Iterator behavior different in Scala 2.13.8 and Scala 3.1.1

[JD557]

Reproduction steps

Unfortunately, I couldn't minimize this bug, but I can point to some relevant commits:

On JD557/minart@5cf7dc8, running sbt +2.13.8 imageJVM/test will fail, while sbt +3.1.1 imageJVM/test will succeed. Simply reimplementing some operations to use next/hasNext fixed the problem.

Scala version: 2.13.8 and 3.1.1 (not sure which one has the "bug")

Problem

It appears that (sometimes) on 2.13.8 calling take(n).toArray multiple times can return an empty array (similar to what happens on Vector.iterator).
OTOH, on 3.1.1, calling take(n).toArray multiple times seems to work as List.iterator, and will just keep on iterating.

I understand that "calling take(n).toArray multiple times" is undefined behavior, but since the stdlib is the same, I expected the code to have the same undefined behavior on both compiler versions

[som-snytt]

Scala 3 uses the Scala 2 standard library but can lag, so it won't necessarily see the latest fixes.

The rule not to reuse iterators is hard and fast. Edit: I see you decided to use only next and hasNext instead of any API that requires discarding the previous iterator.

[SethTisue]

Oh good call, that does seem like a possible cause — 3.1.1 uses the 2.13.6 standard library. (The 2.13.8 upgrade has been merged but it's not clear to me yet if it will make a 3.1.x release or be held for 3.2.)

A bunch of collections changes landed in 2.13.7 (and a few more in 2.13.8).

@JD557 Can you try it with 2.13.6 and let us know?

[SethTisue]

it's not clear to me yet if it will make a 3.1.x release or be held for 3.2

duh... it'll be in 3.1.2. I should have thought to check this:

Welcome to Scala 3.1.2-RC2 (17.0.2, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                    
scala> util.Properties.versionString
val res0: String = version 2.13.8

[JD557]

Indeed, 2.13.6 passes the tests.

Closing this then.
Thanks for the help, this was driving me crazy.