Backport bugfix for splitFileName on windows

Wrt #219

Author: hasufell

System/FilePath/Internal.hs

@@ -602,6 +602,7 @@ isDrive x = not (null x) && null (dropDrive x)
 -- > Posix:   splitFileName "/" == ("/","")
 -- > Windows: splitFileName "c:" == ("c:","")
 -- > Windows: splitFileName "\\\\?\\A:\\fred" == ("\\\\?\\A:\\","fred")
+-- > Windows: splitFileName "\\\\?\\A:" == ("\\\\?\\A:","")
 splitFileName :: FILEPATH -> (STRING, STRING)
 splitFileName x = if null path
     then (dotSlash, file)
@@ -644,20 +645,43 @@ splitFileName_ fp
   -- or UNC location "\\?\UNC\foo", where path separator is a part of the drive name.
   -- We can test this by trying dropDrive and falling back to splitDrive.
   | isWindows
-  , Just (s1, _s2, bs') <- uncons2 dirSlash
-  , isPathSeparator s1
-  -- If bs' is empty, then s2 as the last character of dirSlash must be a path separator,
-  -- so we are in the middle of shared drive.
-  -- Otherwise, since s1 is a path separator, we might be in the middle of UNC path.
-  , null bs' || maybe False isIncompleteUNC (readDriveUNC dirSlash)
-  = (fp, mempty)
+  = case uncons2 dirSlash of
+    Just (s1, s2, bs')
+      | isPathSeparator s1
+      -- If bs' is empty, then s2 as the last character of dirSlash must be a path separator,
+      -- so we are in the middle of shared drive.
+      -- Otherwise, since s1 is a path separator, we might be in the middle of UNC path.
+      , null bs' || maybe False isIncompleteUNC (readDriveUNC dirSlash)
+      -> (fp, mempty)
+      -- This handles inputs like "//?/A:" and "//?/A:foo"
+      | isPathSeparator s1
+      , isPathSeparator s2
+      , Just (s3, s4, bs'') <- uncons2 bs'
+      , s3 == _question
+      , isPathSeparator s4
+      , null bs''
+      , Just (drive, rest) <- readDriveLetter file
+      -> (dirSlash <> drive, rest)
+    _ -> (dirSlash, file)
   | otherwise
-  = (dirSlash, file)
+    = (dirSlash, file)
   where
     (dirSlash, file) = breakEnd isPathSeparator fp
-
+    dropExcessTrailingPathSeparators x
+      | hasTrailingPathSeparator x
+      , let x' = dropWhileEnd isPathSeparator x
+      , otherwise = if | null x' -> singleton (last x)
+                       | otherwise -> addTrailingPathSeparator x'
+      | otherwise = x
+
+    -- an "incomplete" UNC is one without a path (but potentially a drive)
     isIncompleteUNC (pref, suff) = null suff && not (hasPenultimateColon pref)
-    hasPenultimateColon = maybe False (maybe False ((== _colon) . snd) . unsnoc . fst) . unsnoc
+
+    -- e.g. @//?/a:/@ or @//?/a://@, but not @//?/a:@
+    hasPenultimateColon pref
+      | hasTrailingPathSeparator pref
+      = maybe False (maybe False ((== _colon) . snd) . unsnoc . fst) . unsnoc . dropExcessTrailingPathSeparators $ pref
+      | otherwise = False
 
 -- | Set the filename.
 --

changelog.md

@@ -2,6 +2,10 @@
 
 _Note: below all `FilePath` values are unquoted, so `\\` really means two backslashes._
 
+## 1.4.300.0. *Jan 2024*
+
+* Backport bugfix for [`splitFileName`](https://github.com/haskell/filepath/issues/219) on windows
+
 ## 1.4.200.1. *Dec 2023*
 
 * Improve deprecation warnings wrt [#209](https://github.com/haskell/filepath/issues/209)

filepath.cabal

@@ -1,6 +1,6 @@
 cabal-version:      2.2
 name:               filepath
-version:            1.4.200.1
+version:            1.4.300.1
 
 -- NOTE: Don't forget to update ./changelog.md
 license:            BSD-3-Clause

tests/filepath-tests/TestGen.hs

@@ -14,11 +14,11 @@ import Data.String
 import GHC.IO.Encoding.Failure ( CodingFailureMode(..) )
 import GHC.IO.Encoding.UTF16 ( mkUTF16le )
 import GHC.IO.Encoding.UTF8 ( mkUTF8 )
-import System.OsString.Internal.Types
-import System.OsPath.Encoding.Internal
+import System.OsString.Internal.Types.Hidden
+import System.OsPath.Encoding.Internal.Hidden
 import qualified Data.Char as C
-import qualified System.OsPath.Data.ByteString.Short as SBS
-import qualified System.OsPath.Data.ByteString.Short.Word16 as SBS16
+import qualified System.OsPath.Data.ByteString.Short.Hidden as SBS
+import qualified System.OsPath.Data.ByteString.Short.Word16.Hidden as SBS16
 import qualified System.FilePath.Windows as W
 import qualified System.FilePath.Posix as P
 import qualified System.OsPath.Windows as AFP_W
@@ -458,6 +458,8 @@ tests =
     ,("AFP_W.splitFileName (\"c:\") == ((\"c:\"), (\"\"))", property $ AFP_W.splitFileName ("c:") == (("c:"), ("")))
     ,("W.splitFileName \"\\\\\\\\?\\\\A:\\\\fred\" == (\"\\\\\\\\?\\\\A:\\\\\", \"fred\")", property $ W.splitFileName "\\\\?\\A:\\fred" == ("\\\\?\\A:\\", "fred"))
     ,("AFP_W.splitFileName (\"\\\\\\\\?\\\\A:\\\\fred\") == ((\"\\\\\\\\?\\\\A:\\\\\"), (\"fred\"))", property $ AFP_W.splitFileName ("\\\\?\\A:\\fred") == (("\\\\?\\A:\\"), ("fred")))
+    ,("W.splitFileName \"\\\\\\\\?\\\\A:\" == (\"\\\\\\\\?\\\\A:\", \"\")", property $ W.splitFileName "\\\\?\\A:" == ("\\\\?\\A:", ""))
+    ,("AFP_W.splitFileName (\"\\\\\\\\?\\\\A:\") == ((\"\\\\\\\\?\\\\A:\"), (\"\"))", property $ AFP_W.splitFileName ("\\\\?\\A:") == (("\\\\?\\A:"), ("")))
     ,("P.replaceFileName \"/directory/other.txt\" \"file.ext\" == \"/directory/file.ext\"", property $ P.replaceFileName "/directory/other.txt" "file.ext" == "/directory/file.ext")
     ,("W.replaceFileName \"/directory/other.txt\" \"file.ext\" == \"/directory/file.ext\"", property $ W.replaceFileName "/directory/other.txt" "file.ext" == "/directory/file.ext")
     ,("AFP_P.replaceFileName (\"/directory/other.txt\") (\"file.ext\") == (\"/directory/file.ext\")", property $ AFP_P.replaceFileName ("/directory/other.txt") ("file.ext") == ("/directory/file.ext"))