[GHC] #8489: clean up dependency and usages handling in interface files

[GHC]

#8489: clean up dependency and usages handling in interface files
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              Reporter:  errge       |            Owner:  errge
                  Type:  task        |           Status:  new
              Priority:  normal      |        Milestone:  7.10.1
             Component:  Template    |          Version:  7.7
  Haskell                            |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Moderate (less
  Unknown/Multiple                   |  than a day)
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by errge):

 Simon, yes of course, it is important to first agree on what we want.

 On the other hand, this is a much smaller change than my changes from
 previous year, so I do not think that we need a whole wiki page again.

 Let me put it here what I think the issue is and then you can point it out
 where I was not precise enough and we can complete this to a
 "specification".

 Take the following program:

 {{{#!haskell
 {-# LANGUAGE TemplateHaskell #-}

 import Language.Haskell.TH
 import Language.Haskell.TH.Syntax

 $(do let mod = Module (PkgName "binary-0.7.1.0") (ModName "Data.Binary")
      ModuleInfo info <- reifyModule mod
      runIO $ mapM_ print info
      return [])

 main = return ()
 }}}

 On my machine, the output is:

 {{{
 Module (PkgName "base") (ModName "Data.Either")
 Module (PkgName "base") (ModName "Data.Maybe")
 Module (PkgName "base") (ModName "Data.Word")
 Module (PkgName "base") (ModName "GHC.Base")
 Module (PkgName "base") (ModName "GHC.IO")
 Module (PkgName "base") (ModName "GHC.IO.IOMode")
 Module (PkgName "base") (ModName "GHC.Word")
 Module (PkgName "base") (ModName "Prelude")
 Module (PkgName "base") (ModName "System.IO")
 Module (PkgName "binary-0.7.1.0") (ModName "Data.Binary.Class")
 Module (PkgName "binary-0.7.1.0") (ModName "Data.Binary.Generic")
 Module (PkgName "binary-0.7.1.0") (ModName "Data.Binary.Get")
 Module (PkgName "binary-0.7.1.0") (ModName "Data.Binary.Get.Internal")
 Module (PkgName "binary-0.7.1.0") (ModName "Data.Binary.Put")
 Module (PkgName "bytestring-0.10.4.0") (ModName "Data.ByteString")
 Module (PkgName "bytestring-0.10.4.0") (ModName "Data.ByteString.Lazy")
 Module (PkgName "bytestring-0.10.4.0") (ModName
 "Data.ByteString.Lazy.Internal")
 Module (PkgName "ghc-prim") (ModName "GHC.Types")
 }}}

 And looking at http://hackage.haskell.org/package/binary-0.7.1.0/docs/src
 /Data-Binary.html it can be seen that we do not import GHC.Types in
 binary.

 So from the programmer point of view, this change should make the
 ModuleInfo list returned by module reification only contain the actual
 direct imports.

 So this is my goal, before discussing implementation details inside GHC,
 may I ask if this description is clear enough and if others agree with the
 goal?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8489#comment:5>
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