[GHC] #11509: Incorrect error message in StandaloneDeriving: "The data constructors of <typeclass> are not all in scope"

[GHC]

#11509: Incorrect error message in StandaloneDeriving: "The data constructors of
<typeclass> are not all in scope"
-------------------------------------+-------------------------------------
        Reporter:  edsko             |                Owner:  RyanGlScott
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1-rc1
      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:D2558
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"23cf32da76fe6ed29fa141047749d390df763f94/ghc"
 23cf32da/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="23cf32da76fe6ed29fa141047749d390df763f94"
 Disallow standalone deriving declarations involving unboxed tuples or sums

 There was an awful leak where GHC permitted standalone `deriving`
 declarations to create instances for unboxed sum or tuple types. This
 fortifies the checks that GHC performs to catch this scenario and give
 an appropriate error message.

 Fixes #11509.

 Test Plan: ./validate

 Reviewers: goldfire, austin, bgamari

 Reviewed By: bgamari

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D2557

 GHC Trac Issues: #11509
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11509#comment:9>
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