[GHC] #4900: DEPENDS pragma

[GHC]

#4900: DEPENDS pragma
-------------------------------+--------------------------------------------
  Reporter:  cdsmith           |          Owner:  simonmar        
      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:                  
-------------------------------+--------------------------------------------

Comment(by 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.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4900#comment:47>
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