[GHC] #15307: Incorrect -ddump-deriv parenthesization for GND'd fmap implementation

[GHC]

#15307: Incorrect -ddump-deriv parenthesization for GND'd fmap implementation
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      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:D4890
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ryan Scott <ryan.gl.scott@…>):

 In [changeset:"59a15a56e180b59656e45df04f7df61de8298881/ghc" 59a15a5/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="59a15a56e180b59656e45df04f7df61de8298881"
 Fix #15307 by making nlHsFunTy parenthesize more

 Summary:
 `nlHsFunTy` wasn't parenthesizing its arguments at all,
 which led to `-ddump-deriv` producing incorrectly parenthesized
 types (since it uses `nlHsFunTy` to construct those types), as
 demonstrated in #15307. Fix this by changing `nlHsFunTy` to add
 parentheses à la `ppr_ty`: always parenthesizing the argument type
 with function precedence, and recursively processing the result type,
 adding parentheses for each function type it encounters.

 Test Plan: make test TEST=T14578

 Reviewers: bgamari

 Reviewed By: bgamari

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #15307

 Differential Revision: https://phabricator.haskell.org/D4890
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15307#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler