`NoClassDefFoundError:` while executing macro expansion

[WojciechMazur]

When trying to reproduce and minimize OpenCB failure in zio/zio-prelude Open CB logs failing due to too restrictive cyclic macro dependency which is probably a regression (it works in previous version) I've stumbled upon other, possibly related issue.

Compiler version

All Scala 3 versions

Minimized code

// main.scala
package prelude

sealed trait Assertion[-A]:
  def unary_! : Assertion[A] = ???
  def apply(a: A): Either[AssertionError, Unit] = ???
object Assertion:
  val anything: Assertion[Any] = ???
  def greaterThanOrEqualTo[A](value: A)(implicit ordering: Ordering[A]): Assertion[A] = ???

sealed trait AssertionError

abstract class NewtypeCustom[A] {
  type Type
  protected inline def validateInline(inline value: A): Unit

  inline def apply(inline a1: A): Type = {
    validateInline(a1)
    a1.asInstanceOf[Type]
  }
}
abstract class Newtype[A] extends NewtypeCustom[A] {
  def assertion: Assertion[A] = Assertion.anything
  protected inline def validateInline(inline value: A): Unit = ${
    Macros.validateInlineImpl[A]('assertion, 'value)
  }
}


abstract class Subtype[A] extends Newtype[A] {
  type Type <: A
}


package object newtypes {
  type Natural = Natural.Type
  object Natural extends Subtype[Int] {

    override inline def assertion = Assertion.greaterThanOrEqualTo(0)
  
    val one: Natural =  Natural(1) // triggers macro
  }
}

// macro.scala
package prelude
import scala.quoted.*

object Macros {
  def validateInlineImpl[A: Type](assertionExpr: Expr[Assertion[A]], a: Expr[A])(using
      Quotes
  ): Expr[Unit] = {
    import quotes.reflect.*
    val crashRoot = assertionExpr.value
    '{ () }

  }
  given [A](using Type[A]): FromExpr[Assertion[A]] with {
    def unapply(assertion: Expr[Assertion[A]])(using Quotes): Option[Assertion[A]] = {
      import quotes.reflect.*

      assertion match {
        case '{ Assertion.greaterThanOrEqualTo[A](${ LiteralUnlift(value) })($_) } =>
          Some(Assertion.greaterThanOrEqualTo(value)(orderingForValue(value)))
        case _ => None
      }
    }
  }

  object LiteralUnlift {
    def unapply[A: Type](expr: Expr[A])(using Quotes): Option[A] = expr match {
      case '{ ${ Expr(int) }: Int }       => Some(int)
      case '{ Int.MaxValue }              => Some(Int.MaxValue.asInstanceOf[A])
      case '{ Int.MinValue }              => Some(Int.MinValue.asInstanceOf[A])
      case '{ ${ Expr(string) }: String } => Some(string)
      case '{ ${ Expr(double) }: Double } => Some(double)
      case '{ ${ Expr(float) }: Float }   => Some(float)
      case '{ ${ Expr(long) }: Long }     => Some(long)
      case '{ ${ Expr(short) }: Short }   => Some(short)
      case '{ ${ Expr(byte) }: Byte }     => Some(byte)
      case '{ ${ Expr(char) }: Char }     => Some(char)
      case _                              => None
    }
  }

  private def orderingForValue(any: Any)(using Quotes): Ordering[Any] = null.asInstanceOf[Ordering[Any]]
}

Output (click arrow to expand)

