error[E0597]: `arg` does not live long enough
  --> $DIR/issue-74050-end-span.rs:5:19
   |
LL |     let _arg = match args.next() {
   |         ---- borrow later stored here
LL |         Some(arg) => {
LL |             match arg.to_str() {
   |                   ^^^^^^^^^^^^ borrowed value does not live long enough
...
LL |         }
   |         - `arg` dropped here while still borrowed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0597`.