override modifier not allowed for abstract vars

[goshacodes]

Compiler version

3.3.0

Minimized code

This works in scala 2, but it doesn't in scala 3

trait X {
  var y: Int
}

trait Y extends X {
  override def y_=(x: Int) = ()
  override def y = 11
}

While this one is fine in both:

trait Y extends X {
  def y_=(x: Int) = ()
  def y = 11
}

Output

error overriding variable y in trait X of type Int;
  method y of type => Int cannot override a mutable variable

Also there is a problem with concrete vars:

Minimized code

This ones returns override modifier required to override concrete member:

trait X {
  var y: Int = 12
}

trait Y extends X {
  def y_=(x: Int) = ()
}

But when I add override modifier it gives another error mutable variable cannot be overridden|

trait Y extends X {
  override def y_=(x: Int) = ()
}

[bishabosha]

I would assume that this should behave like in Scala 2, as the spec for 2.13 reads:

A variable declaration var x: T is equivalent to the declarations of both a getter function x and a setter function x_=:

def x: T
def x_=(y: T): Unit

An implementation of a class may define a declared variable using a variable definition, or by defining the corresponding setter and getter methods.

therefore one would assume that var desugars to ordinary methods and so can be overridden

[odersky]

Yes, but it's not trivial. Maybe someone could look how it was done in Scala 2 and re-implement it for 3?

[som-snytt]

Relatedly #13019 (where the casual tweak was reverted)

[bishabosha]

lets also close this as duplicate of #13019