[GHC] #13942: Pretty-printer butchers function arrow fixity on GHC HEAD

[GHC]

#13942: Pretty-printer butchers function arrow fixity on GHC HEAD
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.3
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Incorrect result
  Unknown/Multiple                   |  at runtime
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 This code:

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

 $([d| f :: Either Int (Int -> Int)
       f = undefined
     |])
 }}}

 Pretty-prints incorrectly on GHC HEAD:

 {{{
 $ /opt/ghc/head/bin/ghci Bug.hs
 GHCi, version 8.3.20170706: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Bug              ( Bug.hs, interpreted )
 Bug.hs:(5,3)-(7,6): Splicing declarations
     [d| f_a1sG :: Either Int (Int -> Int)
         f_a1sG = undefined |]
   ======>
     f_a4bj :: Either Int Int -> Int
     f_a4bj = undefined
 }}}

 But not on GHC 8.2.1-rc3:

 {{{
 $ /opt/ghc/8.2.1/bin/ghci Bug.hs
 GHCi, version 8.2.0.20170704: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Bug              ( Bug.hs, interpreted )
 Bug.hs:(5,3)-(7,6): Splicing declarations
     [d| f_a1su :: Either Int (Int -> Int)
         f_a1su = undefined |]
   ======>
     f_a4aV :: Either Int (Int -> Int)
     f_a4aV = undefined
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13942>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler