[GHC] #12375: type synonym to unboxed tuple causes crash

[GHC]

#12375: type synonym to unboxed tuple causes crash
-------------------------------------+-------------------------------------
           Reporter:  osa1           |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{#!haskell
 {-# LANGUAGE UnboxedTuples #-}

 module Main where

 -- type Null = (# #)

 {-# NOINLINE showNull #-}
 showNull :: (# #) -> String
 showNull (# #) = "(# #)"

 {-# NOINLINE showNullPair #-}
 showNullPair :: (# (# #), (# #) #) -> String
 showNullPair (# n1, n2 #) = "(# " ++ showNull n1 ++ ", " ++ showNull n2 ++
 "#)"

 main :: IO ()
 main = do
     putStrLn (showNullPair (# (# #), (# #) #))
 }}}

 If I use the `Null` type synonym here instead of `(# #)`, I get:

 {{{
 [1 of 1] Compiling Main             ( empty.hs, empty.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-unknown-linux):
         unboxed tuple PrimRep

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

 Tried with: 8.0.1

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12375>
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