error[E0658]: use of unstable library feature 'unicode_internals'
  --> $DIR/accidental-stable-in-unstable.rs:6:5
   |
LL | use core::unicode::UNICODE_VERSION;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: add `#![feature(unicode_internals)]` to the crate attributes to enable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.