Compiler crash when using implicit class and NotGiven and cats

[jdrphillips]

Compiler version

3.6.3, 3.7.2

Minimized code

Dependencies: cats:2.13.0, cats-effect:3.6.3

Apologies but the bug seems tied to something cats is doing with Apply which I am unable to minimise.

Scastie link

import scala.util.NotGiven
import cats.data.*
import cats.effect.*
import cats.syntax.apply.*

object Testing {

  val unit: EitherT[IO, Exception, Unit] = ???

  implicit class EitherTOps[T](io: IO[T]) {
    def asEitherT(using NotGiven[T <:< Either[?, ?]]): EitherT[IO, Exception, T] = ???
  }

  unit *> IO(Right(5)).asEitherT
                       // ^ this call is the broken bit
}

Notes:

• It only breaks if the NotGiven is not satisfied
• It breaks for any unsatisfied NotGiven condition
• It requires a NotGiven clause, a "normal" unsatisfied implicit fails as expected
• It works fine with extension rather than implicit class
• It works fine with .flatMap(_ =>...) instead of *>
• It seems to break with any monad transformer from cats
• It works fine with a "simple" type like IO, seems to only fail on monad-transformer-like types

Output (click arrow to expand)

error when pickling type T error when pickling tree T of class class dotty.tools.dotc.ast.Trees$InferredTypeTree error when pickling tree cats.syntax.apply.catsSyntaxApplyOps[ [T] =>> cats.data.EitherT[cats.effect.IO, Exception, T], Unit]( Playground.Testing.Foo.unit).*>[T] of class class dotty.tools.dotc.ast.Trees$TypeApply error when pickling tree cats.syntax.apply.catsSyntaxApplyOps[ [T] =>> cats.data.EitherT[cats.effect.IO, Exception, T], Unit]( Playground.Testing.Foo.unit).*>[T]( Playground.Testing.EitherTOps[T]( cats.effect.IO.apply[Right[Nothing, Int]](Right.apply[Nothing, Int](5))). asFoo(scala.util.NotGiven.value) ) of class class dotty.tools.dotc.ast.Trees$Apply error when pickling tree cats.syntax.apply.catsSyntaxApplyOps[ [T] =>> cats.data.EitherT[cats.effect.IO, Exception, T], Unit]( Playground.Testing.Foo.unit).*>[T]( Playground.Testing.EitherTOps[T]( cats.effect.IO.apply[Right[Nothing, Int]](Right.apply[Nothing, Int](5))). asFoo(scala.util.NotGiven.value) )( cats.data.EitherT.catsDataMonadErrorForEitherT[cats.effect.IO, Exception]( cats.effect.IO.asyncForIO) ) of class class dotty.tools.dotc.ast.Trees$Apply error when pickling tree () extends Object() { this: Playground.Testing.type => private def writeReplace(): AnyRef = new scala.runtime.ModuleSerializationProxy(classOf[Playground.Testing.type]) type Foo[T >: Nothing <: Any] = cats.data.EitherT[IO, Exception, T] final lazy module val Foo: Playground.Testing.Foo = new Playground.Testing.Foo() final module class Foo() extends Object() { this: Playground.Testing.Foo.type => private def writeReplace(): AnyRef = new scala.runtime.ModuleSerializationProxy( classOf[Playground.Testing.Foo.type]) def unit: Playground.Testing.Foo[Unit] = ??? } implicit class EitherTOps[T >: Nothing <: Any](io: cats.effect.IO[T]) extends Object() { T private[this] val io: cats.effect.IO[T] def asFoo(using x$1: scala.util.NotGiven[ <:<[EitherTOps.this.T, Either[? >: Nothing <: Any, ? >: Nothing <: Any]] ] ): Playground.Testing.Foo[EitherTOps.this.T] = ??? } final implicit def EitherTOps[T >: Nothing <: Any](io: cats.effect.IO[T]): Playground.Testing.EitherTOps[T] = new Playground.Testing.EitherTOps[T](io) cats.syntax.apply.catsSyntaxApplyOps[ [T] =>> cats.data.EitherT[cats.effect.IO, Exception, T], Unit]( Playground.Testing.Foo.unit).*>[T]( Playground.Testing.EitherTOps[T]( cats.effect.IO.apply[Right[Nothing, Int]](Right.apply[Nothing, Int](5))). asFoo(scala.util.NotGiven.value) )( cats.data.EitherT.catsDataMonadErrorForEitherT[cats.effect.IO, Exception]( cats.effect.IO.asyncForIO) ) } of class class dotty.tools.dotc.ast.Trees$Template error when pickling tree final module class Testing() extends Object() { this: Playground.Testing.type => private def writeReplace(): AnyRef = new scala.runtime.ModuleSerializationProxy(classOf[Playground.Testing.type]) type Foo[T >: Nothing <: Any] = cats.data.EitherT[IO, Exception, T] final lazy module val Foo: Playground.Testing.Foo = new Playground.Testing.Foo() final module class Foo() extends Object() { this: Playground.Testing.Foo.type => private def writeReplace(): AnyRef = new scala.runtime.ModuleSerializationProxy( classOf[Playground.Testing.Foo.type]) def unit: Playground.Testing.Foo[Unit] = ??? } implicit class EitherTOps[T >: Nothing <: Any](io: cats.effect.IO[T]) extends Object() { T private[this] val io: cats.effect.IO[T] def asFoo(using x$1: scala.util.NotGiven[ <:<[EitherTOps.this.T, Either[? >: Nothing <: Any, ? >: Nothing <: Any]] ] ): Playground.Testing.Foo[EitherTOps.this.T] = ??? } final implicit def EitherTOps[T >: Nothing <: Any](io: cats.effect.IO[T]): Playground.Testing.EitherTOps[T] = new Playground.Testing.EitherTOps[T](io) cats.syntax.apply.catsSyntaxApplyOps[ [T] =>> cats.data.EitherT[cats.effect.IO, Exception, T], Unit]( Playground.Testing.Foo.unit).*>[T]( Playground.Testing.EitherTOps[T]( cats.effect.IO.apply[Right[Nothing, Int]](Right.apply[Nothing, Int](5))). asFoo(scala.util.NotGiven.value) )( cats.data.EitherT.catsDataMonadErrorForEitherT[cats.effect.IO, Exception]( cats.effect.IO.asyncForIO) ) } of class class dotty.tools.dotc.ast.Trees$TypeDef error when pickling tree () extends Object(), com.olegych.scastie.api.runtime.ScastieApp { this: Playground.type => private def writeReplace(): AnyRef = new scala.runtime.ModuleSerializationProxy(classOf[Playground.type]) private[this] val instrumentationMap:

