[GHC] #9102: Assertion failure in CoreUtils.lhs

[GHC]

#9102: Assertion failure in CoreUtils.lhs
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       Reporter:  tmcdonell         |             Owner:
           Type:  bug               |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Compiler          |           Version:  7.8.2
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 I happened to be using a debug build of ghc-7.8.2, and got this assertion
 failure compiling [http://hackage.haskell.org/package/fclabels-2.0.1
 fclabels].

 {{{
 [ 7 of 10] Compiling Data.Label.Total ( src/Data/Label/Total.hs,
 dist/build/Data/Label/Total.o )

 <no location info>:
     ghc: panic! (the 'impossible' happened)
   (GHC version 7.8.2.20140429 for x86_64-unknown-linux):
         ASSERT failed!
     file compiler/coreSyn/CoreUtils.lhs line 194
     coercion Nth:0
                dt{v d7gF} [lid] passed to mkCast
 base:Control.Category.id{v rkl} [gid[ClassOp]]
                                                    @ ghc-
 prim:GHC.Prim.*{(w) tc 34d}
                                                    @
 fclabels-2.0.1:Data.Label.Point.Total{tc r1Pm}
 (base:Control.Arrow.$p1Arrow{v r1s} [gid[ClassOp]]
                                                       @
 fclabels-2.0.1:Data.Label.Point.Total{tc r1Pm}
 (base:Control.Arrow.$p1ArrowApply{v rp} [gid[ClassOp]]
                                                          @
 fclabels-2.0.1:Data.Label.Point.Total{tc r1Pm}
                                                          $dArrowApply{v
 a72o} [lid]))
                                                    @ f{tv a8m6} [tv]
                                                    f{v a8hw} [lid] has
 wrong role nominal
 }}}

 Problem does not appear with `-O0`.

 I couldn't test with HEAD because fclabels isn't compatible with the
 changes to Template Haskell yet.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9102>
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