Rust errors / Attributes, macros and features
Rust compiler error · checked with rustc 1.99.0
Rust error E0522: definition of an unknown lang item: `cookie`
What it meansThe lang attribute was used in an invalid context.
What rustc prints
error[E0522]: definition of an unknown lang item: `cookie`
--> main.rs:3:1
|
3 | #[lang = "cookie"]
| ^^^^^^^^^^^^^^^^^^ definition of unknown lang item `cookie`Real output of rustc 1.99.0 compiling the official example below (2021 edition). Your names and line numbers will differ; the first line is the part to match.
The compiler team's explanation
The lang attribute was used in an invalid context.
Erroneous code example:
#![feature(lang_items)]
#[lang = "cookie"]
fn cookie() -> ! { // error: definition of an unknown lang item: `cookie`
loop {}
}The lang attribute is intended for marking special items that are built-in to Rust itself. This includes special traits (like Copy and Sized) that affect how the compiler behaves, as well as special functions that may be automatically invoked (such as the handler for out-of-bounds accesses when indexing a slice).
From rustc --explain E0522 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.
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