NPE when compiling HK type bounds from TASTY

[nicolasstucki]

While compiling tests/pos/i974.scala (source bellow) from TASTY

class Foo[A]
class Bar[CC[X] <: Foo[CC[X]]]

the unpickling fails with

java.lang.NullPointerException
	at dotty.tools.dotc.core.Hashable.finishHash(Hashable.scala:65)
	at dotty.tools.dotc.core.Hashable.finishHash$(Hashable.scala:64)
	at dotty.tools.dotc.core.Types$Type.finishHash(Types.scala:87)
	at dotty.tools.dotc.core.Hashable.doHash(Hashable.scala:89)
	at dotty.tools.dotc.core.Hashable.doHash$(Hashable.scala:88)
	at dotty.tools.dotc.core.Types$Type.doHash(Types.scala:87)
	at dotty.tools.dotc.core.Types$HKLambda.computeHash(Types.scala:2639)
	at dotty.tools.dotc.core.Types$CachedProxyType.hash(Types.scala:1460)
	at dotty.tools.dotc.core.Hashable.finishHash(Hashable.scala:39)
	at dotty.tools.dotc.core.Hashable.finishHash$(Hashable.scala:38)
	at dotty.tools.dotc.core.Types$Type.finishHash(Types.scala:87)
	at dotty.tools.dotc.core.Hashable.finishHash(Hashable.scala:47)
	at dotty.tools.dotc.core.Hashable.finishHash$(Hashable.scala:44)
	at dotty.tools.dotc.core.Types$Type.finishHash(Types.scala:87)
	at dotty.tools.dotc.core.Hashable.doHash(Hashable.scala:80)
	at dotty.tools.dotc.core.Hashable.doHash$(Hashable.scala:79)
	at dotty.tools.dotc.core.Types$Type.doHash(Types.scala:87)
	at dotty.tools.dotc.core.Types$TypeBounds.computeHash(Types.scala:3506)
	at dotty.tools.dotc.core.Types$CachedProxyType.hash(Types.scala:1460)
	at dotty.tools.dotc.core.Uniques$.unique(Uniques.scala:28)
	at dotty.tools.dotc.core.Types$TypeBounds$.apply(Types.scala:3546)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthType$1(TreeUnpickler.scala:261)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readType(TreeUnpickler.scala:361)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readTpt(TreeUnpickler.scala:1057)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readNewDef(TreeUnpickler.scala:709)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readIndexedDef(TreeUnpickler.scala:635)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$Completer.complete(TreeUnpickler.scala:91)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:246)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeInfo$1(SymDenotations.scala:209)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.info(SymDenotations.scala:211)
	at dotty.tools.dotc.core.TypeApplications$.$anonfun$typeParams$extension$1(TypeApplications.scala:175)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
	at dotty.tools.dotc.core.TypeApplications$.typeParams$extension(TypeApplications.scala:171)
	at dotty.tools.dotc.core.TypeApplications$.$anonfun$appliedTo$extension0$1(TypeApplications.scala:336)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
	at dotty.tools.dotc.core.TypeApplications$.appliedTo$extension0(TypeApplications.scala:335)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthType$1(TreeUnpickler.scala:259)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readType(TreeUnpickler.scala:361)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.$anonfun$readType$6(TreeUnpickler.scala:259)
	at dotty.tools.dotc.core.tasty.TastyReader.until(TastyReader.scala:125)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readLengthType$1(TreeUnpickler.scala:259)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readType(TreeUnpickler.scala:361)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.$anonfun$readType$5(TreeUnpickler.scala:224)
	at dotty.tools.dotc.core.Types$HKTypeLambda.<init>(Types.scala:2962)
	at dotty.tools.dotc.core.Types$HKTypeLambda$.apply(Types.scala:3013)
	at dotty.tools.dotc.core.Types$HKTypeLambda$.apply(Types.scala:3009)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.$anonfun$readType$2(TreeUnpickler.scala:222)
	at scala.collection.MapLike.getOrElse(MapLike.scala:128)
	at scala.collection.MapLike.getOrElse$(MapLike.scala:126)
	at scala.collection.AbstractMap.getOrElse(Map.scala:59)
	at dotty.tools.dotc.core.tasty.TreeUnpickler$TreeReader.readMethodic$1(TreeUnpickler.scala:217)
...

[nicolasstucki]

tests/pos/i2888.scala has the same issue.

[smarter]

Like #3816 this is caused by a loop in unpickling (reading def of CC at Addr(9)):

reading def of Bar at Addr(4)
  reading def of CC at Addr(9)
    reading type TYPEBOUNDS at Addr(12)
      reading type TYPEREF at Addr(14)
        reading type TERMREFpkg at Addr(16)
      reading type TYPELAMBDAtype at Addr(18)
        reading type TYPEBOUNDS at Addr(41)
          reading type SHARED at Addr(43)
            reading type TYPEREF at Addr(14)
              reading type TERMREFpkg at Addr(16)
          reading type TYPEREF at Addr(45)
            reading type SHARED at Addr(47)
              reading type TERMREFpkg at Addr(16)
        reading type APPLIEDtype at Addr(20)
          reading type TYPEREF at Addr(22)
            reading type THIS at Addr(24)
              reading type TYPEREFpkg at Addr(25)
          reading type APPLIEDtype at Addr(27)
            reading type TYPEREFsymbol at Addr(29)
              reading type THIS at Addr(31)
                reading type TYPEREFsymbol at Addr(32)
                  reading type SHARED at Addr(34)
                    reading type THIS at Addr(24)
                      reading type TYPEREFpkg at Addr(25)
            reading type PARAMtype at Addr(36)
            reading def of CC at Addr(9)
              reading type TYPEBOUNDS at Addr(12)
                reading type TYPEREF at Addr(14)
                  reading type TERMREFpkg at Addr(16)
                reading type TYPELAMBDAtype at Addr(18)
Exception in thread "main" java.lang.AssertionError: assertion failed
        at scala.Predef$.assert(Predef.scala:204)
        at dotty.tools.dotc.core.Types$HKLambda.computeHash(Types.scala:2637)

[smarter]

Closing as a duplicate of #3816 since they give similar error messages since #3842 and seem to have the same root cause.