[GHC] #14692: Deriving Show with -XEmptyDataDeriving cases on the wrong argument

[GHC]

#14692: Deriving Show with -XEmptyDataDeriving cases on the wrong argument
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  high              |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.4.1-alpha1
      Resolution:                    |             Keywords:  deriving
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4328
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"0074a08ea9dfd1416aa57a9504be73dcdf7a1e2b/ghc"
 0074a08e/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="0074a08ea9dfd1416aa57a9504be73dcdf7a1e2b"
 Fix #14692 by correcting an off-by-one error in TcGenDeriv

 A silly mistake in `gen_Show_binds` was causing derived
 `Show` instances for empty data types to case on the precedence
 argument instead of the actual value being showed.

 Test Plan: make test TEST=drv-empty-data

 Reviewers: bgamari

 Reviewed By: bgamari

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #14692

 Differential Revision: https://phabricator.haskell.org/D4328
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14692#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler