rust-lang/rust · error

this deprecation is always in effect; {since:?}

Error message

this deprecation is always in effect; {since:?}

What it means

This `unreachable!` fires in `deprecated_since_kind` when a deprecation's `since` field is `NonStandard`, `Unspecified`, or `Err` yet `is_in_effect` returned `false`. Those three `DeprecatedSince` variants *mean* the deprecation is always in effect, so the function should have taken the `DeprecatedSinceKind::InEffect` branch at stability.rs:171 and never reached the match on `since`. Hitting it indicates a contradictory `Deprecation` value — the `since` field and `is_in_effect()` disagree — produced upstream by stability-attribute decoding/HIR processing.

Source

Thrown at compiler/rustc_middle/src/middle/stability.rs:181

            diag.subdiagnostic(sub);
        }
        diag
    }
}

fn deprecated_since_kind(is_in_effect: bool, since: DeprecatedSince) -> DeprecatedSinceKind {
    if is_in_effect {
        DeprecatedSinceKind::InEffect
    } else {
        match since {
            DeprecatedSince::RustcVersion(version) => {
                DeprecatedSinceKind::InVersion(version.to_string())
            }
            DeprecatedSince::Future => DeprecatedSinceKind::InFuture,
            DeprecatedSince::NonStandard(_)
            | DeprecatedSince::Unspecified
            | DeprecatedSince::Err => {
                unreachable!("this deprecation is always in effect; {since:?}")
            }
        }
    }
}

pub fn early_report_macro_deprecation(
    lint_buffer: &mut LintBuffer,
    depr: &Deprecation,
    suggestion_span: Span,
    node_id: NodeId,
    path: String,
) {
    if suggestion_span.in_derive_expansion() {
        return;
    }

    let is_in_effect = depr.is_in_effect();
    let suggestion = depr.suggestion;

View on GitHub (pinned to 22057b88b0)

Solutions

1. Inspect the offending crate's `#[deprecated(since = "...")]` attribute and supply a valid SemVer/RustcVersion string or remove the attribute.
2. If reproducing from metadata, force a clean rebuild (`cargo clean`) to regenerate rmeta so stale stability data does not survive a toolchain change.
3. File an ICE report against rustc including the attribute text and the `since` value from the panic message; this path is meant to be unreachable.
4. For rustc hackers: audit the function populating `Deprecation.since` to ensure it sets `is_in_effect=true` for NonStandard/Unspecified/Err.

Example fix

// before
#[deprecated(since = "??", note = "x")]
// (decodes to DeprecatedSince::Err with is_in_effect == false → unreachable!)

// after
#[deprecated(since = "1.65.0", note = "x")]

// deprecated_since_kind is unreachable when is_in_effect == false AND since is
// NonStandard | Unspecified | Err. Reject that combination before relying on it.
fn deprecation_kind_safe(is_in_effect: bool, since: &DeprecatedSince) -> bool {
    if is_in_effect {
        return true; // any `since` is fine
    }
    matches!(
        since,
        DeprecatedSince::RustcVersion(_) | DeprecatedSince::Future
    )
}

if !deprecation_kind_safe(is_in_effect, &since) {
    // Either force is_in_effect=true, or repair `since` to a concrete version.
    return Err("deprecation not in effect and `since` carries no version");
}

let kind = std::panic::catch_unwind(|| deprecated_since_kind(is_in_effect, since.clone()));
match kind {
    Ok(k) => /* use k */,
    Err(_) => /* fall back to treating the item as deprecated-now */,
}

When it happens

Trigger: Decoding a `#[deprecated(since = ...)]` attribute whose `since` value resolves to `NonStandard(s)`, `Unspecified`, or `Err` while `Deprecation::is_in_effect()` simultaneously returns false. Concretely: a corrupted rmeta/crate metadata block for a stability attribute, a hand-constructed `Deprecation` struct in tests/fuzzers, or a regression in `rustc_ast::decode` / the stability query that miscomputes `is_in_effect`.

Common situations: Fuzzing the compiler with malformed `#[deprecated]` attributes; cross-version rmeta incompatibilities after a stability-query refactor; crates built with mismatched std/core stability metadata; custom rustc forks that altered `DeprecatedSince` encoding.

Related errors

• invalid level/lint_id combination
• there must be provenance somewhere here
• statics should not have generic parameters
• layout decided on a larger discriminant type ({min_ity:?}) t
• encountered a non-arbitrary layout during enum layout

AI-assisted analysis of rust-lang/rust@22057b88b0 (2026-08-03). Data as JSON: /data/errors/63581b6cfeac23bc.json. Report an issue: GitHub.