Overzealous warning from scala compiler: Auto-application to `()` is deprecated

Question
1

I’m copying this message here from discord, as it may need additional discussion and reflection.

Can someone help me understand this compiler warning.

[warn] /Users/jnewton/Repos/regular-type-expression/cl-robdd-scala/src/test/scala/bdd/BddTestSuite.scala:93:36: Auto-application to `()` is deprecated. Supply the empty argument list `()` explicitly to invoke method size,
[warn] or remove the empty argument list from its definition (Java-defined methods are exempt).
[warn] In Scala 3, an unapplied method like this will be eta-expanded into a function.
[warn]           case _: BddTerm => assert(bdd.size() == 1)
[warn]                                    ^

Is this really a warning, telling me to do what I’m already doing? or is it rather just an info message and should not be a warning at all? Or am I reading the message wrong?

Is the message telling me to omit the () or to keep them there?

I’m confused.

Here is the offending code

  def genSamples(): Set[Bdd] = {
    ...
  }

  test("size") {
    withNewBddHash {

      val samples = genSamples()

      for (bdd <- samples) {
        bdd match {
          case _: BddTerm => assert(bdd.size() == 1)
          case b: BddNode => assert(bdd.size() <= 1 + b.positive.size() + b.negative.size()) // maybe less because some nodes or terms might be shared
        }
      }
    }
  }

The size method is indeed defined using parens ()

sealed abstract class Bdd {
  ...
  
  def size():Int = {
    ...
  }
...
}