"ClassBType.info not yet assigned" error with Scala 2.13.0-RC1

[xuwei-k]

• https://travis-ci.org/xuwei-k/scalaz/jobs/530543436#L4947
• xuwei-k/scalaz@2201a64

[error] Error while emitting CofreeTest.scala
[error] <error> (of class scala.reflect.internal.Types$ErrorType$)
[error] Error while emitting CofreeTest.scala
[error] assertion failed: ClassBType.info not yet assigned: Lscalaz/CofreeTest$LazyDefns$1$1;
[warn] 402 warnings found
[error] two errors found
[error] (testsJVM / Test / compileIncremental) Compilation failed

[lrytz]

Can reproduce locally

[lrytz]

This seems to be an interaction with scala/scala#6050.

I just attached the debugger to the 2.13.0-RC1 compiler when running. Here's the tree that reaches the backend. Note the error type, which is causing the warning https://github.com/scala/scala/blob/v2.13.0-RC1/src/compiler/scala/tools/nsc/backend/jvm/BTypesFromSymbols.scala#L185.

object CofreeTest extends Object {
  final <static> <artifact> def $anonfun$new$1(lazyDefns$1$1: scalaz.CofreeTest$LazyDefns$1$1): scalaz.Order = lazyDefns$1$1.<rec$1: error>();
  def <init>(): scalaz.CofreeTest.type = {
    CofreeTest.super.<init>();
    scala.Predef.implicitly({
      final <synthetic> val lazyDefns$1: scalaz.CofreeTest$LazyDefns$1$1 = new scalaz.CofreeTest$LazyDefns$1$1();
      scalaz.this.Cofree.cofreeOrder(scalaz.std.anyVal.intInstance().$asInstanceOf[scalaz.Order](), {
        $anonfun(lazyDefns$1)
      })
    });
    ()
  }
}

The by-name implicit is https://github.com/xuwei-k/scalaz/blob/2201a647b81100df72ff74ab1d150e005339adf6/core/src/main/scala-2.13+/scalaz/CofreeInstancesVersionSpecific.scala#L14

To reproduce

• check out https://github.com/xuwei-k/scalaz/tree/2201a647b81100df72ff74ab1d150e005339adf6 (at this revision)
• run sbt, then ++2.13.0-RC1, then rootJVM/test:compile

A minimization would be helpful.. But @milessabin maybe you can take a look anyway?

[milessabin]

I'll try and find time in the next day or two. @xuwei-k a minimization would be really helpful.

[joroKr21]

Another instance in kittens: #11591

[milessabin]

Continuing this on #11591.

[milessabin]

#11591 fixed in scala/scala#8201.

@xuwei-k it'd be great if you could confirm that this also fixes your issue ... most likely it will turn the compiler crash into vanilla implicit resolution failure.

[xuwei-k]

confirmed! thanks!