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# Error code E0264

An unknown external lang item was used.

Erroneous code example:

    #![allow(unused)]
    #![feature(lang_items)]
    #![allow(internal_features)]

    fn main() {
    extern "C" {
        #[lang = "cake"] // error: unknown external lang item: `cake`
        fn cake();
    }
    }

A list of available external lang items is available in `compiler/rustc_hir/src/weak_lang_items.rs`. Example:

    #![allow(unused)]
    #![feature(lang_items)]
    #![allow(internal_features)]

    fn main() {
    extern "C" {
        #[lang = "panic_impl"] // ok!
        fn cake();
    }
    }