[GHC] #12417: API annotations for unboxed sums needs reworking

[GHC]

#12417: API annotations for unboxed sums needs reworking
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           Reporter:  osa1           |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 API annotations for unboxed sums are not entirely correct. As far as I
 understand, some of the bars (`|`) in the concrete syntax are not properly
 attached to any of the AST nodes. Some discussion can be seen in
 [https://phabricator.haskell.org/D2259#69809  the Phab page].

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12417>
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