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/Info.hs

@@ -7,16 +7,20 @@ import Control.Applicative ((<$>))
 import Data.Function (on)
 import Data.List (sortBy)
 import Data.Maybe (catMaybes)
+import System.FilePath
 import Exception (ghandle, SomeException(..))
 import GHC (GhcMonad, LHsBind, LHsExpr, LPat, Id, TypecheckedModule(..), SrcSpan, Type)
 import qualified GHC as G
-import Language.Haskell.GhcMod.Doc (showPage)
-import Language.Haskell.GhcMod.Gap (HasType(..))
 import qualified Language.Haskell.GhcMod.Gap as Gap
+
+import Language.Haskell.GhcMod.Convert
+import Language.Haskell.GhcMod.Doc
+import Language.Haskell.GhcMod.DynFlags
+import Language.Haskell.GhcMod.Gap
+import Language.Haskell.GhcMod.Logging
 import Language.Haskell.GhcMod.Monad
 import Language.Haskell.GhcMod.SrcUtils
 import Language.Haskell.GhcMod.Types
-import Language.Haskell.GhcMod.Convert
 
 ----------------------------------------------------------------
 
@@ -25,14 +29,21 @@ info :: IOish m
      => FilePath     -- ^ A target file.
      -> Expression   -- ^ A Haskell expression.
      -> GhcModT m String
-info file expr = do
+info file expr = runGmLoadedT' [Left file] deferErrors $ withContext $ do
     opt <- options
     convert opt <$> ghandle handler body
   where
-    body = inModuleContext file $ \dflag style -> do
+    handler (SomeException ex) = do
+        gmLog GmException "info" $
+                text "" $$ nest 4 (showDoc ex)
+        return "Cannot show info"
+
+    body = do
         sdoc <- Gap.infoThing expr
-        return $ showPage dflag style sdoc
-    handler (SomeException _) = return "Cannot show info"
+        st <- getStyle
+        dflag <- G.getSessionDynFlags
+        return $ showPage dflag st sdoc
+
 
 ----------------------------------------------------------------
 
@@ -42,15 +53,18 @@ types :: IOish m
       -> Int          -- ^ Line number.
       -> Int          -- ^ Column number.
       -> GhcModT m String
-types file lineNo colNo = do
-    opt <- options
-    convert opt <$> ghandle handler body
-  where
-    body = inModuleContext file $ \dflag style -> do
-        modSum <- Gap.fileModSummary file
+types file lineNo colNo =
+    runGmLoadedT' [Left file] deferErrors $ ghandle handler $ withContext $ do
+        crdl <- cradle
+        modSum <- Gap.fileModSummary (cradleCurrentDir crdl </> file)
         srcSpanTypes <- getSrcSpanType modSum lineNo colNo
-        return $ map (toTup dflag style) $ sortBy (cmp `on` fst) srcSpanTypes
-    handler (SomeException _) = return []
+
+        dflag <- G.getSessionDynFlags
+        st <- getStyle
+
+        convert' $ map (toTup dflag st) $ sortBy (cmp `on` fst) srcSpanTypes
+ where
+   handler (SomeException _) = return []
 
 getSrcSpanType :: GhcMonad m => G.ModSummary -> Int -> Int -> m [(SrcSpan, Type)]
 getSrcSpanType modSum lineNo colNo = do