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(); } }