[GSOC][PROPOSAL v2]: Refactoring in order to reduce Git’s global state

[Shreyansh Paliwal <shreyanshpaliwalcmsmn@gmail.com>]

Hello,

This is my second draft of GSoC 2026 proposal for the project
'Refactoring in order to reduce Git’s global state'.

Doc version can be read at:
https://docs.google.com/document/d/16MRNUv6dJi6vtNvI5Ro0WmHf20dRRBHjFLpmhAuaUOA/edit?usp=sharing

Any feedback or suggestions would be greatly appreciated.

Thanks for reading.
---

Changes in v2:
 - Added links in the 'About Me' section and updated reference numbering.
 - Rephrased and revised the 'Pre-GSoC', 'History' and 'Proposed Plan' sections.
 - Updated patch statuses and changed some wordings.
---

Refactoring in order to reduce Git's global state

Personal Information:
---------------------

Name: Shreyansh Paliwal
Email: Shreyanshpaliwalcmsmn@gmail.com
Alternate Email: Shreyansh.01014803123@it.mait.ac.in
Mobile No.: +91-9335120023

Education: GGSIPU, New Delhi, India
Year: III / IV
Degree: Bachelor of Technology in Information Technology

Github: https://github.com/shreyp135
Time-zone: UTC +5:30 (IST)

About Me:
---------

I am Shreyansh Paliwal, a pre-final year undergraduate student at Guru
Gobind Singh Indraprastha University, New Delhi, India. I am a technology
enthusiast, who began programming in 2018 with Java as my first language
and later transitioned to C/C++ in 2023 as my primary focus. I enjoy
exploring new technologies and programming languages, and have developed
solid experience building applications such as [1] using TypeScript,
React.js, Node.js, and AWS. I actively participate in technical events and
have organized multiple hackathons [2], tech-fests [3], and related
activities at my college as the SIG-Head of IOSD [4], a tech-focused
student community.

I started using Git in 2023, which is also when I made my first open-source
contribution to the Git project. I was a winner of Augtoberfest 2024 [5],
an open-source competition organized by C4GT India. Over the past several
months, I have been involved with the Git project, studying the codebase,
submitting patches, and incorporating review feedback. I am motivated to
improve the experience of Git for end users, and this project is an
excellent opportunity to continue that work.

Overview:
---------

Git relies heavily on global state for managing environment variables and
configuration data. In particular, many parts of the codebase depend on the
global struct repository instance, the_repository, which represents the
currently active repository. Instead of passing a repository instance
explicitly, several internal functions implicitly rely on this global
object. Additionally, various configuration derived values and
environment-related variables such as the_hash_algo, default_abbrev, and
comment_line_str are stored globally, most of them defined in
environment.c.

This design assumes that only one repository is active within a process at
a time. As a result, the repository state becomes shared across the entire
process, weakening isolation and making behavior implicitly dependent on
global context. Such global dependencies make the code harder to reason
about, test, and maintain, and can introduce subtle bugs when operations
interact with multiple repositories. They also limit long-term goals such
as safely supporting multiple repositories within a single process and
continuing Git’s ongoing libification efforts.

To address these issues, global environment and configuration state should
be refactored into better-scoped contexts. Repository-specific data can be
moved into struct repository or related structures, while
subsystem-specific state should be localized appropriately. Passing
repository instances explicitly through function interfaces will improve
modularity, reduce hidden dependencies, and make the codebase easier to
maintain while moving Git closer to supporting multiple repositories safely
within a single process.

The difficulty of this project is medium, and it is estimated to take 175
to 350 hours.

Pre-GSOC:
---------

I first explored the Git codebase in December 2023, when I submitted a
small patch fixing the wording of an error message that I noticed while
browsing the source code. At that time I had recently started using Git and
GitHub for version control in my projects, which sparked my curiosity about
how Git works internally. A few months ago, when I had some free time
from college, I decided to start contributing to Git more actively. I built
Git from source, read parts of the documentation, and familiarized myself
with the mailing list workflow. While going through the documentation, I
noticed a few inconsistencies in the MyFirstContribution page and submitted
patches to fix them. I also completed a microproject involving a test
cleanup, and later worked on adding a warning for a quiet fallback.

