src/test/ui/feature-gate-fundamental.stderr

error: the `#[fundamental]` attribute is an experimental feature (see issue #29635)
  --> $DIR/feature-gate-fundamental.rs:11:1
   |
11 | #[fundamental] //~ ERROR the `#[fundamental]` attribute is an experimental feature
   | ^^^^^^^^^^^^^^
   |
   = help: add #![feature(fundamental)] to the crate attributes to enable

error: aborting due to previous error