id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
3421,Iface Lint failure panic with HEAD ghc-stage1,Ashley Yakeley,,"A.hs:
{{{
module A where

class C1 a where
    c1 :: p a -> Maybe a

class C2 a where
    c2 :: a

instance (C1 a) => C2 (Maybe a) where
    c2 = c1 undefined
}}}

B.hs:
{{{
module B where
import A

c2' :: (C1 a) => Maybe a
c2' = c2
}}}
Compiling them with ""ghc-stage1 -dcore-lint -O2"" gives this:
{{{
inplace/bin/ghc-stage1 -c A.hs -dcore-lint -O2 && inplace/bin/ghc-stage1 -c B.hs -dcore-lint -O2
ghc-stage1: panic! (the 'impossible' happened)
  (GHC version 6.11.20090806 for x86_64-unknown-linux):
	Iface Lint failure
    Unfolding of main:A.$fC2Maybe_c2{v r33}
      <no location info>:
          In the expression: ($dC1{v aed} [lid]
                              `cast` (main:A.NTCo:T:C1{tc r31} a{tv aec} [tv]
                                      :: <pred>main:A.T:C1{tc r36} a{tv aec} [tv]
                                                 ~
                                               forall (p{tv ael} [tv] :: ghc-prim:GHC.Prim.*{(w) tc 34d}
                                                                         -> ghc-prim:GHC.Prim.*{(w) tc 34d}).
                                               p{tv ael} [tv] a{tv aec} [tv]
                                               -> base:Data.Maybe.Maybe{tc rm} a{tv aec} [tv]))
                               @ ghc-prim:GHC.Prim.Any{(w) tc 31N}
          Kinds don't match in type application:
          Type variable:
              p{tv ael} [tv] :: ghc-prim:GHC.Prim.*{(w) tc 34d}
                                -> ghc-prim:GHC.Prim.*{(w) tc 34d}
          Arg type:
              ghc-prim:GHC.Prim.Any{(w) tc 31N} :: ghc-prim:GHC.Prim.*{(w) tc 34d}

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
}}}
",bug,closed,normal,,Compiler,6.11,fixed,,,Linux,x86_64 (amd64),,Unknown,,,,