rustc::lint::builtin::UNKNOWN_CRATE_TYPES

pub static UNKNOWN_CRATE_TYPES: &'static Lint = &::rustc::lint::Lint{name: "UNKNOWN_CRATE_TYPES",
                     default_level: ::rustc::lint::Deny,
                     desc:
                         "unknown crate type found in #[crate_type] directive",}

Unstable (rustc_private)