Tuple.toList.toArray raise java.lang.ClassCastException

[esse-byte]

Compiler version

Scala 3.1.0, Scala 3.1.1, Scala 3.1.2 RC1, Scala 3.1.2

Minimized code

val xs = (1, 2).toList
val a1 = xs.toArray              // fine
println((1, 2).toList.toArray)  // this works without exception, but the result is wrong: get a [Ljava.lang.Object rather than [I@
val a2 = (1, 2).toList.toArray // java.lang.ClassCastException

Output

java.lang.ClassCastException: class [Ljava.lang.Object; cannot be cast to class [I ([Ljava.lang.Object; and [I are in module java.base of loader 'bootstrap')
  ... 65 elided
java.lang.NoClassDefFoundError: Could not initialize class rs$line$1$
  at rs$line$1.a1(rs$line$1)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.base/java.lang.reflect.Method.invoke(Method.java:566)
  at dotty.tools.repl.Rendering.$anonfun$4(Rendering.scala:110)
  at scala.Option.map(Option.scala:242)
  at dotty.tools.repl.Rendering.valueOf(Rendering.scala:110)
  at dotty.tools.repl.Rendering.renderVal(Rendering.scala:139)
  at dotty.tools.repl.ReplDriver.$anonfun$10(ReplDriver.scala:335)
  at scala.collection.immutable.List.flatMap(List.scala:293)
  at scala.collection.immutable.List.flatMap(List.scala:79)
  at dotty.tools.repl.ReplDriver.extractAndFormatMembers$1(ReplDriver.scala:335)
  at dotty.tools.repl.ReplDriver.renderDefinitions$$anonfun$2(ReplDriver.scala:358)
  at scala.Option.map(Option.scala:242)
  at dotty.tools.repl.ReplDriver.renderDefinitions(ReplDriver.scala:361)
  at dotty.tools.repl.ReplDriver.compile$$anonfun$2(ReplDriver.scala:280)
  at scala.util.Either.fold(Either.scala:189)
  at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:296)
  at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:230)
  at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:162)
  at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:165)
  at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:186)
  at dotty.tools.repl.ReplDriver.runBody$$anonfun$1(ReplDriver.scala:174)
  at dotty.tools.runner.ScalaClassLoader$.asContext(ScalaClassLoader.scala:80)
  at dotty.tools.repl.ReplDriver.runBody(ReplDriver.scala:174)
  at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:165)
  at xsbt.ConsoleInterface.run(ConsoleInterface.java:52)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.base/java.lang.reflect.Method.invoke(Method.java:566)
  at sbt.internal.inc.AnalyzingCompiler.invoke(AnalyzingCompiler.scala:329)
  at sbt.internal.inc.AnalyzingCompiler.console(AnalyzingCompiler.scala:233)
  at sbt.Console.console0$1(Console.scala:64)
  at sbt.Console.$anonfun$apply$5(Console.scala:74)
  at sbt.Run$.executeSuccess(Run.scala:186)
  at sbt.Console.$anonfun$apply$4(Console.scala:74)
  at sbt.internal.util.Terminal.withRawInput(Terminal.scala:145)
  at sbt.internal.util.Terminal.withRawInput$(Terminal.scala:143)
  at sbt.internal.util.Terminal$ProxyTerminal$.withRawInput(Terminal.scala:384)
  at sbt.Console.$anonfun$apply$3(Console.scala:74)
  at sbt.internal.util.Terminal$TerminalImpl.withRawOutput(Terminal.scala:975)
  at sbt.internal.util.Terminal$ProxyTerminal$.withRawOutput(Terminal.scala:423)
  at sbt.Console.apply(Console.scala:71)
  at sbt.Console.apply(Console.scala:49)
  at sbt.Console.apply(Console.scala:41)
  at sbt.Defaults$.$anonfun$consoleTask$1(Defaults.scala:2232)
  at sbt.Defaults$.$anonfun$consoleTask$1$adapted(Defaults.scala:2218)
  at scala.Function1.$anonfun$compose$1(Function1.scala:49)
  at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:62)
  at sbt.std.Transform$$anon$4.work(Transform.scala:68)
  at sbt.Execute.$anonfun$submit$2(Execute.scala:282)
  at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:23)
  at sbt.Execute.work(Execute.scala:291)
  at sbt.Execute.$anonfun$submit$1(Execute.scala:282)
  at sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
  at sbt.CompletionService$$anon$2.call(CompletionService.scala:64)
  at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
  at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
  at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
  at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
  at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
  at java.base/java.lang.Thread.run(Thread.java:829)
java.lang.NoClassDefFoundError: Could not initialize class rs$line$1$
  at rs$line$1.a2(rs$line$1)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.base/java.lang.reflect.Method.invoke(Method.java:566)
