Refactoring to use cabal-helper-wrapper

This turned out to be quite involved but save for this huge commit it's
actually quite awesome and squashes quite a few bugs and nasty
problems (hopefully). Most importantly we now have native cabal
component support without the user having to do anything to get it!

To do this we traverse imports starting from each component's
entrypoints (library modules or Main source file for executables) and
use this information to find which component's options each module will
build with. Under the assumption that these modules have to build with
every component they're used in we can now just pick one.

Quite a few internal assumptions have been invalidated by this
change. Most importantly the runGhcModT* family of cuntions now change
the current working directory to `cradleRootDir`.

Language/Haskell/GhcMod/GhcPkg.hs

@@ -4,20 +4,14 @@ module Language.Haskell.GhcMod.GhcPkg (
   , ghcPkgDbStackOpts
   , ghcDbStackOpts
   , ghcDbOpt
-  , fromInstalledPackageId
-  , fromInstalledPackageId'
-  , getPackageDbStack
   , getPackageCachePaths
   ) where
 
 import Config (cProjectVersion, cTargetPlatformString, cProjectVersionInt)
 import Control.Applicative ((<$>))
-import Data.List (intercalate)
 import Data.List.Split (splitOn)
 import Data.Maybe
-import Distribution.Package (InstalledPackageId(..))
 import Exception (handleIO)
-import Language.Haskell.GhcMod.PathsAndFiles
 import Language.Haskell.GhcMod.Types
 import System.Directory (doesDirectoryExist, getAppUserDataDirectory)
 import System.FilePath ((</>))
@@ -25,29 +19,6 @@ import System.FilePath ((</>))
 ghcVersion :: Int
 ghcVersion = read cProjectVersionInt
 
-getPackageDbStack :: FilePath -- ^ Project Directory (where the
-                                 -- cabal.sandbox.config file would be if it
-                                 -- exists)
-                  -> IO [GhcPkgDb]
-getPackageDbStack cdir =
-    ([GlobalDb] ++) . maybe [UserDb] return <$> getSandboxDb cdir
-
-----------------------------------------------------------------
-
-fromInstalledPackageId' :: InstalledPackageId -> Maybe Package
-fromInstalledPackageId' pid = let
-    InstalledPackageId pkg = pid
-    in case reverse $ splitOn "-" pkg of
-      i:v:rest -> Just (intercalate "-" (reverse rest), v, i)
-      _ -> Nothing
-
-fromInstalledPackageId :: InstalledPackageId -> Package
-fromInstalledPackageId pid =
-    case fromInstalledPackageId' pid of
-      Just p -> p
-      Nothing -> error $
-        "fromInstalledPackageId: `"++show pid++"' is not a valid package-id"
-
 ----------------------------------------------------------------
 
 -- | Get options needed to add a list of package dbs to ghc-pkg's db stack
@@ -82,12 +53,10 @@ ghcDbOpt (PackageDb pkgDb)
 
 ----------------------------------------------------------------
 
-
 getPackageCachePaths :: FilePath -> Cradle -> IO [FilePath]
 getPackageCachePaths sysPkgCfg crdl =
     catMaybes <$> resolvePackageConfig sysPkgCfg `mapM` cradlePkgDbStack crdl
 
-
 -- TODO: use PkgConfRef
 --- Copied from ghc module `Packages' unfortunately it's not exported :/
 resolvePackageConfig :: FilePath -> GhcPkgDb -> IO (Maybe FilePath)