-- Error: /Users/wmazur/projects/sandbox/core.scala:40:31 ----------------------
40 |    val one: Natural =  Natural(1) // triggers macro
   |                        ^^^^^^^^^^
   |Exception occurred while executing macro expansion.
   |java.lang.NoClassDefFoundError: prelude/Assertion$
   |    at prelude.Macros$given_FromExpr_Assertion.unapply(macro.scala:19)
   |    at scala.quoted.Quotes.value(Quotes.scala:68)
   |    at scala.quoted.Quotes.value$(Quotes.scala:44)
   |    at scala.quoted.runtime.impl.QuotesImpl.value(QuotesImpl.scala:41)
   |    at prelude.Macros$.validateInlineImpl(macro.scala:9)
   |Caused by: java.lang.ClassNotFoundException: prelude.Assertion$
   |    at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:445)
   |    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:587)
   |    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
   |    at prelude.Macros$given_FromExpr_Assertion.unapply(macro.scala:19)
   |    at scala.quoted.Quotes.value(Quotes.scala:68)
   |    at scala.quoted.Quotes.value$(Quotes.scala:44)
   |    at scala.quoted.runtime.impl.QuotesImpl.value(QuotesImpl.scala:41)
   |    at prelude.Macros$.validateInlineImpl(macro.scala:9)
   |    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   |    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
   |    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   |    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
   |    at dotty.tools.dotc.quoted.Interpreter.interpretedStaticMethodCall$$anonfun$1(Interpreter.scala:174)
   |    at dotty.tools.dotc.quoted.Interpreter.stopIfRuntimeException(Interpreter.scala:231)
   |    at dotty.tools.dotc.quoted.Interpreter.interpretedStaticMethodCall(Interpreter.scala:174)
   |    at dotty.tools.dotc.quoted.Interpreter.interpretTree(Interpreter.scala:80)
   |    at dotty.tools.dotc.transform.Splicer$SpliceInterpreter.interpretTree(Splicer.scala:266)
   |    at dotty.tools.dotc.quoted.Interpreter.interpretTree$$anonfun$2(Interpreter.scala:99)
   |    at dotty.tools.dotc.transform.Splicer$.$anonfun$2(Splicer.scala:61)
   |    at scala.Option.fold(Option.scala:263)
   |    at dotty.tools.dotc.transform.Splicer$.splice(Splicer.scala:61)
   |    at dotty.tools.dotc.inlines.Inliner.dotty$tools$dotc$inlines$Inliner$$expandMacro(Inliner.scala:1051)
   |    at dotty.tools.dotc.inlines.Inliner$InlineTyper.typedSplice(Inliner.scala:838)
   |    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3160)
   |    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3199)
   |    at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:174)
   |    at dotty.tools.dotc.inlines.Inliner$InlineTyper.typedUnadapted(Inliner.scala:918)
   |    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3276)
   |    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3280)
   |    at dotty.tools.dotc.typer.ReTyper.typedTyped(ReTyper.scala:65)
   |    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3120)
   |    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3199)
   |    at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:174)
   |    at dotty.tools.dotc.inlines.Inliner$InlineTyper.typedUnadapted(Inliner.scala:918)
   |    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3276)
   |    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3280)
   |    at dotty.tools.dotc.inlines.Inliner.inlined(Inliner.scala:680)
   |    at dotty.tools.dotc.inlines.Inlines$InlineCall.expand(Inlines.scala:481)
   |    at dotty.tools.dotc.inlines.Inlines$.inlineCall(Inlines.scala:152)
   |    at dotty.tools.dotc.inlines.Inliner$InlineTyper.inlineIfNeeded(Inliner.scala:914)
   |    at dotty.tools.dotc.inlines.Inliner$InlineTyper.typedApply(Inliner.scala:819)
   |    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3115)
   |    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3199)
   |    at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:174)
   |    at dotty.tools.dotc.inlines.Inliner$InlineTyper.typedUnadapted(Inliner.scala:918)
   |    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3276)
   |    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3280)
   |    at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3329)
   |    at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3348)
   |    at dotty.tools.dotc.typer.Typer.typedBlockStats(Typer.scala:1193)
   |    at dotty.tools.dotc.typer.Typer.typedBlock(Typer.scala:1197)
   |    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3123)
   |    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3199)
   |    at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:174)
   |    at dotty.tools.dotc.inlines.Inliner$InlineTyper.typedUnadapted(Inliner.scala:918)
   |    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3276)
   |    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3280)
   |    at dotty.tools.dotc.typer.ReTyper.typedTyped(ReTyper.scala:65)
   |    at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3120)
   |    at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3199)
   |    at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:174)
   |    at dotty.tools.dotc.inlines.Inliner$InlineTyper.typedUnadapted(Inliner.scala:918)
   |    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3276)
   |    at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3280)
   |    at dotty.tools.dotc.inlines.Inliner.inlined(Inliner.scala:680)
   |    at dotty.tools.dotc.inlines.Inlines$InlineCall.expand(Inlines.scala:481)
