The Rust Project manages several developer tools (Miri, Rust Analyzer, Clippy, etc.) in separate repositories that must integrate with the main rust-lang/rust repo. After experiencing pain with git submodules (poor ergonomics, no atomic cross-repo changes) and git subtrees (prohibitively slow for large repos), the team adopted Josh — a Rust-written tool that performs fast, reversible algebraic filtering operations on git histories. Josh enables bidirectional subtree-style syncs that are orders of magnitude faster and produce cleaner history. The team also built josh-sync, a lightweight wrapper with reusable GitHub Actions workflows for automated periodic pulls. Josh is now used for Miri, Rust Analyzer, compiler-builtins, stdarch, and the Rust Compiler Development Guide, with plans to migrate remaining subprojects from git subtree.
