Non Exhaustive Public Errors

RUST-NON-EXHAUSTIVE-PUBLIC-ERRORS

Summary

Mark public error enums non-exhaustive unless exhaustive matching is part of the contract. This preserves room for future integration, validation, or provider failures without needless downstream breakage.

Rule

Use #[non_exhaustive] for public error enums unless exhaustive matching is intentional.

Why

Public error enums often need new variants as integrations, validation, and provider behavior expand. #[non_exhaustive] preserves room to add variants without breaking downstream exhaustive matches unless exhaustive matching is the intended contract.

Helps

Helps libraries add future error cases without forcing every downstream match expression to break at the next release.

Limits

Use exhaustive error enums when callers must handle every case and the set is genuinely closed by the domain contract.

Agent Instruction

Use `#[non_exhaustive]` for public error enums unless exhaustive matching is intentional; integrations,
validation, and provider behavior often add variants over time.

Mechanisms

Add #[non_exhaustive] to public error enums or variants, provide accessor methods when useful, and document how callers should handle unknown future cases.