[GHC] #10309: ApiAnnotations : mkGadtDecl discards annotations for HsFunTy

[GHC]

#10309: ApiAnnotations : mkGadtDecl discards annotations for HsFunTy
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        Reporter:  alanz             |                   Owner:  alanz
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:  7.10.2
       Component:  Compiler          |                 Version:  7.10.1
  (Parser)                           |                Keywords:
      Resolution:                    |  ApiAnnotations
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by alanz):

 This occurs for the `HsFunTy` which loses its SrcSpan. The only annotation
 at this level is an `AnnRarrow`.

 {{{
         | btype '->'     ctype          {% ams (sLL $1 $> $ HsFunTy $1 $3)
                                                [mj AnnRarrow $2] }
 }}}

 One potential solution is the keep the annotation where it is, but also
 add it to `$1`, which will then only be used in tooling for the GADT case.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10309#comment:1>
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