[GHC] #10598: DeriveAnyClass and GND don't work well together

[GHC]

#10598: DeriveAnyClass and GND don't work well together
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        Reporter:  osa1              |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.11
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Changes (by goldfire):

 * cc: jpm@… (added)


Comment:

 I'm less worried about implementing the correct behavior than figuring out
 what the correct behavior should be. You're saying that `DeriveAnyClass`
 should never fail... but is that different from what 7.10.1 actually does?

 I think issuing a warning in this case is a great step. But I'd still love
 to see a specification (preferably in the user manual) of how all this
 works. In any case, submitting a patch for review via Phab is never the
 wrong thing to do. (And, of course, thanks for writing the patch!)

 I'm cc'ing Pedro, who (if memory serves) wrote this feature.

 (Full disclosure: I was involved in the design of `DeriveAnyClass`, and
 I'm sure that at some point in history, I knew the answers to the
 questions I'm asking. But it's all lost now, and I'm hoping Pedro can fill
 in the details.)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10598#comment:7>
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