Simon Redding (Oct 05 2026 at 16:48): Simon Redding (Oct 05 2026 at 16:48):Hi All,
Since upgrading to nightly-2026-10-04-130536d previously working source code (Cliff.roc) is now throwing:
simon@neckbeard:~/working/cliff$ roc check Cliff.roc
thread 457108 panic: compiler bug: instantiation widened a closed tag union
Cannot print stack trace: stack tracing is disabled
Aborted (core dumped)
I'd be very grateful for any suggestions on how to troubleshoot this issue.
Anton (Oct 05 2026 at 17:49):Hi @Simon Redding,
It looks like we already have an issue for that open with the label urgent. Feel free to add your source code to that issue to make sure we resolve both cases.
Anton (Oct 05 2026 at 17:58):Can you give roc check Cliff.roc --no-cache a try?
Simon Redding (Oct 05 2026 at 18:01):--no-cache doesn't make any difference.
Anton (Oct 05 2026 at 18:06):Alright, so this may have a different cause. Can you make a new github issue and mention #11678 as possibly related? You do not need to make a minimal reproduction, we can fix it given the full source code.
Simon Redding (Oct 05 2026 at 18:07):OK. Will do.
Anton (Oct 05 2026 at 18:08):I'd be very grateful for any suggestions on how to troubleshoot this issue.
While you wait on a fix for the issue you could ask an LLM to make a minimal repro so that you can avoid the specific pattern that triggers the panic.
Simon Redding (Oct 05 2026 at 19:54):Anton said:
Alright, so this may have a different cause. Can you make a new github issue and mention #11678 as possibly related? You do not need to make a minimal reproduction, we can fix it given the full source code.
I've raised #12095
Anton (Oct 06 2026 at 13:56):Excellent, Richard has already assigned himself to the issue :)
Simon Redding (Oct 08 2026 at 10:35):This appears to be resolve in the latest nightly.
Thank you @Anton @Richard Feldman
Last updated: Oct 15 2026 at 17:56 UTC