error: unused implementer of `Critical` that must be used
  --> $DIR/must_use-trait.rs:21:5
   |
LL |     get_critical();
   |     ^^^^^^^^^^^^^^^
   |
note: lint level defined here
  --> $DIR/must_use-trait.rs:1:9
   |
LL | #![deny(unused_must_use)]
   |         ^^^^^^^^^^^^^^^

error: aborting due to previous error