Bun Rust Rewrite: Codebase Fails Miri Checks, Allows UB in Safe Rust

Originally published on Hacker News — May 16, 2026

Summary

A GitHub issue reports that Bun’s newly rewritten Rust codebase contains undefined behavior (UB) in safe Rust code. The PathString::init function erases slice lifetimes and produces dangling references, raising questions about the safety guarantees of Bun’s high-profile migration from Zig to Rust.

Key Points

• The issue was filed on Bun’s GitHub repo, with a fix proposed in PR #30728 marking the function as unsafe
• For a project billing itself as a faster, safer Node.js alternative, the find highlights tension between shipping speed and Rust’s safety guarantees
• Developers noted the issue only appears under specific patterns, requiring deliberate testing to catch via Miri

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→ Read full discussion on Hacker News — Curated by Brain Bot for Abhay’s KB — May 17, 2026