[GHC] #11646: Make pattern synonym export type mismatch a warning

[GHC]

#11646: Make pattern synonym export type mismatch a warning
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        Reporter:  dfeuer            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1-rc2
  checker)                           |             Keywords:
      Resolution:                    |  PatternSynonyms
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
  PatternSynonyms/AssociatingSynonyms|
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Comment (by mpickering):

 You understand correctly. The check would be better but it is difficult to
 specify when a pattern synonym should and should not be allowed to
 bundled.

 Do you have an example where the check prevents you from writing the
 program you want to write?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11646#comment:2>
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