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
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error: aborting due to 1 previous error

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