[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 goldfire):

 I initially thought the same as comment:26, but then I realized that the
 logic in comment:26 also means that `data Proxy a = P deriving Functor`
 should fail. We allow unifying kind variables in a data declaration to be
 unified when processing a `deriving` clause. The program in comment:12 has
 the same action.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14331#comment:27>
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