[GHC] #8827: Inferring Safe mode with GeneralizedNewtypeDeriving is wrong

[GHC]

#8827: Inferring Safe mode with GeneralizedNewtypeDeriving is wrong
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        Reporter:  goldfire          |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  7.8.1-rc2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:  8226, 8745
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Comment (by ekmett):

 Ah. I had missed the addition of `Data.Coerce`.

 I think the least pain would be temporarily marking that module Unsafe,
 and reverting to the pre 7.8 rule of no GND under `Safe` and then all
 we'll have "done no harm" as all code that worked before will continue to
 work and no new security problems will have been introduced.

 I'd also be okay with looking into the 'if you don't export all your
 constructors you get a nominal role' rule for 7.10, but I am somewhat
 leery of introducing it in 7.8 after folks have already braced for a
 rather different impact.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8827#comment:26>
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