[GHC] #14681: More incorrect Template Haskell parenthesization

[GHC]

#14681: More incorrect Template Haskell parenthesization
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Template       |           Version:  8.2.2
  Haskell                            |
           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:
-------------------------------------+-------------------------------------
 The latest installment of "RyanGlScott finds bugs in Template Haskell
 pretty-printing". Here is what's featured on today's episode:

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

 import Data.Functor.Identity
 import Language.Haskell.TH

 $([d| f = \(Identity x) -> x |])
 $([d| g = $(pure $ VarE '(+) `AppE` LitE (IntegerL (-1)) `AppE` (LitE
 (IntegerL (-1)))) |])
 }}}

 Running this with GHC 8.2 or later yields some incorrectly parenthesized
 output:

 {{{
 $ /opt/ghc/8.2.2/bin/ghc Bug.hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
 Bug.hs:8:3-31: Splicing declarations
     [d| f_azO = \ (Identity x_azP) -> x_azP |]
   ======>
     f_a3Nx = \ Identity x_a3Ny -> x_a3Ny
 Bug.hs:9:3-90: Splicing declarations
     [d| g_a3NU
           = $(pure
                 $ VarE '(+) `AppE` LitE (IntegerL (- 1))
                     `AppE` (LitE (IntegerL (- 1)))) |]
     pending(rn) [<splice_a3NV, pure
                                  $ VarE '(+) `AppE` LitE (IntegerL (- 1))
                                      `AppE` (LitE (IntegerL (- 1)))>]
   ======>
     g_a4dU = ((+) -1) -1
 }}}

 In particular, look at these two lines:

 {{{
 f_a3Nx = \ Identity x_a3Ny -> x_a3Ny
 g_a4dU = ((+) -1) -1
 }}}

 These should be:

 {{{
 f_a3Nx = \ (Identity x_a3Ny) -> x_a3Ny
 g_a4dU = ((+) (-1)) (-1)
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14681>
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