[GHC] #8225: Type Nats cause crash if GHC.TypeLits not imported

[GHC]

#8225: Type Nats cause crash if GHC.TypeLits not imported
----------------------------------+-------------------------------
       Reporter:  MikeIzbicki     |             Owner:
           Type:  bug             |            Status:  new
       Priority:  normal          |         Milestone:
      Component:  Compiler        |           Version:  7.6.3
       Keywords:                  |  Operating System:  Linux
   Architecture:  x86_64 (amd64)  |   Type of failure:  GHCi crash
     Difficulty:  Unknown         |         Test Case:
     Blocked By:                  |          Blocking:
Related Tickets:                  |
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 If I create a file "test.hs" with the following code:

 {{{
 data Poly (a::a)
 x = undefined :: Poly 1
 }}}

 when I load it into ghci, I get the error message:

 {{{
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.6.3 for x86_64-unknown-linux):
         lookupVers2
 <<details unavailable>>

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

 Now, modify the file into

 {{{
 import GHC.TypeLits

 data Poly (a::a)
 x = undefined :: Poly 1
 }}}

 and no error is reported.  What's weird is that if we now modify the file
 back to the original, then the error is still not reported.  Everything
 compiles perfectly fine.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8225>
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