[GHC] #8244: Removing the Cabal dependency

[GHC]

#8244: Removing the Cabal dependency
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              Reporter:  nh2         |            Owner:  duncan
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.6.3
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:  D172        |
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Comment (by refold):

 Replying to [comment:29 duncan]:
 > It could read the text files, but this would be slower than using the
 binary cache. The performance of ghc-pkg dump is actually important. It's
 used by cabal to get the installed packages.

 Maybe Cabal should have its own binary cache for the data it gets out of
 `ghc-pkg dump`? We can check whether compiler's package DB is older than
 our cache and only use the slow path (`ghc-pkg dump`) when it's not.
 Perhaps we could also share the `Binary` instance for
 `InstalledPackageInfo` between `Cabal` and `ghc-pkg`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8244#comment:31>
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