  scala.collection.mutable.Map[com.olegych.scastie.api.Position,
    com.olegych.scastie.api.Render]

=
root.scala.collection.mutable.Map.empty[
root.com.olegych.scastie.api.Position,
root.com.olegych.scastie.api.Render]
def instrumentations: List[com.olegych.scastie.api.Instrumentation] =
Playground.instrumentationMap.toList.map[
com.olegych.scastie.api.Instrumentation]((
x$1: (com.olegych.scastie.api.Position, com.olegych.scastie.api.Render))
=>
x$1 match
{
case
Tuple2.unapply[com.olegych.scastie.api.Position,
com.olegych.scastie.api.Render](pos @ _, r @ _)
=>
root.com.olegych.scastie.api.Instrumentation.apply(pos, r)
}
)
import scala.util.NotGiven
import cats.data.*
import cats.effect.*
import cats.syntax.package.apply.*
final lazy module val Testing: Playground.Testing = new Playground.Testing()
final module class Testing() extends Object() {
this: Playground.Testing.type =>
private def writeReplace(): AnyRef =
new scala.runtime.ModuleSerializationProxy(
classOf[Playground.Testing.type])
type Foo[T >: Nothing <: Any] = cats.data.EitherT[IO, Exception, T]
final lazy module val Foo: Playground.Testing.Foo =
new Playground.Testing.Foo()
final module class Foo() extends Object() {
this: Playground.Testing.Foo.type =>
private def writeReplace(): AnyRef =
new scala.runtime.ModuleSerializationProxy(
classOf[Playground.Testing.Foo.type])
def unit: Playground.Testing.Foo[Unit] = ???
}
implicit class EitherTOps[T >: Nothing <: Any](io: cats.effect.IO[T])
extends Object() {
T
private[this] val io: cats.effect.IO[T]
def asFoo(using
x$1:
scala.util.NotGiven[
<:<[EitherTOps.this.T,
Either[? >: Nothing <: Any, ? >: Nothing <: Any]]
]
): Playground.Testing.Foo[EitherTOps.this.T] = ???
}
final implicit def EitherTOps[T >: Nothing <: Any](io: cats.effect.IO[T]):
Playground.Testing.EitherTOps[T] =
new Playground.Testing.EitherTOpsT
cats.syntax.apply.catsSyntaxApplyOps
[T] =>> cats.data.EitherT[cats.effect.IO, Exception, T], Unit.*>[T](
Playground.Testing.EitherTOps[T](
cats.effect.IO.apply[Right[Nothing, Int]](Right.applyNothing, Int))
.asFoo(scala.util.NotGiven.value)
)(
cats.data.EitherT.catsDataMonadErrorForEitherTcats.effect.IO, Exception
)
}
} of class class dotty.tools.dotc.ast.Trees$Template
error when pickling tree @sourcefile("src/main/scala/main.scala") final module class Playground() extends
Object(), com.olegych.scastie.api.runtime.ScastieApp {
this: Playground.type =>
private def writeReplace(): AnyRef =
new scala.runtime.ModuleSerializationProxy(classOf[Playground.type])
private[this] val instrumentationMap:

  scala.collection.mutable.Map[com.olegych.scastie.api.Position,
    com.olegych.scastie.api.Render]

