warning: the feature `const_generics` is incomplete and may cause the compiler to crash
  --> $DIR/generic_params.rs:6:37
   |
LL | #![feature(decl_macro, rustc_attrs, const_generics)]
   |                                     ^^^^^^^^^^^^^^
   |
   = note: `#[warn(incomplete_features)]` on by default

warning: 1 warning emitted