) - Write a detailed report on the entire project. - Fix bugs if any. - Reflect on the project, noting challenges faced and lessons learned. Blogging: --------- I have also set up a blogging page at [10]. While reading blogs from previous GSoC contributors, I found them useful in understanding the challenges they faced and how they approached their projects. Their experiences gave me a better idea of what to expect and how to navigate the development process. Inspired by this, I decided to start my own blog to document my journey throughout GSoC. This will not only help me track my own progress but also serve as a resource for future contributors who might work on similar projects. I plan to share updates on my work, challenges encountered and insights gained from discussions with mentors and the community. Additionally, I hope my blog encourages more people to contribute to open source by providing a transparent look into the development process. Writing about my experience will also help me reflect on my work and improve my ability to communicate technical ideas effectively. I liked the format and structure of Chandra's blog, so I decided to use the same template for my own blogging page. Availability: ------------- As a college student, I intend to utilise my summer breaks from May to July to work on the project. After completing my University exams in April, I can start working in May. I can dedicate 40 hours a week from May to July, while in August after the classes commence, I can dedicate about 25 hours a week. There are no exams or planned vacations throughout the coding period. Besides this project, I have no commitments/vacations planned for the summer. I shall keep my status posted to all the community members and maintain transparency in the project. Post-GSOC: ---------- Beyond contributing code, I strongly believe in giving back to the community and helping others grow. Open source thrives on mentorship, knowledge sharing, and long-term involvement, and I would love to continue contributing even after GSoC ends. I have always valued mentorship, both as a mentee and as someone who enjoys guiding others. If given the opportunity, I would be more than happy to mentor/co-mentor future GSoC contributors. By staying involved in the community, whether through contributing, reviewing patches, or mentoring, I hope to help sustain and expand the project’s reach. I look at GSoC as not just as a one-time contribution but as a step toward a longer-term relationship with open source. I will continue to be involved with Git even after GSoC by contributing patches, reviewing code, and participating in discussions. My work on refactoring Git’s state aligns with long-term improvements to the codebase, and I plan to keep refining it beyond the program. I see GSoC as just the beginning of my journey with Git. Appreciation: ------------- I appreciate the Git community for its excellent documentation, which made it much easier for me to understand Git in depth. The well-structured resources helped me navigate the codebase and gain a deeper understanding of how Git works internally. Beyond the documentation, I am also grateful for how welcoming and supportive the community has been. Whether through discussions on the mailing list or feedback on my patches, the information and guidance I received made my experience even better. Additionally, I read the blogs and proposals of Chandra, Jialuo, and Ghanashyam, which provided valuable insights into their journeys and helped me shape my own approach to contributing. Thanks for reviewing this proposal. References: ----------- [1] https://github.com/sdslabs/beast/pull/374 [2] https://github.com/sdslabs/beast/tree/add-teams-with-hint [3] https://github.com/sdslabs/playCTF/pull/177 [4] https://public-inbox.org/git/pull.1826.git.git.1730926082.gitgitgadget@xxxxxxxxx/ [5] https://public-inbox.org/git/20250303-b4-pks-objects-without-the-repository-v1-0-c5dd43f2476e@xxxxxx/ [6] https://public-inbox.org/git/20250206-b4-pks-path-drop-the-repository-v1-0-4e77f0313206@xxxxxx/ [7] https://public-inbox.org/git/pull.1829.git.1731653548549.gitgitgadget@xxxxxxxxx/#t [8] https://public-inbox.org/git/cover.1733236936.git.karthik.188@xxxxxxxxx/ [9] https://public-inbox.org/git/cover.1724923648.git.ps@xxxxxx/ [10] https://ayu-ch.github.io
