Error code E0259

The name chosen for an external crate conflicts with another external crate that has been imported into the current module.

Erroneous code example:

extern crate core;
extern crate std as core;

fn main() {}

The solution is to choose a different name that doesn't conflict with any external crate imported into the current module.

Correct example:

extern crate core;
extern crate std as other_name;

fn main() {}