Pickling test crash on widened SkolemTypes inside annotation type arguments

[noti0na1]

Block #22909

Compiler version

nightly
3.7.2-RC1-bin-20250515-c481e91-NIGHTLY-git-c481e91

Minimized code

class R[T] extends annotation.StaticAnnotation

// the type param is necessary here to cause crash
class A[T]:
  val next: A[T] = null
  def f: (A[T] @R[this.type], A[T] @R[this.next.type]) = ???

def test =
  val (a, b) = A[String]().f

Output (click arrow to expand)

Run the test:

scala compile --server=false -S 3.nightly -Ytest-pickler Stest.scala

  exception occurred while compiling List(/dotty/Stest.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: <no file>
        during phase: parser
                mode: Mode(ImplicitsEnabled)
     library version: version 2.13.16
    compiler version: version 3.7.2-RC1-bin-20250515-c481e91-NIGHTLY-git-c481e91
            settings: ...

Exception in thread "main" scala.MatchError: AppliedType(TypeRef(ThisType(TypeRef(ThisType(TypeRef(NoPrefix,module class <root>)),module class <empty>)),A),List(TypeRef(TermRef(TermRef(ThisType(TypeRef(NoPrefix,module class <root>)),object scala),Predef),String))) (of class dotty.tools.dotc.core.Types$CachedAppliedType)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readPathTree$1(TreeUnpickler.scala:1267)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readSimpleTree$1(TreeUnpickler.scala:1344)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTree(TreeUnpickler.scala:1687)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readSimpleTree$1(TreeUnpickler.scala:1336)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTree(TreeUnpickler.scala:1687)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTpt(TreeUnpickler.scala:1712)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.$anonfun$46(TreeUnpickler.scala:1628)
        at dotty.tools.tasty.TastyReader.until(TastyReader.scala:135)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTree$1(TreeUnpickler.scala:1628)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTree(TreeUnpickler.scala:1687)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTpt(TreeUnpickler.scala:1712)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readSimpleTree$1(TreeUnpickler.scala:1332)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTree(TreeUnpickler.scala:1687)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTree$1(TreeUnpickler.scala:1551)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTree(TreeUnpickler.scala:1687)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTree$1(TreeUnpickler.scala:1486)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTree(TreeUnpickler.scala:1687)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTree$1(TreeUnpickler.scala:1478)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTree(TreeUnpickler.scala:1687)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthType$1(TreeUnpickler.scala:420)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readType(TreeUnpickler.scala:504)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.$anonfun$6(TreeUnpickler.scala:412)
        at dotty.tools.tasty.TastyReader.until(TastyReader.scala:135)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthType$1(TreeUnpickler.scala:412)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readType(TreeUnpickler.scala:504)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthType$1(TreeUnpickler.scala:420)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readType(TreeUnpickler.scala:504)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTpt(TreeUnpickler.scala:1715)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTree$1(TreeUnpickler.scala:1495)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTree(TreeUnpickler.scala:1687)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthTree$1(TreeUnpickler.scala:1536)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTree(TreeUnpickler.scala:1687)
