behaviour change in getDirectoryContents in GHC 7.2?

[Max Bolingbroke]

On 6 November 2011 04:14, John Millikin <jmillikin at gmail.com> wrote:
> For what it's worth, on my Ubuntu system, Nautilus ignores the locale
> and just treats all paths as either UTF8 or invalid.
> To me, this seems like the most reasonable option; the concept of
> "locale encoding" is entirely vestigal, and should only be used in
> certain specialized cases.

Unfortunately non-UTF8 locale encodings are seen in practice quite
often. I'm not sure about Linux, but certainly lots of Windows systems
are configured with a locale encoding like GBK or Big5.

> Paths as text is what *Windows* programmers expect. Paths as bytes is
> what's expected by programmers on non-Windows OSes, including Linux
> and OS X.

IIRC paths on OS X are guaranteed to be valid UTF-8. The only platform
that uses bytes for paths (that we care about) is Linux.

> I'm not saying one is inherently better than the other, but
> considering that various UNIX  and UNIX-like operating systems have
> been using byte-based paths for near on forty years now, trying to
> abolish them by redefining the type is not a useful action.

We have to:
 1. Provide an API that makes sense on all our supported OSes
 2. Have getArgs :: IO [String]
 3. Have it such that if you go to your console and write
(./MyHaskellProgram 你好) then getArgs tells you ["你好"]

Given these constraints I don't see any alternative to PEP-383 behaviour.

> If you're going to make all the System.IO stuff use text, at least
> give us an escape hatch. The "unix" package is ideally suited, as it's
> already inherently OS-specific. Something like this would be perfect:

You can already do this with the implemented design. We have:

openFile :: FilePath -> IO Handle

The FilePath will be encoded in the fileSystemEncoding. On Unix this
will have PEP383 roundtripping behaviour. So if you want openFile' ::
[Byte] -> IO Handle you can write something like this:

escape = map (\b -> if b < 128 then chr b else chr (0xEF00 + b))
openFile = openFile' . escape

The bytes that reach the API call will be exactly the ones you supply.
(You can also implement "escape" by just encoding the [Byte] with the
fileSystemEncoding).

Likewise, if you have a String and want to get the [Byte] we decoded
it from, you just need to encode the String again with the
fileSystemEncoding.

If this is not enough for you please let me know, but it seems to me
that it covers all your use cases, without any need to reimplement the
FFI bindings.

Max