testmthread: Contains an unsupported closure type (whose implementation is missing)

[runeksvendsen]

Using GHC 8.6.5 on macOS, the testmthread test suite occasionally fails with the following output:

Multithreaded test program for serialisation
normal evaluation (take 3), should be
[10946,17711,28657]
[10946,17711,28657]
014256f379testmthread: Contains an unsupported closure type (whose implementation is missing)
8testmthread: Contains an unsupported closure type (whose implementation is missing)
otestmthread: Contains an unsupported closure type (whose implementation is missing)
testmthread: Contains an unsupported closure type (whose implementation is missing)
testmthread: Contains an unsupported closure type (whose implementation is missing)
testmthread: Contains an unsupported closure type (whose implementation is missing)
testmthread: Contains an unsupported closure type (whose implementation is missing)
testmthread: rContains an unsupported closure type (whose implementation is missing)
k::e  dOO,KK 		w11a07i97t41i61n

g
testmthread: thread blocked indefinitely in an MVar operation

It doesn't always happen, but if I keep running the given test suite repeatedly as follows, it happens after a few runs.

for n in $(seq 1 1000); do if ! cabal run test:testmthread; then break; fi; done

The test failure can be observed in the following CI run: https://github.com/runeksvendsen/packman/actions/runs/12525280654/job/34936688671

TODO

• [ ] Revert #25 once this issue is fixed