Rules for 2nd constructor differ from Scala2

[liufengyun]

Dotty accepts the first two constructors, while they are rejected by Scala2:

class A(x: Int, y: Int) {
  def this() = {          // only Dotty
    this()
  }

  def this(x: Long) = {   // only Dotty
    this(x.toInt)
  }

  def this(a: Int) = {   // both Dotty & Scala2
    this(a, a)
  }
}

A related question: do we allow 2nd constructor for traits?

[liufengyun]

Clarified during the meeting: the checks are missing in Dotty.

As there is no known use case for 2nd constructors of traits, there is no need to support them now.