Compiler crashes with a combination of context function and extends AnyVal

[lenguyenthanh]

Compiler version

I tried with 3.3.0, 3.3.5, 3.6.4 and 3.nightly

Minimized code

//> using scala 3.nightly
// if we removed `extends AnyVal` it works
class Inner(body: Int ?=> Int) extends AnyVal:
  // this needs to be context function to makes compiler crashes
  def rescue: Int ?=> Int = ???

Output (click arrow to expand)

unhandled exception while running erasure on {retracted}/compiler-crash.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: {retracted}/scripts/compiler-crash.scala
    during phase: erasure
            mode: Mode(ImplicitsEnabled)
 library version: version 2.13.16
compiler version: version 3.7.0-RC1-bin-20250308-133dcb3-NIGHTLY-git-133dcb3
        settings: -classpath {retracted}/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala3-library_3/3.7.0-RC1-bin-20250308-133dcb3-NIGHTLY/scala3-library_3-3.7.0-RC1-bin-20250308-133dcb3-NIGHTLY.jar:{retracted}/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.16/scala-library-2.13.16.jar -d /{retracted}/.scala-build/scripts_84160669fb-59de36a8e6/classes/main -sourceroot {retracted}/scripts

Exception in thread "main" scala.MatchError: Apply(Ident(rescue$extension),List(This(Ident(Inner)))) (of class dotty.tools.dotc.ast.Trees$Apply)
at dotty.tools.dotc.transform.Erasure$Typer.skipContextClosures$1(Erasure.scala:952)
at dotty.tools.dotc.transform.Erasure$Typer.typedDefDef(Erasure.scala:954)
at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3555)
at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3657)
at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3735)
at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3740)
at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3762)
at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3808)
at dotty.tools.dotc.transform.Erasure$Typer.typedStats(Erasure.scala:1085)
at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:3236)
at dotty.tools.dotc.transform.Erasure$Typer.typedClassDef(Erasure.scala:1061)
at dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:3561)
at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3565)
at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3657)
at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3735)
at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3740)
at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3762)
at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3808)
at dotty.tools.dotc.transform.Erasure$Typer.typedStats(Erasure.scala:1085)
at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:3369)
at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3607)
at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3658)
at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3735)
at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3740)
at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3851)
at dotty.tools.dotc.transform.Erasure.run(Erasure.scala:145)
at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:383)
at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
at scala.collection.immutable.List.foreach(List.scala:334)
at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:376)
at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:346)
at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1324)
at dotty.tools.dotc.Run.runPhases$1(Run.scala:339)
at dotty.tools.dotc.Run.compileUnits$$anonfun$1$$anonfun$2(Run.scala:386)
at dotty.tools.dotc.Run.compileUnits$$anonfun$1$$anonfun$adapted$1(Run.scala:386)
at scala.Function0.apply$mcV$sp(Function0.scala:42)
at dotty.tools.dotc.Run.showProgress(Run.scala:448)
at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:386)
at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:398)
at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
at dotty.tools.dotc.Run.compileUnits(Run.scala:398)
at dotty.tools.dotc.Run.compileSources(Run.scala:285)
at dotty.tools.dotc.Run.compile(Run.scala:270)
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.dotc.Main.mai

[odersky]

I think we need to disallow context functions as value class arguments. To do this, we need to edit Checking.checkDerivedValueClass.

[bracevac]

We should probably forbid value classes for context-function types in the first place. That's not what the mechanism is designed for. Crashing over this is of course not good and requires fixing regardless.

Edit: Martin beat me to it :P

[olhotak]

Potential spree candidate. @mbovel