[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:  simonpj
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      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 edsko):

 We could probably work around this by adding a dummy class method in
 `Throws` and call that in `throwChecked`.

 (But I think there are other use cases of method-less classes out there in
 the wild :)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11369#comment:1>
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