VectorMap#{remove, init, tail} broken in Scala 2.13.0-M5

[xuwei-k]

https://github.com/scala/scala/blob/98a68df30390337425388bc9d586a46dacc7c6c4/src/library/scala/collection/immutable/VectorMap.scala#L65-L72

Welcome to Scala 2.13.0-M5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_181).
Type in expressions for evaluation. Or try :help.

scala> import scala.collection.immutable.VectorMap
import scala.collection.immutable.VectorMap

scala> val x = VectorMap(1 -> "a", 2 -> "b")
x: scala.collection.immutable.VectorMap[Int,String] = VectorMap(1 -> a, 2 -> b)

scala> lazy val y = x remove 1
y: scala.collection.immutable.VectorMap[Int,String] = <lazy>

scala> y.size
res0: Int = 1

scala> y.toString
java.util.NoSuchElementException: key not found: 1
  at scala.collection.MapOps.default(Map.scala:217)
  at scala.collection.MapOps.default$(Map.scala:216)
  at scala.collection.AbstractMap.default(Map.scala:343)
  at scala.collection.MapOps.apply(Map.scala:133)
  at scala.collection.MapOps.apply$(Map.scala:132)
  at scala.collection.AbstractMap.apply(Map.scala:343)
  at scala.collection.immutable.VectorMap$$anon$1.next(VectorMap.scala:56)
  at scala.collection.immutable.VectorMap$$anon$1.next(VectorMap.scala:49)
  at scala.collection.Iterator$$anon$9.next(Iterator.scala:552)
  at scala.collection.IterableOnceOps.addString(IterableOnce.scala:1131)
  at scala.collection.IterableOnceOps.addString$(IterableOnce.scala:1126)
  at scala.collection.AbstractIterator.addString(Iterator.scala:1186)
  at scala.collection.MapOps.addString(Map.scala:290)
  at scala.collection.MapOps.addString$(Map.scala:289)
  at scala.collection.AbstractMap.addString(Map.scala:343)
  at scala.collection.IterableOnceOps.mkString(IterableOnce.scala:1076)
  at scala.collection.IterableOnceOps.mkString$(IterableOnce.scala:1074)
  at scala.collection.AbstractIterable.mkString(Iterable.scala:898)
  at scala.collection.Iterable.toString(Iterable.scala:83)
  at scala.collection.Iterable.toString$(Iterable.scala:83)
  at scala.collection.Map.toString(Map.scala:60)
  at scala.collection.Map.toString$(Map.scala:60)
  at scala.collection.AbstractMap.toString(Map.scala:343)
  ... 40 elided

scala> y + (1 -> "c")
res2: scala.collection.immutable.VectorMap[Int,String] = VectorMap(1 -> c, 1 -> c)

/cc @mdedetrich

[xuwei-k]

Welcome to Scala 2.13.0-M5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_181).
Type in expressions for evaluation. Or try :help.

scala> import scala.collection.immutable.VectorMap
import scala.collection.immutable.VectorMap

scala> val x = VectorMap(1 -> "a", 2 -> "b")
x: scala.collection.immutable.VectorMap[Int,String] = VectorMap(1 -> a, 2 -> b)

