"AssertionError: duplicate type ..." when importing traits from 2.13.4 compiled library

[marcinzh]

Minimized code

This is peculiar case to minimize, because of the dependency. Scastie seems like the best option to me, I hope it's ok.

• Link to minimized Scastie project.

• Link to definitions of imported traits in the imported 2.13.4 library.

• Link to definition of DottyBug in the imported 2.13.4 library.

Now Scala 3 code. Some import statements trigger the error, some don't:

import turbolift.std_effects.Except      /* ERROR */
import turbolift.std_effects.ExceptK     /* OK */
import turbolift.std_effects.Validation  /* ERROR */
import turbolift.std_effects.ValidationK /* ERROR */

Wildcard import does not trigger the error. But using the imported trait does:

import turbolift.std_effects._             /* OK */

case object MyExcept extends Except[Int]   /* ERROR */

I modified the imported 2.13.4 library by putting cloned definitions of troublesome traits inside object DottyBug {‥}. Now importing works fine:

import turbolift.std_effects.DottyBug.Except       /* OK */
import turbolift.std_effects.DottyBug.ExceptK      /* OK */
import turbolift.std_effects.DottyBug.Validation   /* OK */
import turbolift.std_effects.DottyBug.ValidationK  /* OK */

Output (click arrow to expand)

This output comes from 3.0.0-RC1-bin-20210117-65b17af-NIGHTLY.

For 3.0.0-M3 output, please see provided Scastie link.

java.lang.AssertionError: assertion failed: duplicate type E#7824; previous was type E#7817
    scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
    dotty.tools.dotc.core.Scopes$MutableScope.enter(Scopes.scala:275)
    dotty.tools.dotc.core.SymDenotations$ClassDenotation.enterNoReplace(SymDenotations.scala:1867)
    dotty.tools.dotc.core.SymDenotations$ClassDenotation.enter(SymDenotations.scala:1858)
    dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.finishSym$1(Scala2Unpickler.scala:493)
    dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.readDisambiguatedSymbol(Scala2Unpickler.scala:546)
    dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.readSymbol(Scala2Unpickler.scala:327)
    dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.run(Scala2Unpickler.scala:182)
    dotty.tools.dotc.core.classfile.ClassfileParser.unpickleScala$1(ClassfileParser.scala:860)
    dotty.tools.dotc.core.classfile.ClassfileParser.unpickleOrParseInnerClasses(ClassfileParser.scala:966)
    dotty.tools.dotc.core.classfile.ClassfileParser.parseClass(ClassfileParser.scala:165)
    dotty.tools.dotc.core.classfile.ClassfileParser.run$$anonfun$1(ClassfileParser.scala:87)
    dotty.tools.dotc.core.classfile.ClassfileParser.run(ClassfileParser.scala:82)
    dotty.tools.dotc.core.ClassfileLoader.load(SymbolLoaders.scala:414)
    dotty.tools.dotc.core.ClassfileLoader.doComplete(SymbolLoaders.scala:409)
    dotty.tools.dotc.core.SymbolLoader.complete(SymbolLoaders.scala:343)
    dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:167)
    dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:188)
    dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:190)
    dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:369)
    dotty.tools.dotc.core.SymDenotations$SymDenotation.flags(SymDenotations.scala:65)
    dotty.tools.dotc.core.SymDenotations$SymDenotation.is(SymDenotations.scala:106)
    dotty.tools.dotc.sbt.ExtractDependencies.recordDependency(ExtractDependencies.scala:156)
    dotty.tools.dotc.sbt.ExtractDependencies.run$$anonfun$4(ExtractDependencies.scala:100)
    scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
    scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
    scala.collection.mutable.HashSet$Node.foreach(HashSet.scala:435)
    scala.collection.mutable.HashSet.foreach(HashSet.scala:361)
    dotty.tools.dotc.sbt.ExtractDependencies.run(ExtractDependencies.scala:100)
    dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:300)
    scala.collection.immutable.List.map(List.scala:246)
    dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:301)
    dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:185)
    scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
    scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
    scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
    dotty.tools.dotc.Run.runPhases$5(Run.scala:195)
    dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:203)
    scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
    dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
    dotty.tools.dotc.Run.compileUnits(Run.scala:210)
    dotty.tools.dotc.Run.compileSources(Run.scala:146)
    dotty.tools.dotc.Run.compile(Run.scala:130)
    dotty.tools.dotc.Driver.doCompile(Driver.scala:39)
    dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:88)
    dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)
    sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:92)
    sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:186)
    scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
    sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:241)
    sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:176)
    sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:157)
    sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:239)
    sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:157)
    sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:204)
    sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:573)
    sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:573)
    sbt.internal.inc.Incremental$.$anonfun$apply$5(Incremental.scala:174)
    sbt.internal.inc.Incremental$.$anonfun$apply$5$adapted(Incremental.scala:172)
    sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:459)
    sbt.internal.inc.IncrementalCommon$CycleState.next(IncrementalCommon.scala:116)
    sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:56)
    sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:52)
    sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:261)
    sbt.internal.inc.Incremental$.$anonfun$incrementalCompile$8(Incremental.scala:414)
    sbt.internal.inc.Incremental$.withClassfileManager(Incremental.scala:499)
    sbt.internal.inc.Incremental$.incrementalCompile(Incremental.scala:401)
    sbt.internal.inc.Incremental$.apply(Incremental.scala:166)
    sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:573)
    sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:491)
    sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:332)
    sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:420)
    sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137)
    sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:2177)
    sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2134)
    sbt.internal.io.Retry$.apply(Retry.scala:40)
    sbt.internal.io.Retry$.apply(Retry.scala:23)
    sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:31)
    sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2130)
    scala.Function1.$anonfun$compose$1(Function1.scala:49)
    sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:62)
    sbt.std.Transform$$anon$4.work(Transform.scala:68)
    sbt.Execute.$anonfun$submit$2(Execute.scala:282)
    sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:23)
    sbt.Execute.work(Execute.scala:291)
    sbt.Execute.$anonfun$submit$1(Execute.scala:282)
    sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
    sbt.CompletionService$$anon$2.call(CompletionService.scala:64)
    java.util.concurrent.FutureTask.run(FutureTask.java:266)
    java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    java.util.concurrent.FutureTask.run(FutureTask.java:266)
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    java.lang.Thread.run(Thread.java:748)

