[GHC] #12168: panic! (the 'impossible' happened) with gi-gtk 3.0.4

[GHC]

#12168: panic! (the 'impossible' happened) with gi-gtk 3.0.4
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        Reporter:  drb226            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by drb226):

 I've created a persistent tagged docker image that can reproduce this
 issue. (It isn't the exact same image as before, but very similar.)

 {{{
 $ docker pull danburton/stackage-build-server:2016-07-11
 2016-07-11: Pulling from danburton/stackage-build-server
 Digest:
 sha256:1de56d2d293eeb3234cc9eadea06e0a9ef154052281905252442c520b1123f45
 Status: Image is up to date for danburton/stackage-build-server:2016-07-11
 }}}

 You can follow the docker-based repro instructions above, replacing
 {{{snoyberg/stackage:nightly}}} with {{{danburton/stackage-build-
 server:2016-07-11}}}, and you should get the same result.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12168#comment:6>
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