[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:  7.12.1
       Component:  Compiler          |                 Version:  7.9
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:  #8226, #8745      |  Differential Revisions:
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Comment (by oerjan):

 My hunch about `nominal` default is that it would be annoying in the same
 way that authors forgetting to provide a useful type class for a type is
 annoying, but worse because a user of the package ''cannot'' afterwards
 declare an orphan `Coercible` instance, even if they need it.  You could
 write an explicit coercion function, or use `unsafeCoerce`, but if you
 were an intermediate package writer declaring a wrapping type, you
 couldn't then provide `Coercible` for the users of ''your'' type.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8827#comment:44>
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