GHC2021 makes the impossible possible (No skolem info)
Summary
Tried to use GHC2021, but GHC crashes. I didn't figure out the exact problem yet. It probably has to do with a specific extension.
The error message leads to this piece of code: https://github.com/jumper149/deriving-trans/blob/fb8492bc8347eac8b3c7844d0b54dae0b683c719/src/Control/Monad/Trans/Compose.hs#L189
deriving via Mtl.T.ContT r (t2 (m :: Type -> Type))
instance Mtl.MonadCont (ComposeT (Mtl.T.ContT r) t2 m)
Steps to reproduce
Run nix build
on this commit: https://github.com/jumper149/deriving-trans/commit/fb8492bc8347eac8b3c7844d0b54dae0b683c719
You can also look at the GitHub Actions of the commit, but I'm pretty sure only this is relevant:
building
Preprocessing library for deriving-trans-0.6.1.0..
Building library for deriving-trans-0.6.1.0..
[1 of 7] Compiling Control.Monad.Accum.OrphanInstances ( src/Control/Monad/Accum/OrphanInstances.hs, dist/build/Control/Monad/Accum/OrphanInstances.o, dist/build/Control/Monad/Accum/OrphanInstances.dyn_o )
[2 of 7] Compiling Control.Monad.Select.OrphanInstances ( src/Control/Monad/Select/OrphanInstances.hs, dist/build/Control/Monad/Select/OrphanInstances.o, dist/build/Control/Monad/Select/OrphanInstances.dyn_o )
[3 of 7] Compiling Control.Monad.Trans.Elevator ( src/Control/Monad/Trans/Elevator.hs, dist/build/Control/Monad/Trans/Elevator.o, dist/build/Control/Monad/Trans/Elevator.dyn_o )
[4 of 7] Compiling Control.Monad.Trans.Compose.Transparent ( src/Control/Monad/Trans/Compose/Transparent.hs, dist/build/Control/Monad/Trans/Compose/Transparent.o, dist/build/Control/Monad/Trans/Compose/Transparent.dyn_o )
[5 of 7] Compiling Control.Monad.Trans.Compose ( src/Control/Monad/Trans/Compose.hs, dist/build/Control/Monad/Trans/Compose.o, dist/build/Control/Monad/Trans/Compose.dyn_o )
src/Control/Monad/Trans/Compose.hs:189:37: error:ghc: panic! (the 'impossible' happened)
(GHC version 9.2.4:
No skolem info:
[k_aeaQ]
Call stack:
CallStack (from HasCallStack):
callStackDoc, called at compiler/GHC/Utils/Panic.hs:181:37 in ghc:GHC.Utils.Panic
pprPanic, called at compiler/GHC/Tc/Errors.hs:2912:17 in ghc:GHC.Tc.Errors
Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug
Expected behavior
Just works (tm)?
Environment
- GHC version used: 9.2.4
- Nix 2.12.0 with flakes enabled
Optional:
- Operating System: NixOS Linux
- System Architecture: x86_64