[GHC] #8067: -XDefaultSignatures panic in type error diagnostic

[GHC]

#8067: -XDefaultSignatures panic in type error diagnostic
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       Reporter:  exFalso            |             Owner:
           Type:  bug                |            Status:  new
       Priority:  normal             |         Milestone:
      Component:  Compiler           |           Version:  7.6.3
       Keywords:  defaultsignatures  |  Operating System:  Linux
  panic                              |   Type of failure:  Compile-time
   Architecture:  x86_64 (amd64)     |  crash
     Difficulty:  Unknown            |         Test Case:
     Blocked By:                     |          Blocking:
Related Tickets:                     |
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 The following piece of code shouldn't (and doesn't) typecheck, however GHC
 panics during the diagnostic.

 {{{
 $ cat /tmp/Weird.hs
 {-# LANGUAGE DefaultSignatures #-}
 module Weird where

 import Control.Monad.Trans

 class Class a where
     fun :: () -> () -> a
     default fun :: () -> () -> m a
     fun = lift

 $ ghc /tmp/Weird.hs
 [1 of 1] Compiling Weird            ( /tmp/Weird.hs, /tmp/Weird.o )

 /tmp/Weird.hs:9:11:
     Couldn't match kind `* -> *' with `*'
     Expected type: ()ghc: panic! (the 'impossible' happened)
   (GHC version 7.6.3 for x86_64-unknown-linux):
         kindFunResult ghc-prim:GHC.Prim.*{(w) tc 34d}
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8067>
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