[GHC] #9174: Haddock fails with "Module defined in multiple files"

[GHC]

#9174: Haddock fails with "Module defined in multiple files"
----------------------------------+---------------------------------
       Reporter:  mietek          |             Owner:
           Type:  bug             |            Status:  new
       Priority:  normal          |         Milestone:
      Component:  Compiler        |           Version:  7.8.2
       Keywords:                  |  Operating System:  MacOS X
   Architecture:  x86_64 (amd64)  |   Type of failure:  None/Unknown
     Difficulty:  Unknown         |         Test Case:
     Blocked By:                  |          Blocking:
Related Tickets:                  |
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 Haddock fails to cooperate with OS X clang CPP:
 {{{
 <no location info>:
     module ‘pkgid-pkgversion:Main’ is defined in multiple files:
 dist/build/tmp-#####/Stuff
 }}}

 A workaround is to pass `--ghc-options=-optP-P` to `cabal haddock`.

 This prevents `cabal-install` from being boostrapped, unless `--no-doc` is
 specified.

 The original Haddock ticket and the corresponding Cabal issue were both
 closed as invalid, but there appears to be no GHC ticket to track the
 underlying cause.
 http://trac.haskell.org/haddock/ticket/284
 https://github.com/haskell/cabal/issues/1740

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9174>
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