produce a compiler warning/error for a code block which goes as a first indentation region statement

[unkarjedy]

Consider the example below.
Note that f1 has an indentation region with a code block as a first statement.
IMO such syntax is quite misleading and it's easy to be confused.
Even if you use indentaion-based syntax f1 very much looks like a method definition with some badly-indented println(2) (like in f2)
It's especially easy to misread if there is a new line after the code block.
If such code exists in some project one could think that it's something wrong with the formatting and unindent println(2) breaking the semantics

object O:
  def f1(): Unit =
    {
      println(1)
    }

    println(2)

  def f2(): Unit =
  {
    println(3)
  }
    println(4)
  
  def f3(): Unit =
  {
    println(5)
  }
  println(6)

[odersky]

Not clear whether a warning is needed, and what the precise rules would be to emit it. In fact I doubt that one can come up with precise rules that are worth it. But I am keeping the issue open for a while to see whether we get suggested spec wordings that would hold up.