[GHC] #14875: -ddump-splices pretty-printing oddities with case statements

2 Mar 2018

      #14875: -ddump-splices pretty-printing oddities with case statements
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.2
           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:
-------------------------------------+-------------------------------------
 The latest installment in "Ryan finds minor bugs in `-ddump-splices`".
 Take this program:

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

 $([d| f :: Bool -> Bool
       f x = case x of
               (True :: Bool) -> True
               (False :: Bool) -> False

       g :: Bool -> Bool
       g x = (case x of
                True -> True
                False -> False) :: Bool
     |])
 }}}

 Compiling this gives:

 {{{
 $ /opt/ghc/8.2.2/bin/ghci Bug.hs
 GHCi, version 8.2.2: 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)-(15,6): Splicing declarations
     [d| f_a1sB :: Bool -> Bool
         f_a1sB x_a1sD
           = case x_a1sD of
               (True :: Bool) -> True
               (False :: Bool) -> False
         g_a1sC :: Bool -> Bool
         g_a1sC x_a1sE
           = (case x_a1sE of
                True -> True
                False -> False) ::
               Bool |]
   ======>
     f_a49Z :: Bool -> Bool
     f_a49Z x_a4a0
       = case x_a4a0 of
           True :: Bool -> True
           False :: Bool -> False
     g_a49Y :: Bool -> Bool
     g_a49Y x_a4a1
       = case x_a4a1 of
           True -> True
           False -> False ::
           Bool
 }}}

 Neither the `-ddump-splices` output for `f` nor `g` parse are legal
 Haskell:

 * In `f`, GHC fails to parenthesize the pattern signatures `True :: Bool`
 and `False :: Bool`.
 * In `g`, GHC fails to parenthesize the `case` expression which has an
 explicit `Bool` signature.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14875
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