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/DynFlags.hs

@@ -12,8 +12,6 @@ import qualified Language.Haskell.GhcMod.Gap as Gap
 import Language.Haskell.GhcMod.Types
 import System.IO.Unsafe (unsafePerformIO)
 
-data Build = CabalPkg | SingleFile deriving Eq
-
 setEmptyLogger :: DynFlags -> DynFlags
 setEmptyLogger df = Gap.setLogAction df $ \_ _ _ _ _ -> return ()
 
@@ -41,37 +39,15 @@ setModeIntelligent df = df {
   , optLevel  = 0
   }
 
-setIncludeDirs :: [IncludeDir] -> DynFlags -> DynFlags
-setIncludeDirs idirs df = df { importPaths = idirs }
-
-setBuildEnv :: Build -> DynFlags -> DynFlags
-setBuildEnv build = setHideAllPackages build . setCabalPackage build
-
--- | With ghc-7.8 this option simply makes GHC print a message suggesting users
--- add hiddend packages to the build-depends field in their cabal file when the
--- user tries to import a module form a hidden package.
-setCabalPackage :: Build -> DynFlags -> DynFlags
-setCabalPackage CabalPkg df = Gap.setCabalPkg df
-setCabalPackage _ df = df
-
--- | Enable hiding of all package not explicitly exposed (like Cabal does)
-setHideAllPackages :: Build -> DynFlags -> DynFlags
-setHideAllPackages CabalPkg df = Gap.setHideAllPackages df
-setHideAllPackages _ df = df
-
 -- | Parse command line ghc options and add them to the 'DynFlags' passed
 addCmdOpts :: GhcMonad m => [GHCOption] -> DynFlags -> m DynFlags
 addCmdOpts cmdOpts df =
-    tfst <$> G.parseDynamicFlags df (map G.noLoc cmdOpts)
+    fst3 <$> G.parseDynamicFlags df (map G.noLoc cmdOpts)
   where
-    tfst (a,_,_) = a
+    fst3 (a,_,_) = a
 
 ----------------------------------------------------------------
 
--- | Return the 'DynFlags' currently in use in the GHC session.
-getDynamicFlags :: IO DynFlags
-getDynamicFlags = G.runGhc (Just libdir) G.getSessionDynFlags
-
 withDynFlags :: GhcMonad m
              => (DynFlags -> DynFlags)
              -> m a
@@ -119,3 +95,7 @@ setNoMaxRelevantBindings df = df { maxRelevantBinds = Nothing }
 #else
 setNoMaxRelevantBindings = id
 #endif
+
+deferErrors :: DynFlags -> Ghc DynFlags
+deferErrors df = return $
+  Gap.setWarnTypedHoles $ Gap.setDeferTypeErrors $ setNoWarningFlags df