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 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to the crate attributes to enable = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0658`.