Dark Clouds Over Bun’s Rust Migration? Undefined Behavior Exposed Due to Miri Check Failures

📰 News Summary

• Miri Check Failure: The rewritten Rust codebase for Bun has been flagged by the Rust memory safety tool, “Miri,” for detecting Undefined Behavior (UB).
• Critical Memory Bug: A “dangling reference” was identified in src/main.rs, constructed without a valid pointer provenance.
• Wake-Up Call for AI Coding: The reporter emphasized that “AI isn’t great at writing Rust” and suggested halting AI-driven “vibe coding” in favor of hiring professional Rust engineers.

💡 Key Points

• Implementation mistakes within unsafe blocks using core::slice::from_raw_parts are causing Undefined Behavior, even in safe Rust code.
• A typical “Use-after-free” behavior was illustrated in a code example, where a slice was referenced after the data it pointed to had been dropped.

🦈 Shark’s Eye (Curator’s Perspective)

This is shocking news! It’s a reality check that migrating to Rust doesn’t magically make everything safe! The bug this time stems from unsafe operations that disregard the strict management of pointer provenance that Rust enforces. The reporter’s term “vibe coding” is a biting commentary on how AI-generated code, while plausible-sounding, lacks the rigor necessary for real-world applications! If you’re going to bypass Rust’s type system with unsafe, Miri verification is still an absolutely essential process in 2026!

🚀 What’s Next?

The development team of Bun will likely have to significantly enhance their verification process for AI-generated code. Particularly for Rust code involving low-level memory operations, automated Miri checks integrated into CI and comprehensive code reviews by human experts will become more crucial than ever.

💬 A Word from Haru-Same

AI is handy, but it still can’t pull off the unsafe tricks to fool Rust’s borrow checker like a seasoned human can. To navigate these safe waters, you definitely need the keen eye of a skilled shark (engineer)! 🦈🔥

📚 Terminology Explanation

• Miri: An interpreter that executes Rust’s MIR (Mid-level Intermediate Representation), detecting memory leaks and Undefined Behavior (UB). It’s like a guardian angel for Rust development.

• Undefined Behavior (UB): A state where a program breaks the language’s rules, leading to unpredictable behavior (crashes or vulnerabilities).

• Provenance: The concept of where a pointer originates in memory allocation. If this is incorrect, even if the memory address is right, it can be seen as an illegal access.

• Source: Bun Rust rewrite: “codebase fails basic miri checks, allows for UB in safe rust”