[GHC] #12132: Type representations missing for promoted boxed tuples

[GHC]

#12132: Type representations missing for promoted boxed tuples
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        Reporter:  bgamari           |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.2
       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 bgamari):

 Sadly `-ddump-if-trace` doesn't appear to be so helpful here,
 {{{
 $ inplace/bin/ghc-stage2 --interactive
 GHCi, version 8.1.20160528: http://www.haskell.org/ghc/  :? for help
 Prelude> :set -XDataKinds
 Prelude> :m + Data.Typeable Data.Proxy
 Prelude Data.Typeable Data.Proxy> typeOf (Proxy :: Proxy (Int,Int))
 Proxy * (Int,Int)
 Prelude Data.Typeable Data.Proxy> typeOf (Proxy :: Proxy '(Int,Int))
 GHC error in desugarer lookup in Ghci2:
   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-stage2: panic! (the 'impossible' happened)
   (GHC version 8.1.20160528 for x86_64-unknown-linux):
         initDs IOEnv failure

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

 Prelude Data.Typeable Data.Proxy>
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12132#comment:2>
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