function-forms.ts:38:3 - error SC1090: functions with optional or defaulted parameters as values, except where the target type spells the completed signature with required parameters (a '(x?: T) => R' function flows into a '(x: T | undefined) => R' slot, and a package/'any' slot takes any signature that can cross the island boundary; otherwise call the function directly) are not supported yet

  37 | function outer(): number {
  38 |   function inner(n = 2): number {
     |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  39 |     return n;