escape-hatch-variant

Level: warn · Article: Errors

Granular enough to make different decisions. If two errors require identical handling, they’re the same type. If they require different recovery strategies, split them.

What it checks

An enum whose name ends in Error with a variant named Other, Unknown, Custom, Internal, Generic, Misc or Unexpected, holding a String, a boxed error, or nothing.

Don’t

#![allow(unused)]
fn main() {
enum PaymentError {
    CardDeclined { reason: DeclineReason },
    Other(String),
}
}

Six months later Other carries network timeouts, a provider outage, a currency mismatch and a typo. The retry logic matches on CardDeclined and guesses at everything else.

Do

#![allow(unused)]
fn main() {
enum PaymentError {
    CardDeclined {
        reason: DeclineReason,
    },
    CurrencyMismatch {
        expected: Currency,
        got: Currency,
    },
    Provider {
        retry_after: Option<Duration>,
        #[source]
        source: ProviderError,
    },
}
}

Each variant is a decision the caller can make. Adding a failure mode means adding a variant, and the compiler finds every match that has to decide about it.

Options

[naming]
escape-hatch-variants = ["Custom", "Generic", "Internal", "Misc", "Other", "Unexpected", "Unknown"]

Silence it

#![allow(unused)]
fn main() {
// rabot: allow(escape-hatch-variant) FFI boundary: the C library reports free-form strings we cannot classify
}