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

[GHC]

#12389: Limit duplicate export warnings for datatypes
-------------------------------------+-------------------------------------
        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 dfeuer):

 Sure. That would solve (much of) the problem. I'd want leading commas too,
 because I tend to prefer a leading-comma style. And I'd want to silence
 the warning from duplicate constructors/patterns within the list. Because
 I could, hypothetically, have

 {{{#!hs
   Foo (
 #if Condition1
       Foo, Bar
 #endif
 #if Condition2
     , Bar, Baz
 #endif
     )
 }}}

 and wouldn't want to have to get fancy with the CPP if `Condition1` and
 `Condition2` both happen to hold.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12389#comment:4>
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