  at dotty.tools.repl.Rendering.$anonfun$4(Rendering.scala:110)
  at scala.Option.map(Option.scala:242)
  at dotty.tools.repl.Rendering.valueOf(Rendering.scala:110)
  at dotty.tools.repl.Rendering.renderVal(Rendering.scala:139)
  at dotty.tools.repl.ReplDriver.$anonfun$10(ReplDriver.scala:335)
  at scala.collection.immutable.List.flatMap(List.scala:293)
  at scala.collection.immutable.List.flatMap(List.scala:79)
  at dotty.tools.repl.ReplDriver.extractAndFormatMembers$1(ReplDriver.scala:335)
  at dotty.tools.repl.ReplDriver.renderDefinitions$$anonfun$2(ReplDriver.scala:358)
  at scala.Option.map(Option.scala:242)
  at dotty.tools.repl.ReplDriver.renderDefinitions(ReplDriver.scala:361)
  at dotty.tools.repl.ReplDriver.compile$$anonfun$2(ReplDriver.scala:280)
  at scala.util.Either.fold(Either.scala:189)
  at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:296)
  at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:230)
  at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:162)
  at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:165)
  at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:186)
  at dotty.tools.repl.ReplDriver.runBody$$anonfun$1(ReplDriver.scala:174)
  at dotty.tools.runner.ScalaClassLoader$.asContext(ScalaClassLoader.scala:80)
  at dotty.tools.repl.ReplDriver.runBody(ReplDriver.scala:174)
  at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:165)
  at xsbt.ConsoleInterface.run(ConsoleInterface.java:52)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.base/java.lang.reflect.Method.invoke(Method.java:566)
  at sbt.internal.inc.AnalyzingCompiler.invoke(AnalyzingCompiler.scala:329)
  at sbt.internal.inc.AnalyzingCompiler.console(AnalyzingCompiler.scala:233)
  at sbt.Console.console0$1(Console.scala:64)
  at sbt.Console.$anonfun$apply$5(Console.scala:74)
  at sbt.Run$.executeSuccess(Run.scala:186)
  at sbt.Console.$anonfun$apply$4(Console.scala:74)
  at sbt.internal.util.Terminal.withRawInput(Terminal.scala:145)
  at sbt.internal.util.Terminal.withRawInput$(Terminal.scala:143)
  at sbt.internal.util.Terminal$ProxyTerminal$.withRawInput(Terminal.scala:384)
  at sbt.Console.$anonfun$apply$3(Console.scala:74)
  at sbt.internal.util.Terminal$TerminalImpl.withRawOutput(Terminal.scala:975)
  at sbt.internal.util.Terminal$ProxyTerminal$.withRawOutput(Terminal.scala:423)
  at sbt.Console.apply(Console.scala:71)
  at sbt.Console.apply(Console.scala:49)
  at sbt.Console.apply(Console.scala:41)
  at sbt.Defaults$.$anonfun$consoleTask$1(Defaults.scala:2232)
  at sbt.Defaults$.$anonfun$consoleTask$1$adapted(Defaults.scala:2218)
  at scala.Function1.$anonfun$compose$1(Function1.scala:49)
  at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:62)
  at sbt.std.Transform$$anon$4.work(Transform.scala:68)
  at sbt.Execute.$anonfun$submit$2(Execute.scala:282)
  at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:23)
  at sbt.Execute.work(Execute.scala:291)
  at sbt.Execute.$anonfun$submit$1(Execute.scala:282)
  at sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
  at sbt.CompletionService$$anon$2.call(CompletionService.scala:64)
  at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
  at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
  at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
  at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
  at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
  at java.base/java.lang.Thread.run(Thread.java:829)

Expectation

Both works

[nicolasstucki]

The source of the problem seems to be in typer while inferring the ClassTag argument.

Tuple2.apply[Int, Int](1, 2).toList.toArray[(Int | (Int | Nothing))](
            scala.reflect.ClassTag.apply[(Int | (Int | Nothing))](
              classOf[Object]
            )
          )

[nicolasstucki]

We get Int | (Int | Nothing) from Tuple.Union[(Int, Int)]

[nicolasstucki]

It seems we are not summoning the correct ClassTag when we have an | type with a Nothing

  println(summon[reflect.ClassTag[Int]]) // classOf[Int]
  println(summon[reflect.ClassTag[Int | Int]]) // classOf[Int]
  println(summon[reflect.ClassTag[Int | 1]]) // classOf[Int]
  println(summon[reflect.ClassTag[Int | Nothing]]) // classOf[Object]

[nicolasstucki]

At line https://github.com/lampepfl/dotty/blob/main/compiler/src/dotty/tools/dotc/typer/Synthesizer.scala#L42,
erasure returns the type Object for Int | Nothing.

Should the erasure of Int | Nothing be Int? If so this would fix our issue. See #14970