[GHC] #11369: Suppress redundant-constraint warnings in case of empty classes

[GHC]

#11369: Suppress redundant-constraint warnings in case of empty classes
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        Reporter:  hvr               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11370            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 I think this is just a bug in the code that infers the context for the
 instance declaration that arises from GND.  We should tet
 {{{
 instance {- Empty context!! -} C (Identity a) where
   type T (Identity a) = T a
 }}}
 Where is that code?  I can help with this after the PLDI deadline.

 Anyway, I think this is unrelated to the original topic of the ticket.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11369#comment:18>
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