assertion failed: class Array while introspecting Array[Byte] in a macro

[pshirshov]

I had a feeling like we already reported this, but can't find anything.

The compiler fails while izumi-reflect introspects Array[Byte] with an obscure stacktrace:

java.lang.AssertionError: assertion failed: class Array
	at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
	at dotty.tools.backend.jvm.BCodeHelpers.primitiveOrClassToBType$1(BCodeHelpers.scala:717)
	at dotty.tools.backend.jvm.BCodeHelpers.dotty$tools$backend$jvm$BCodeHelpers$$typeToTypeKind(BCodeHelpers.scala:737)
	at dotty.tools.backend.jvm.BCodeHelpers$BCInnerClassGen.toTypeKind(BCodeHelpers.scala:202)
	at dotty.tools.backend.jvm.BCodeHelpers$BCInnerClassGen.toTypeKind$(BCodeHelpers.scala:130)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.toTypeKind(BCodeSkelBuilder.scala:134)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genConstant(BCodeBodyBuilder.scala:581)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadTo(BCodeBodyBuilder.scala:450)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:303)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.loop$1(BCodeBodyBuilder.scala:1209)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadArguments(BCodeBodyBuilder.scala:1216)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genApply(BCodeBodyBuilder.scala:835)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadTo(BCodeBodyBuilder.scala:385)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadTo(BCodeBodyBuilder.scala:465)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:303)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadTo(BCodeBodyBuilder.scala:320)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:303)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genStat(BCodeBodyBuilder.scala:117)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genBlockTo$$anonfun$1(BCodeBodyBuilder.scala:1093)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:334)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genBlockTo(BCodeBodyBuilder.scala:1093)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadTo(BCodeBodyBuilder.scala:457)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:303)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.loop$1(BCodeBodyBuilder.scala:1209)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadArguments(BCodeBodyBuilder.scala:1216)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genApply(BCodeBodyBuilder.scala:835)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadTo(BCodeBodyBuilder.scala:385)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:303)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genStat(BCodeBodyBuilder.scala:117)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genBlockTo$$anonfun$1(BCodeBodyBuilder.scala:1093)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:334)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genBlockTo(BCodeBodyBuilder.scala:1093)
	at dotty.tools.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadTo(BCodeBodyBuilder.scala:457)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.emitNormalMethodBody$1(BCodeSkelBuilder.scala:893)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genDefDef(BCodeSkelBuilder.scala:916)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen(BCodeSkelBuilder.scala:693)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen$$anonfun$1(BCodeSkelBuilder.scala:699)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:334)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.gen(BCodeSkelBuilder.scala:699)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genPlainClass(BCodeSkelBuilder.scala:293)
	at dotty.tools.backend.jvm.CodeGen.genClass(CodeGen.scala:160)
	at dotty.tools.backend.jvm.CodeGen.genClassDef$1(CodeGen.scala:62)
	at dotty.tools.backend.jvm.CodeGen.genClassDefs$1(CodeGen.scala:117)
	at dotty.tools.backend.jvm.CodeGen.genClassDefs$1$$anonfun$1(CodeGen.scala:115)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:334)
	at dotty.tools.backend.jvm.CodeGen.genClassDefs$1(CodeGen.scala:115)
	at dotty.tools.backend.jvm.CodeGen.genUnit(CodeGen.scala:120)
	at dotty.tools.backend.jvm.GenBCode.run(GenBCode.scala:90)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:380)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:334)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:373)
	at dotty.tools.backend.jvm.GenBCode.runOn(GenBCode.scala:98)
	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:343)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:336)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:384)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:396)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:396)
	at dotty.tools.dotc.Run.compileSources(Run.scala:282)
	at dotty.tools.dotc.Run.compile(Run.scala:267)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
	at dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:141)
	at dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)
	at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:91)
	at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:193)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
	at sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:248)
	at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:183)
	at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:163)
	at sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:239)
	at sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:163)
	at sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:211)
	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:534)
	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:534)
	at sbt.internal.inc.Incremental$.$anonfun$apply$5(Incremental.scala:180)
	at sbt.internal.inc.Incremental$.$anonfun$apply$5$adapted(Incremental.scala:178)
	at sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:464)
	at sbt.internal.inc.IncrementalCommon$CycleState.next(IncrementalCommon.scala:116)
	at sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:56)
	at sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:52)
	at sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:263)
	at sbt.internal.inc.Incremental$.$anonfun$incrementalCompile$8(Incremental.scala:419)
	at sbt.internal.inc.Incremental$.withClassfileManager(Incremental.scala:506)
	at sbt.internal.inc.Incremental$.incrementalCompile(Incremental.scala:406)
	at sbt.internal.inc.Incremental$.apply(Incremental.scala:172)
	at sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:534)
	at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:488)
	at sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:332)
	at sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:425)
	at sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137)
	at sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:2371)
	at sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2321)
	at sbt.internal.server.BspCompileTask$.$anonfun$compute$1(BspCompileTask.scala:31)
	at sbt.internal.io.Retry$.apply(Retry.scala:47)
	at sbt.internal.io.Retry$.apply(Retry.scala:29)
	at sbt.internal.io.Retry$.apply(Retry.scala:24)
	at sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:31)
	at sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2319)
	at scala.Function1.$anonfun$compose$1(Function1.scala:49)
	at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:63)
	at sbt.std.Transform$$anon$4.work(Transform.scala:69)
	at sbt.Execute.$anonfun$submit$2(Execute.scala:283)

	at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:24)

Here is the repro: https://scastie.scala-lang.org/3P7O5JyuSaaEzHQ9WUGoGQ

It fails on any Scala 3 version.

It looks like it's a compiler bug as it only happens with Arrays. If we improperly use the API, the diagnostic message should be improved, at the moment it's completely misleading.

Once this is resolved, zio/izumi-reflect#474 might be closed and the bounty should remain unclaimed.

[Gedochao]

Scala CLI repro:

//> using dep dev.zio::izumi-reflect:2.3.10
@main def main() = izumi.reflect.Tag.tagFromTagMacro[Array[Byte]]

We'll need this minimized without the izumi-reflect dependency.

[pshirshov]

I don't think I can do it. We have a stable repro and a reasonable stacktrace. Although this bug seem to be happening lot later than the macro phase and i-r macros are ones of the most complicated ones which ever existed for Scala. Moreover, from what I can remember, there were similarly looking bugs which were affected by mere syntactic rearrangements.

So, for me the effort required for further minimization looks insurmountable.

[jchyb]

Minimisation:
Macro.scala:

import scala.quoted._

object Macro:
  inline def test() = ${testImpl}
  def testImpl(using Quotes): Expr[Any] = {
    import quotes.reflect._
    val tpe = TypeRepr.of[Array[Byte]] match
      case AppliedType(tycons, _) => tycons
    Literal(ClassOfConstant(tpe)).asExpr
  }

Main.scala:

@main def main() = Macro.test()

We need to add -Xcheck-macros check for parameters of classOf[] (and perhaps other type parameter lists too) - though for classOf this probably only matters for Arrays

As a side note, for anyone struggling with similar issues, calling macro methods with -Xprint:inlining scalac option is always useful for noticing any incoherency in the outputted code.

[pshirshov]

@jchyb : there is an open bounty for this: zio/izumi-reflect#474 , you may claim it if you wish. You can't open an empty P/R, but a single-line test would suffice.