---

The imported 2.13.4 dependency is:

resolvers += Resolver.jcenterRepo
libraryDependencies += ("com.github.marcinzh" %% "turbolift-core" % "0.8.0").withDottyCompat(scalaVersion.value)

[griggt]

A minimized standalone reproducer:

Scala 2

// s2/Lib.scala

package i11173

trait DU[A, B]
trait H[F[_]]

trait Foo[E] {
  def foo: H[({type L[A] = DU[E, A]})#L]
}

trait Bar[E] extends Foo[E] {
  def bar = foo   // important note: return type not specified
}

Scala 3

// s3/Main.scala

import i11173.Bar

def test(x: Bar[_]): Unit = ()

These may be compiled using the following build.sbt:

lazy val s2 = project.in(file("s2"))
  .settings(scalaVersion := "2.13.4")

lazy val s3 = project.in(file("s3"))
  .dependsOn(s2)
  .settings(scalaVersion := "3.0.0-RC1-bin-20210117-65b17af-NIGHTLY")

or directly on the command line:

$ scalac -version
Scala compiler version 2.13.4 -- Copyright 2002-2020, LAMP/EPFL and Lightbend, Inc.

$ dotc -version
Scala compiler version 3.0.0-RC1-bin-SNAPSHOT-git-cc8ffb1 -- Copyright 2002-2021, LAMP/EPFL

