error: generic parameters may not be used in const operations
  --> $DIR/issue-61747.rs:7:30
   |
LL |     fn successor() -> Const<{C + 1}> {
   |                              ^ cannot perform const operation using `C`
   |
   = help: const parameters may only be used as standalone arguments, i.e. `C`
   = help: use `#![feature(const_generics)]` and `#![feature(const_evaluatable_checked)]` to allow generic const expressions

error: aborting due to previous error