[GHC] #14331: Overzealous free-floating kind check causes deriving clause to be rejected

[GHC]

#14331: Overzealous free-floating kind check causes deriving clause to be rejected
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  merge
        Priority:  normal            |            Milestone:  8.2.2
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |
      Resolution:                    |             Keywords:  deriving
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:
  valid program                      |  deriving/should_compile/T14331
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Replying to [comment:29 goldfire]:
 > I do think it's worth asking if anyone ever really needs variables
 shared between the data decl and the `deriving` (Simon's last point in
 comment:28).

 We certainly do. Here's an example from #3955:

 {{{#!hs
 newtype T a x = T (Reader a x)
    deriving (Monad, MonadReader a)
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14331#comment:30>
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