[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 rwbarton):

 Well the first `Foo` export certainly looks redundant (as long as at least
 one of the CPP flags is enabled).

 I don't really see how your second version is any better than what you say
 is "so horrible [...]":
 {{{#!hs
 module Foo (
    Foo (
 #ifdef TESTING
      Foo,
 #endif
 #ifdef USE_PATTERN_SYNONYMS
      Pat1, Pat2,
 #endif
    )
   )
 }}}

 (A trailing comma is legal here right? Otherwise it really is a mess.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12389#comment:1>
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