error[E0254]: the name `core` is defined multiple times --> $DIR/unresolved-extern-mod-suggestion.rs:2:5 | LL | extern crate core; | ------------------ previous import of the extern crate `core` here LL | use core; | ^^^^ `core` reimported here | = note: `core` must be defined only once in the type namespace of this module error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0254`.