Assertion failure in CoreUtils.lhs

I happened to be using a debug build of ghc-7.8.2, and got this assertion failure compiling 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.

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture