ghc panic: mergeSATInfo

[tianxiaogu]

ghc panic with option -O and -fstatic-argument-transformation. Affected versions include 8.2.2 and HEAD (8.5.20180108)

{-# LANGUAGE DataKinds             #-}
{-# LANGUAGE PartialTypeSignatures #-}
{-# LANGUAGE PolyKinds             #-}
{-# LANGUAGE TypeFamilies          #-}
{-# LANGUAGE TypeOperators         #-}

module T12844 where

barWraper :: ('(r,r') ~ Head rngs, Foo rngs) => FooData rngs
barWraper = bar

bar :: (_) => FooData rngs
bar = barWraper

data FooData rngs

class Foo xs where foo :: (Head xs ~ '(r,r')) => FooData xs

type family Head (xs :: [k]) where Head (x ': xs) = x

Log:

ghc: panic! (the 'impossible' happened)
  (GHC version 8.5.20180108 for x86_64-unknown-linux):
	mergeSATInfo
  Left:STSTSTSTSTSVSV, Right:STSTSTSTSTSVSC
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable
        pprPanic, called at compiler/simplCore/SAT.hs:152:20 in ghc:SAT

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

[simonpj]

Thanks for reporting this.

The Static Argument Transformation could really do with some love from someone.