[Rd] R-4.3 version list.files function could not work correctly in chinese

[Ivan Krylov]

В Tue, 15 Aug 2023 08:38:11 +0200
Tomas Kalibera <tomas.kalibera using gmail.com> пишет:

> As this was reported to be regression in 4.3, it is entirely possible 
> this change came with a regression (though a bit surprising we didn't 
> catch it earlier by testing), so it would be a great help if I could 
> have the example and debug it.

Sorry, let me try to be more clear.

The Windows filename length limit is 255(?) wide characters. The
WIN32_FIND_DATAA structure contains a 260-byte buffer for the filename
to be returned by FindFirstFileA()/FindNextFileA(). If a wide character
takes more than one byte to be represented in UTF-8, it may overflow
the 260 byte limit in the WIN32_FIND_DATAA structure despite being
below the 260 wide character limit. When such an overflow happens,
FindNextFile() returns FALSE with GetLastError() == ERROR_MORE_DATA,
which results in R_readdir() returning NULL and makes list_files() stop
before listing the rest of the directory.

This is easier to make happen by accident with Chinese characters,
because they take three UTF-8 bytes per character.

Take the ø (\uf8) letter. It takes two bytes to represent in UTF-8.
Create a file with a name consisting of this symbol repeated 140 times.
When you run list.files() on the resulting directory on Windows with a
UTF-8 locale, Windows tries to fit (0xc3 0xb8) times 140 into a
260-byte buffer, which doesn't work. I'm afraid the only way to avoid
such a failure is to rewrite R_readdir using the wide character API and
convert the file names on the fly. (Just like mingw readdir() did in
the past?)

stopifnot(.Platform$OS.type == 'windows', l10n_info()$`UTF-8`)
# any character for which nchar(enc2utf8(.), 'bytes') > 1 will do
# any number >260/2 should do
file.create(strrep('\uf8', 140))
list.files()

Does this work? I don't have access to a UTF-8 Windows machine right
now.

-- 
Best regards,
Ivan