[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 nomeata):

 Is it hijacking this ticket to discuss the impact of GND-via-coerce here?

 Anyways, feature request #2850 will be broken if we do GND-via-coerce.
 Four tickets are broken because of #8548 (Coercible not working for
 `newtype instance` yet), these will be fixable.

 The remaining ones (`TEST="print018 cgrun068 T4203 drvrun019 T3955 T7474
 T3423 IndTypesPerf T5246 integerConstantFolding gadt6 T7332 drv015"`)
 cause panics, looking into them now.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8503#comment:32>
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