NullPointerException using Vector in 2.13.8 and 3.1.1

[jackkoenig]

Reproduction steps

Scala version: 2.13.8, 3.1.1

val vector1 = Vector.fill(1000)(0)

// Some prepending, manifesting the bug seems to require 2 separate prepends
val vector2 = List.fill(25)(1) ++: 2 +: vector1

// Now append for fun and profit
val vector3 = vector2 ++ List.fill(40)(3)

// Any iteration will do although might hit NullPointerException in different place
vector3.collect { case n => n }

Scala 2.13.8 Scastie: https://scastie.scala-lang.org/Z2g0dZaoRvG6iZchGULXBQ
Scala 3.1.1 Scastie: https://scastie.scala-lang.org/fA91IRCPRi2PSDkPWUOFOg

Problem

Run the above and you will see the stack trace:

java.lang.NullPointerException: Cannot read the array length because "this.a1" is null
	at scala.collection.immutable.NewVectorIterator.advance(Vector.scala:2031)
	at scala.collection.immutable.NewVectorIterator.next(Vector.scala:1992)
	at scala.collection.StrictOptimizedIterableOps.collect(StrictOptimizedIterableOps.scala:150)
	at scala.collection.StrictOptimizedIterableOps.collect$(StrictOptimizedIterableOps.scala:136)
	at scala.collection.immutable.Vector.collect(Vector.scala:113)
	at Playground$.delayedEndpoint$Playground$1(main.scala:12)
	at Playground$delayedInit$body.apply(main.scala:2)
	at scala.Function0.apply$mcV$sp(Function0.scala:39)
	at scala.Function0.apply$mcV$sp$(Function0.scala:39)
	at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:17)
	at scala.App.$anonfun$main$1(App.scala:76)
	at scala.App.$anonfun$main$1$adapted(App.scala:76)
	at scala.collection.IterableOnceOps.foreach(IterableOnce.scala:563)
	at scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:561)
	at scala.collection.AbstractIterable.foreach(Iterable.scala:926)
	at scala.App.main(App.scala:76)
	at scala.App.main$(App.scala:74)
	at Playground$.main(main.scala:2)
	at Main$.main(main.scala:19)

[SethTisue]

nice catch and minimization!

@scala/collections anyone feel like digging into this?

[jackkoenig]

Note of interest, if you change the appended collection size from 40 to 30, you get the NullPointerException on the append:

val vector1 = Vector.fill(1000)(0)

// Some prepending, manifesting the bug seems to require 2 separate prepends
val vector2 = List.fill(25)(1) ++: 2 +: vector1

// Now append for fun and profit
val vector3 = vector2 ++ List.fill(30)(3)

Gives:

java.lang.NullPointerException: Cannot read the array length because "copyIfDifferentSize_a" is null
	at scala.collection.immutable.VectorBuilder.result(Vector.scala:1761)
	at scala.collection.immutable.Vector.appendedAll0(Vector.scala:235)
	at scala.collection.immutable.Vector3.appendedAll0(Vector.scala:637)
	at scala.collection.immutable.Vector.appendedAll(Vector.scala:203)
	at scala.collection.immutable.Vector.appendedAll(Vector.scala:113)
	at scala.collection.SeqOps.concat(Seq.scala:187)
	at scala.collection.SeqOps.concat$(Seq.scala:187)
	at scala.collection.AbstractSeq.concat(Seq.scala:1161)
	at scala.collection.IterableOps.$plus$plus(Iterable.scala:726)
	at scala.collection.IterableOps.$plus$plus$(Iterable.scala:726)
	at scala.collection.AbstractIterable.$plus$plus(Iterable.scala:926)
	at Playground$.delayedEndpoint$Playground$1(main.scala:9)
	at Playground$delayedInit$body.apply(main.scala:2)
	at scala.Function0.apply$mcV$sp(Function0.scala:39)
	at scala.Function0.apply$mcV$sp$(Function0.scala:39)
	at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:17)
	at scala.App.$anonfun$main$1(App.scala:76)
	at scala.App.$anonfun$main$1$adapted(App.scala:76)
	at scala.collection.IterableOnceOps.foreach(IterableOnce.scala:563)
	at scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:561)
	at scala.collection.AbstractIterable.foreach(Iterable.scala:926)
	at scala.App.main(App.scala:76)
	at scala.App.main$(App.scala:74)
	at Playground$.main(main.scala:2)
	at Main$.main(main.scala:19)
	at Main.main(main.scala)

Scala 2.13.8 Scastie: https://scastie.scala-lang.org/xmHvVtcCQuCkwdIN4SRCJA

[griggt]

Hmm...

scala> vector2.##
java.lang.ArrayIndexOutOfBoundsException: 8
  at scala.collection.immutable.Vector3.apply(Vector.scala:549)
  at scala.util.hashing.MurmurHash3.indexedSeqHash(MurmurHash3.scala:259)
  at scala.util.hashing.MurmurHash3$.seqHash(MurmurHash3.scala:354)
  at scala.collection.Seq.hashCode(Seq.scala:41)
  at scala.collection.Seq.hashCode$(Seq.scala:41)
  at scala.collection.AbstractSeq.hashCode(Seq.scala:1161)
  at scala.runtime.Statics.anyHash(Statics.java:127)
  ... 32 elided

[griggt]

Scala 2.13.2 is OK, 2.13.3 is bad. Maybe regressed in scala/scala#9036 ?

[lrytz]

incorrect assumption that k is positive

scala/scala#9036 (comment)