flutter-error-handling
Implement functional error recovery with Either/Failure patterns in Flutter. Use when writing repositories, handling exceptions, or using dartz Either types.
What this skill does
# Error Handling
## **Priority: P1 (HIGH)**
## Implementation Workflow
1. **Define failures** — Create domain-specific failures using `@freezed` unions (e.g., `UnauthorizedFailure`, `OutOfStockFailure`).
2. **Return Either** — Repositories return `Either<Failure, T>`. No exceptions in UI/BLoC.
3. **Catch in Infrastructure only** — Infrastructure catches exceptions (e.g., `DioException`) and returns `Left(Failure)`. Never rethrow to UI.
4. **Fold in BLoC** — Use `.fold(failure, success)` in BLoC to emit corresponding states. Remove try/catch from BLoC.
5. **Localize messages** — Use `failure.failureMessage` (returns `TRObject` or localized string) for UI-safe text.
6. **Log with stable templates** — Use low-cardinality message templates; pass variable data via metadata/context.
7. **No Silent Catch**: Never swallow errors without logging or documented retry.
8. **Crashlytics Routing**: All UI/BLoC `catch` blocks MUST route errors via `AppLogger.error(AppException.fromException(e).message, error: e, stackTrace: st)` for observability and type-safe UI messages.
### Repository & BLoC Examples
See [implementation examples](references/implementation.md) for repository error mapping and BLoC consumption patterns.
## Reference & Examples
For Failure definitions and API error mapping:
See [references/REFERENCE.md](references/REFERENCE.md).
## Anti-Patterns
- **No Try-Catch in BLoC**: BLoC receives `Either` and `folds`; try/catch belongs in Infrastructure
- **No Plain String Failures**: Define typed `@freezed` Failure subclasses instead of `Left('Something went wrong')`
- **No Empty Catch Blocks**: Always log and propagate; never swallow errors silently
- **No Repositories Throwing Status**: Return `Left(Failure)` instead of throwing `Exception`
- **No Missing Log Registration**: Use `AppLogger.error` in BLoC/UI `catch` to ensure Crashlytics tracking and type-safe UI messages
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