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
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Operating system
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changed weight to 5

added Tbug Trac import labels

Sorry, forgot to mention:

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.8.2.20140429

Test system is Ubuntu 12.04, x86_64.

mentioned in commit 4cfc1fae

This is the actual fix for #9102 (closed):

commit 21f17d06aa5c33e639f1b0d37b4bf888b494c441
Author: Simon Peyton Jones <simonpj@microsoft.com>
Date:   Tue May 13 13:17:19 2014 +0100

    Fix invariant in mkAppCoFlexible
    
    mkAppCoFlexible was breaking the invariant that the head of a TyConAppCo cannot
    be a type synonym.  This small patch fixes it.

 compiler/types/Coercion.lhs |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

I forgot to mention the ticket in the commit message.

Simon

Merge to 7.8.2.

I didn't get to a small test case, so no regression test for now.

Simon

added 1 deleted label

mentioned in commit 022f8750

changed milestone to %7.8.3

closed

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

removed 1 deleted label

added Pnormal label