Dotty crashing when using a loop variable in an enum in a loop local class

[Sparkaar]

Compiler version

Scala compiler version 3.5.2 -- Copyright 2002-2024, LAMP/EPFL
Scala compiler version 3.6.0-RC1-bin-SNAPSHOT-git-18af52a -- Copyright 2002-2024, LAMP/EPFL

Minimized code

object bla{
  for ( NotFound: Char<- (List('a'))) {class crashing{
    enum issue{
    NotFound
  case obligatory
    }
  }
  ;64.asInstanceOf[Char]}
}

Output (click arrow to expand)

-- Warning: bla.scala:2:16 ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
2 |  for ( NotFound: Char<- (List('a'))) {class crashing{
  |                ^
  |                Type ascriptions after patterns other than:
  |                  * variable pattern, e.g. `case x: String =>`
  |                  * number literal pattern, e.g. `case 10.5: Double =>`
  |                are no longer supported. Remove the type ascription or move it to a separate variable pattern.
-- [E129] Potential Issue Warning: bla.scala:4:4 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
4 |    NotFound 
  |    ^^^^^^^^
  |    A pure expression does nothing in statement position
  |
  | longer explanation available when compiling with `-explain`

  unhandled exception while running MegaPhase{lambdaLift, elimStaticThis, countOuterAccesses} on bla.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 -Xno-enrich-error-messages.

     while compiling: bla.scala
        during phase: MegaPhase{lambdaLift, elimStaticThis, countOuterAccesses}
                mode: Mode(ImplicitsEnabled)
     library version: version 2.13.14
    compiler version: version 3.5.2
            settings: 

Exception in thread "main" java.lang.IllegalArgumentException: Could not find proxy for NotFound: Char in [parameter NotFound, method $anonfun, constructor bla, object bla, package <empty>, package <root>], encl = constructor $anon, owners = constructor $anon, anonymous class crashing.this.issue with scala.runtime.EnumValue with scala.deriving.Mirror.Singleton {...}, method $new, object issue, class crashing, method $anonfun, constructor bla, object bla, package <empty>, package <root>; enclosures = constructor $anon, anonymous class crashing.this.issue with scala.runtime.EnumValue with scala.deriving.Mirror.Singleton {...}, package <empty>, package <root>
	at dotty.tools.dotc.transform.LambdaLift$Lifter.searchIn$1(LambdaLift.scala:137)
	at dotty.tools.dotc.transform.LambdaLift$Lifter.proxy(LambdaLift.scala:150)
	at dotty.tools.dotc.transform.LambdaLift$Lifter.proxyRef(LambdaLift.scala:168)
	at dotty.tools.dotc.transform.LambdaLift$Lifter.addFreeArgs$$anonfun$1(LambdaLift.scala:174)
	at scala.collection.immutable.List.map(List.scala:247)
	at dotty.tools.dotc.transform.LambdaLift$Lifter.addFreeArgs(LambdaLift.scala:174)
	at dotty.tools.dotc.transform.LambdaLift.transformApply(LambdaLift.scala:312)
	at dotty.tools.dotc.transform.LambdaLift.transformApply(LambdaLift.scala:311)
	at dotty.tools.dotc.transform.MegaPhase.goApply(MegaPhase.scala:681)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:297)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.loop$2(MegaPhase.scala:471)
	at dotty.tools.dotc.transform.MegaPhase.transformBlock(MegaPhase.scala:476)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:315)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.mapDefDef$1(MegaPhase.scala:265)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:268)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:452)
	at dotty.tools.dotc.transform.MegaPhase.transformSpecificTree(MegaPhase.scala:461)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:373)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:272)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:452)
	at dotty.tools.dotc.transform.MegaPhase.loop$2(MegaPhase.scala:471)
	at dotty.tools.dotc.transform.MegaPhase.transformBlock(MegaPhase.scala:476)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:315)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.mapDefDef$1(MegaPhase.scala:265)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:268)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:452)
	at dotty.tools.dotc.transform.MegaPhase.loop$1(MegaPhase.scala:465)
	at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:465)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:376)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:272)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:452)
	at dotty.tools.dotc.transform.MegaPhase.loop$1(MegaPhase.scala:465)
	at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:465)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:376)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:272)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:452)
	at dotty.tools.dotc.transform.MegaPhase.loop$2(MegaPhase.scala:471)
	at dotty.tools.dotc.transform.MegaPhase.transformBlock(MegaPhase.scala:476)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:315)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.mapDefDef$1(MegaPhase.scala:265)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:268)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:452)
	at dotty.tools.dotc.transform.MegaPhase.loop$2(MegaPhase.scala:471)
	at dotty.tools.dotc.transform.MegaPhase.transformBlock(MegaPhase.scala:476)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:315)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.loop$3(MegaPhase.scala:486)
	at dotty.tools.dotc.transform.MegaPhase.transformTrees(MegaPhase.scala:486)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:296)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.loop$2(MegaPhase.scala:471)
	at dotty.tools.dotc.transform.MegaPhase.transformBlock(MegaPhase.scala:476)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:315)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.mapDefDef$1(MegaPhase.scala:265)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:268)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:452)
	at dotty.tools.dotc.transform.MegaPhase.transformSpecificTree(MegaPhase.scala:461)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:373)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.transformNamed$1(MegaPhase.scala:272)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:452)
	at dotty.tools.dotc.transform.MegaPhase.loop$1(MegaPhase.scala:465)
	at dotty.tools.dotc.transform.MegaPhase.transformStats(MegaPhase.scala:465)
	at dotty.tools.dotc.transform.MegaPhase.mapPackage$1(MegaPhase.scala:396)
	at dotty.tools.dotc.transform.MegaPhase.transformUnnamed$1(MegaPhase.scala:399)
	at dotty.tools.dotc.transform.MegaPhase.transformTree(MegaPhase.scala:454)
	at dotty.tools.dotc.transform.MegaPhase.transformUnit(MegaPhase.scala:481)
	at dotty.tools.dotc.transform.MegaPhase.run(MegaPhase.scala:493)
	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.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.dotc.Driver.process(Driver.scala:201)
	at dotty.tools.dotc.Driver.process(Driver.scala:169)
	at dotty.tools.dotc.Driver.process(Driver.scala:181)
	at dotty.tools.dotc.Driver.main(Driver.scala:211)
	at dotty.tools.MainGenericCompiler$.run$1(MainGenericCompiler.scala:162)
	at dotty.tools.MainGenericCompiler$.main(MainGenericCompiler.scala:186)
	at dotty.tools.MainGenericCompiler.main(MainGenericCompiler.scala)

[Gedochao]

A slightly more readable version of the reproduction:

object bla {
  for (NotFound: Char <- (List('a'))) {
    class crashing {
      enum issue {
        NotFound
        case obligatory
      }
    }; 64.asInstanceOf[Char]
  }
}

[KacperFKorban]

Some proress, a minimization with less interacting features. The problem seems to be in LambdaLift. My current hypothesis is that the extends issue() call should be recorded as a dependency in this case:

scala3/compiler/src/dotty/tools/dotc/transform/Dependencies.scala

Line 238 in dc0bb59

case tree: Select =>

but isn't.

def f() =
  val NotFound: Char = 'a'
  class crashing() {
    class issue() {
      NotFound
    }
    class issueM() {
      val obligatory: issue =
        class anonIssue()
          extends issue() {}
        new anonIssue()
    }
  }

[KacperFKorban]

fixed by #22356