[scala-reflect] arguments get replaced with null in MethodMirror.apply when there are both implicit and non-implicit parameters

[John Sullivan]

Good morning everyone and happy MLK day!

I seem to have found a bug in scala-reflect - when invoking apply on a MethodMirror, I end up getting a null where I have supplied a non-null value.

Here is some sample code. You can see I get a null where I should get a B(7):

object Test extends App {

  object a {

    case class B(i: Int)

    implicit class C(val i: Int) extends AnyVal

    case class D(b: B, c: C)

  }

  import a._

  import scala.reflect.runtime.currentMirror

  import scala.reflect.runtime.universe._

  val tpe = typeOf[D]

  val classSymbol: ClassSymbol = tpe.typeSymbol.asClass

  val moduleSymbol: ModuleSymbol = classSymbol.companion.asModule

  val moduleMirror: ModuleMirror = currentMirror.reflectModule(moduleSymbol)

  val moduleInstance: Any = moduleMirror.instance

  val instanceMirror = currentMirror.reflect(moduleInstance)

  val typeSignature = instanceMirror.symbol.typeSignature

  val applyMethod = typeSignature.member(TermName("apply")).asMethod

  val applyMirror = instanceMirror.reflectMethod(applyMethod)

  val applyResult = applyMirror(B(7), new C(8))

  println(applyResult)

  // output is D(null,Test$a$C@8)

  // the null seems to be due to a fall-through at line 433 of JavaMirrors.scala

}

This seems to happen whenever I have a MethodMirror with both implicit and non-implicit parameters. I am not familiar with this code at all, but to me it seems like an "else args1(i) = arg" is missing just below line 433 of JavaMirrors.scala.

This test was run against Scala 2.11.5, but I got the same results against 2.11.2, 2.11.3, and 2.11.4. I tried against 2.10 as well, but the API has changed a lot and I would have had to refactor to get it to compile there.

If you like I can submit a bug report.

Thanks! -John

[Som Snytt]

Your fix fixes it. It's the AnyVal that sends it down that code path.

I bet they would appreciate a Jira issue.

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[John Sullivan]

Thanks som-snytt. I'll file a bug tomorrow if I don't hear anything further. Best, John

[John Sullivan]

Sorry for noise, just wanted to follow up with link to created issue: https://issues.scala-lang.org/browse/SI-9102

Thanks!