never-example.tsx

type Never<T> = { [P in keyof T]?: never };

interface ControlledProps {
  open: boolean;
  toggle: () => void;
}

interface UnControlledProps {
  defaultOpen: boolean;
}

type ExpandableProps =
  | (ControlledProps & Never<UnControlledProps>)
  | (UnControlledProps & Never<ControlledProps>);

const Expandable: React.FC<ExpandableProps> = props => {
  // Expandable can now take either open + toggle OR defaultOpe
};

const Usage = () => {
  const [open, setOpen] = React.useState(false);

  return (
    <>
      <Expandable defaultOpen={false} />
      <Expandable open={open} toggle={() => setOpen(!open)} />
      {/* The one below this line will error */}
      <Expandable defaultOpen={false} open={true} />
    </>
  );
};