Future incompatibility report: Future breakage diagnostic:
warning: this function depends on never type fallback being `()`
  --> $DIR/defaulted-never-note.rs:38:1
   |
LL | fn main() {
   | ^^^^^^^^^
   |
   = help: specify the types explicitly
note: in edition 2024, the requirement `!: OnlyUnit` will fail
  --> $DIR/defaulted-never-note.rs:40:19
   |
LL |     requires_unit(x);
   |                   ^
help: use `()` annotations to avoid fallback changes
   |
LL |     let x: () = return;
   |          ++++

