[GHC] #12423: Panic with DeriveAnyClass and DefaultSignatures

[GHC]

#12423: Panic with DeriveAnyClass and DefaultSignatures
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           Reporter:  knrafto        |             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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 With the code
 {{{#!hs
 {-# LANGUAGE DefaultSignatures, DeriveAnyClass #-}
 class Eq1 f where
   (==#) :: Eq a => f a -> f a -> Bool
   default (==#) :: Eq (f a) => f a -> f a -> Bool
   (==#) = (==)

 data Foo a = Foo (Either a a)
     deriving (Eq, Eq1)
 }}}
 GHC 8.0.1 and 7.10.3 both panic:
 {{{
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-apple-darwin):
         in other argument

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

 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12423>
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