mightEqualLater finds an unbound cbv
Summary
The file Bug.hs produces
{-# LANGUAGE
DataKinds,
GADTs,
QuantifiedConstraints,
TypeFamilies
#-}
module Bug where
type family Foo x where
Foo (Maybe a) = a
data Bug1 a b c where
Bug1 :: (a ~ 'True => Show b, a ~ 'False => Show c) => Bug1 a b c
data Bug2 f a b where
Bug2 :: (a ~ 'True => f b) => Bug2 f a b
bug :: b ~ Maybe (Foo b) => Bug2 Show a (Foo b) -> Bug1 a (Foo b) Int
bug Bug2 = Bug1
ghc: panic! (the 'impossible' happened)
(GHC version 9.2.0.20210422:
mightEqualLater finds an unbound cbv
cbv_aLN[cbv:1]
[]
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/Solver/Monad.hs:2558:16 in ghc:GHC.Tc.Solver.Monad
Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug
Steps to reproduce
Run ghci Bug
.
Expected behavior
File should type check successfully.
Environment
- GHC version used: 9.2.1-alpha2 (9.2.0.20210422)
Optional:
- Operating System: Arch Linux
- System Architecture: x86-64