Scala 3 Support?

[patryk-celinski]

Are there any plans to update cron4s for Scala 3?

I see that shapeless is used in 10 files and there are some plugins like macro paradise and kind projector that I'm not sure how to assess their influence. Albeit macro paradise uses partialVersion so this is probably not a problem. Shapeless is the main blocker and the fact that it is not needed in Scala 3 and supposedly was replaced by language-level features.

[i10416]

plan for Scala 3 migration

• update some dependencies that don't require hard works: https://github.com/alonsodomin/cron4s/pull/489
• update compiler plugins and test stuffs https://github.com/alonsodomin/cron4s/pull/493
• address compiler warnings/errors for 3
  • https://github.com/alonsodomin/cron4s/pull/501
• formatting(kind projector syntax is not supported by current scalafmt version)
  • https://github.com/alonsodomin/cron4s/pull/502
• improve test coverage
  • it seems current tests overlook some bugs
• update shapeless stuffs
  • [x] https://github.com/alonsodomin/cron4s/pull/504

extra&idea

• replace momentjs with dayjs
  • momentjs is now maintenance mode: https://momentjs.com/docs/#/-project-status/
  • scalajs momentjs binding don't support Scala 3: https://index.scala-lang.org/vpavkin/scala-js-momentjs
• try cats-parse
  • scala parser combinator often uses back-tracking, which sometimes makes it hard to infer behavior
  • cats-parse seems more performant than scala parser combinator

[alonsodomin]

There are several things in the library that need a clean up but it would be better to address after the Scala 3 support is released. I believe it's better to allow users to keep using the same features with latest Scala as that would allow for a smoother transition.

Among the things I would like to clean up is in fact the Scala 2 support. This is a very simple library whose primary functionality is quite stable and most users are happy with it. So once a path towards Scala 3 is given, removing Scala 2 would allow to also remove a lot of warts or convoluted code.

Other changes that I would like to address would be:

• Remove the ability to calculate previous date times. This was an ill-informed feature with a very niche use case and one that can only work reliably in short date ranges. Because of that, it should be removed.
• Change the parser logic. I was never happy with the parser implementation. The first implementation was using fast parse which, yeah, it's fast, and also a hell to maintain (it was basically a macro-porn library with very obscure compilation error messages). As you can see in the code, there is a benchmark using atto parser, the choice of using Scala parser combinators was done based on the fact that being slower than fastparse, it was faster than atto and easy to maintain. Regardless of that, it's true that this is ripe for an improvement and I'm happy to explore the possibilities of other libraries.
• Drop support for MomentJS. As you say, it doesn't have Scala 3 bindings and I believe the community has moved on to better tooling. It's also a library that uses mutation a lot, which makes the implementation having to account for that.
• Support for JS-Joda. Not sure if this can be implemented in the Joda module itself, as cross-platform module. It would be great if it could be done so but it wouldn't be a big deal to have a specific cron4s-js-joda module either.
• Scala Native support? Maybe this one makes sense before removing the Scala 2 support so users could use the library in Scala before having to commit to Scala 3.

Happy to hear about other proposals. In way, I like the idea of keeping the library simple as hell, just being a glorified parser of CRON expressions and a calculator for future dates with a very simple user experience that way other projects can build more advanced systems around it.

[mbaechler]

Hi, I would be quite interested in a release of cron4s with scala 3 support. If there are things to fix, I can offer some help. Let me know. Cheers,

[alonsodomin]

hi @mbaechler, to be fair, everything should be more or less ready, the code in main is already compatible with Scala 3 the only remaining bit is publishing it.

We have an attempt some time ago that failed and live got in the way and I didn't have much time to look into it: https://github.com/alonsodomin/cron4s/actions/runs/5462541330/job/14789162567

I'll try to trigger the build once again so I can see what the problem is and get the published version through the line.

[mbaechler]

Hi @alonsodomin , thank you for your answer, i can't find your new try at publishing the artifacts, if you run it, I can probably have a look at the logs.

Cheers,

[alonsodomin]

Hi @mbaechler just made a general upgrade of the dependencies and gave it another go. The build is failing at the stage in which it generates the Scala docs for Scala 3. You can see the run here:

https://github.com/alonsodomin/cron4s/actions/runs/7366389197

Seems similar to the following issue, although somewhat unrelated... https://github.com/lampepfl/dotty/issues/14143

[mbaechler]

Hi @alonsodomin

I think I nailed the issue here : https://github.com/alonsodomin/cron4s/pull/552

Could you have a look?

[alonsodomin]

thanks a lot @mbaechler

[alonsodomin]

cron4s with support for Scala 3 has been published with version 0.7.0