Fix an issue in module chasing caused by unnormalized file paths (#1303)

On Windows we can end up with rootModDir having / in the filepath
while rootPathDir uses \ so stripSuffix didn’t work.

This fixes #1284

src/Development/IDE/Functions/Compile.hs

@@ -233,7 +233,12 @@ runGhcSession IdeOptions{..} modu env act = runGhcEnv env $ do
 moduleImportPaths :: GHC.ParsedModule -> Maybe FilePath
 moduleImportPaths pm
   | rootModDir == "." = Just rootPathDir
-  | otherwise = dropTrailingPathSeparator <$> stripSuffix rootModDir rootPathDir
+  | otherwise =
+    -- TODO (MK) stripSuffix (normalise rootModDir) (normalise rootPathDir)
+    -- would be a better choice but at the moment we do not consistently
+    -- normalize file paths in the Shake graph so we can end up with the
+    -- same module being represented twice in the Shake graph.
+    Just $ dropTrailingPathSeparator $ dropEnd (length rootModDir) rootPathDir
   where
     ms   = GHC.pm_mod_summary pm
     file = GHC.ms_hspp_file ms