   |    at dotty.tools.dotc.inlines.Inlines$.inlineCall(Inlines.scala:152)
   |    at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:96)
   |    at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1595)
   |    at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:67)
   |    at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:90)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.loop$2(tpd.scala:1254)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1254)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1256)
   |    at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:58)
   |    at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:109)
   |    at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1600)
   |    at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:67)
   |    at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:90)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.loop$2(tpd.scala:1254)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1254)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1256)
   |    at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:58)
   |    at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:109)
   |    at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1600)
   |    at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:67)
   |    at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:90)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.loop$2(tpd.scala:1254)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1254)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1256)
   |    at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1611)
   |    at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:67)
   |    at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:98)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.loop$2(tpd.scala:1254)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1254)
   |    at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1256)
   |    at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1611)
   |    at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:67)
   |    at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:98)
   |    at dotty.tools.dotc.transform.Inlining$$anon$2.transform(Inlining.scala:59)
   |    at dotty.tools.dotc.transform.MacroTransform.run(MacroTransform.scala:18)
   |    at dotty.tools.dotc.transform.Inlining.run(Inlining.scala:35)
   |    at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:354)
   |    at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
   |    at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
   |    at scala.collection.immutable.List.foreach(List.scala:333)
   |    at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:360)
   |    at dotty.tools.dotc.transform.Inlining.runOn(Inlining.scala:39)
   |    at dotty.tools.dotc.Run.runPhases$1$$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.compileUnits(Run.scala:267)
   |    at dotty.tools.dotc.Run.compileSuspendedUnits(Run.scala:371)
   |    at dotty.tools.dotc.Driver.finish(Driver.scala:57)
   |    at dotty.tools.dotc.Driver.doCompile(Driver.scala:38)
   |    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)
   |
   |----------------------------------------------------------------------------
   |Inline stack trace
   |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   |This location contains code that was inlined from core.scala:23
23 |  protected inline def validateInline(inline value: A): Unit = ${
   |                                                               ^
24 |    Macros.validateInlineImpl[A]('assertion, 'value)
25 |  }
   |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   |This location contains code that was inlined from core.scala:23
17 |    validateInline(a1)
   |    ^^^^^^^^^^^^^^^^^^
    ----------------------------------------------------------------------------

[som-snytt]

Someone just mentioned this error on discord -- I said something about the scala 2 options for macro classloader, and they said they were on Scala 3. I don't remember which room. I'll follow up if I can.

[nicolasstucki]

There is a cyclic dependency in the macro. This should have been caught by the macro expansion and reported as such.

object newtypes should be defined in a different file because the macro expansion depends on the compiled implementation of Assertion.

[WojciechMazur]

object newtypes should be defined in a different file because the macro expansion depends on the compiled implementation of Assertion.

There might have been a simplificaiton in the reproducer - in the original most of types are placed in multiple files:

• trait Assertion
• class AssertionError
• class NewType, class NewTypeCustom
• object newtypes
  However, when split like that the reproducer compiles. It might suggest that the reproducer is incomplete and the bug might be still around. When current fix would be merged I'll check if the project compiles.

[nicolasstucki]

When current fix would be merged I'll check if the project compiles.

If the classes are in the same file it might not compile. Now we detect the cycle correctly and suspend the compilation of that file. We could have two outcomes: (1) the non-suspended files are compiled and allow the compilation of the suspended file, or (2) there is a true cycle and the compilation fails, in this later case we need to split the files.