Making case class constructor package-private crashes the compiler when there's a circular dependency

[lbialy]

Compiler version

3.3.1

Minimized code

This caused by a circular reference between stack.scala (the trait StackFactory references Export) and macro.scala. If the trait is moved to another file this example compiles (and that's the workaround).

3 files, same directory, scala-cli setup:

package.scala

//> using scala 3.3.1

stack.scala

package crash.test

case class Stack private[crash] ( // remove private[crash] to make error go away
    exports: String,
    dependsOn: Vector[Int]
)

trait StackFactory:
  val exports: Export.type = Export

  def apply(dependsOn: Int*): Stack =
    Export().copy(dependsOn = dependsOn.toVector)

macro.scala

package crash.test

import scala.language.dynamics

import scala.quoted.*

object Export extends Dynamic:
  inline def applyDynamic(name: "apply")(inline args: Any*): Stack = ${
    applyDynamicImpl('args)
  }

  def applyDynamicImpl(args: Expr[Seq[Any]])(using Quotes): Expr[Stack] =
    import quotes.reflect.*

    '{ Stack("", Vector.empty) }

Output (click arrow to expand)

scala-cli compile --server=false .

  unhandled exception while running inlining on /Users/lbialy/Projects/foss/dotty-crash-replication/stack.scala

  An unhandled exception was thrown in the compiler.
  Please file a crash report here:
  https://github.com/lampepfl/dotty/issues/new/choose

     while compiling: <no file>
        during phase: <no phase>
                mode: Mode(ImplicitsEnabled)
     library version: version 2.13.10
    compiler version: version 3.3.1
            settings: -classpath /Users/lbialy/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala3-library_3/3.3.1/scala3-library_3-3.3.1.jar:/Users/lbialy/Library/Caches/Coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.10/scala-library-2.13.10.jar -d /Users/lbialy/Projects/foss/dotty-crash-replication/.scala-build/dotty-crash-replication_3a37a7372a/classes/main -java-output-version 17 -sourceroot /Users/lbialy/Projects/foss/dotty-crash-replication

                tree: EmptyTree
       tree position: :<unknown>
           tree type: <notype>
              symbol: val <none>
           call site: package <root> in module class <root>

  == Source file context for tree position ==


Exception while compiling /Users/lbialy/Projects/foss/dotty-crash-replication/macro.scala, /Users/lbialy/Projects/foss/dotty-crash-replication/package.scala, /Users/lbialy/Projects/foss/dotty-crash-replication/stack.scala
Exception in thread "main" java.lang.NoClassDefFoundError: crash/test/Stack$
	at java.base/java.lang.Class.getDeclaredMethods0(Native Method)
	at java.base/java.lang.Class.privateGetDeclaredMethods(Class.java:3402)
	at java.base/java.lang.Class.getMethodsRecursive(Class.java:3543)
	at java.base/java.lang.Class.getMethod0(Class.java:3529)
	at java.base/java.lang.Class.getMethod(Class.java:2225)
	at dotty.tools.dotc.quoted.Interpreter.getMethod(Interpreter.scala:219)
	at dotty.tools.dotc.quoted.Interpreter.interpretedStaticMethodCall(Interpreter.scala:171)
	at dotty.tools.dotc.quoted.Interpreter.interpretTree(Interpreter.scala:80)
	at dotty.tools.dotc.transform.Splicer$SpliceInterpreter.interpretTree(Splicer.scala:258)
	at dotty.tools.dotc.quoted.Interpreter.interpretTree$$anonfun$2(Interpreter.scala:99)
	at dotty.tools.dotc.transform.Splicer$.$anonfun$2(Splicer.scala:60)
	at scala.Option.fold(Option.scala:263)
	at dotty.tools.dotc.transform.Splicer$.splice(Splicer.scala:60)
	at dotty.tools.dotc.inlines.Inliner.dotty$tools$dotc$inlines$Inliner$$expandMacro(Inliner.scala:1048)
	at dotty.tools.dotc.inlines.Inliner$InlineTyper.typedSplice(Inliner.scala:839)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3092)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3112)
	at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:146)
	at dotty.tools.dotc.inlines.Inliner$InlineTyper.typedUnadapted(Inliner.scala:915)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3184)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3188)
	at dotty.tools.dotc.typer.ReTyper.typedTyped(ReTyper.scala:65)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3053)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3112)
	at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:146)
	at dotty.tools.dotc.inlines.Inliner$InlineTyper.typedUnadapted(Inliner.scala:915)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3184)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3181)
	at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3188)
	at dotty.tools.dotc.inlines.Inliner.inlined(Inliner.scala:681)
	at dotty.tools.dotc.inlines.Inlines$InlineCall.expand(Inlines.scala:444)
	at dotty.tools.dotc.inlines.Inlines$.inlineCall(Inlines.scala:152)
	at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:95)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1567)
	at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:67)
	at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:89)
	at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.loop$2(tpd.scala:1244)
	at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1244)
	at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformBlock(tpd.scala:1249)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1518)
	at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:43)
	at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:91)
	at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:50)
	at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:89)
	at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.loop$2(tpd.scala:1244)
	at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1244)
	at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1246)
	at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:58)
	at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:108)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1572)
	at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:67)
	at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:89)
	at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.loop$2(tpd.scala:1244)
	at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1244)
	at dotty.tools.dotc.ast.tpd$TreeMapWithPreciseStatContexts.transformStats(tpd.scala:1246)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1580)
	at dotty.tools.dotc.ast.TreeMapWithImplicits.transform(TreeMapWithImplicits.scala:67)
	at dotty.tools.dotc.transform.Inlining$InliningTreeMap.transform(Inlining.scala:97)
	at dotty.tools.dotc.transform.Inlining$$anon$2.transform(Inlining.scala:58)
	at dotty.tools.dotc.transform.MacroTransform.run(MacroTransform.scala:18)
	at dotty.tools.dotc.transform.Inlining.run(Inlining.scala:34)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:327)
	at scala.collection.immutable.List.map(List.scala:246)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:331)
	at dotty.tools.dotc.transform.Inlining.runOn(Inlining.scala:38)
	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:246)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1321)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:262)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:270)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:279)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:279)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:200)
	at dotty.tools.dotc.Driver.finish(Driver.scala:58)
	at dotty.tools.dotc.Driver.doCompile(Driver.scala:38)
	at dotty.tools.dotc.Driver.process(Driver.scala:197)
	at dotty.tools.dotc.Driver.process(Driver.scala:165)
	at dotty.tools.dotc.Driver.process(Driver.scala:177)
	at dotty.tools.dotc.Driver.main(Driver.scala:207)
	at dotty.tools.dotc.Main.main(Main.scala)
Caused by: java.lang.ClassNotFoundException: crash.test.Stack$
	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)
	... 82 more
Compilation failed

[WojciechMazur]

It seems to be a regression introduced in 3.0.3-RC1-bin-20210804-07c3b4d-NIGHTLY, bisect points to 9fd494a

[nicolasstucki]

The crash is already fixed by #19645.

The code now has a compilation error due to a cyclic dependency between the two files. This dependency is a consequence of the unstable inline accessor that gets generated by the access to private the constructor of Stack. This can be detected with -WunstableInlineAccessors.

There are two ways to fix this code:

1. Split Stack and StackFactory into two files. Stack and export can be compiled before it is used in StackFactory
2. Avoid the creation of the inline acceesors by defining the apply method of Stack with @publicInBinary

object Stack:
  @scala.annotation.publicInBinary
  private[crash] def apply(exports: String, dependsOn: Vector[Int]): Stack = new Stack(exports, dependsOn)