[GHC] #12389: Limit duplicate export warnings for datatypes

[GHC]

#12389: Limit duplicate export warnings for datatypes
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        Reporter:  dfeuer            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11959            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 Well you don't really want to "silence the warning from duplicate
 constructors/patterns within the list". You want to silence ''this''
 duplicate of `Bar`. If you happen to repeat a different constructor
 elsewhere in the export list by accident, you'd still want a warning about
 that. So it would more appropriate to use a mechanism for locally
 disabling warnings.

 Since you can already write what you need with `#if Condition1 ||
 Condition2`, it's not a problem anyways. At some point you may be better
 off just disabling the warning entirely. Warnings about redundancies are
 too hard when the compiler can't see your entire program at once.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12389#comment:5>
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