error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants
  --> $DIR/issue-43105.rs:3:17
   |
LL | const NUM: u8 = xyz();
   |                 ^^^^^

error: any use of this value will cause an error
  --> $DIR/issue-43105.rs:3:17
   |
LL | const NUM: u8 = xyz();
   | ----------------^^^^^-
   |                 |
   |                 calling non-const function `xyz`
   |
   = note: `#[deny(const_err)]` on by default

error: could not evaluate constant pattern
  --> $DIR/issue-43105.rs:9:9
   |
LL |         NUM => unimplemented!(),
   |         ^^^

error: aborting due to 3 previous errors

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