[GHC] #15264: Warn about implicit kind variables with -Wcompat

[GHC]

#15264: Warn about implicit kind variables with -Wcompat
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        Reporter:  int-index         |                Owner:  (none)
            Type:  task              |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4834
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"8df24474d0194d28b8273c1539af05793156e23f/ghc"
 8df24474/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="8df24474d0194d28b8273c1539af05793156e23f"
 Warn about implicit kind variables with -Wcompat

 According to an accepted proposal
 https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/002
 4-no-kind-vars.rst

     With -Wcompat, warn if a kind variable is brought into scope
     implicitly in a type with an explicit forall. This applies to type
     signatures and to other contexts that allow a forall with the
     forall-or-nothing rule in effect (for example, class instances).

 Test Plan: Validate

 Reviewers: goldfire, hvr, bgamari, RyanGlScott

 Reviewed By: goldfire

 Subscribers: RyanGlScott, rwbarton, thomie, carter

 GHC Trac Issues: #15264

 Differential Revision: https://phabricator.haskell.org/D4834
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15264#comment:4>
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