Why it is worth attention

It demonstrates a novel approach to maintaining a fork by leveraging LLMs for code refactoring and cleanup, while removing over 11,000 lines of dead code and targeting sub-second incremental builds.

Who it is for

Developers curious about Bun internals or Zig-based JavaScript runtimes
Contributors comfortable with LLM-assisted development workflows
System programmers interested in fast incremental compilation of WebKit
Early adopters willing to experiment with a non-production fork

Use cases

Iterative development with sub-second incremental rebuilds
Testing and contributing to a Zig-based JavaScript runtime fork
Exploring code reduction and refactoring at scale using LLMs
Learning about building JavaScriptCore and ICU from source

Strengths

Sub-second incremental compilation via Zig's build system
Over 11,000 lines of dead code removed from upstream Bun
Tracks Zig's master branch for up-to-date toolchain support
Builds most dependencies from source, including JavaScriptCore and ICU

Considerations

Only x86_64-linux-gnu builds and tests are currently in scope
The full upstream test suite does not pass yet
Contains known, unpatched vulnerabilities and should not be used in production

README quick start

Buz

Buz is an early-stage experimental fork of pre-Rust Bun. The goal of the fork is to be a drop-in replacement for Bun.

Features

Tracks Zig's master branch.
Supports sub-second incremental compilation.
Uses build.zig as the build-system entry point.
Builds most dependencies from source, including JavaScriptCore and ICU, enabling fast incremental builds of vendored WebKit code.
Over 11,000 lines of dead code removed from upstream Bun.
Includes Bun's upstream test suite.

Work in progress

Currently only native x86_64-linux-gnu builds and tests are in scope.
The full upstream test suite does not pass yet.
The codebase is still being refactored and deslopified. It is not ready for human review. It will take at least a few weeks of LLM-assisted cleanup before it's worthy of human contributor attention.
This codebase contains numerous known, unpatched vulnerabilities and uses an outdated version of JavaScriptCore that lacks the latest security fixes. Do not use in production.

Contributing

All contributions at this stage must be LLM-assisted. This policy will be lifted when the test suite is passing and the codebase is sufficiently cleaned up.

All accepted contributions must conform to the following:

Make all tests pass in at least one currently failing test file.
Fix the problem at the right scope. If a whole subsystem needs a rewrite, do not send in a set of small patches on a bad foundation.
Your changes should make the codebase cleaner and more idiomatic. Always reduce technical debt.
The PR must be merge-ready as far as you can tell. If either Sol Max or Fable Max finds anything actionable in your PR, it will not be accepted. This includes correctness, performance, simplicity, and maintainability. Human time will not be wasted on flaws that non-humans can spot.
By submitting a contribution, you agree to license your contribution under the Unlicense.

Building

Bootstrap Zig

You will need CMake >=3.15, LLVM + Clang + LLD at Zig's currently supported version (22.x as of writing), Git, Ruby with ERB, Python 3, and Perl.

git submodule update --init --recursive

cd zig-upstream
mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
make install
cd ../..

Build commands

Incremental debug build:

./zig build --watch -fincremental

Release build (for running the fu

Description

A fork of Bun based on modern Zig

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