[GHC] #12881: GHC 8.0.2 regression involving OVERLAP annotations

[GHC]

#12881: GHC 8.0.2 regression involving OVERLAP annotations
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        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:
       Component:  Compiler          |              Version:  8.0.2-rc1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 It should be noted that if you add explicit `OVERLAP*` annotations:

 {{{#!hs
 {-# LANGUAGE FlexibleInstances #-}
 module Bug where

 class Arbitrary a where
   shrink :: a -> [a]
   shrink _ = []

 instance {-# OVERLAPPABLE #-} Arbitrary a
 instance {-# OVERLAPPING  #-} Arbitrary Int
 }}}

 Then it will compile again, so there's at least a simple workaround.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12881#comment:1>
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