How to deprecate a parameter with default value in Scala?

Question

In the metrics-scala library we have the following method:

def timer(name: String, scope: String = null): Timer

I want to deprecate the scope parameter and remove it from the next major version.

I tried this:

def timer(name: String): Timer
@deprecated(...)
def timer(name: String, scope: String): Timer

But that causes binary backward compatibility problems (see below *) already within the current major version.

I also tried this:

def timer(name: String, @deprecated(...) scope: String = null): Timer

But that gives warnings inside timer, and not for the caller of timer.

Did I miss something or is it really not possible to deprecate a parameter with default values?

(*) Mima report for option 1:

sbt:metrics4-scala-root> mimaReportBinaryIssues
[error]  * synthetic method timer$default$2()java.lang.String in class nl.grons.metrics4.scala.MetricBuilder does not have a correspondent in current version
[error]    filter with: ProblemFilters.exclude[DirectMissingMethodProblem]("nl.grons.metrics4.scala.MetricBuilder.timer$default$2")

Answer 1

I believe (but I don't have MiMa setup now to check) that you can use traits:

object Foo extends DeprecatedFoo {
  def timer(name: String): Unit = { println("called new shiny version") }
}

trait DeprecatedFoo {
  @deprecated("", "")
  def timer(name: String, scope: String = null) = { println("called bad old version")}
}

Foo.timer("xx") // calls new version
Foo.timer("xx", null) // calls old version and issues a warning:

The code compiled for old version would be doing invokevirtual Foo/timer(Ljava/lang/String;Ljava/lang/String;)Z, that would resolve to the old version too.