$ scalac s2/Lib.scala && dotc s3/Main.scala

Compiler output - click to expand

exception caught when loading trait Bar: java.lang.AssertionError: assertion failed: duplicate type E#4433; previous was type E#4426
exception occurred while typechecking s3/Main.scala
exception occurred while compiling s3/Main.scala
java.lang.AssertionError: assertion failed: duplicate type E#4433; previous was type E#4426 while compiling s3/Main.scala
Exception in thread "main" java.lang.AssertionError: assertion failed: duplicate type E#4433; previous was type E#4426
	at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
	at dotty.tools.dotc.core.Scopes$MutableScope.enter(Scopes.scala:275)
	at dotty.tools.dotc.core.SymDenotations$ClassDenotation.enterNoReplace(SymDenotations.scala:1867)
	at dotty.tools.dotc.core.SymDenotations$ClassDenotation.enter(SymDenotations.scala:1858)
	at dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.finishSym$1(Scala2Unpickler.scala:493)
	at dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.readDisambiguatedSymbol(Scala2Unpickler.scala:546)
	at dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.readSymbol(Scala2Unpickler.scala:327)
	at dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.run(Scala2Unpickler.scala:182)
	at dotty.tools.dotc.core.classfile.ClassfileParser.unpickleScala$1(ClassfileParser.scala:860)
	at dotty.tools.dotc.core.classfile.ClassfileParser.unpickleOrParseInnerClasses(ClassfileParser.scala:966)
	at dotty.tools.dotc.core.classfile.ClassfileParser.parseClass(ClassfileParser.scala:165)
	at dotty.tools.dotc.core.classfile.ClassfileParser.run$$anonfun$1(ClassfileParser.scala:87)
	at dotty.tools.dotc.core.classfile.ClassfileParser.run(ClassfileParser.scala:82)
	at dotty.tools.dotc.core.ClassfileLoader.load(SymbolLoaders.scala:414)
	at dotty.tools.dotc.core.ClassfileLoader.doComplete(SymbolLoaders.scala:409)
	at dotty.tools.dotc.core.SymbolLoader.complete(SymbolLoaders.scala:343)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:167)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeOnce(SymDenotations.scala:361)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.isAbsent(SymDenotations.scala:570)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.isAccessibleFrom(SymDenotations.scala:863)
	at dotty.tools.dotc.core.Denotations$SingleDenotation.accessibleFrom(Denotations.scala:613)
	at dotty.tools.dotc.typer.Typer.selection$3(Typer.scala:213)
	at dotty.tools.dotc.typer.Typer.recur$1(Typer.scala:247)
	at dotty.tools.dotc.typer.Typer.namedImportRef$1(Typer.scala:254)
	at dotty.tools.dotc.typer.Typer.loop$1(Typer.scala:393)
	at dotty.tools.dotc.typer.Typer.findRefRecur$1(Typer.scala:415)
	at dotty.tools.dotc.typer.Typer.findRef(Typer.scala:418)
	at dotty.tools.dotc.typer.Typer.typedIdent(Typer.scala:473)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2521)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2613)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2679)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2683)
	at dotty.tools.dotc.typer.Typer.typedAppliedTypeTree(Typer.scala:1766)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2578)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2614)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2679)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2683)
	at dotty.tools.dotc.typer.Namer.typedAheadType$$anonfun$1(Namer.scala:1300)
	at dotty.tools.dotc.typer.Namer.typedAhead(Namer.scala:1292)
	at dotty.tools.dotc.typer.Namer.typedAheadType(Namer.scala:1300)
	at dotty.tools.dotc.typer.Namer.valOrDefDefSig(Namer.scala:1512)
	at dotty.tools.dotc.typer.Namer$Completer.typeSig(Namer.scala:699)
	at dotty.tools.dotc.typer.Namer$Completer.completeInCreationContext(Namer.scala:830)
	at dotty.tools.dotc.typer.Namer$Completer.complete(Namer.scala:731)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:167)
	at dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:188)
	at dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:190)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:369)
	at dotty.tools.dotc.typer.Typer.retrieveSym(Typer.scala:2494)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2519)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2613)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2679)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2683)
	at dotty.tools.dotc.typer.Namer.typedAheadExpr$$anonfun$1(Namer.scala:1305)
	at dotty.tools.dotc.typer.Namer.typedAhead(Namer.scala:1292)
	at dotty.tools.dotc.typer.Namer.typedAheadExpr(Namer.scala:1305)
	at dotty.tools.dotc.typer.Namer.completeParams$$anonfun$1(Namer.scala:1321)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.typer.Namer.completeParams(Namer.scala:1321)
	at dotty.tools.dotc.typer.Namer.defDefSig$$anonfun$3(Namer.scala:1550)
	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.typer.Namer.defDefSig(Namer.scala:1550)
	at dotty.tools.dotc.typer.Namer$Completer.typeSig(Namer.scala:703)
	at dotty.tools.dotc.typer.Namer$Completer.completeInCreationContext(Namer.scala:830)
	at dotty.tools.dotc.typer.Namer$Completer.complete(Namer.scala:731)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:167)
	at dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:188)
	at dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:190)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:369)
	at dotty.tools.dotc.typer.Typer.retrieveSym(Typer.scala:2494)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2519)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2613)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2679)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2683)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2705)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2755)
	at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2202)
	at dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$2(Typer.scala:2540)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:2544)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2613)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2679)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2683)
	at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:2705)
	at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:2755)
	at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2337)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:2585)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:2614)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2679)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:2683)
	at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:2799)
	at dotty.tools.dotc.typer.FrontEnd.liftedTree1$1(FrontEnd.scala:79)
	at dotty.tools.dotc.typer.FrontEnd.typeCheck$$anonfun$1(FrontEnd.scala:84)
	at dotty.tools.dotc.typer.FrontEnd.monitor(FrontEnd.scala:43)
	at dotty.tools.dotc.typer.FrontEnd.typeCheck(FrontEnd.scala:85)
	at dotty.tools.dotc.typer.FrontEnd.runOn$$anonfun$3(FrontEnd.scala:120)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.dotc.typer.FrontEnd.runOn(FrontEnd.scala:120)
	at dotty.tools.dotc.Run.runPhases$4$$anonfun$4(Run.scala:185)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.dotc.Run.runPhases$5(Run.scala:195)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:203)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:210)
	at dotty.tools.dotc.Run.compileSources(Run.scala:146)
	at dotty.tools.dotc.Run.compile(Run.scala:130)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:39)
	at dotty.tools.dotc.Driver.process(Driver.scala:186)
	at dotty.tools.dotc.Driver.process(Driver.scala:155)
	at dotty.tools.dotc.Driver.process(Driver.scala:167)
	at dotty.tools.dotc.Driver.main(Driver.scala:194)
	at dotty.tools.dotc.Main.main(Main.scala)

