Swift 5.9 Backtraces and Debugging
Article Summary
Alastair Houghton from Apple's Swift runtime team just dropped a game-changer for debugging: Swift 5.9 now catches crashes and lets you inspect them interactively before your program dies.
Swift 5.9 introduces a sophisticated out-of-process crash handler that transforms cryptic segfaults into readable, interactive debugging sessions. The feature is particularly powerful on Linux (where it's enabled by default) but also works on macOS with manual configuration.
Key Takeaways
- Crashes now show source code context with exact line highlighting, not just stack traces
- 30-second interactive window lets you attach debugger or inspect memory before program exits
- Async/await backtraces correctly follow concurrency chains, not just physical stack frames
- Auto-skips system frames and thunks, showing only relevant application code
- Configure via SWIFT_BACKTRACE environment variable for CI/automated environments
Critical Insight
Swift 5.9's crash handler turns opaque segfaults into readable, interactive debugging sessions with source context and concurrency-aware backtraces.
