Bug Archeology: Solving a decade-old Swift/C++ mystery with LLMs (samkhawase.com)

In a fascinating exploration of how Large Language Models (LLMs) can assist in debugging, a developer reflects on a decade-old bug encountered while developing the iOS music app, Juke. The bug, which emerged after an upgrade to iOS 11, prevented users from playing offline songs saved by the app due to an issue with the decryption process facilitated through a series of cross-language calls from Swift to C++. The debugging process was arduous, requiring multiple downgrades and upgrades of the iOS version to track down the problematic inout parameter in Swift, which had shifted in behavior after key changes in Swift 4.0 regarding memory exclusivity. In 2026, the developer revisited this haunting bug with the help of the AI model, Claude Opus. The LLM not only connected the dots regarding the changes in Swift's inout semantics that caused the issue but also suggested that the original approach’s reliance on direct pointer access had become outdated. This insight not only resolved the decade-long mystery but showcased the transformative potential of AI in software development, emphasizing the importance of rigorous documentation and underlining how LLMs could revolutionize debugging practices in the AI/ML community.