[GHC] #11775: singleton classes in ghc.generics are defined but not exported

[GHC]

#11775: singleton classes in ghc.generics are defined but not exported
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        Reporter:  carter            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1-rc2
      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 bgamari):

 Yes, it's used in instances defined in `GHC.Generics`. e.g.,
 {{{#!hs
      instance (KnownSymbol n, SingI f, SingI r)
          => Constructor ('MetaCons n f r) where
        conName     _ = symbolVal (Proxy :: Proxy n)
        conFixity   _ = fromSing  (sing  :: Sing f)
        conIsRecord _ = fromSing  (sing  :: Sing r)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11775#comment:1>
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