During this process, I attempted to remove the usage of the_repository from
a file. After discussion on the mailing list [23], Phillip directed me
towards wt-status, which led me to explore parts of the codebase such as
the wt-status and worktree subsystems. Through this, I learned that such
refactors are generally more valuable in core library code. Following this
discussion, I shifted my focus toward understanding the broader global
state refactoring effort. To better understand the project area, I studied
previous patches and blog posts by Ayush Chandekar and Olamide Bello,
followed related discussions on the mailing list, and explored the relevant
parts of the codebase. This motivated me to work further in this area and
shaped my interest in this project.

The following is a list of my contributions, ordered from earliest to most
recent:

Patches for Git:
----------------

* test-lib-functions.sh: fix test_grep fail message wording
        Status: Released in v2.43.1
        Mailing List: https://lore.kernel.org/git/20231203171956.771-1-shreyanshpaliwalcmsmn@gmail.com/
        Commit: 37e8d795bed7b93d3f12bcdd3fbb86dfe57921e6
        Log: This was my first patch to Git in 2023. While browsing the
                 source code and past issues, I noticed that even after
                 the test_i18ngrep function was deprecated, an error message
                 referring to test_i18ngrep was left behind. I updated
                 the wording to correctly reference test_grep.

* doc: MyFirstContribution: fix missing dependencies and clarify build steps
        Status: Merged into master
        Mailing List: https://lore.kernel.org/git/20260112195625.391821-1-shreyanshpaliwalcmsmn@gmail.com/
        Commit: 81021871eaa8b16a892b9c8791a0c905ab26e342
        Log: While getting familiar with the codebase, I followed the
                 MyFirstContribution documentation and encountered a few
                 issues. Some include headers were missing, the synopsis
                 format was incorrect, and the explanation for -j$(nproc)
                 was absent. I submitted fixes to improve the clarity and
                 correctness of the documentation.

* t5500: simplify test implementation and fix git exit code suppression (Microproject)
        Status: Merged into master
        Mailing List: https://lore.kernel.org/git/20260121130012.888299-1-shreyanshpaliwalcmsmn@gmail.com/
        Commit: a824421d3644f39bfa8dfc75876db8ed1c7bcdbf
        Log: This was completed as a microproject for GSoC. Instead of
                constructing the pack protocol using a complex combination
                of here-docs and echo commands, the patch captures command
                outputs beforehand and uses the test-tool pkt-line pack
                helper to construct the protocol input in a temporary file
                before feeding it to git upload-pack.

* show-index: add warning and wrap error messages with gettext
        Status: Merged into master
        Mailing List: https://lore.kernel.org/git/20260130153603.290196-1-shreyanshpaliwalcmsmn@gmail.com/
        Commit: ea39808a22714b8f61b9472de7ef467ced15efea,
                227e2cc4e1415c4aeadceef527dd33e478ad5ec3
        Log: While exploring the code, I noticed a TODO comment suggesting
                automatic hash detection. After discussion on the mailing
                list, it was concluded that there was no future-proof
                approach to implement this until a new index file format
                came into use. Instead, an explicit warning was added rather
                than silently falling back to SHA-1. Additionally, several
                error messages were missing gettext wrapping, which was also
                fixed.

* wt-status: reduce reliance on global state
        Status: Will merge to next
        Mailing List: https://lore.kernel.org/git/20260218175654.66004-1-shreyanshpaliwalcmsmn@gmail.com/
        Commit: a7cd24de0b3b679c16ae3ee8215af06aeea1e6a3,
                9d0d2ba217f3ceefb0315b556f012edb598b9724,
                4631e22f925fa2af8d8548af97ee2215be101409
        Log: This has been the most significant patch series in my journey
                so far. It began with a suggestion from Phillip to clean up
                some the_repository usages in wt-status.c. I extended the
                effort to remove all usages of the_repository and
                the_hash_algo from the file. During review discussions, it
                was suggested that some worktree API cleanup should happen
                first, particularly regarding the representation of worktrees
                as NULL. Some related changes were later moved to a separate
                series, after which this refactoring proceeded.

* worktree: change representation and usage of primary worktree
        Status: Merged into master after being continued by Phillip Wood [6]
        Mailing List: https://lore.kernel.org/git/20260213120529.15475-1-shreyanshpaliwalcmsmn@gmail.com/
        Log: This worktree API cleanup series started while I was working
                on wt-status. The intention was to modify the representation
                of the current worktree so that struct worktree would not be
                NULL. During discussion, Phillip clarified that NULL actually
                represents the current worktree rather than the primary
                worktree. Since Phillip already had a patch based on the right
                logic, he continued the series and it was eventually merged
                into master.

