error[E0658]: use of unstable library feature 'unstable_test_feature'
  --> $DIR/allowed-through-unstable.rs:9:5
   |
LL | use allowed_through_unstable_core::unstable_module::NewStableTraitNotAllowedThroughUnstable;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #1 <https://github.com/rust-lang/rust/issues/1> for more information
   = help: add `#![feature(unstable_test_feature)]` to the crate attributes to enable

error: aborting due to previous error

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