Swift Diagnostics
Systematic debugging workflows for iOS/macOS development. These patterns help identify root causes in minutes rather than hours by following structured diagnostic approaches.
Reference Loading Guide
ALWAYS load reference files if there is even a small chance the content may be required. It's better to have the context than to miss a pattern or make a mistake.
| Reference | Load When |
|---|---|
| Navigation | NavigationStack not responding, unexpected pops, deep link failures |
| Build Issues | SPM resolution, "No such module", dependency conflicts |
| Memory | Retain cycles, memory growth, deinit not called |
| Build Performance | Slow builds, Derived Data issues, Xcode hangs |
| Xcode Debugging | LLDB commands, breakpoints, view debugging |
Core Workflow
- Identify symptom category - Navigation, build, memory, or performance
- Load the relevant reference - Each has diagnostic decision trees
- Run mandatory first checks - Before changing any code
- Follow the decision tree - Reach diagnosis in 2-5 minutes
- Apply fix and verify - One fix at a time, test each
Key Principle
80% of "mysterious" issues stem from predictable patterns:
- Navigation: Path state management or destination placement
- Build: Stale caches or dependency resolution
- Memory: Timer/observer leaks or closure captures
- Performance: Environment problems, not code bugs
Diagnose systematically. Never guess.
Common Mistakes
- Skipping mandatory first checks — Jumping straight to code changes before running diagnostics (clean build, restart simulator, restart Xcode) means you'll chase ghosts. Always start with the mandatory checks.
- Changing multiple things at once — "Let me delete DerivedData AND restart simulator AND kill Xcode" means you can't isolate which fix actually worked. Change one variable at a time.
- Assuming you know the cause — "NavigationStack stopped working, must be my reducer" — actually it was stale DerivedData. Diagnostic trees prevent assumptions. Follow the tree, don't guess.
- Missing memory basics — Calling
deinitnot being called is a retain cycle, but beginners often blame architecture. Use Instruments to verify leaks before refactoring. Data, not intuition. - Not isolating the problem — Testing with your whole app complicates diagnosis. Create a minimal reproducible example with just the problematic feature. Isolation reveals root causes.