[GHC] #8503: New GeneralizedNewtypeDeriving check still isn't permissive enough

[GHC]

#8503: New GeneralizedNewtypeDeriving check still isn't permissive enough
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        Reporter:  goldfire          |            Owner:  goldfire
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.7
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:  8548
        Blocking:                    |  Related Tickets:  #8541
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Comment (by goldfire):

 Please push when ready.

 And, re `ScopedTypeVariables`, you're right -- we do need that extension.
 But, see
 [http://git.haskell.org/ghc.git/blob/refs/heads/wip/T8503:/compiler/typecheck/TcDeriv.lhs#l410
 here] -- the extension is enabled just over the code that needs it.

 Thanks for taking the last leg on this one!

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8503#comment:38>
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