[GHC] #13919: Incorrect unused top binding warning when interacting with GHC.Generics

[GHC]

#13919: Incorrect unused top binding warning when interacting with GHC.Generics
-------------------------------------+-------------------------------------
        Reporter:  Taneb             |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  Generics
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #1954             |  Differential Rev(s):  Phab:D3704
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"15fcd9adb75b95b32fbe08d066a2ada5f298d667/ghc"
 15fcd9ad/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="15fcd9adb75b95b32fbe08d066a2ada5f298d667"
 Suppress unused warnings for selectors for some derived classes

 Although derived `Read`, `Show`, and `Generic` instances technically
 don't //use// the record selectors of the data type for which an
 instance is being derived, the derived code is affected by the
 //presence// of record selectors. As a result, we should suppress
 `-Wunused-binds` for those record selectors when deriving these classes.
 This is accomplished by threading through more information from
 `hasStockDeriving`.

 Test Plan: make test TEST=T13919

 Reviewers: austin, bgamari

 Reviewed By: bgamari

 Subscribers: rwbarton, thomie

 GHC Trac Issues: #13919

 Differential Revision: https://phabricator.haskell.org/D3704
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13919#comment:2>
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