[GHC] #11515: PartialTypeSignatures suggests a redundant constraint with constraint families

[GHC]

#11515: PartialTypeSignatures suggests a redundant constraint with constraint
families
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:  TypedHoles
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 RyanGlScott):

 This appears to be fixed, as of GHC 8.2.2:

 {{{
 $ /opt/ghc/8.2.2/bin/ghci Bug.hs
 GHCi, version 8.2.2: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Bug              ( Bug.hs, interpreted )

 Bug.hs:7:20: error:
     • Found type wildcard ‘_’ standing for ‘()’
       To use the inferred type, enable PartialTypeSignatures
     • In the type signature: foo :: (ShowSyn a, _) => a -> String
   |
 7 | foo :: (ShowSyn a, _) => a -> String
   |                    ^
 }}}

 I'll add a regression test.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11515#comment:2>
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