A recent Hacker News post exposed a Rust codebase that fails even the most basic Miri checks, allowing Undefined Behavior in safe Rust. The offending snippet constructs a slice from a raw pointer after the underlying allocation has been dropped, triggering a dangling reference error flagged by Miri. Reviewers urged developers to stop relying on AI‑generated Rust.

The problematic function lives in src/main.rs line 97, where an unsafe block calls core::slice::from_raw_parts with a pointer lacking provenance. Miri reports the UB and prints a stack backtrace pointing to PathString::slice. The surrounding main routine allocates a boxed byte string, passes a reference to PathString::init, then drops the box before slicing, reproducing the bug.

Community members recommend replacing the unsafe conversion with a safe abstraction or ensuring the source data outlives any derived slices. The incident underscores that AI code generators still struggle with Rust’s strict safety guarantees, and hiring experienced Rust engineers remains essential for production‑grade projects. Ignoring these warnings could let subtle memory errors slip into released binaries.

The original poster also linked to the nightly Rust reference on undefined behavior, urging readers to consult the documentation before attempting similar patterns. As the Rust ecosystem matures, tooling like Miri provides a vital safety net, catching errors that the compiler’s borrow checker cannot. Developers should integrate such checks into CI pipelines to prevent regressions.