newlocale: Linux incompatibility

Corinna Vinschen
Thu Mar 23 21:14:23 GMT 2023

On Mar 23 15:48, Ken Brown via Cygwin wrote:
> I'm reporting this here rather than the newlib list because the behavior is
> compatible with Posix but not Linux, so I think it's a Cygwin issue.

Actually, it's a Windows issue :)

> Consider the following test case:
> $ cat locale_test.c
> #include <stdio.h>
> #include <locale.h>
> int main ()
> {
>   const char *locale = "en_DE.UTF-8";
>   locale_t loc = newlocale (LC_COLLATE_MASK | LC_CTYPE_MASK, locale, 0);
>   if (!loc)
>     perror ("newlocale");
>   else
>     printf ("newlocale succeeded on invalid locale %s\n", locale);
> }
> $ gcc -o locale_test locale_test.c
> $ ./locale_test.exe
> newlocale succeeded on invalid locale en_DE.UTF-8
> On Linux, the newlocale call fails with ENOENT, as is documented on the man
> page.  Posix doesn't say what should happen on an invalid locale, so this is
> not, strictly speaking, a bug.

Three bugs in fact.

First, it's a bug in the Emacs testsuite.  The test simply assumes that
there's no en_DE locale on any system, but that's just not true.
Windows support the RFC 5646 locale "en-DE", which is called "English
(Germany)" in the "Region" settings.

You can also check with `locale -av | less' and search for en_DE.

For the reminder of this mail, I assume you're talking about Cygwin 3.5.
I won't fix this for 3.4 anymore, given how much locale handling has
changed for 3.5.

The second bug is that Cygwin blindly trusts the Windows function
ResolveLocaleName().  That function blatantly converts even vaguely
similar locales into something it supports.  E.g., it converts "en-XY"
to "en-US".  I. .e., even if you use "en_XY.utf8" as locale, the above
testcase will wrongly succeed.  So I have to rethink how I resolve POSIX
locales to Windows locales.

And the third bug is that Cygwin fails to set errno if it doesn't
support a locale, but that's a minor inconvenience in comparison.

Thanks for the report, I totally missed the above problem with


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