[GHC] #16183: GHC HEAD regression: -ddump-splices incorrectly parenthesizes HsKindSig applications

[GHC]

#16183: GHC HEAD regression: -ddump-splices incorrectly parenthesizes HsKindSig
applications
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.8.1
          Component:  Template       |           Version:  8.7
  Haskell                            |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Debugging
  Unknown/Multiple                   |  information is incorrect
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 When you compile this file with GHC 8.6.3 and HEAD:

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

 import Data.Kind

 type F = $([t| (Maybe :: Type -> Type) Int |])
 }}}

 You get two different results:

 {{{
 $ /opt/ghc/8.6.3/bin/ghc -fforce-recomp Bug.hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
 Bug.hs:8:12-45: Splicing type
     [t| (Maybe :: Type -> Type) Int |]
   ======>
     (Maybe :: Type -> Type) Int

 $ ~/Software/ghc4/inplace/bin/ghc-stage2 -fforce-recomp Bug.hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
 Bug.hs:8:12-45: Splicing type
     [t| (Maybe :: Type -> Type) Int |]
   ======>
     Maybe :: Type -> Type Int
 }}}

 Notice how in the GHC HEAD output, GHC forgets to put parentheses around
 `Maybe :: Type -> Type`, leading to the utterly nonsensical type `Maybe ::
 Type -> Type Int`.

 The commit that introduced this regression is
 [https://gitlab.haskell.org/ghc/ghc/commit/ae2c9b40f5b6bf272251d1f4107c60003f541b62
 ae2c9b40f5b6bf272251d1f4107c60003f541b62].

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16183>
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