[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 cdsmith):

 Replying to [comment:10 simonmar]:
 > Note that the `DEPENDS` pragma idea in this ticket is better than an
 `addDependentFile` function in TH, for two reasons:

 Agreed, there are definitely advantages that way, which is a lot of why I
 originally proposed it that way.

 I recall that in the context of optimizing the fclabels package a few
 weeks ago, it came up that TH could actually emit INLINE pragmas.  Is
 there a design where it would be possible for TH to emit DEPENDS pragmas?
 Then we'd have two scenarios:

 1. You could add an explicit DEPENDS pragma, and this would make `ghc -M`
 and other external tools work.

 2. You could have your TH emit a DEPENDS pragma, which means it would be
 opaque to static tools like `ghc -M` and `cabal`, but GHC would still use
 it when deciding whether to rebuild.

 In some ways, this seems messy; but the only effect of resolving TH would
 be to *add* dependencies, so the statically derived list would at least be
 an approximation to the complete list.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4900#comment:12>
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