GADTs: (.text+0xc6): undefined reference to `Main_IsEqual_con_info'

With this module:

{-# LANGUAGE ScopedTypeVariables, GADTs #-}

import Unsafe.Coerce

data IsEqual a b where
    IsEqual :: IsEqual a a

contextsEqual :: cxt1 -> cxt2 -> IsEqual cxt1 cxt2
contextsEqual = unsafeCoerce IsEqual

data Seq from to where
    Nil :: Seq here here

foo :: forall from to . Seq from to
foo = f undefined undefined
    where f :: from -> to -> Seq from to
          f x y = case contextsEqual x y of
                  IsEqual -> Nil

main :: IO ()
main = case foo :: Seq () () of
           Nil -> return ()

I get:

$ ghc --make z -fforce-recomp -O
[1 of 1] Compiling Main             ( z.hs, z.o )
Linking z ...
z.o: In function `smk_info':
(.text+0xc6): undefined reference to `Main_IsEqual_con_info'
collect2: ld returned 1 exit status

with the HEAD and 6.8.2.

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown