[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 RyanGlScott):

 I attempted the `docker`-based directions, but was unable to reproduce the
 issue.

 Also, it is rather hard to know what the issue might be just from an
 arcane series of `stack` commands, with no Haskell code to look at. Why is
 it that in the two methods you used above, you had different numbers of
 modules (650 vs 654)? In fact, when I ran in, I only had 516 modules to
 compile. If this code is autogenerated, it would be tremendously helpful
 to know what exactly is being generated, because I am not nearly
 experienced enough in the `haskell-gi` internals to know what could be
 going on.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12168#comment:2>
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