[GHC] #13185: haskell-relational-query: ghc: panic! (the 'impossible' happened)

[GHC]

#13185: haskell-relational-query: ghc: panic! (the 'impossible' happened)
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        Reporter:  LocutusOfBorg     |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Compile-time      |            Test Case:  build
  crash or panic                     |  relational-query with ghc 8.0.2
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 Here's a weird thing (possibly a separate bug?): if I `cabal clean; cabal
 configure --with-ghc=...; cabal build`, I get the failure. If I then
 `cabal build` again without cleaning, it works. Reid thinks this has
 something to do with a bug causing different info to pass from phase to
 phase through `.hi` files than otherwise; I haven't yet checked if it's
 been fixed.

 I'm currently bisecting this panic, and have narrowed it down to somewhere
 between d5518f72f3033ceaadc9b56a5d9012425b3a8956 and the 8.0.2 release.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13185#comment:12>
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