error[E0015]: cannot call non-const closure in constants
  --> $DIR/issue-102985.rs:6:14
   |
LL |         n => n(),
   |              ^^^
   |
   = note: closures need an RFC before allowed to be called in constants
   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
help: add `#![feature(effects)]` to the crate attributes to enable
   |
LL + #![feature(effects)]
   |

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0015`.