error: macro-expanded `extern crate` items cannot shadow names passed with `--extern` --> $DIR/ice-6255.rs:6:9 | LL | extern crate std as core; | ^^^^^^^^^^^^^^^^^^^^^^^^^ ... LL | define_other_core!(); | -------------------- in this macro invocation | = note: this error originates in the macro `define_other_core` (in Nightly builds, run with -Z macro-backtrace for more info) error: aborting due to 1 previous error