        at dotty.tools.dotc.core.tasty.TreeUnpickler.readRhs$1$$anonfun$1$$anonfun$1(TreeUnpickler.scala:901)
        at dotty.tools.dotc.core.tasty.TreeUnpickler$LazyReader.complete(TreeUnpickler.scala:1827)
        at dotty.tools.dotc.ast.Trees$WithLazyFields.force(Trees.scala:1134)
        at dotty.tools.dotc.ast.Trees$WithLazyFields.force$(Trees.scala:1130)
        at dotty.tools.dotc.ast.Trees$ValOrDefDef.force(Trees.scala:417)
        at dotty.tools.dotc.ast.Trees$ValDef.forceFields(Trees.scala:929)
        at dotty.tools.dotc.ast.Trees$ValDef.rhs(Trees.scala:930)
        at dotty.tools.dotc.printing.RefinedPrinter.rhsValDef(RefinedPrinter.scala:1069)
        at dotty.tools.dotc.printing.RefinedPrinter.valDefToText$$anonfun$1$$anonfun$1(RefinedPrinter.scala:1003)
        at dotty.tools.dotc.printing.RefinedPrinter.withEnclosingDef(RefinedPrinter.scala:53)
        at dotty.tools.dotc.printing.RefinedPrinter.valDefToText$$anonfun$1(RefinedPrinter.scala:1003)
        at dotty.tools.dotc.printing.RefinedPrinter.dclTextOr(RefinedPrinter.scala:984)
        at dotty.tools.dotc.printing.RefinedPrinter.valDefToText(RefinedPrinter.scala:1004)
        at dotty.tools.dotc.printing.RefinedPrinter.toTextCore(RefinedPrinter.scala:660)
        at dotty.tools.dotc.printing.RefinedPrinter.toText$$anonfun$2(RefinedPrinter.scala:867)
        at dotty.tools.dotc.printing.MessageLimiter.controlled(MessageLimiter.scala:23)
        at dotty.tools.dotc.printing.PlainPrinter.controlled(PlainPrinter.scala:48)
        at dotty.tools.dotc.printing.RefinedPrinter.toText(RefinedPrinter.scala:938)
        at dotty.tools.dotc.ast.Trees$Tree.toText(Trees.scala:193)
        at dotty.tools.dotc.printing.Printer.toText$$anonfun$1(Printer.scala:188)
        at scala.collection.immutable.List.map(List.scala:247)
        at scala.collection.immutable.List.map(List.scala:79)
        at dotty.tools.dotc.printing.Printer.toText(Printer.scala:188)
        at dotty.tools.dotc.printing.RefinedPrinter.blockText(RefinedPrinter.scala:373)
        at dotty.tools.dotc.printing.RefinedPrinter.blockToText(RefinedPrinter.scala:369)
        at dotty.tools.dotc.printing.RefinedPrinter.toTextCore(RefinedPrinter.scala:547)
        at dotty.tools.dotc.printing.RefinedPrinter.toText$$anonfun$2(RefinedPrinter.scala:867)
        at dotty.tools.dotc.printing.MessageLimiter.controlled(MessageLimiter.scala:23)
        at dotty.tools.dotc.printing.PlainPrinter.controlled(PlainPrinter.scala:48)
        at dotty.tools.dotc.printing.RefinedPrinter.toText(RefinedPrinter.scala:938)
        at dotty.tools.dotc.printing.RefinedPrinter.optText(RefinedPrinter.scala:1192)
        at dotty.tools.dotc.printing.RefinedPrinter.rhsDefDef(RefinedPrinter.scala:1073)
        at dotty.tools.dotc.printing.RefinedPrinter.defDefToText$$anonfun$1$$anonfun$1(RefinedPrinter.scala:1062)
        at dotty.tools.dotc.printing.RefinedPrinter.withEnclosingDef(RefinedPrinter.scala:53)
        at dotty.tools.dotc.printing.RefinedPrinter.defDefToText$$anonfun$1(RefinedPrinter.scala:1063)
        at dotty.tools.dotc.printing.RefinedPrinter.dclTextOr(RefinedPrinter.scala:984)
        at dotty.tools.dotc.printing.RefinedPrinter.defDefToText(RefinedPrinter.scala:1064)
        at dotty.tools.dotc.printing.RefinedPrinter.toTextCore(RefinedPrinter.scala:662)
        at dotty.tools.dotc.printing.RefinedPrinter.toText$$anonfun$2(RefinedPrinter.scala:867)
        at dotty.tools.dotc.printing.MessageLimiter.controlled(MessageLimiter.scala:23)
        at dotty.tools.dotc.printing.PlainPrinter.controlled(PlainPrinter.scala:48)
        at dotty.tools.dotc.printing.RefinedPrinter.toText(RefinedPrinter.scala:938)
