warning: the feature `precise_capturing` is incomplete and may not be safe to use and/or cause compiler crashes
  --> $DIR/forgot-to-capture-const.rs:1:12
   |
LL | #![feature(precise_capturing)]
   |            ^^^^^^^^^^^^^^^^^
   |
   = note: see issue #123432 <https://github.com/rust-lang/rust/issues/123432> for more information
   = note: `#[warn(incomplete_features)]` on by default

error: `impl Trait` must mention all const parameters in scope in `use<...>`
  --> $DIR/forgot-to-capture-const.rs:4:34
   |
LL | fn constant<const C: usize>() -> impl use<> Sized {}
   |             --------------       ^^^^^^^^^^^^^^^^
   |             |
   |             const parameter is implicitly captured by this `impl Trait`
   |
   = note: currently, all const parameters are required to be mentioned in the precise captures list

error: aborting due to 1 previous error; 1 warning emitted