scala.MatchError

[Bersier]

Compiler version

Scala 3.4.1

Minimized code

val d1 = foo(Empty)
foo(d1)

type Identity[T] = T

def foo[L <: TList[Int]](t: L): Identity[Bar[L]] = ???

type Bar[L <: TList[Int]] <: TList[Int] = L match
  case Empty.type => Cons[Int, 0, Empty.type]

trait TList[+T]
object Empty extends TList[Nothing]
class Cons[+E, +H <: E, +T <: TList[E]] extends TList[E]

Compiler crash error

error when pickling tree 
...

See https://scastie.scala-lang.org/dPSBEEYPTSOgoqqtut7exw

[Gedochao]

To reproduce outside of scastie:

@main def main = {
  val d1 = foo(Empty)
  foo(d1)
}

type Identity[T] = T

def foo[L <: TList[Int]](t: L): Identity[Bar[L]] = ???

type Bar[L <: TList[Int]] <: TList[Int] = L match
  case Empty.type => Cons[Int, 0, Empty.type]

trait TList[+T]
object Empty extends TList[Nothing]
class Cons[+E, +H <: E, +T <: TList[E]] extends TList[E]

output:

error when pickling tree 
  Identity[
    <error Match type reduction failed since selector Cons[Int, (0 : Int), Empty.type]
matches none of the cases

    case Empty.type => Cons[Int, (0 : Int), Empty.type]>
    ]

error when pickling tree @main def main:
  
    Identity[
      <error Match type reduction failed since selector Cons[Int, (0 : Int), Empty.type]
matches none of the cases

    case Empty.type => Cons[Int, (0 : Int), Empty.type]>
      ]
  
 =
  {
    val d1: Identity[Cons[Int, (0 : Int), Empty.type]] = foo[Empty.type](Empty)
    foo[Cons[Int, (0 : Int), Empty.type]](d1)
  }
error when pickling tree () extends Object() { this: repro$package.type =>
  private def writeReplace(): AnyRef =
    new scala.runtime.ModuleSerializationProxy(classOf[repro$package.type])
  @main def main:
    
      Identity[
        <error Match type reduction failed since selector Cons[Int, (0 : Int), Empty.type]
matches none of the cases

    case Empty.type => Cons[Int, (0 : Int), Empty.type]>
        ]
    
   =
    {
      val d1: Identity[Cons[Int, (0 : Int), Empty.type]] =
        foo[Empty.type](Empty)
      foo[Cons[Int, (0 : Int), Empty.type]](d1)
    }
  type Identity[T >: Nothing <: Any] = T
  def foo[L >: Nothing <: TList[Int]](t: L): Identity[Bar[L]] = ???
  type Bar[L >: Nothing <: TList[Int]] =
    L match 
      {
        case Empty.type => Cons[Int, 0.type, Empty.type]
      }
     <: TList[Int]
}
error when pickling tree @SourceFile("repro.scala") final module class repro$package() extends Object() {
   this: repro$package.type =>
  private def writeReplace(): AnyRef =
    new scala.runtime.ModuleSerializationProxy(classOf[repro$package.type])
  @main def main:
    
      Identity[
        <error Match type reduction failed since selector Cons[Int, (0 : Int), Empty.type]
matches none of the cases

    case Empty.type => Cons[Int, (0 : Int), Empty.type]>
        ]
    
   =
    {
      val d1: Identity[Cons[Int, (0 : Int), Empty.type]] =
        foo[Empty.type](Empty)
      foo[Cons[Int, (0 : Int), Empty.type]](d1)
    }
  type Identity[T >: Nothing <: Any] = T
  def foo[L >: Nothing <: TList[Int]](t: L): Identity[Bar[L]] = ???
  type Bar[L >: Nothing <: TList[Int]] =
    L match 
      {
        case Empty.type => Cons[Int, 0.type, Empty.type]
      }
     <: TList[Int]
}
error when pickling tree package <empty> {
  final lazy module val repro$package: repro$package = new repro$package()
  @SourceFile("repro.scala") final module class repro$package() extends Object()
     { this: repro$package.type =>
    private def writeReplace(): AnyRef =
      new scala.runtime.ModuleSerializationProxy(classOf[repro$package.type])
    @main def main:
      
