Static UNUSED_EXTERN_CRATES

pub static UNUSED_EXTERN_CRATES: &'static Lint

The unused_extern_crates lint guards against extern crate items that are never used.

Example

#![deny(unused_extern_crates)]
#![deny(warnings)]
extern crate proc_macro;

{{produces}}

Explanation

extern crate items that are unused have no effect and should be removed. Note that there are some cases where specifying an extern crate is desired for the side effect of ensuring the given crate is linked, even though it is not otherwise directly referenced. The lint can be silenced by aliasing the crate to an underscore, such as extern crate foo as _. Also note that it is no longer idiomatic to use extern crate in the 2018 edition, as extern crates are now automatically added in scope.

This lint is “allow” by default because it can be noisy, and produce false-positives. If a dependency is being removed from a project, it is recommended to remove it from the build configuration (such as Cargo.toml) to ensure stale build entries aren’t left behind.