Do not rely on ArrayIndexOOBE in new-Vector Vector.{head,last}.
#8827
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szeiger
reviewed
Mar 26, 2020
This is necessary for Scala.js, where
`ArrayIndexOutOfBoundsException`s are Undefined Behavior, and
cannot be reliably caught.
Those methods throw a `NoSuchElementException` for an empty vector,
and those exceptions have never been considered UB in Scala.js
before. It is therefore a breach of contract for
`Vector.{head,last}` to become UB on empty vectors.
There are many other places where we catch AIOOBEs, but in those
other places we throw an `IndexOutOfBoundsException` instead.
While it is not quite correct to turn them into UBs either, at
*least* there is precedent for OOBEs to be considered UB in
Scala.js. So this commit does not change them, being afraid of the
consequences to JVM performance.
It *is* still bad, though (index out of bounds on Scala collections
were never UB before), but at least it is a bit less bad than
before.
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ArrayIndexOOBE in Vector.{head,last}.ArrayIndexOOBE in new-Vector Vector.{head,last}.
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…alajs
Do not rely on `ArrayIndexOOBE` in `Vector.{head,last}`.
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…alajs
Do not rely on `ArrayIndexOOBE` in `Vector.{head,last}`.
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This is necessary for Scala.js, where
ArrayIndexOutOfBoundsExceptions are Undefined Behavior, and cannot be reliably caught.Those methods throw a
NoSuchElementExceptionfor an empty vector, and those exceptions have never been considered UB in Scala.js before. It is therefore a breach of contract forVector.{head,last}to become UB on empty vectors.There are many other places where we catch AIOOBEs, but in those other places we throw an
IndexOutOfBoundsExceptioninstead. While it is not quite correct to turn them into UBs either, at least there is precedent for OOBEs to be considered UB in Scala.js. So this commit does not change them, being afraid of the consequences to JVM performance.It is still bad, though (index out of bounds on Scala collections were never UB before), but at least it is a bit less bad than before.
This combines with #8828 to fix scala/bug#11920.