[GHC] #14907: Error message: (%, %) shows up when with accidental paren

[GHC]

#14907: Error message: (%,%) shows up when with accidental paren
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           Reporter:  Iceland_jack   |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.5
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Poor/confusing
  Unknown/Multiple                   |  error message
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I accidentally wrote an extra closing parens in instance declaration

 {{{#!hs
 $ ghci -ignore-dot-ghci -XRankNTypes
 GHCi, version 8.2.1: http://www.haskell.org/ghc/  :? for help
 Prelude> class (Category (Src f), forall xx. xx => Eq xx)) => Functor f

 <interactive>:1:8: error:
     Unexpected type ‘Category (Src f)’
     In the class declaration for ‘GHC.Classes.(%,%)’
     A class declaration should have form
       class GHC.Classes.(%,%) a b where ...
 Prelude>
 }}}

 `(%,%)` shouldn't show up here, same happens on 8.5.20180105

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14907>
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