[GHC] #13415: Instance declarations don't recognize named wildcards

[GHC]

#13415: Instance declarations don't recognize named wildcards
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13324            |  Differential Rev(s):  Phab:D3332
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Replying to [comment:2 simonpj]:
 > If #13324 doesn't fly, this change is just an unnecessary complication.

 I don't agree. This ticket demonstrates a somewhat orthogonal bug: the
 error messages for using named wildcards in instance declarations are
 wildly misleading! We should be able to fix this, even if it takes longer
 to make `PartialTypeSignatures` work for arbitrary instances with
 wildcards.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13415#comment:3>
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