Reflector: use companion object apply method

[shanielh]

even when constructors are available.

This is because companion.apply(...) in Scala has more power than secondary c'tors.

• Changed Reflector
• Added Test

Maintainers: I had to change reflector to lookup the type parameters by name and not by instance because the apply method in scala (that is generated for case classes) has different instances of type parameters than those of the class. That means that if someone will create Foo.apply[A](..) for case class Foo[B](..), it might not work. I can throw exception in that case, or whatever - Just let me know what you want, if you want this pull request 😄

[seratch]

Thanks, LGTM.

[shanielh]

Thanks for merging 🎊

[pwyczes]

Hi @shanielh - thanks for this PR. I think it is very valuable.

Unfortunately I have a suspicion, that it breaks Extraction.decompose() for the case, when case class is generic and apply() method in companion object has different signature than constructor of the case class.

Something like

object CaseClassWithCompanion {
  def apply[A](v: A): CaseClassWithCompanion[A] = CaseClassWithCompanion(v, "Bar")
}
case class CaseClassWithCompanion[A](value: A, other: String)

It throws

org.json4s.package$MappingException: Can't find constructor for CaseClassWithCompanion
	at org.json4s.reflect.package$.fail(package.scala:95)
	at org.json4s.reflect.ScalaSigReader$.$anonfun$readConstructor$3(ScalaSigReader.scala:21)
	at scala.Option.getOrElse(Option.scala:121)
	at org.json4s.reflect.ScalaSigReader$.readConstructor(ScalaSigReader.scala:21)
	at org.json4s.reflect.Reflector$ClassDescriptorBuilder.ctorParamType(Reflector.scala:93)
	at org.json4s.reflect.Reflector$ClassDescriptorBuilder.$anonfun$createConstructorDescriptors$6(Reflector.scala:153)
	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
	at scala.collection.mutable.ResizableArray.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ResizableArray.foreach$(ResizableArray.scala:52)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
	at scala.collection.TraversableLike.map(TraversableLike.scala:234)
	at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
	at scala.collection.AbstractTraversable.map(Traversable.scala:104)
	at org.json4s.reflect.Reflector$ClassDescriptorBuilder.$anonfun$createConstructorDescriptors$3(Reflector.scala:139)
	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
	at scala.collection.IndexedSeqOptimized.foreach(IndexedSeqOptimized.scala:32)
	at scala.collection.IndexedSeqOptimized.foreach$(IndexedSeqOptimized.scala:29)
	at scala.collection.mutable.WrappedArray.foreach(WrappedArray.scala:38)
	at scala.collection.TraversableLike.map(TraversableLike.scala:234)
	at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
	at scala.collection.AbstractTraversable.map(Traversable.scala:104)
	at org.json4s.reflect.Reflector$ClassDescriptorBuilder.createConstructorDescriptors(Reflector.scala:133)
	at org.json4s.reflect.Reflector$ClassDescriptorBuilder.constructorsAndCompanion(Reflector.scala:129)
	at org.json4s.reflect.Reflector$ClassDescriptorBuilder.result(Reflector.scala:180)
	at org.json4s.reflect.Reflector$.createDescriptor(Reflector.scala:53)
	at org.json4s.reflect.Reflector$.$anonfun$describe$1(Reflector.scala:48)
	at org.json4s.reflect.package$Memo.apply(package.scala:36)
	at org.json4s.reflect.Reflector$.describe(Reflector.scala:48)
	at org.json4s.Extraction$.decomposeObject$1(Extraction.scala:119)
	at org.json4s.Extraction$.internalDecomposeWithBuilder(Extraction.scala:230)
	at org.json4s.Extraction$.decomposeWithBuilder(Extraction.scala:65)
	at org.json4s.Extraction$.decompose(Extraction.scala:244)
	at org.json4s.ExtractionBugs.$anonfun$new$101(ExtractionBugs.scala:299)
	at org.specs2.matcher.MatchResult$$anon$12.$anonfun$asResult$1(MatchResult.scala:344)
	at org.specs2.execute.ResultExecution.execute(ResultExecution.scala:23)
	at org.specs2.execute.ResultExecution.execute$(ResultExecution.scala:21)
	at org.specs2.execute.ResultExecution$.execute(ResultExecution.scala:118)
	at org.specs2.execute.Result$$anon$11.asResult(Result.scala:246)
	at org.specs2.execute.AsResult$.apply(AsResult.scala:32)
	at org.specs2.matcher.MatchResult$$anon$12.asResult(MatchResult.scala:344)
	at org.specs2.execute.AsResult$.apply(AsResult.scala:32)
	at org.specs2.specification.core.AsExecution$$anon$1.$anonfun$execute$1(AsExecution.scala:15)
	at org.specs2.execute.ResultExecution.execute(ResultExecution.scala:23)
	at org.specs2.execute.ResultExecution.execute$(ResultExecution.scala:21)
	at org.specs2.execute.ResultExecution$.execute(ResultExecution.scala:118)
	at org.specs2.execute.Result$$anon$11.asResult(Result.scala:246)
	at org.specs2.execute.AsResult$.apply(AsResult.scala:32)
	at org.specs2.execute.AsResult$.$anonfun$safely$1(AsResult.scala:40)
	at org.specs2.execute.ResultExecution.execute(ResultExecution.scala:23)
	at org.specs2.execute.ResultExecution.execute$(ResultExecution.scala:21)
	at org.specs2.execute.ResultExecution$.execute(ResultExecution.scala:118)
	at org.specs2.execute.AsResult$.safely(AsResult.scala:40)
	at org.specs2.specification.core.Execution$.$anonfun$result$1(Execution.scala:305)
	at org.specs2.specification.core.Execution$.$anonfun$withEnvSync$3(Execution.scala:323)
	at org.specs2.execute.ResultExecution.execute(ResultExecution.scala:23)
	at org.specs2.execute.ResultExecution.execute$(ResultExecution.scala:21)
	at org.specs2.execute.ResultExecution$.execute(ResultExecution.scala:118)
	at org.specs2.execute.Result$$anon$11.asResult(Result.scala:246)
	at org.specs2.execute.AsResult$.apply(AsResult.scala:32)
	at org.specs2.execute.AsResult$.$anonfun$safely$1(AsResult.scala:40)
	at org.specs2.execute.ResultExecution.execute(ResultExecution.scala:23)
	at org.specs2.execute.ResultExecution.execute$(ResultExecution.scala:21)
	at org.specs2.execute.ResultExecution$.execute(ResultExecution.scala:118)
	at org.specs2.execute.AsResult$.safely(AsResult.scala:40)
	at org.specs2.specification.core.Execution$.$anonfun$withEnvSync$2(Execution.scala:323)
	at org.specs2.specification.core.Execution.$anonfun$startExecution$3(Execution.scala:135)
	at scala.util.Success.$anonfun$map$1(Try.scala:251)
	at scala.util.Success.map(Try.scala:209)
	at scala.concurrent.Future.$anonfun$map$1(Future.scala:289)
	at scala.concurrent.impl.Promise.liftedTree1$1(Promise.scala:29)
	at scala.concurrent.impl.Promise.$anonfun$transform$1(Promise.scala:29)
	at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)

Do you think that this is a small fix, or maybe I should create another issue for this case?

[shanielh]

@eventuallyinconsistent Hi! I created a test case which doesn't seem to work as you told. I'll try to figure out what's wrong with it in the weekend. You should open an issue for this case 👍

[pwyczes]

Thank you @shanielh :)
I created an issue: #507