[GHC] #12546: GeneralizedNewtypeDeriving produces error messages with incorrect kind signatures

[GHC]

#12546: GeneralizedNewtypeDeriving produces error messages with incorrect kind
signatures
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        Reporter:  lexi.lambda       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by mniip):

 Looks like it tries to unify `k -> Constrant ~ * -> (* -> *) ->
 Constraint`. It zonks `k ~ *` and then fails with `(* -> *) -> Constraint
 ~ Constraint`, and the `k = *` leaks into the error message

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12546#comment:2>
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