[GHC] #15398: GADT deriving Ord generates inaccessible code in a pattern with constructor.

[GHC]

#15398: GADT deriving Ord generates inaccessible code in a pattern with
constructor.
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        Reporter:  philderbeast  |                Owner:  (none)
            Type:  bug           |               Status:  new
        Priority:  normal        |            Milestone:  8.6.1
       Component:  Compiler      |              Version:  8.2.2
      Resolution:                |             Keywords:
Operating System:  MacOS X       |         Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown  |            Test Case:
      Blocked By:                |             Blocking:
 Related Tickets:                |  Differential Rev(s):
       Wiki Page:                |
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Comment (by RyanGlScott):

 I have no objection to the proposal in comment:4. That being said, it's
 far from clear to me how to implement it. Unlike other flags that
 `deriving` toggles, which primarily live in the renamer, `-Winaccessible-
 code` warnings are emitted during error reporting, which happens after
 typechecking. What's more, when `-Winaccessible-code` warnings are
 created, GHC only has access to an `Implication`, which gives no
 indication about whether it was created from derived code or not...

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15398#comment:5>
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