        at dotty.tools.dotc.ast.Trees$Tree.toText(Trees.scala:193)
        at dotty.tools.dotc.printing.Printer.toText$$anonfun$1(Printer.scala:188)
        at scala.collection.immutable.List.map(List.scala:251)
        at scala.collection.immutable.List.map(List.scala:79)
        at dotty.tools.dotc.printing.Printer.toText(Printer.scala:188)
        at dotty.tools.dotc.printing.Printer.toTextGlobal$$anonfun$2(Printer.scala:196)
        at dotty.tools.dotc.printing.Printer.atPrec(Printer.scala:44)
        at dotty.tools.dotc.printing.Printer.toTextGlobal(Printer.scala:196)
        at dotty.tools.dotc.printing.RefinedPrinter.toTextTemplate(RefinedPrinter.scala:1119)
        at dotty.tools.dotc.printing.RefinedPrinter.templateText$$anonfun$1(RefinedPrinter.scala:1130)
        at dotty.tools.dotc.printing.RefinedPrinter.withEnclosingDef(RefinedPrinter.scala:53)
        at dotty.tools.dotc.printing.RefinedPrinter.templateText(RefinedPrinter.scala:1130)
        at dotty.tools.dotc.printing.RefinedPrinter.recur$2(RefinedPrinter.scala:672)
        at dotty.tools.dotc.printing.RefinedPrinter.toTextCore(RefinedPrinter.scala:682)
        at dotty.tools.dotc.printing.RefinedPrinter.toText$$anonfun$2(RefinedPrinter.scala:867)
        at dotty.tools.dotc.printing.MessageLimiter.controlled(MessageLimiter.scala:23)
        at dotty.tools.dotc.printing.PlainPrinter.controlled(PlainPrinter.scala:48)
        at dotty.tools.dotc.printing.RefinedPrinter.toText(RefinedPrinter.scala:938)
        at dotty.tools.dotc.ast.Trees$Tree.toText(Trees.scala:193)
        at dotty.tools.dotc.printing.Printer.toText$$anonfun$1(Printer.scala:188)
        at scala.collection.immutable.List.map(List.scala:251)
        at scala.collection.immutable.List.map(List.scala:79)
        at dotty.tools.dotc.printing.Printer.toText(Printer.scala:188)
        at dotty.tools.dotc.printing.Printer.toTextGlobal$$anonfun$2(Printer.scala:196)
        at dotty.tools.dotc.printing.Printer.atPrec(Printer.scala:44)
        at dotty.tools.dotc.printing.Printer.toTextGlobal(Printer.scala:196)
        at dotty.tools.dotc.printing.RefinedPrinter.packageDefText(RefinedPrinter.scala:1142)
        at dotty.tools.dotc.printing.RefinedPrinter.toTextCore(RefinedPrinter.scala:692)
        at dotty.tools.dotc.printing.RefinedPrinter.toText$$anonfun$2(RefinedPrinter.scala:867)
        at dotty.tools.dotc.printing.MessageLimiter.controlled(MessageLimiter.scala:23)
        at dotty.tools.dotc.printing.PlainPrinter.controlled(PlainPrinter.scala:48)
        at dotty.tools.dotc.printing.RefinedPrinter.toText(RefinedPrinter.scala:938)
        at dotty.tools.dotc.ast.Trees$Tree.toText(Trees.scala:193)
        at dotty.tools.dotc.printing.Showable.show(Showable.scala:23)
        at dotty.tools.dotc.printing.Showable.show$(Showable.scala:9)
        at dotty.tools.dotc.ast.Trees$Tree.show(Trees.scala:55)
        at dotty.tools.dotc.core.Decorators$.tryToShow(Decorators.scala:286)
        at dotty.tools.dotc.printing.Formatting$ShownDef$Shown$.toStr(Formatting.scala:43)
        at dotty.tools.dotc.printing.Formatting$ShownDef$.dotty$tools$dotc$printing$Formatting$ShownDef$$$toStr(Formatting.scala:57)
        at dotty.tools.dotc.printing.Formatting$ShownDef$Show$given_Show_Seq$InlinedCtxShow$3.run$$anonfun$2(Formatting.scala:88)
        at scala.collection.immutable.List.map(List.scala:247)
        at scala.collection.immutable.List.map(List.scala:79)
        at dotty.tools.dotc.printing.Formatting$ShownDef$Show$given_Show_Seq$InlinedCtxShow$3.run(Formatting.scala:88)
        at dotty.tools.dotc.printing.Formatting$ShownDef$Shown$.runCtxShow(Formatting.scala:38)
        at dotty.tools.dotc.printing.Formatting$StringFormatter.treatArg(Formatting.scala:174)
        at dotty.tools.dotc.printing.Formatting$StringFormatter.$anonfun$3(Formatting.scala:195)
