error[E0573]: expected type, found const parameter `C`
  --> $DIR/struct-with-invalid-const-param.rs:4:23
   |
LL | struct S<const C: u8>(C);
   |                       ^ not a type

warning: the feature `const_generics` is incomplete and may not be safe to use and/or cause compiler crashes
  --> $DIR/struct-with-invalid-const-param.rs:1:12
   |
LL | #![feature(const_generics)]
   |            ^^^^^^^^^^^^^^
   |
   = note: `#[warn(incomplete_features)]` on by default
   = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information

error: aborting due to previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0573`.