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Support OsString #252
Description
Motivation
The next filepath release will add support for a new API, which fixes subtle encoding issues and improves cross platform code and memory residence.
You can read about the state of the newly added API here: haskellfoundation/tech-proposals#35
Release is here: https://hackage.haskell.org/package/filepath-1.4.100.0
Demonstration about unsoundness of base with exotic encodings and how the new API fixes them is here: https://gist.github.com/hasufell/c600d318bdbe010a7841cc351c835f92
Migrations
Migrations can happen once the filepath, unix and Win32 packages are updated and in sync. A migration would usually involve using the new types from System.OsPath and the new API variants from unix/Win32.
When writing low-level cross platform code manually (shouldn't generally be necessary), the usual strategy is this:
#if defined(mingw32_HOST_OS) || defined(__MINGW32__)
import qualified System.OsPath.Data.ByteString.Short.Word16 as SBS
import qualified System.OsPath.Windows as PFP
#else
import qualified System.OsPath.Data.ByteString.Short as SBS
import qualified System.OsPath.Posix as PFP
#endif
crossPlatformFunction :: OsPath -> IO ()
#if defined(mingw32_HOST_OS) || defined(__MINGW32__)
crossPlatformFunction (OsString pfp@(WS ba)) = do
-- use filepath functions for windows specific operating system strings
let ext = PFP.takeExtension pfp
-- operate directly on the underlying bytestring (which is a wide character bytestring, so uses Word16)
let foo = SBS.takeWhile
...
#else
crossPlatformFunction (OsString pfp@(PS ba)) = do
-- use filepath functions for posix specific operating system strings
let ext = PFP.takeExtension pfp
-- operate directly on the underlying bytestring (which is just Word8 bytestring)
let foo = SBS.takeWhile
...
#endifPlatform specific code can be written using PosixPath/WindowsPath types.
If you have further questions, please let me know. I'm going to write a blog post outlining the affairs and more in-depth intro and migration strategies close after the release. This is a heads up.
Activity
hasufell commentedon Jul 16, 2022
Migration info can be found here: https://hasufell.github.io/posts/2022-06-29-fixing-haskell-filepaths.html
[-]Support `AbstractFilePath`[/-][+]Support `OsString`[/+]tomjaguarpaw commentedon Mar 21, 2026
Is further action in the
processrepo needed here?hasufell commentedon Mar 23, 2026
@tomjaguarpaw yes
tomjaguarpaw commentedon Mar 23, 2026
Thanks for confirming. Can you elaborate on what further action is necessary?
hasufell commentedon Mar 23, 2026
@tomjaguarpaw all of
System.Processneeds to be convertedtomjaguarpaw commentedon Mar 23, 2026
Do you mean for every function that
processexposes withFilePathin its type there should be an equivalent function withOsString?hasufell commentedon Mar 23, 2026
Yes
joeyh commentedon Jun 9, 2026
FilePath use in System.Process is mostly limited to the filename of the executable. However, when using OsString and running child processes, it's quite likely that one will also want to pass OsStrings to a process as parameters. Or in the environment.