[valdo404]

Another example of failure would be with the following main.scala code:

package com.powerspace.dns

import cats.effect.{Resource, IO}

object app:
  def main(args: Array[String]): Unit =
    val clientResource = Resource.make[IO, DefaultKubernetesClient](
      IO(DefaultKubernetesClient(Config())))(client => IO.delay(???))

case class DefaultKubernetesClient(config: Config)
case class Config()

And the following build.sbt

name := "domain-management"

version := "0.1"

scalaVersion := "3.0.0-RC1"
scalacOptions += "-Ytasty-reader"

libraryDependencies += ("co.fs2" % "fs2-core_2.13" % "3.0.0-M9").withDottyCompat(scalaVersion.value)

The code portion which is triggering the error is Resource.make[IO, DefaultKubernetesClient] which is failing with the following assert error:

[error] ## Exception when compiling 1 sources to /Users/lvaldes/Projects/domain-management/target/scala-3.0.0-RC1/classes
[error] java.lang.AssertionError: assertion failed: duplicate type F#29860; previous was type F#29662
[error] scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
[error] dotty.tools.dotc.core.Scopes$MutableScope.enter(Scopes.scala:275)
[error] dotty.tools.dotc.core.SymDenotations$ClassDenotation.enterNoReplace(SymDenotations.scala:1868)
[error] dotty.tools.dotc.core.SymDenotations$ClassDenotation.enter(SymDenotations.scala:1859)
[error] dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.finishSym$1(Scala2Unpickler.scala:493)
[error] dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.readDisambiguatedSymbol(Scala2Unpickler.scala:546)
[error] dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.readSymbol(Scala2Unpickler.scala:327)
[error] dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.run(Scala2Unpickler.scala:182)
[error] dotty.tools.dotc.core.classfile.ClassfileParser.unpickleScala$1(ClassfileParser.scala:866)
[error] dotty.tools.dotc.core.classfile.ClassfileParser.unpickleOrParseInnerClasses(ClassfileParser.scala:969)
[error] dotty.tools.dotc.core.classfile.ClassfileParser.parseClass(ClassfileParser.scala:165)
[error] dotty.tools.dotc.core.classfile.ClassfileParser.run$$anonfun$1(ClassfileParser.scala:87)
[error] dotty.tools.dotc.core.classfile.ClassfileParser$$Lambda$7789/0x00000000bbb5ea20.apply(Unknown Source)
[error] dotty.tools.dotc.core.classfile.ClassfileParser.run(ClassfileParser.scala:82)
[error] dotty.tools.dotc.core.ClassfileLoader.load(SymbolLoaders.scala:414)
[error] dotty.tools.dotc.core.ClassfileLoader.doComplete(SymbolLoaders.scala:409)
[error] dotty.tools.dotc.core.SymbolLoader.complete(SymbolLoaders.scala:343)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:167)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.completeOnce(SymDenotations.scala:361)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.unforcedDecls(SymDenotations.scala:385)
[error] dotty.tools.dotc.core.SymDenotations$ClassDenotation.typeParamsFromDecls(SymDenotations.scala:1706)
[error] dotty.tools.dotc.core.SymDenotations$ClassDenotation.typeParams(SymDenotations.scala:1719)
[error] dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.readType(Scala2Unpickler.scala:777)
[error] dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler.readTypeRef$$anonfun$1(Scala2Unpickler.scala:896)
[error] dotty.tools.dotc.core.unpickleScala2.Scala2Unpickler$$Lambda$8042/0x00000000bb2ce420.apply(Unknown Source)

[felixbr]

Hi, I also encountered this issue and tried to make a very minimal but executable repro-case: https://github.com/felixbr/repro-case-11173

Hope this helps.

Cheers
~ Felix