Repeated "impossible" go_axiom_rule error.
I am getting the following error repeatedly:
ghc: panic! (the 'impossible' happened) (GHC version 8.4.1 for x86_64-unknown-linux): go_axiom_rule Sub0R Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/iface/TcIface.hs:1371:15 in ghc:TcIface
I got it on 8.2.1, and tried upgrading to 8.4.1 to see if it went away, but it did not.
It occurs frequently when I do a
--make and recompile a subset of modules. I can avoid it by force-recompiling all modules, although of course this is inefficient.
Since I'm working with a codebase of thousands of lines and don't understand ghc's innards, I'm not sure where to start looking for the cause, to produce a minimal failing example. But it did start happening around the time I expanded my use of this module:
Since there are unsafe operations in there, it is possible it is doing something illicit, but it is hard to see how it would cause this.