Nested Switch infers additional undefined on return type. #23281

const foo = (a: 1 | 2 | 3): 'a' | 'b' | 'c' => { // <- Errors here with: Function lacks ending return statement and return type does not include 'undefined'.
  switch (a) {
    case 1:
      return 'a'
    default:
      switch (a) {
        case 2:
          return 'b'
        case 3:
          return 'c'
      }
  }
}

const foo = (a: 1 | 2 | 3): 'a' | 'b' | 'c' => { // No error
  switch (a) {
    case 1:
      return 'a'
    default:
          return (() => {
              switch (a) {
                  case 2:
                      return 'b'
                  case 3:
                      return 'c'
              }
          })()
  }
}