Fix build on case-insensitive filesystems (#873)

GhcModExe/PkgDoc.hs

@@ -0,0 +1,29 @@
+module GhcModExe.PkgDoc (pkgDoc) where
+
+import Language.Haskell.GhcMod.Types
+import Language.Haskell.GhcMod.GhcPkg
+import Language.Haskell.GhcMod.Monad
+import Language.Haskell.GhcMod.Output
+
+import Control.Applicative
+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 <$> readProc ghcPkg (toModuleOpts pkgDbStack) ""
+    if pkg == "" then
+        return "\n"
+      else do
+        htmlpath <- liftIO $ readProc ghcPkg (toDocDirOpts pkg pkgDbStack) ""
+        let ret = pkg ++ " " ++ drop 14 htmlpath
+        return ret
+  where
+    toModuleOpts dbs = ["find-module", mdl, "--simple-output"]
+                   ++ ghcPkgDbStackOpts dbs
+    toDocDirOpts pkg dbs = ["field", pkg, "haddock-html"]
+                       ++ ghcPkgDbStackOpts dbs
+    trim = takeWhile (`notElem` " \n")