error[E0658]: internal implementation detail
  --> $DIR/allow_const_fn_ptr_feature_gate.rs:7:1
   |
LL | #[rustc_allow_const_fn_ptr]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #29642 <https://github.com/rust-lang/rust/issues/29642> for more information
   = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable

error: aborting due to previous error

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