[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:  patch
        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):  Phab:D2968
       Wiki Page:                    |
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Comment (by Alan Zimmerman <alan.zimm@…>):

 In [changeset:"38f289fa2a8715d2d5869e144b764c35cba16c6a/ghc"
 38f289fa/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="38f289fa2a8715d2d5869e144b764c35cba16c6a"
 Fix API Annotations for unboxed sums

 An unboxed tuple such as

     (# | b | | | | | #)

 Ends up in the parser via `tup_exprs` as

     Sum 2 7 lexp

 where `lexp` is a `LHsExpr`

 From an API annotation perspective, the 5 `AnnVbar`s after the `b` were
 attached
 to `lexp`, but the leading `AnnVbar`s did not have a home.

 This patch attaches them all to the the parent tuple expression. The first
 (alt
 - 1) of them come before `lexp`, and the remaining (arity - alt) come
 after.

 Test Plan: ./validate

 Reviewers: osa1, austin, bgamari

 Subscribers: thomie, mpickering

 Differential Revision: https://phabricator.haskell.org/D2968

 GHC Trac Issues: #12417
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12417#comment:4>
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