[GHC] #8944: Warn instead of stopping on misplaced Haddock comments

[GHC]

#8944: Warn instead of stopping on misplaced Haddock comments
-------------------------------------+-------------------------------------
       Reporter:  Fuuzetsu           |             Owner:
           Type:  feature request    |            Status:  new
       Priority:  normal             |         Milestone:
      Component:  Compiler (Parser)  |           Version:  7.9
       Keywords:                     |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple   |   Type of failure:  None/Unknown
     Difficulty:  Unknown            |         Test Case:
     Blocked By:                     |          Blocking:
Related Tickets:                     |
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 Given a simple module like

 {{{
 module H where

 data F = F () -- ^ Comment for first type argument
            ()
 }}}

 and trying to run Haddock on it, we'll get back

 {{{
 /tmp/H.hs:4:12: parse error on input ‘(’
 }}}

 The error message is rather sub-par in this scenario. It'd be great if we
 could instead print a warning saying that a Haddock comment is unexpected
 in that position and then continue on parsing.

 Best case scenario would be a more informative message such as
 “Documenting each constructor argument is not supported” but that might be
 quite a bit harder.

 Filing on GHC Trac as it's the parser that needs changing I believe.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8944>
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