[GHC] #11681: ghc panic with TypeError

[GHC]

#11681: ghc panic with TypeError
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        Reporter:  inaki             |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc2
  checker)                           |
      Resolution:                    |             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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Comment (by inaki):

 Replying to [comment:5 aavogt]:
 > I can't reproduce the original problem with -rc2 either
 This is very bizarre: I just updated to the latest build in fedora (which
 still identifies itself with the same version) and couldn't reproduce the
 crash either. But the example by aavogt above also crashes for me. And
 playing around with my original example, the following **does** crash:
 {{{#!hs

 {-# LANGUAGE DataKinds, FlexibleContexts, TypeOperators,
      FlexibleInstances #-}

 import GHC.TypeLits

 class C t where

 instance
     (TypeError (Text "A" :<>: {- Text -} "B"))
     => C t where

 main :: IO ()
 main = return ()
 }}}

 Notice the absence of the `UndecidableInstances` extension, the content is
 otherwise identical. It is not impossible I made a mistake when copying
 the original example for the crash, apologies if this was the case.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11681#comment:6>
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