error[E0658]: the `#[rustc_variance]` attribute is just used for rustc unit tests and will never be stable (see issue #29642)
  --> $DIR/feature-gate-rustc-attrs.rs:15:1
   |
LL | #[rustc_variance] //~ ERROR the `#[rustc_variance]` attribute is just used for rustc unit tests and will never be stable
   | ^^^^^^^^^^^^^^^^^
   |
   = help: add #![feature(rustc_attrs)] to the crate attributes to enable

error[E0658]: the `#[rustc_error]` attribute is just used for rustc unit tests and will never be stable (see issue #29642)
  --> $DIR/feature-gate-rustc-attrs.rs:16:1
   |
LL | #[rustc_error] //~ ERROR the `#[rustc_error]` attribute is just used for rustc unit tests and will never be stable
   | ^^^^^^^^^^^^^^
   |
   = help: add #![feature(rustc_attrs)] to the crate attributes to enable

error[E0658]: unless otherwise specified, attributes with the prefix `rustc_` are reserved for internal compiler diagnostics (see issue #29642)
  --> $DIR/feature-gate-rustc-attrs.rs:17:1
   |
LL | #[rustc_foo]
   | ^^^^^^^^^^^^
   |
   = help: add #![feature(rustc_attrs)] to the crate attributes to enable

error: aborting due to 3 previous errors

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