[GHC] #9628: Add Annotations to the AST to simplify source to source conversions

[GHC]

#9628: Add Annotations to the AST to simplify source to source conversions
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              Reporter:  alanz       |            Owner:  alanz
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.3
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by alanz):

 On further reflection, option 1 will allow for example a smart editor
 which uses the annotated `ParsedSource` as a primary data structure and
 submits changes through for incremental renaming/type checking and
 eventual code generation.

 This way the normal command line invocation will lock the annotation down
 as a `SrcSpan`, but it can be replaced all the way through when used for
 tooling.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9628#comment:8>
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