[GHC] #8851: Standalone deriving and GND behave differently

[GHC]

#8851: Standalone deriving and GND behave differently
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        Reporter:  simonpj                       |            Owner:
            Type:  bug                           |           Status:  new
        Priority:  normal                        |        Milestone:  7.8.1
       Component:  Compiler (Type checker)       |          Version:
      Resolution:                                |  7.8.1-rc2
Operating System:  Unknown/Multiple              |         Keywords:
 Type of failure:  None/Unknown                  |     Architecture:
       Test Case:                                |  Unknown/Multiple
  deriving/should_compile/T8851                  |       Difficulty:
        Blocking:                                |  Unknown
                                                 |       Blocked By:
                                                 |  Related Tickets:
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Comment (by goldfire):

 You have a better perspective on the difficulty of implementation here, so
 I'm happy enough to agree. It does seem a little silly that we can accept
 `deriving instance Parsing MyParser` (with no context at all) but not
 `newtype MyParser ... deriving Parsing`. But, this behavior is fully
 consistent with the articulation of the two `deriving` features, so
 there's nothing wrong with it. And, keeping the code simpler when the fix
 for users is so trivial is a good thing.

 Thanks for taking another look.

 We should modify the test case to reflect this change. I can do that later
 this week when I spend some time working on GHC.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8851#comment:14>
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