=
root.scala.collection.mutable.Map.empty[
root.com.olegych.scastie.api.Position,
root.com.olegych.scastie.api.Render]
def instrumentations: List[com.olegych.scastie.api.Instrumentation] =
Playground.instrumentationMap.toList.map[
com.olegych.scastie.api.Instrumentation]((
x$1: (com.olegych.scastie.api.Position, com.olegych.scastie.api.Render))
=>
x$1 match
{
case
Tuple2.unapply[com.olegych.scastie.api.Position,
com.olegych.scastie.api.Render](pos @ _, r @ _)
=>
root.com.olegych.scastie.api.Instrumentation.apply(pos, r)
}
)
import scala.util.NotGiven
import cats.data.*
import cats.effect.*
import cats.syntax.package.apply.*
final lazy module val Testing: Playground.Testing = new Playground.Testing()
final module class Testing() extends Object() {
this: Playground.Testing.type =>
private def writeReplace(): AnyRef =
new scala.runtime.ModuleSerializationProxy(
classOf[Playground.Testing.type])
type Foo[T >: Nothing <: Any] = cats.data.EitherT[IO, Exception, T]
final lazy module val Foo: Playground.Testing.Foo =
new Playground.Testing.Foo()
final module class Foo() extends Object() {
this: Playground.Testing.Foo.type =>
private def writeReplace(): AnyRef =
new scala.runtime.ModuleSerializationProxy(
classOf[Playground.Testing.Foo.type])
def unit: Playground.Testing.Foo[Unit] = ???
}
implicit class EitherTOps[T >: Nothing <: Any](io: cats.effect.IO[T])
extends Object() {
T
private[this] val io: cats.effect.IO[T]
def asFoo(using
x$1:
scala.util.NotGiven[
<:<[EitherTOps.this.T,
Either[? >: Nothing <: Any, ? >: Nothing <: Any]]
]
): Playground.Testing.Foo[EitherTOps.this.T] = ???
}
final implicit def EitherTOps[T >: Nothing <: Any](io: cats.effect.IO[T]):
Playground.Testing.EitherTOps[T] =
new Playground.Testing.EitherTOpsT
cats.syntax.apply.catsSyntaxApplyOps
[T] =>> cats.data.EitherT[cats.effect.IO, Exception, T], Unit.>[T](
Playground.Testing.EitherTOps[T](
cats.effect.IO.apply[Right[Nothing, Int]](Right.applyNothing, Int))
.asFoo(scala.util.NotGiven.value)
)(
cats.data.EitherT.catsDataMonadErrorForEitherTcats.effect.IO, Exception
)
}
} of class class dotty.tools.dotc.ast.Trees$TypeDef
error when pickling tree package {
import root.com.olegych.scastie.api.runtime.
final lazy module val Playground: Playground = new Playground()
@sourcefile("src/main/scala/main.scala") final module class Playground()
extends Object(), com.olegych.scastie.api.runtime.ScastieApp {
this: Playground.type =>
private def writeReplace(): AnyRef =
new scala.runtime.ModuleSerializationProxy(classOf[Playground.type])
private[this] val instrumentationMap:

    scala.collection.mutable.Map[com.olegych.scastie.api.Position,
      com.olegych.scastie.api.Render]
  
