Fix slash direction on Windows with the new filePath code

compiler/main/DriverPipeline.hs

@@ -582,17 +582,22 @@ runPhase :: Phase	-- Do this phase first
 -- Unlit phase 
 
 runPhase (Unlit sf) _stop dflags _basename _suff input_fn get_output_fn maybe_loc
-  = do let unlit_flags = getOpts dflags opt_L
-       -- The -h option passes the file name for unlit to put in a #line directive
+  = do
        output_fn <- get_output_fn dflags (Cpp sf) maybe_loc
 
-       SysTools.runUnlit dflags 
-		(map SysTools.Option unlit_flags ++
-       			  [ SysTools.Option     "-h"
- 			  , SysTools.Option     input_fn
-			  , SysTools.FileOption "" input_fn
-			  , SysTools.FileOption "" output_fn
-			  ])
+       let unlit_flags = getOpts dflags opt_L
+           flags = map SysTools.Option unlit_flags ++
+                   [ -- The -h option passes the file name for unlit to
+                     -- put in a #line directive
+                     SysTools.Option     "-h"
+                     -- cpp interprets \b etc as escape sequences,
+                     -- so we use / for filenames in pragmas
+                   , SysTools.Option $ reslash Forwards $ normalise input_fn
+                   , SysTools.FileOption "" input_fn
+                   , SysTools.FileOption "" output_fn
+                   ]
+
+       SysTools.runUnlit dflags flags
 
        return (Cpp sf, dflags, maybe_loc, output_fn)
 

compiler/utils/Util.lhs

@@ -70,6 +70,7 @@ module Util (
         splitLongestPrefix,
         escapeSpaces,
         parseSearchPath,
+        Direction(..), reslash,
     ) where
 
 -- XXX This define is a bit of a hack, and should be done more nicely
@@ -841,4 +842,17 @@ searchPathSeparator = ';'
 #else
 searchPathSeparator = ':'
 #endif
+
+data Direction = Forwards | Backwards
+
+reslash :: Direction -> FilePath -> FilePath
+reslash d = f
+    where f ('/'  : xs) = slash : f xs
+          f ('\\' : xs) = slash : f xs
+          f (x    : xs) = x     : f xs
+          f ""          = ""
+          slash = case d of
+                  Forwards -> '/'
+                  Backwards -> '\\'
 \end{code}
+