[GHC] #1290: ghc runs preprocessor too much

[GHC]

#1290: ghc runs preprocessor too much
-------------------------------------+-------------------------------------
        Reporter:  guest             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Driver            |              Version:  6.7
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 I think this is essentially impossible to fix. Along with the ''import''
 dependencies, there are also the ''preprocessing'' dependencies. If I have

 {{{#!hs
 module Blah where
 #include Foo.h
 }}}

 then I need to preprocess `Blah.hs` any time `Foo.h` changes. But that
 means we need to know that `Blah.hs` depends on `Foo.h`. Without detailed
 knowledge of the preprocessor language, I don't see any way to determine
 this. I'm very tempted to close this ticket as invalid, but let's see if
 anyone disagrees.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1290#comment:12>
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