* tree-diff: remove the usage of the_hash_algo global
        Status: Merged into master
        Mailing List: https://lore.kernel.org/git/20260220175331.1250726-1-shreyanshpaliwalcmsmn@gmail.com/
        Commit: 1e50d839f8592daf364778298a61670c4b998654
        Log: This was a straightforward patch that removed the remaining
                usages of the global the_hash_algo in tree-diff.c by using the
                repository’s local instance instead.

* send-email: UTF-8 encoding in subject line
        Status: Will merge to master
        Mailing List: https://lore.kernel.org/git/20260228112210.270273-1-shreyanshpaliwalcmsmn@gmail.com/
        Commit: c52f085a477c8eece87821c5bbc035e5a900eb12
        Log: This patch was motivated by an issue I personally encountered
                while sending a GSoC discussion email [7]. Initially the
                change only modified the wording of the prompt, but after
                discussion on the mailing list it was extended to include
                proper validation to prevent invalid charset encodings from
                being used in git send-email and to reduce confusion.

* Remove global state from editor.c
        Status: Waiting for further feedback
        Mailing List: https://lore.kernel.org/git/20260301105228.1738388-1-shreyanshpaliwalcmsmn@gmail.com/
        Log: This originated from a question I had about localizing
                editor_program in editor.c [7]. The patch received some
                mixed feedback on whether editor_program state should
                instead become repository-scoped, since it can also be set
                via git config --local. I am currently awaiting further
                guidance from mentors on the appropriate direction.

Patches for git.github.io:
--------------------------

* SoC-2026-ideas: Remove an extra backtick
        Status: merged into master
        PR Link: https://github.com/git/git.github.io/pull/831
        Merge Commit: c1e4aa87a54430953eaa7355061139fdf1ff6796
        Log: Minor Typo fix.

* rn-132: fixed 2 typos
        Status: merged into master
        PR Link: https://github.com/git/git.github.io/pull/832
        Merge Commit: 92876114d855d472ce2e0e5337e72a4b97b81681
        Log: Fixed typos in Git Rev News Edition 132.

I have also been involved in additional discussions on the Git mailing
list [8][9][10][11].

History / Background:
--------------------

Efforts to reduce Git’s reliance on global state began as several
subsystems moved toward libification, enabling Git’s internal functionality
to be reused as a library. Early examples include the libification of git
mailinfo by Junio [12] and git apply by Christian [13], these large patch
series exposed the limitations of relying on global state and highlighted
the need for better encapsulation of repository-related data. A key step
was the introduction of struct repository through refactoring by Stefan
Beller [14] and Brandon Williams [15], which was motivated to centralize
repository-related state instead of relying on scattered global variables,
improving code clarity while laying groundwork for future improvements such
as safer multithreading and handling submodules in the same process. Later
work by Patrick further reduced reliance on the global the_repository in
the config [16] and path [17] subsystems, consolidating several variables
into environment.c so environment-related state could be managed in one
place [18]. The macro #define USE_THE_REPOSITORY_VARIABLE was also
introduced to help transition code away from implicit global repository
access [19].

During GSoC 2025, Ayush Chandekar [20] removed additional usages of
the_repository across the codebase and moved several global configuration
variables (such as core_preload_index and merge_log_config) into
repository-scoped structures. More recently, during Outreachy, Olamide
Bello improved configuration handling by introducing repo_config_values, a
structure linked to struct repository that stores repository-specific
configuration values [21][22]. A supporting private structure,
config_values_private, was added for initialization and internal handling.
Discussions around this work also highlighted an important design
constraint: directly moving globals into repository structures or
introducing lazy loading helpers can cause user experience regressions if
configuration errors are detected later.

These efforts collectively form the foundation of the ongoing work to
gradually remove Git’s reliance on global state and move toward a more
modular, repository-scoped architecture.

Proposed Plan:
-------------

I started exploring the codebase by browsing relevant files and identifying
global variables by temporarily removing the USE_THE_REPOSITORY_VARIABLE
macro. My primary focus was on core library files rather than builtin code
[23]. Through this exploration, I observed that a large number of files still
depend on the_repository.

