I hope the type checker to report an error when I call a function which return never.

[zhuobinggang]

For example:

class OpenBox implements Box{
  open(): never{
    throw "No I should not call this method"
  }
  close(): CloseBox{
    return new CloseBox();
  }
}

new OpenBox().open() // I want the type checker to report an error.

[DanielRosenwasser]

It's no more of an error to call a never-returning function than it is to write a throw statement.

Maybe what you're requesting is that we report an error on unreachable code following that statement, but that's a design limitation (see #33622).