[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 duncan):

 Replying to [comment:31 refold]:

 > 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`.

 I don't think cabal calling `ghc-pkg dump` is currently a performance
 bottleneck. If it becomes one, there's several things we can do to improve
 it before adding caching.

 In a sense we already have a cache, when we `cabal configure` we read it
 only once and don't re-read it for `cabal build`. When installing a bunch
 of packages, it's read once for dep planning, and again for each package
 installed.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8244#comment:33>
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