[GHC] #13803: Panic while forcing the thunk for TyThing IsFile (regression)

[GHC]

#13803: Panic while forcing the thunk for TyThing IsFile (regression)
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        Reporter:  inaki             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1-rc2
      Resolution:                    |             Keywords:  hs-boot
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by ezyang):

 This is a family instance consistency check problem, as can be seen when
 you turn on tracing:

 {{{
 checkForConflictsghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.3.20170517 for x86_64-unknown-linux):
         tcIfaceGlobal (local): not found
 }}}

 We begin checking for conflicts immediately before the panic.

 The problem is reminiscent of #11062 (fixed in
 25b70a29f6236b591252bf5a361a1547f0ffee51).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13803#comment:11>
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