error[E0658]: const generics are unstable
  --> $DIR/issue-60263.rs:1:16
   |
LL | struct B<const I: u8>;
   |                ^
   |
   = note: for more information, see https://github.com/rust-lang/rust/issues/44580
   = help: add `#![feature(const_generics)]` to the crate attributes to enable

error: aborting due to previous error

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