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

[GHC]

#12417: API annotations for unboxed sums needs reworking
-------------------------------------+-------------------------------------
        Reporter:  osa1              |                Owner:  alanz
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
  (Parser)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect API     |  Unknown/Multiple
  annotation                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by alanz):

 An unboxed tuple such as

 {{{#!hs
 (# | b | | | | | #)
 }}}

 Ends up in the parser via `tup_exprs` as

 {{{#!hs
 Sum 2 7 lexp
 }}}

 where `lexp` is a `LHsExpr`

 From an annotation perspective, the 5 `AnnVbar`s after the `b` are
 attached to `lexp`, but currently the leading `AnnVbar`s do not have a
 home.

 They need to be attached to the parent tuple expression.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12417#comment:2>
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