Fix doc command not using right ghc-pkg exe

Language/Haskell/GhcMod/GhcPkg.hs

@@ -6,6 +6,7 @@ module Language.Haskell.GhcMod.GhcPkg (
   , ghcDbOpt
   , getPackageDbStack
   , getPackageCachePaths
+  , getGhcPkgProgram
   ) where
 
 import Config (cProjectVersion, cTargetPlatformString, cProjectVersionInt)
@@ -59,6 +60,18 @@ ghcDbOpt (PackageDb pkgDb)
 
 ----------------------------------------------------------------
 
+getGhcPkgProgram :: IOish m => GhcModT m FilePath
+getGhcPkgProgram = do
+  crdl <- cradle
+  progs <- optPrograms <$> options
+  case cradleProjectType crdl of
+    StackProject -> do
+        Just ghcPkg <- getStackGhcPkgPath (cradleRootDir crdl)
+        return ghcPkg
+    _ ->
+        return $ ghcPkgProgram progs
+
+
 getPackageDbStack :: IOish m => GhcModT m [GhcPkgDb]
 getPackageDbStack = do
   crdl <- cradle

Language/Haskell/GhcMod/PkgDoc.hs

@@ -3,7 +3,7 @@ module Language.Haskell.GhcMod.PkgDoc (pkgDoc) where
 import Language.Haskell.GhcMod.Types
 import Language.Haskell.GhcMod.GhcPkg
 import Language.Haskell.GhcMod.Monad
-import Language.Haskell.GhcMod.Utils
+import Language.Haskell.GhcMod.Output
 
 import Control.Applicative
 import Prelude
@@ -11,12 +11,14 @@ import Prelude
 -- | Obtaining the package name and the doc path of a module.
 pkgDoc :: IOish m => String -> GhcModT m String
 pkgDoc mdl = do
+    ghcPkg <- getGhcPkgProgram
+    readProc <- gmReadProcess
     pkgDbStack <- getPackageDbStack
-    pkg <- liftIO $ trim <$> readProcess "ghc-pkg" (toModuleOpts pkgDbStack) ""
+    pkg <- liftIO $ trim <$> readProc ghcPkg (toModuleOpts pkgDbStack) ""
     if pkg == "" then
         return "\n"
       else do
-        htmlpath <- liftIO $ readProcess "ghc-pkg" (toDocDirOpts pkg pkgDbStack) ""
+        htmlpath <- liftIO $ readProc ghcPkg (toDocDirOpts pkg pkgDbStack) ""
         let ret = pkg ++ " " ++ drop 14 htmlpath
         return ret
   where