error[E0618]: expected function, found `S`
  --> $DIR/issue-80853.rs:4:5
   |
LL | fn repro_ref(thing: S) {
   |              ----- `thing` has type `S`
LL |     thing();
   |     ^^^^^--
   |     |
   |     call expression requires function

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0618`.