Reports class parameters that shadow a superclass var.

Example:

class Animal {
  var name: String = ""
}

class Cat(name: String = "") extends Animal {
  // Makes `name` a private[this] val, which shadows the var
  def usage = name
}

When extending a class with a non-private var, the user might expect that a class parameter of the subclass will override the var from the superclass, but in fact it will only shadow it. This may sometimes lead to non-trivial errors.

Please note that the highlight will appear only if the value is actually used.