[GHC] #10250: API Annotations : add Locations in hsSyn were layout occurs

[GHC]

#10250: API Annotations : add Locations in hsSyn were layout occurs
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              Reporter:  alanz       |             Owner:  alanz
                  Type:  task        |            Status:  new
              Priority:  normal      |         Milestone:  7.10.2
             Component:  Compiler    |           Version:  7.10.1
              Keywords:              |  Operating System:  Unknown/Multiple
  ApiAnnotations                     |   Type of failure:  None/Unknown
          Architecture:              |        Blocked By:
  Unknown/Multiple                   |   Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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 At the moment ghc-exactprint, which uses the GHC API Annotations to
 provide a framework for roundtripping Haskell source code with optional
 AST edits, has to implement a horrible workaround to manage the points
 where layout needs to be captured.

 These are

   MatchGroup
   HsDo
   HsCmdDo
   HsLet
   LetStmt
   HsCmdLet
   GRHSs

 To provide a more natural representation, the contents subject to layout
 rules need to be wrapped in a SrcSpan.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10250>
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