ListBuffer's insert, insertAll, update and updated accept negative positions

[scabug]

None of the following operations should succeed:

scala> import collection.mutable.ListBuffer
import collection.mutable.ListBuffer

scala> val lb = ListBuffer('a, 'b, 'c, 'd, 'e)
lb: scala.collection.mutable.ListBuffer[Symbol] = ListBuffer('a, 'b, 'c, 'd, 'e)

scala> lb.insert(-1, 'x)

scala> lb
res19: scala.collection.mutable.ListBuffer[Symbol] = ListBuffer('a, 'x, 'b, 'c, 'd, 'e)

scala> lb.insertAll(-2, Array('y, 'z))

scala> lb
res21: scala.collection.mutable.ListBuffer[Symbol] = ListBuffer('a, 'y, 'z, 'x, 'b, 'c, 'd, 'e)

scala> lb.update(-3, 'u)

scala> lb
res23: scala.collection.mutable.ListBuffer[Symbol] = ListBuffer('a, 'u, 'z, 'x, 'b, 'c, 'd, 'e)

scala> lb.updated(-4, 'd)
res24: scala.collection.mutable.ListBuffer[Symbol] = ListBuffer('d, 'u, 'z, 'x, 'b, 'c, 'd, 'e)

The documentation even specifies:

IndexOutOfBoundsException
if the index n is not in the valid range 0 <= n <= length. 

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-6632?orig=1
Reporter: @soc
Affected Versions: 2.9.2, 2.10.0-RC1, 2.10.0-RC2, 2.10.0, 2.11.0-M1

[scabug]

@soc said:
Merged scala/scala@522ef79 which fixes this issue for insert, insertAll and update.
updated is not fixed, discussion needed where exactly the fix needs to be added.

[scabug]

@JamesIry said:
Making this change could break user code that "works" with negative indexes. I'm kicking to 2.11.0

[scabug]

@adriaanm said:
Un-assigning to foster work stealing, as announced in https://groups.google.com/forum/?fromgroups=#!topic/scala-internals/o8WG4plpNkw

[scabug]

@gkossakowski said:
Unassigning and rescheduling to M7 as previous deadline was missed.

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@Ichoran said:
Updated still not fixed. I'm happy to do so, if we agree it should be fixed rather than documenting the admittedly weird behavior.

[scabug]

@SethTisue said:
+1 on fixing for 2.11

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@soc said:
Yes, we should fix it. That it hasn't been fixed yet was just due to my limited time available, not the lack of desire.

Imho a good way to start would be to survey whether there is some kind of implicit consensus in the other implementations on how to behave and it's just this one which behaves differently, or whether implementations' behavior in error cases is all over the place.
Additionally, it would make sense to see how other languages/libraries deal with those kinds of input and try to learn whether their approach works better than maybe the straightforward approach we might gather while looking at Scala's collections solely.

[scabug]

@soc said:
This is kind of fishy, too:

scala> import collection.mutable.{ArrayBuffer => ListBuffer}
import collection.mutable.{ArrayBuffer=>ListBuffer}

scala> val lb = ListBuffer('a, 'b, 'c, 'd, 'e)
lb: scala.collection.mutable.ArrayBuffer[Symbol] = ArrayBuffer('a, 'b, 'c, 'd, 'e)

scala> lb.updated(-4, 'd)
res7: scala.collection.mutable.ArrayBuffer[Symbol] = ArrayBuffer('d, 'b, 'c, 'd, 'e)

scala> lb.updated(12, 'd)
java.lang.UnsupportedOperationException: empty.tail
  at scala.collection.TraversableLike$class.tail(TraversableLike.scala:449)
  at scala.collection.mutable.IndexedSeqLike$$anon$1.scala$collection$IndexedSeqOptimized$$super$tail(IndexedSeqLike.scala:52)
  at scala.collection.IndexedSeqOptimized$class.tail(IndexedSeqOptimized.scala:129)
  at scala.collection.mutable.IndexedSeqLike$$anon$1.tail(IndexedSeqLike.scala:52)
  at scala.collection.SeqLike$class.updated(SeqLike.scala:516)
  at scala.collection.AbstractSeq.updated(Seq.scala:41)
  ... 32 elided

[scabug]

@adriaanm said:
Since 2.11.0-RC1 is one week away, pushing all non-blockers without PR to 2.11.1-RC1. Please undo the change if I missed work in progress.

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@Ichoran said:
Fixed updated. Waiting for Jenkins to tell me the fallout, if any.

scala/scala#3530