[GHC] #10749: Boot file instances should imply superclasses

[GHC]

#10749: Boot file instances should imply superclasses
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        Reporter:  ezyang            |                Owner:  ezyang
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:  backpack
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 ezyang):

 I took a look into solving this, but I realized that I don't actually know
 how we normally report an error when an instance declaration is made but
 the superclasses do not hold. The error isn't reported until late when
 we're discharging top-level wanteds so  I actually have no idea where the
 wanted is coming from (or why it's not coming in the case of hs-boot.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10749#comment:3>
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