        at scala.collection.LazyZip2$$anon$1$$anon$2.next(LazyZipOps.scala:42)
        at scala.collection.mutable.Growable.addAll(Growable.scala:62)
        at scala.collection.mutable.Growable.addAll$(Growable.scala:57)
        at scala.collection.mutable.ArrayBuilder.addAll(ArrayBuilder.scala:75)
        at scala.collection.IterableOnceOps.toArray(IterableOnce.scala:1505)
        at scala.collection.IterableOnceOps.toArray$(IterableOnce.scala:1498)
        at scala.collection.AbstractIterable.toArray(Iterable.scala:935)
        at scala.Array$.from(Array.scala:73)
        at scala.collection.immutable.ArraySeq$.from(ArraySeq.scala:282)
        at scala.collection.immutable.ArraySeq$.from(ArraySeq.scala:273)
        at scala.collection.ClassTagIterableFactory$AnyIterableDelegate.from(Factory.scala:671)
        at scala.collection.BuildFromLowPriority2$$anon$11.fromSpecific(BuildFrom.scala:115)
        at scala.collection.BuildFromLowPriority2$$anon$11.fromSpecific(BuildFrom.scala:112)
        at scala.collection.LazyZip2.map(LazyZipOps.scala:37)
        at dotty.tools.dotc.printing.Formatting$StringFormatter.assemble(Formatting.scala:195)
        at dotty.tools.dotc.core.Decorators$.i(Decorators.scala:315)
        at dotty.tools.dotc.transform.Pickler.testUnpickler$$anonfun$2(Pickler.scala:461)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.IterableOnceOps.foreach(IterableOnce.scala:619)
        at scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:617)
        at scala.collection.AbstractIterable.foreach(Iterable.scala:935)
        at scala.collection.IterableOps$WithFilter.foreach(Iterable.scala:905)
        at dotty.tools.dotc.transform.Pickler.testUnpickler(Pickler.scala:442)
        at dotty.tools.dotc.transform.Pickler.runOn(Pickler.scala:412)
        at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:368)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
        at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
        at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1324)
        at dotty.tools.dotc.Run.runPhases$1(Run.scala:361)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$1$$anonfun$2(Run.scala:408)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$1$$anonfun$adapted$1(Run.scala:408)
        at scala.Function0.apply$mcV$sp(Function0.scala:42)
        at dotty.tools.dotc.Run.showProgress(Run.scala:470)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:408)
        at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:420)
        at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
        at dotty.tools.dotc.Run.compileUnits(Run.scala:420)
        at dotty.tools.dotc.Run.compileSources(Run.scala:307)
        at dotty.tools.dotc.Run.compile(Run.scala:292)
        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.main(Main.scala)
Compilation failed

Analysis

Before pickling, the match case contains SkolemTypes in the singleton types. When we unpickle the class, it tries to read a path from a singleton type, but it gets an applied type, which is widened from the original skolem type, so it crashes.

[noti0na1]

A side note, is it possible to get rid of the patter matching here?

The generated

        val $1$: Tuple2 =
          matchResult1[Tuple2]: 
            {
              case val x1: Tuple2 = new A().f():Tuple2
              if x1 ne null then
                {
                  case val a: A = x1._1().asInstanceOf[A]
                  case val b: A = x1._2().asInstanceOf[A]
                  return[matchResult1] Tuple2.apply(a, b)
                }
               else ()
              throw new MatchError(x1)
            }
        val a: A = $1$._1().asInstanceOf[A]
        val b: A = $1$._2().asInstanceOf[A]

[noti0na1]

I think the issue may be at Annotation.mapWith