[GHC] #2530: deriving Show adds extra parens for constructor with record syntax

[GHC]

#2530: deriving Show adds extra parens for constructor with record syntax
-------------------------------------+-------------------------------------
        Reporter:  spl               |                Owner:  bgamari
            Type:  bug               |               Status:  patch
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  6.8.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D669,
       Wiki Page:                    |  Phab:D2027
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * status:  new => patch
 * differential:  Phab:D669 => Phab:D669, Phab:D2027


@@ -6,1 +6,1 @@
- {{{
+ {{{#!hs

New description:

 Since record construction binds more tightly than function application, no
 parentheses are needed when passing a constructor with record syntax to a
 function constructor. As a result, we can pass {{{Just A {x = 5}}}} as
 shown below.

 {{{#!hs
 module Main where

 data A = A {x :: Int} deriving (Show)

 main :: IO ()
 main = print $ Just A {x = 5}
 }}}

 But we get the result in the GHCi session below:

 {{{
 *Main> main
 Just (A {x = 5})
 }}}

 I tried looking through {{{TcGenDeriv}}}, but didn't figure out quite
 where the parenifying was done. {{{nested_compose_Expr}}}?
 {{{show_thingies}}}?

 I just wanted to make a ticket for general knowledge. Of course, this is
 not a real bug. Perhaps you could reclassify it as a feature. Either way,
 it would be nice to have.

--

Comment:

 Phab:D2027 reverts to the previous behavior including redundant parens as
 described in comment:36.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/2530#comment:38>
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