[GHC] #4900: DEPENDS pragma

[GHC]

#4900: DEPENDS pragma
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    Reporter:  cdsmith           |        Owner:              
        Type:  feature request   |       Status:  new         
    Priority:  normal            |    Milestone:  7.4.1       
   Component:  Build System      |      Version:              
    Keywords:                    |     Testcase:              
   Blockedby:                    |   Difficulty:              
          Os:  Unknown/Multiple  |     Blocking:              
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown
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Comment(by simonmar):

 I think the proposed solution is fine.  (note that a related problem was
 fixed in GHC 7.2.1: see #481)

 It will need some plumbing and some refactoring in GHC.  The list of
 depended-upon files has to be collected in the `Q` monad and stored in the
 `ModIface`, and then we have to check the dates of those files when
 deciding whether to recompile.  The obvious place to do the check is in
 `MkIface.checkOldIface`, but it doesn't have information about the
 modification time of the object file - we would have to plumb that
 information in, probably by elaborating the `SourceModified` parameter.

 This would also be useful in fixing another bug we have: when using CPP,
 we don't recompile when a `#included` file changes.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4900#comment:8>
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