Any and Nothing fail with play-json in Scala 2.13

[nehaev]

Any and Nothing fail on Json.reads macro for case classes with more than one param. On Scala 2.12 same code compiles fine.

Build settings:

scalaVersion := "2.13.0"
libraryDependencies += "com.typesafe.play" %% "play-json" % "2.7.4"
wartremoverErrors in (Compile, compile) ++= Warts.all

Example code:

import play.api.libs.json._

final case class Greeting(id: Long, greeting: String)

object Greeting {
  implicit val reads: Reads[Greeting] = Json.reads[Greeting]
}

Error:

[error] [wartremover:Any] Inferred type containing Any
[error]   implicit val reads: Reads[Greeting] = Json.reads[Greeting]
[error]                                                   ^

Output of -Xprint:typer for the part which is presumably responsible for this:

scala 2.13: val underlying: play.api.libs.json.Reads[example.Greeting] = play.api.libs.functional.syntax.`package`.toFunctionalBuilderOps[play.api.libs.json.Reads, Long](play.api.libs.json.JsPath.\(json.this.JsonConfiguration.default[play.api.libs.json.Json.MacroOptions](MacroOptions.this.Default.macroOptionsDefault).naming.apply("id")).read[Long](json.this.Reads.LongReads))(functional.this.FunctionalCanBuild.functionalCanBuildApplicative[[A]play.api.libs.json.Reads[A]](json.this.Reads.applicative(json.this.JsResult.applicativeJsResult))).and[String](play.api.libs.json.JsPath.\(json.this.JsonConfiguration.default[play.api.libs.json.Json.MacroOptions](MacroOptions.this.Default.macroOptionsDefault).naming.apply("greeting")).read[String](json.this.Reads.StringReads)).apply[example.Greeting](((id: Long, greeting: String) => Greeting.apply(id, greeting)))(json.this.Reads.functorReads(json.this.Reads.applicative(json.this.JsResult.applicativeJsResult)));
scala 2.12: val underlying: play.api.libs.json.Reads[example.Greeting] = play.api.libs.functional.syntax.`package`.toFunctionalBuilderOps[play.api.libs.json.Reads, Long](play.api.libs.json.JsPath.\(json.this.JsonConfiguration.default[play.api.libs.json.Json.MacroOptions](MacroOptions.this.Default.macroOptionsDefault).naming.apply("id")).read[Long](json.this.Reads.LongReads))(functional.this.FunctionalCanBuild.functionalCanBuildApplicative[play.api.libs.json.Reads](json.this.Reads.applicative(json.this.JsResult.applicativeJsResult))).and[String](play.api.libs.json.JsPath.\(json.this.JsonConfiguration.default[play.api.libs.json.Json.MacroOptions](MacroOptions.this.Default.macroOptionsDefault).naming.apply("greeting")).read[String](json.this.Reads.StringReads)).apply[example.Greeting]({((id: Long, greeting: String) => Greeting.apply(id, greeting))})(json.this.Reads.functorReads(json.this.Reads.applicative(json.this.JsResult.applicativeJsResult)));

[nehaev]

Minimized example.

The code below compiles fine even on Scala 2.13:

  import play.api.libs.json.{ JsPath, Reads }
  import play.api.libs.functional.FunctionalCanBuild
  import play.api.libs.functional.syntax
  val x = syntax.toFunctionalBuilderOps((JsPath \ "id").read[Long])(FunctionalCanBuild.functionalCanBuildApplicative[Reads])

From WartTraverser perspective it looks like:

...
class scala.reflect.internal.Trees$Select >>> play.api.libs.functional.FunctionalCanBuild.functionalCanBuildApplicative
class scala.reflect.internal.Trees$Select >>> play.api.libs.functional.FunctionalCanBuild
class scala.reflect.internal.Trees$Select >>> play.api.libs.functional
class scala.reflect.internal.Trees$Select >>> play.api.libs
class scala.reflect.internal.Trees$Select >>> play.api
class scala.reflect.internal.Trees$Ident >>> play
class scala.reflect.internal.Trees$TypeTree >>> play.api.libs.json.Reads
class scala.reflect.internal.Trees$ApplyToImplicitArgs >>> json.this.Reads.applicative(json.this.JsResult.applicativeJsResult)
...

The following code is generated by macros and causes Inferred type containing Any on Scala 2.13:

  import play.api.libs.json.{ JsPath, Reads }
  import play.api.libs.functional.FunctionalCanBuild
  import play.api.libs.functional.syntax
  val x = syntax.toFunctionalBuilderOps((JsPath \ "id").read[Long])

From WartTraverser perspective it looks like:

...
class scala.reflect.internal.Trees$Select >>> functional.this.FunctionalCanBuild.functionalCanBuildApplicative
class scala.reflect.internal.Trees$Select >>> functional.this.FunctionalCanBuild
class scala.reflect.internal.Trees$This >>> functional.this
class scala.reflect.internal.Trees$TypeTree >>> [A]play.api.libs.json.Reads[A]
class scala.reflect.internal.Types$PolyType xxx [A]play.api.libs.json.Reads[A]
class scala.reflect.internal.Trees$ApplyToImplicitArgs >>> json.this.Reads.applicative(json.this.JsResult.applicativeJsResult)
...

So this PolyType(typeParams = List(type A), resultType = play.api.libs.json.Reads[A]) is what causes the problem, because the base class for A is Any.

[nehaev]

Does anyone have an idea how to fix this?

What comes to my mind is to ignore PolyType in https://github.com/wartremover/wartremover/blob/master/core/src/main/scala/wartremover/warts/ForbidInference.scala#L36 just like it's done for ExistentialType. But given that not only Any and Nothing use ForbidInference, I'm not sure that this change won't break anything else.

[mikail-khan]

I have the same issue. Bumped a project to Scala 2.13.2 and using play-json-derived-codecs (v 7.0.0) and wartremover complains:

Given this model:

sealed trait A extends Product with Serializable

object A{
  case object B extends A
  case object C extends A

  implicit val format: OFormat[A] = derived.oformat()
}

Wartremover complains :

 [wartremover: Any] Inferred type containing Any: julienrf.json.derived.DerivedReads[A]

Even trying:

implicit val format: OFormat[A] = derived.oformat[A]()

doesn't work

[mikail-khan]

Same occurs even for this:

final case class AuthenticatedRequest[A](request: MessagesRequest[A]) extends WrappedRequest[A](request)

[wartremover:Any] Inferred type containing Any: [A] AuthenticatedRequest[A]

[solarmosaic-kflorence]

Same problem for a pretty simple play-json use case:

case class Response(name: String, data: Map[String, String])
object Response {
  implicit val format: Format[Response] = Json.format
}

Results in:

[wartremover:Any] Inferred type containing Any: [A]play.api.libs.json.Reads[A]

Strangely, it does not complain about:

case class Request(data: Map[String, String])
object Request {
  implicit val format: Format[Request] = Json.format
}

Time to slap @SuppressWarnings(Array("org.wartremover.warts.Any")) all over the place :(

[solarmosaic-kflorence]

I have also seen:

[wartremover:Product] Inferred type containing Product: ProducerMessage with Product with Serializable
[error]   implicit val format: Format[ProducerMessage] = Json.format

Which has to be suppressed with:

@SuppressWarnings(Array("org.wartremover.warts.Product", "org.wartremover.warts.Serializable"))