 =
  _root_.scala.collection.mutable.Map.empty[
    _root_.com.olegych.scastie.api.Position,
    _root_.com.olegych.scastie.api.Render]
def instrumentations: List[com.olegych.scastie.api.Instrumentation] =
  Playground.instrumentationMap.toList.map[
    com.olegych.scastie.api.Instrumentation]((
    x$1: (com.olegych.scastie.api.Position, com.olegych.scastie.api.Render))
     =>
    x$1 match 
      {
        case 
          Tuple2.unapply[com.olegych.scastie.api.Position,
            com.olegych.scastie.api.Render](pos @ _, r @ _)
         =>
          _root_.com.olegych.scastie.api.Instrumentation.apply(pos, r)
      }
  )
import scala.util.NotGiven
import cats.data.*
import cats.effect.*
import cats.syntax.package.apply.*
final lazy module val Testing: Playground.Testing = new Playground.Testing()
final module class Testing() extends Object() {
  this: Playground.Testing.type =>
  private def writeReplace(): AnyRef =
    new scala.runtime.ModuleSerializationProxy(
      classOf[Playground.Testing.type])
  type Foo[T >: Nothing <: Any] = cats.data.EitherT[IO, Exception, T]
  final lazy module val Foo: Playground.Testing.Foo =
    new Playground.Testing.Foo()
  final module class Foo() extends Object() {
    this: Playground.Testing.Foo.type =>
    private def writeReplace(): AnyRef =
      new scala.runtime.ModuleSerializationProxy(
        classOf[Playground.Testing.Foo.type])
    def unit: Playground.Testing.Foo[Unit] = ???
  }
  implicit class EitherTOps[T >: Nothing <: Any](io: cats.effect.IO[T])
     extends Object() {
    T
    private[this] val io: cats.effect.IO[T]
    def asFoo(using 
      x$1:
        scala.util.NotGiven[
          <:<[EitherTOps.this.T,
            Either[? >: Nothing <: Any, ? >: Nothing <: Any]]
        ]
    ): Playground.Testing.Foo[EitherTOps.this.T] = ???
  }
  final implicit def EitherTOps[T >: Nothing <: Any](io: cats.effect.IO[T])
    : Playground.Testing.EitherTOps[T] =
    new Playground.Testing.EitherTOps[T](io)
  cats.syntax.apply.catsSyntaxApplyOps[
    [T] =>> cats.data.EitherT[cats.effect.IO, Exception, T], Unit](
    Playground.Testing.Foo.unit).*>[T](
    Playground.Testing.EitherTOps[T](
      cats.effect.IO.apply[Right[Nothing, Int]](Right.apply[Nothing, Int](5)
        )
    ).asFoo(scala.util.NotGiven.value)
  )(
    cats.data.EitherT.catsDataMonadErrorForEitherT[cats.effect.IO, Exception
      ](cats.effect.IO.asyncForIO)
  )
}

}
} of class class dotty.tools.dotc.ast.Trees$PackageDef

unhandled exception while running pickler on /tmp/scastie13261002748272130033/src/main/scala/main.scala

An unhandled exception was thrown in the compiler.
Please file a crash report here:
https://github.com/scala/scala3/issues/new/choose
For non-enriched exceptions, compile with -Xno-enrich-error-messages.

 while compiling: /tmp/scastie13261002748272130033/src/main/scala/main.scala
    during phase: pickler
            mode: Mode(ImplicitsEnabled)
 library version: version 2.13.16
compiler version: version 3.7.2
        settings: -classpath /tmp/scastie13261002748272130033/target/scala-3.7.2/classes:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala3-library_3/3.7.2/scala3-library_3-3.7.2.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/typelevel/cats-core_3/2.13.0/cats-core_3-2.13.0.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/typelevel/cats-effect_3/3.6.3/cats-effect_3-3.6.3.jar:/home/sbtRunnerContainer/.ivy2/local/org.scastie/runtime-scala_3/1.0.0-SNAPSHOT/jars/runtime-scala_3.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.16/scala-library-2.13.16.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/typelevel/cats-kernel_3/2.13.0/cats-kernel_3-2.13.0.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/typelevel/cats-effect-kernel_3/3.6.3/cats-effect-kernel_3-3.6.3.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/typelevel/cats-effect-std_3/3.6.3/cats-effect-std_3-3.6.3.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/org/typelevel/cats-mtl_3/1.3.1/cats-mtl_3-1.3.1.jar:/home/sbtRunnerContainer/.ivy2/local/org.scastie/api_3/0.30.0-SNAPSHOT/jars/api_3.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/typesafe/play/play-json_3/2.10.0-RC5/play-json_3-2.10.0-RC5.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/typesafe/play/play-functional_3/2.10.0-RC5/play-functional_3-2.10.0-RC5.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-core/2.11.4/jackson-core-2.11.4.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-annotations/2.11.4/jackson-annotations-2.11.4.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/fasterxml/jackson/datatype/jackson-datatype-jdk8/2.11.4/jackson-datatype-jdk8-2.11.4.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/fasterxml/jackson/datatype/jackson-datatype-jsr310/2.11.4/jackson-datatype-jsr310-2.11.4.jar:/home/sbtRunnerContainer/.cache/coursier/v1/https/repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.11.4/jackson-databind-2.11.4.jar -d /tmp/scastie13261002748272130033/target/scala-3.7.2/classes -deprecation true -feature true

[Gedochao]

dependencies for reproduction:

//> using deps org.typelevel::cats-core:2.13.0
//> using deps org.typelevel::cats-effect:3.6.3