rust-lang/cargo · error · anyhow::Error

crate types can only be specified for libraries and example…

Error message

crate types can only be specified for libraries and example libraries.
Binaries, tests, and benchmarks are always the `bin` crate type

What it means

Thrown by override_rustc_crate_types after the single-unit check passed, but that unit's TargetKind is neither Lib nor ExampleLib. Binaries, tests, and benchmarks are always the `bin` crate type, so overriding crate types on them is meaningless and rejected.

Solutions

1. Apply --crate-type to the library target instead: `cargo rustc --lib --crate-type cdylib`.
2. Add a dedicated [lib] or [[example]] with crate-type = [...] in Cargo.toml rather than overriding a bin.
3. Drop the --crate-type flag if you actually want to build the existing bin/test/bench.

Example fix

# before
cargo rustc --bin myapp --crate-type cdylib
# after
cargo rustc --lib --crate-type cdylib

// Only lib/example-lib targets may receive crate-type overrides.
fn can_override_crate_type(kind: &TargetKind) -> bool {
    matches!(kind, TargetKind::Lib(_) | TargetKind::ExampleLib(_))
}

When it happens

Trigger: Running `cargo rustc --crate-type cdylib --bin myapp` (or --test, --bench), i.e. requesting a crate-type override on a non-library target.

Common situations: Misunderstanding that only libraries and example libraries are crate-type overridable; trying to produce a cdylib from a binary target instead of a lib target.

Related errors

• crate types to rustc can only be passed to one target…
• malformed output when learning about crate-type
• cannot compile ` ` as the target ` ` does not support any…
• cannot mix `proc-macro` crate type with others
• cannot produce for ` ` as the target ` ` does not support…

AI-assisted analysis of rust-lang/cargo@495c385d08 (2026-08-11). Data as JSON: /api/errors/a419934aa0a19518. Report an issue: GitHub.

Appendix: source

Thrown at src/ops/cargo_compile/mod.rs:1184

            unit.profile.clone(),
            unit.kind,
            unit.mode,
            unit.features.clone(),
            unit.rustflags.clone(),
            unit.rustdocflags.clone(),
            unit.links_overrides.clone(),
            unit.is_std,
            unit.dep_hash,
            unit.artifact,
            unit.artifact_target_for_features,
            unit.skip_non_compile_time_dep,
        )
    };
    units[0] = match unit.target.kind() {
        TargetKind::Lib(_) => override_unit(TargetKind::Lib),
        TargetKind::ExampleLib(_) => override_unit(TargetKind::ExampleLib),
        _ => {
            anyhow::bail!(
                "crate types can only be specified for libraries and example libraries.\n\
                Binaries, tests, and benchmarks are always the `bin` crate type"
            );
        }
    };

    Ok(())
}

/// Gets all of the features enabled for a package, plus its dependencies'
/// features.
///
/// Dependencies are added as `dep_name/feat_name` because `required-features`
/// wants to support that syntax.
pub fn resolve_all_features(
    resolve_with_overrides: &Resolve,
    resolved_features: &features::ResolvedFeatures,
    package_set: &PackageSet<'_>,

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