src/test/ui/feature-gate/allow-features.stderr

   1 error[E0725]: the feature `unknown_stdlib_feature` is not in the list of allowed features
   2   --> $DIR/allow-features.rs:6:12
   3    |
   4 LL | #![feature(unknown_stdlib_feature)]
   5    |            ^^^^^^^^^^^^^^^^^^^^^^
   6
   7 error: aborting due to previous error
   8
   9 For more information about this error, try `rustc --explain E0725`.