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No TypeTag available for String (in object, derived from parametrized class) #6259

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scabug opened this issue Aug 19, 2012 · 7 comments
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@scabug scabug commented Aug 19, 2012

try to compile next text:

package stringtag

import scala.reflect.runtime.universe._

abstract class PrimitiveTC[X:TypeTag] {
   def is[T:TypeTag]: Boolean = typeOf[X] <:< typeOf[T]
}

object StringTypeTag extends PrimitiveTC[String]

receive:
No TypeTag available for String

materializing requested reflect.runtime.universe.type.TypeTag[String] using `package`.this.materializeTypeTag[String](scala.reflect.runtime.`package`.universe)
reifying = String
universe = scala.reflect.runtime.`package`.universe
mirror = <empty>
Locatable: type String (type) owned by object Predef (module class) at scala.Predef
=============================
// produced from source-C:\Projects\Kepler\sandbox\Test.scala,line-7,offset=160
object Test extends App {
  val $u: scala.reflect.runtime.`package`.universe.type = scala.reflect.runtime.`package`.universe;
  val $m: $u.Mirror = scala.reflect.runtime.`package`.universe.runtimeMirror(this.getClass.getClassLoader);
  import $u._, $m._
  val tpe = TypeRef(SingleType(ThisType(staticPackage("scala").asModule.moduleClass), staticModule("scala.Predef")), build.selectType(staticModule("scala.Predef").asModule.moduleClass, "String"), List())
  println(tpe)
}
=============================
Test.scala:7: cannot materialize TypeTag[String] as {
  val $u: reflect.runtime.universe.type = scala.reflect.runtime.`package`.universe;
  val $m: $u.Mirror = scala.reflect.runtime.`package`.universe.runtimeMirror(this.getClass.getClassLoader);
  $u.TypeTag.apply[String]($m, {
    final class $typecreator1 extends TypeCreator {
      def <init>(): $typecreator1 = {
        $typecreator1.super.<init>();
        ()
      };
      def apply[U >: Nothing <: scala.reflect.base.Universe with Singleton]($m$untyped: MirrorOf[U]): U#Type = {
        val $u: U = $m$untyped.universe;
        val $m: $u.Mirror = $m$untyped.asInstanceOf[$u.Mirror];
        $u.TypeRef($u.SingleType($u.ThisType($m.staticPackage("scala").asModule.moduleClass), $m.staticModule("scala.Predef")), $u.build.selectType($m.staticModule("scala.Predef").asModule.moduleClass, "String"), scala.collection.immutab
le.List.apply())
      }
    };
    new $typecreator1()
  })
} because:
scala.reflect.internal.Types$TypeError: this can be used only in a class, object, or template
object StringTypeTag extends PrimitiveTC[String]
                     ^
Test.scala:7: `package`.this.materializeTypeTag[String](scala.reflect.runtime.`package`.universe) is not a valid implicit value for reflect.runtime.universe.TypeTag[String] because:
failed to typecheck the materialized tag:
No TypeTag available for String
object StringTypeTag extends PrimitiveTC[String]
                     ^
Test.scala:7: error: No TypeTag available for String
object StringTypeTag extends PrimitiveTC[String]
                     ^
one error found
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@scabug scabug commented Aug 19, 2012

Imported From: https://issues.scala-lang.org/browse/SI-6259?orig=1
Reporter: ruslan shevchenko (rssh)
Affected Versions: 2.10.0-M6
See #6666
Attachments:

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@scabug scabug commented Sep 5, 2012

@xeno-by said:
When creating a type tag for universe of type JavaUniverse (usually, a singleton value scala.reflect.runtime.universe), the reifier tries to play smart and automatically instantiate it in a correct mirror (ru.runtimeMirror(this.getClass.getClassLoader) instead of ru.rootMirror) [1].

To do that, it calls reifyEnclosingRuntimeClass for the current typer [2], which checks whether emitting this.getClass in current context makes sense. It seems this logic gets screwed up here as the type error says: "scala.reflect.internal.Types$TypeError: this can be used only in a class, object, or template".

[1] https://github.com/scalamacros/kepler/blob/5415272018114bb2e15036c5d6f9ae9c5af625d2/src/compiler/scala/reflect/reify/package.scala#L26
[2] https://github.com/scalamacros/kepler/blob/5415272018114bb2e15036c5d6f9ae9c5af625d2/src/compiler/scala/reflect/reify/package.scala#L64

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@scabug scabug commented Sep 12, 2012

@jsuereth said:
scala/scala#1292

A workaround for now.

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@scabug scabug commented Jan 23, 2013

@retronym said:
While the workaround compiles, it triggers a VerifyError

 RUNNER=scala scala-hash v2.10.0 -nc 
[info] v2.10.0 => /Users/jason/usr/scala-v2.10.0-0-g18481ce
Welcome to Scala version 2.10.0-20121205-112020-18481cef9b (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_27).
Type in expressions to have them evaluated.
Type :help for more information.

scala> import scala.reflect.runtime.universe._
import scala.reflect.runtime.universe._

scala> 

scala> class A[X](implicit val tt: TypeTag[X]) {println(tt)}
defined class A

scala> 

scala> object Obj {
     |   val x = {
     |     object InVal extends A[String]
     |     InVal
     |     5
     |   }
     | }
defined module Obj

scala> Obj
java.lang.VerifyError: (class: Obj$InVal$2$, method: <init> signature: ()V) Expecting to find object/array on stack
	at Obj$.InVal$1$lzycompute(<console>:13)

With my in-progress patch for #6666:

ticket/6666 ~/code/./build/quick/bin/scalac test/files/run/t6259b.scala
test/files/run/t6259b.scala:9: error: Implementation restriction: anonymous class $anon requires premature access to object InVal.
    object InVal extends A[String]
                         ^
one error found
ticket/6666 ~/code/scala2 cat !$
cat test/files/run/t6259b.scala
package t6259

import scala.reflect.runtime.universe._

class A[X](implicit val tt: TypeTag[X]) {println(tt)}

object Obj {
  val x = {
    object InVal extends A[String]
    InVal
    5
  }
}

object Test extends App {
  Obj
}
ticket/6666 ~/code/scala2 ./build/quick/bin/scalac test/files/run/t6259b.scala
test/files/run/t6259b.scala:9: error: Implementation restriction: anonymous class $anon requires premature access to object InVal.
    object InVal extends A[String]
                         ^
one error found

We could make this problem go away by allowing moduleClassOf[Companion.type].

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@scabug scabug commented Jan 23, 2013

@retronym said:
Relates to #6666.

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@scabug scabug commented Feb 8, 2013

@jsuereth said:
Yeah, the workaround is wholly unnecessary if you had control to generate moduleClassOf byte code or had such a method.

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@scabug scabug commented Dec 10, 2013

@adriaanm said:
seems fixed in master

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