[solved] Stuck on Scala 2.13.3 -> How to upgrade?

[lefou]

Hi all, we are currently stuck at Scala 2.13.3, as for any bump to 2.13.4 or 2.13.5 our CI fails with a ConcurrentModificationException thrown by zinc. I, for some reasons, didn't even figured out how to reproduce it locally and also wasn't able to communicate our/my problem in the sbt channel properly.

Here are some pointers: #1116, #1185, #1197, scala/scala#9174

Any help would be really appreciated. 🙏

First posted on Gitter: https://gitter.im/lihaoyi/mill?at=60769326c60826673ba24516

[lefou]

TweKei made some progress in isolating the issue (posted on Gitter):

TzeKei Lee @chikei 08:38
maybe we can refine further (like not using ammonite or something may change classloader ) but this gist https://gist.github.com/chikei/413956ffbf737402a3ae96f2010635c7 reproduce it under ammonite repl 2.3.8-47-7e8c5dd3 with scala 2.13 and with empty out/main/client/compile/dest folder.

Seems to be related to our Java code in mill client.

[chikei]

Here is the minimal example under sbt https://github.com/chikei/zinc-ConcurrentModificationException , it looks like an actual zinc bug. Interestingly I've tried extends some other jdk class and only Thread cause the problem, maybe we can just rewrite FileToStreamTailer without directly extends thread to work around.

[lefou]

Great, I can now reproduce the issue. It's also a nice small example so that a zinc developer can review if we use the zinc compiler API correctly. I'll play a bit with it to see, if we can work around the issue. And I guess, we should report this upstream.

[lefou]

I opened an Issue in sbt/zinc: sbt/zinc#974

[lefou]

My PR sbt/zinc#975 got merged. I hope a new zinc release is cut soon, so that we can update the Scala versions in mill too.

[lefou]

See #1197

[lefou]

Meanwhile, we have mill 0.9.8 released, which is build on Scala 2.13.5!

@chikei Thank you very much for your help! Without it, we couldn't report and identify the issue in zinc that easy. 🙏