[GHC] #12692: Can't find interface-file decl with Typeable

[GHC]

#12692: Can't find interface-file decl with Typeable
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           Reporter:  crockeea       |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The attached code produces the following error:

 {{{
 GHC error in desugarer lookup in Main:
   Can't find interface-file declaration for variable $tc'(,)
     Probable cause: bug in .hi-boot file, or inconsistent .hi file
     Use -ddump-if-trace to get an idea of which file caused the error
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-unknown-linux):
         initDs IOEnv failure
 }}}

 when I run `stack bench lol`. The issue seems to be related to `Typeable`
 instances for types created with singletons.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12692>
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