While developing a typechecker plugin, I experienced this error message. > ghc: panic! (the 'impossible' happened) > (GHC version 8.6.2 for x86_64-unknown-linux): > flatten_args wandered into deeper water than usual > Call stack: > CallStack (from HasCallStack): > callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in ghc:Outputable > pprPanic, called at compiler/typecheck/TcFlatten.hs:1331:24 in ghc:TcFlatten > > Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
I'm sending this email just in case a dev is curious how this panic arises or if another plugin developer sees the same thing -- the error message is not very informative, and the corresponding GHC source code is a bit obtuse. Based on the relevant GHC source code and my recent plugin edits, I was able to guess correctly that this was due to me generating an extra sort argument to a promoted datacon. Specifically, I was incorrectly using > mkTyConApp (promoteDataCon _) [typeKind k,k,...] instead of just > mkTyConApp (promoteDataCon _) [k,...] Thanks! HTH. -Nick
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