[GHC] #10869: Option to dump preprocessed source

[GHC]

#10869: Option to dump preprocessed source
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              Reporter:  phischu     |             Owner:
                  Type:  feature     |            Status:  new
  request                            |
              Priority:  low         |         Milestone:
             Component:  Driver      |           Version:  7.10.2
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
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 It would be awesome if GHC had an option `-ddump-preprocessed` that dumps
 the source code for each module after preprocessing. I am not sure what
 the current definition of "preprocessing" is but I mean the output of at
 least the following tools: happy, alex, c2hs, hsc2hs and cpp. Additionally
 even if a module was not subject to any preprocessing it should be dumped
 anyway.

 Use case: I want to parse module files from packages from hackage with
 `haskell-src-exts` but find it prohibitively difficult to get the
 preprocessing right. The idea is that after `cabal install` with ghc
 options `-ddump-preprocessed -ddump-to-file -dumpdir real_modules` you get
 a complete working set of haskell modules that can be parsed directly
 without any preprocessing in folder `real_modules`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10869>
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