        Identity[
          <error Match type reduction failed since selector Cons[Int, (0 : Int), Empty.type]
matches none of the cases

    case Empty.type => Cons[Int, (0 : Int), Empty.type]>
          ]
      
     =
      {
        val d1: Identity[Cons[Int, (0 : Int), Empty.type]] =
          foo[Empty.type](Empty)
        foo[Cons[Int, (0 : Int), Empty.type]](d1)
      }
    type Identity[T >: Nothing <: Any] = T
    def foo[L >: Nothing <: TList[Int]](t: L): Identity[Bar[L]] = ???
    type Bar[L >: Nothing <: TList[Int]] =
      L match 
        {
          case Empty.type => Cons[Int, 0.type, Empty.type]
        }
       <: TList[Int]
  }
}

  unhandled exception while running pickler on /Users/pchabelski/IdeaProjects/scala-cli-tests/compiler-repro/repro.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 -Yno-enrich-error-messages.

     while compiling: /Users/pchabelski/IdeaProjects/scala-cli-tests/compiler-repro/repro.scala
        during phase: pickler
                mode: Mode(ImplicitsEnabled)
     library version: version 2.13.12
    compiler version: version 3.4.1
            settings: -classpath /Users/pchabelski/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala3-library_3/3.4.1/scala3-library_3-3.4.1.jar:/Users/pchabelski/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.12/scala-library-2.13.12.jar -d /Users/pchabelski/IdeaProjects/scala-cli-tests/compiler-repro/.scala-build/compiler-repro_8f95553e06-28ebf8438e/classes/main -java-output-version 17 -sourceroot /Users/pchabelski/IdeaProjects/scala-cli-tests/compiler-repro

Exception in thread "main" scala.MatchError: dotty.tools.dotc.core.Types$PreviousErrorType@115dcaea (of class dotty.tools.dotc.core.Types$PreviousErrorType)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleNewType(TreePickler.scala:297)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleType(TreePickler.scala:165)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleNewType$$anonfun$2(TreePickler.scala:186)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleNewType(TreePickler.scala:186)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleType(TreePickler.scala:165)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:648)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTpt(TreePickler.scala:322)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleDef(TreePickler.scala:346)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:594)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleStats$$anonfun$2(TreePickler.scala:386)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleStats(TreePickler.scala:386)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:630)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleDef(TreePickler.scala:345)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:596)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleStats$$anonfun$2(TreePickler.scala:386)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleStats(TreePickler.scala:386)
        at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:646)
        at dotty.tools.dotc.core.tasty.TreePickler.pickle$$anonfun$1(TreePickler.scala:851)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.core.tasty.TreePickler.pickle(TreePickler.scala:858)
        at dotty.tools.dotc.transform.Pickler.run$$anonfun$1$$anonfun$1(Pickler.scala:125)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.transform.Pickler.run$$anonfun$1(Pickler.scala:180)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.transform.Pickler.run(Pickler.scala:180)
        at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:354)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.immutable.List.foreach(List.scala:333)
        at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:360)
        at dotty.tools.dotc.transform.Pickler.runOn(Pickler.scala:197)
        at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:315)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
        at dotty.tools.dotc.Run.runPhases$1(Run.scala:337)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:350)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:360)
        at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
        at dotty.tools.dotc.Run.compileUnits(Run.scala:360)
        at dotty.tools.dotc.Run.compileSources(Run.scala:261)
        at dotty.tools.dotc.Run.compile(Run.scala:246)
        at dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
        at dotty.tools.dotc.Driver.process(Driver.scala:196)
        at dotty.tools.dotc.Driver.process(Driver.scala:164)
        at dotty.tools.dotc.Driver.process(Driver.scala:176)
        at dotty.tools.dotc.Driver.main(Driver.scala:206)
        at dotty.tools.dotc.Main.main(Main.scala)

[odersky]

It works for me on main.