[GHC] #4900: DEPENDS pragma

[GHC]

#4900: DEPENDS pragma
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  Reporter:  cdsmith           |          Owner:                  
      Type:  feature request   |         Status:  patch           
  Priority:  normal            |      Milestone:  7.6.1           
 Component:  Compiler          |        Version:                  
Resolution:                    |       Keywords:                  
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown      |     Difficulty:  Unknown         
  Testcase:  TH_Depends        |      Blockedby:                  
  Blocking:                    |        Related:                  
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Changes (by parcs):

  * status:  new => patch


Comment:

 Replying to [comment:47 simonmar]:
 > While looking at the patch I noticed something odd: in order to look up
 the modification times of the "usage files" while constructing the
 `ModSummary`, we have to look for the `ModIface` in the HPT.  The first
 time around, it won't be there, so we'll have `Nothing` for the
 `ms_uf_date`, but the second time it will, which will force us to re-
 summarise all the modules.  This is very fishy.  I'm worried about (a)
 correctness when the module is not in the HPT, and (b) performance.
 >
 > I'm leaving the patch for now until I figure out the right thing to do.

 It turns out that, very conveniently, the mtimes of a module's usage files
 are already calculated during compilation. With that in mind, I have
 created a new patch addresses this issue and also makes it a little
 simpler to reason about.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4900#comment:50>
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