scala> x.init
java.util.NoSuchElementException: key not found: 1
  at scala.collection.MapOps.default(Map.scala:217)
  at scala.collection.MapOps.default$(Map.scala:216)
  at scala.collection.AbstractMap.default(Map.scala:343)
  at scala.collection.MapOps.apply(Map.scala:133)
  at scala.collection.MapOps.apply$(Map.scala:132)
  at scala.collection.AbstractMap.apply(Map.scala:343)
  at scala.collection.immutable.VectorMap$$anon$1.next(VectorMap.scala:56)
  at scala.collection.immutable.VectorMap$$anon$1.next(VectorMap.scala:49)
  at scala.collection.Iterator$SliceIterator.next(Iterator.scala:1126)
  at scala.collection.Iterator$$anon$9.next(Iterator.scala:552)
  at scala.collection.IterableOnceOps.addString(IterableOnce.scala:1131)
  at scala.collection.IterableOnceOps.addString$(IterableOnce.scala:1126)
  at scala.collection.AbstractIterator.addString(Iterator.scala:1186)
  at scala.collection.IterableOnceOps.mkString(IterableOnce.scala:1076)
  at scala.collection.IterableOnceOps.mkString$(IterableOnce.scala:1074)
  at scala.collection.AbstractIterator.mkString(Iterator.scala:1186)
  at scala.runtime.ScalaRunTime$.inner$1(ScalaRunTime.scala:230)
  at scala.runtime.ScalaRunTime$.stringOf(ScalaRunTime.scala:239)
  at scala.runtime.ScalaRunTime$.replStringOf(ScalaRunTime.scala:247)
  at .$print$lzycompute(<synthetic>:8)
  ... 37 elided

scala> x.tail
java.util.NoSuchElementException: key not found: 2
  at scala.collection.MapOps.default(Map.scala:217)
  at scala.collection.MapOps.default$(Map.scala:216)
  at scala.collection.AbstractMap.default(Map.scala:343)
  at scala.collection.MapOps.apply(Map.scala:133)
  at scala.collection.MapOps.apply$(Map.scala:132)
  at scala.collection.AbstractMap.apply(Map.scala:343)
  at scala.collection.immutable.VectorMap$$anon$1.next(VectorMap.scala:56)
  at scala.collection.immutable.VectorMap$$anon$1.next(VectorMap.scala:49)
  at scala.collection.Iterator$SliceIterator.next(Iterator.scala:1126)
  at scala.collection.Iterator$$anon$9.next(Iterator.scala:552)
  at scala.collection.IterableOnceOps.addString(IterableOnce.scala:1131)
  at scala.collection.IterableOnceOps.addString$(IterableOnce.scala:1126)
  at scala.collection.AbstractIterator.addString(Iterator.scala:1186)
  at scala.collection.IterableOnceOps.mkString(IterableOnce.scala:1076)
  at scala.collection.IterableOnceOps.mkString$(IterableOnce.scala:1074)
  at scala.collection.AbstractIterator.mkString(Iterator.scala:1186)
  at scala.runtime.ScalaRunTime$.inner$1(ScalaRunTime.scala:230)
  at scala.runtime.ScalaRunTime$.stringOf(ScalaRunTime.scala:239)
  at scala.runtime.ScalaRunTime$.replStringOf(ScalaRunTime.scala:247)
  at .$print$lzycompute(<synthetic>:8)
  ... 37 elided

[mdedetrich]

Will fix this today

[adriaanm]

@mdedetrich I've invited you to the contributors team, so we can actually assign this to you ;-)

[SethTisue]

@Ichoran (who I think is on vacation) might a wave of the collections-laws wand turn up any other such bugs...?

[SethTisue]

@xuwei-k nice catch!

@mdedetrich cool, sounds good. we discussed internally whether to rebuild M5 over this (and it also came up on Gitter), but I don't think rebuilding is necessary. this is brand new code nobody is relying on yet, RC1 is fine for a fix. and if anyone wants to beat on VectorMap specifically, they can use a nightly build that includes the fix.

we're extremely pleased to have VectorMap landing, regardless. 💯

[adriaanm]

@emilypi and @fommil, if you have anything of substance to contribute, great! If not, please do refrain. (Wow this is getting old.)

[fommil]

@adriaanm why am I being pulled into this conversation, and why are my comments (asking you why I'm being pulled in) being deleted?

Actually, I don't care. Please just stop pestering me. I am no longer interested in Scala.

[emilypi]

Thanks for your report @xuwei-k! This is a difficult problem to abstract, but it does come down to testing each method of your data structure in a variety of settings. If there is not one present already, I would hope that this contribution came with both a test suite and example usages that would expose bugs like this, and I hope this is Scala's stance in the future to require these sorts of things.