scalamock 7+ not uses Scala LTS

[visma-alexander-maslov]

Scala has LTS version https://virtuslab.com/blog/technology/the-scala-3-compatibility-story/#lts-and-scala-next

It feels like for the generally used library it is better to stick to the LTS branch and and upgrade to the next one when it is absolutely necessary.

The ScalaMock 7.0.0 introduced dependency to Scala 3.4.2 which breaks builds depending on LTS Scala 3.3.x as compiler is not able to read TASTY format from the 3.4.2.

some info about versioning and binary compatibility
https://virtuslab.com/blog/technology/the-scala-3-compatibility-story/
https://docs.scala-lang.org/scala3/reference/language-versions/binary-compatibility.html
https://www.scala-lang.org/blog/2022/08/17/long-term-compatibility-plans.html

[visma-alexander-maslov]

More info about Scala versions and development guarantees: https://www.scala-lang.org/development/

[goshacodes]

Hi, @visma-alexander-maslov.

scalamock 6 uses scala 3 experimental features and exploits compiler bug which breaks @experimental correct behavior.

current LTS not gives you an opportunity to add Test / scalaOptions := "-experimental", so actually you can't use scalamock on LTS without exploiting this bug

If you are afraid of migrating to at least 3.4.3 you should wait till next LTS release.

scalamock will use next LTS (and will give guaranties on that in the future) as soon as it is released

[prolativ]

@goshacodes what's the compiler bug that's being exploited exactly?

[goshacodes]

Annotation @experimental is present here.
https://github.com/paulbutcher/ScalaMock/blob/maintenance-6.x/shared/src/main/scala-3/org/scalamock/clazz/MockMaker.scala#L27

But you can omit it outside of macro scope. No annotation here, as you see.
https://github.com/paulbutcher/ScalaMock/blob/maintenance-6.x/shared/src/test/scala-3/com/paulbutcher/test/Scala3Spec.scala

This is a bug, which allows you to use scalamock 6.x.x actually without annotating every peace of your test code with @experimental
https://github.com/paulbutcher/ScalaMock/blob/maintenance-6.x/build.sbt#L7-L11

I guess, exploit word was too harsh for this one, this bug is not very scary in terms of scalamock

[prolativ]

So in theory, if scala LTS provided the -experimental compiler flag, would the compiler version used by scalamock be downgraded to 3.3.x?
I'm wondering if the inability of using scalamock with scala LTS is a valid use case for backporting this compiler flag to LTS at all (putting aside whether this change could/should be done in the compiler itself) or if there were some other blockers for using LTS from scalamocks'perspective or if it's already too late to rollback things and downgrade the compiler as scalamocks' new stable major version is already out

[goshacodes]

I can't be sure, it is now impossible to compile even with 3.3.0, since TupledFunction is used, but I think everything should work and compiler version used by scalamock can be downgraded without any problems

[goshacodes]

No backport of experimental compiler flag to LTS from compiler team, so the issue will be open and pinned until next LTS

scala/scala3#18571 (comment)

[goshacodes]

I'm going to backport everything to 2.13 and downgrade scala 3 to LTS