To tackle this project systematically, I propose classifying these files into
two categories:

1. Files using the_repository or the_hash_algo where a repository
   instance already exists: These files rely on global variables even
   though a struct repository instance is available somewhere in the
   call stack. A simple example is my patch in tree-diff.c, where a
   repository instance was already available through struct diff_options
   *opt, but the_hash_algo was still used. I replaced it with
   opt->repo->hash_algo.

   In such cases, the refactor mainly involves passing the repository
   instance through the function call stack and replacing the global
   usages. If a repository instance is not directly available in the
   file, I will trace the callers and propagate it from higher levels in
   the call hierarchy.
   Examples of such files include alias.c, archive*.c, walker.c, and
   xdiff-interface.c. These typically require localized refactoring and
   are good candidates for incremental patches.

2. Files relying on other global variables defined in environment.c:
   Some files depend on additional global variables that are parsed and
   accessed through environment.c. In these cases, there is no existing
   repository-scoped instance, making the refactor slightly more involved.

   Examples include wt-status.c (default_abbrev, comment_line_str) and
   apply.c (has_symlink, ignore_case, trust_executable_bit,
   apply_default_whitespace, apply_default_ignorewhitespace).
   For such variables, I will evaluate whether they should be moved into
   repository-scoped structures (e.g., repo_settings or
   repo_config_values), or instead be localized and passed explicitly
   where needed. The appropriate approach will depend on how widely the
   variable is used and whether it logically belongs in a
   multi-repository standpoint.

I plan to begin with the first category, addressing straightforward
refactors file by file. In parallel, I will analyze and work on specific
groups of global variables from the second category, designing
appropriate repository-scoped replacements while preserving the
original parsing timing and availability of those variables.

The end goal is to remove reliance on global state and eventually eliminate
the USE_THE_REPOSITORY_VARIABLE macro from these files.

Project Timeline:
----------------

* Community Bonding (Until May 24):
        - Discuss the project direction and design approaches with mentors.
        - Identify and prioritize two main areas of work:
                + files that rely on the_repository.
                + global variables defined in environment.c.
        - Study the previous patches by Olamide Bello and Ayush Chandekar
                in depth, and identify any remaining tasks while discussing
                their approaches and challenges with them.
        - Interact with all the people involved in this work to better
                 understand design decisions and potential pitfalls.
        - Experiment with small RFC patches, if needed to validate approaches.

* Coding period (May 25 - August 16):
        - Send patches for any remaining cleanup or refactoring related to
                git_default_config() and repo_config_values [22], as well as
                the worktree API [24], if any.
        - Identify straightforward refactors to remove usages of the_repository
                 in files such as xdiff-interface.c, archive*.c, fsmonitor*.c etc.
        - Work file by file with the goal of eliminating
                 #define USE_THE_REPOSITORY_VARIABLE by replacing global usages
                 with explicit repository instances.
        - Concurrently maintain at least two parallel patch series:
                + Small / straightforward refactors and replacements like
                         the_hash_algo or the_repostitory.
                + Larger structural refactors involving globals such as
                         DEFAULT_ABBREV, comment_line_str etc.
        - Publish weekly or biweekly blog updates documenting progress and design
                 decisions.

* Final week (August 17 - August 24):
        - Address any remaining tasks or pending patches.
        - Receive final feedback from mentors and reviewers.
        - Prepare a detailed report summarizing the work completed during the project.

Blogging:
---------

I believe blogging is an important part of any open-source project. It
helps others understand the ongoing work and also enables the contributor
to develop a deeper understanding and keep a better track of their own
progress. I experienced this firsthand, early in my journey I was unsure
about various aspects, but reading the blogs of Ayush and Olamide Bello
gave me valuable insight into the contributor perspective and their overall
work.

With the goal of helping future contributors in a similar way, I plan to
document my journey and project progress through regular blog posts. I will
publish updates on a weekly or biweekly basis, depending on the amount of
meaningful progress made. I have set up my blogging area on Medium, and my
posts will be available at [25].


Availability:
-------------

The main coding period runs from June to August. Most of June and July
coincide with my summer vacation, which allows me to dedicate significant
time to the project. My final exams are scheduled for May and will last
approximately one week, but they will be completed before the coding period
begins and should not affect my availability.

During June and July, I will be able to dedicate around 40 hours per week to
the project. In August, when my regular semester resumes, I expect to
contribute approximately 25–30 hours per week.
I do not have any other exams, internships, or planned vacations during the
coding period. Apart from this project, I have no other major commitments
for the summer.

