E0110: Misplaced ?

f()? returns early with the error (or the empty Option) and is otherwise the value. It must end its own statement (x := f()?, return f()?, f()?), can't be in an if/for/switch header, and needs the function to return what it passes on: an error last or a Result for errors, an Option for an Option.

Wrong

func parse(s string) int {
	n := strconv.Atoi(s)?
	return n
}

Right

func parse(s string) (int, error) {
	n := strconv.Atoi(s)?
	return n, nil
}