rust-errors

Use thiserror for libraries, where callers need typed error enums they can match on. Use anyhow for applications, where you only need to add context and report errors. Mixing is normal: libraries return typed errors and the app collects them into anyhow.

Use Result when an operation can fail in normal operation and the caller must decide. Use Option when absence is normal and carries no reason. Use panic only for violated invariants or programmer bugs that are not recoverable.

No, unwrap() on a reachable production path is a bug because it panics with no context. Prefer expect() with a message when a panic is genuinely justified, or return Result and propagate with ?. unwrap is fine in tests, benches, and examples.

Use anyhow's context() or with_context() methods to attach descriptive messages at boundaries. Prefer with_context with a closure when the message allocates, and include the failing value like a path or ID rather than generic strings.

Retry only transient failures with exponential backoff, jitter, and an attempt cap. You can hand-roll a loop with tokio sleep or use the backon crate with ExponentialBuilder and a when() predicate gated on your error's is_transient() classification.

Never retry permanent errors like 404s, validation failures, or auth errors, and avoid retrying non-idempotent operations without an idempotency key. Unbounded retries without a cap or timeout can turn a small failure into an outage.