[GHC] #15324: -ddump-splices does not parenthesize rank-n contexts correctly

[GHC]

#15324: -ddump-splices does not parenthesize rank-n contexts correctly
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Template       |           Version:  8.4.3
  Haskell                            |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Ryan discovers another `-ddump-splices` bug—news at 11:

 {{{#!hs
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TemplateHaskell #-}
 {-# OPTIONS_GHC -ddump-splices #-}
 module Bug where

 $([d| f :: forall a. (Show a => a) -> a
       f _ = undefined
     |])
 }}}
 {{{
 $ /opt/ghc/8.4.3/bin/ghci Bug.hs -dsuppress-uniques
 GHCi, version 8.4.3: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Bug              ( Bug.hs, interpreted )
 Bug.hs:(6,3)-(8,6): Splicing declarations
     [d| f :: forall a. (Show a => a) -> a
         f _ = undefined |]
   ======>
     f :: forall a. Show a => a -> a
     f _ = undefined
 }}}

 Notice that `f`'s type signature is pretty-printed as `forall a. Show a =>
 a -> a`, which is just wrong. Patch incoming.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15324>
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