I will keep the community regularly updated on my progress throughout the
project. My primary mode of communication will be email, and I will also be
available for calls or meetings if/when required. My preferred availability
window is 13:00–19:00 UTC.

Post GSoC:
----------

Being part of the Git community and contributing to the codebase has been a
very valuable experience for me. The process of understanding Git’s internals,
submitting patches, and receiving feedback on the mailing list has helped me
grow significantly as a developer. The feeling of working on code that is used
by millions of developers and companies around the world is very rewarding.

I plan to remain involved with the Git community even after GSoC by continuing
to contribute patches, review code, and participate in discussions to help make
Git better for end users. The work on refactoring Git’s global state is part of
a long-term effort, and I would love to continue working on it beyond the GSoC
timeline.

I would also be happy to mentor, co-mentor, or volunteer in the future to help
new and upcoming contributors whenever I get the chance. I see GSoC as the
starting point of a long-term relationship with the Git community.

Closing & Appreciation:
-----------------------

I would like to thank the Git community for the excellent documentation and the
welcoming environment. I am also grateful for the patience and guidance shown
in the feedback and discussions on the mailing list by Junio, Phillip, Karthik,
Ben, and others, which have helped me improve my understanding and contributions.

I also read blogs and proposals by Ayush, Lucas, Kousik Sanagavarapu, and Olamide
Bello, which provided valuable insights and helped shape my approach to contributing.

Thank you for reviewing my proposal :)

References:
-----------

[1]- https://github.com/shreyp135/Alethea

[2]- https://unstop.com/hackathons/hackmait-50-iosd-impulse-2024-maharaja-agrasen-institute-of-technology-mait-new-delhi-941779

[3]- https://cse.mait.ac.in/index.php/academics/9-computer-center/1249-iosd-mait-impulse-25, https://unstop.com/college-fests/impulse-2025-maharaja-agrasen-institute-of-technology-mait-new-delhi-348321

[4]- https://iosd-web.vercel.app/

[5]- https://www.linkedin.com/posts/code-for-goodtech_augtoberfest-c4gt2024-activity-7242923677032312834-XMul

[6]- https://lore.kernel.org/git/cover.1771511192.git.phillip.wood@dunelm.org.uk/

[7]- https://lore.kernel.org/git/20260304145823.189440-1-shreyanshpaliwalcmsmn@gmail.com/T/#m65b9b4547036991a7b7f3c861b9663428891f588

[8]- https://lore.kernel.org/git/20260114143238.536312-1-shreyanshpaliwalcmsmn@gmail.com/

[9]- https://lore.kernel.org/git/20260115211609.17420-1-shreyanshpaliwalcmsmn@gmail.com/

[10]- https://lore.kernel.org/git/20260204111343.71975-1-shreyanshpaliwalcmsmn@gmail.com/

[11]- https://lore.kernel.org/git/20260205131132.44282-1-shreyanshpaliwalcmsmn@gmail.com/

[12]- https://lore.kernel.org/git/1444778207-859-1-git-send-email-gitster@pobox.com/

[13]- https://lore.kernel.org/git/20160511131745.2914-1-chriscool@tuxfamily.org/

[14]- https://lore.kernel.org/git/20180205235508.216277-1-sbeller@google.com/

[15]- https://lore.kernel.org/git/20170531214417.38857-1-bmwill@google.com/

[16]- https://lore.kernel.org/git/cover.1715339393.git.ps@pks.im/

[17]- https://lore.kernel.org/git/20250206-b4-pks-path-drop-the-repository-v1-16-4e77f0313206@pks.im/

[18]- https://lore.kernel.org/git/20250717-pks-config-wo-the-repository-v1-20-d888e4a17de1@pks.im/

[19]- https://lore.kernel.org/git/cover.1718347699.git.ps@pks.im/

[20]- https://ayu-ch.github.io/2025/08/29/gsoc-final-report.html

[21]- https://cloobtech.hashnode.dev/week-5-and-6-design-reviews-rfcs-and-refining-the-path-forward

[22]- https://lore.kernel.org/all/cover.1771258573.git.belkid98@gmail.com/

[23]- https://lore.kernel.org/git/7b5dd0c4-0ca0-458e-89db-621a70dac9ae@gmail.com/

[24]- https://lore.kernel.org/git/20260217163909.55094-1-shreyanshpaliwalcmsmn@gmail.com/

[25]- https://medium.com/@shreyanshpaliwal18