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Subject: Re: Bug in collation functions?
To: cygwin AT cygwin DOT com
References: <563148AF DOT 1000502 AT cornell DOT edu> <5631996D DOT 7040908 AT redhat DOT com> <20151029075050 DOT GE5319 AT calimero DOT vinschen DOT de> <20151029083057 DOT GH5319 AT calimero DOT vinschen DOT de> <56321815 DOT 7000203 AT cornell DOT edu> <20151029153516 DOT GJ5319 AT calimero DOT vinschen DOT de> <56323F2E DOT 4030807 AT cornell DOT edu> <56324598 DOT 9060604 AT cornell DOT edu> <56324E82 DOT 7000402 AT redhat DOT com>
From: Ken Brown <kbrown AT cornell DOT edu>
Message-ID: <563268A4.6000005@cornell.edu>
Date: Thu, 29 Oct 2015 14:42:44 -0400
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On 10/29/2015 12:51 PM, Eric Blake wrote:
> On 10/29/2015 10:13 AM, Ken Brown wrote:
>
>> Never mind.  My test case was flawed, because it didn't check for the
>> possibility that wcscoll might return 0.  Here's a revised definition of
>> the "compare" function:
>>
>> void
>> compare (const wchar_t *a, const wchar_t *b, const char *loc)
>> {
>>    setlocale (LC_COLLATE, loc);
>>    int res = wcscoll (a, b);
>>    char c = res < 0 ? '<' : res > 0 ? '>' : '=';
>>    printf ("\"%ls\" %c \"%ls\" in %s locale\n", a, c, b, loc);
>> }
>>
>> With this change (and the use of NORM_IGNORESYMBOLS) the test returns
>> the following on Cygwin:
>>
>> $ ./wcscoll_test
>> "11" > "1.1" in POSIX locale
>> "11" = "1.1" in en_US.UTF-8 locale
>> "11" > "1 2" in POSIX locale
>> "11" < "1 2" in en_US.UTF-8 locale
>>
>> It still differs from Linux, but it's good enough to make the emacs test
>> pass.  Moreover, this behavior actually seems more reasonable to me than
>> the Linux behavior.  After all, if you're ignoring punctuation, how can
>> you decide which of "11" or "1.1" comes first?
>
> Careful.  POSIX is proposing some wording that say that normal locales
> should always implement a fallback of last resort (and that locales that
> do not do so should have a special name including '@', to make it
> obvious).  It is not standardized yet, but worth thinking about.
>
> http://austingroupbugs.net/view.php?id=938
> http://austingroupbugs.net/view.php?id=963
>
> The intent of that wording is that if ignoring punctuation could cause
> two strings to otherwise compare equal, the fallback of a total ordering
> on all characters means that the final result of strcoll() will not be 0
> unless the two strings are identical.

In that case, I think Cygwin should start by using NORM_IGNORESYMBOLS in 
non-POSIX locales, with the goal of eventually moving toward emulating 
glibc.  I don't know what fallback glibc uses or how hard it would be to 
implement this on Cygwin.

Here's a tangentially related issue, also motivated by a failing emacs 
test: Should setlocale return null to indicate an error if it's given an 
invalid locale name?  This happens on Linux but not on Cygwin, as the 
following modified test case shows:

$ cat wcscoll_test.c
#include <wchar.h>
#include <stdio.h>
#include <locale.h>

void
compare (const wchar_t *a, const wchar_t *b, const char *loc)
{
   if (! setlocale (LC_COLLATE, loc))
     printf ("Unable to set locale to %s\n", loc);
   else
     {
       int res = wcscoll (a, b);
       char c = res < 0 ? '<' : res > 0 ? '>' : '=';
       printf ("\"%ls\" %c \"%ls\" in %s locale\n", a, c, b, loc);
     }
}

int
main ()
{
   compare (L"11", L"1.1", "POSIX");
   compare (L"11", L"1.1", "en_US.UTF-8");
   compare (L"11", L"1 2", "POSIX");
   compare (L"11", L"1 2", "en_US.UTF-8");
   compare (L"11", L"1 2", "en_DE.UTF-8");
}

On Cygwin (with NORM_IGNORESYMBOLS), the output is

"11" > "1.1" in POSIX locale
"11" = "1.1" in en_US.UTF-8 locale
"11" > "1 2" in POSIX locale
"11" < "1 2" in en_US.UTF-8 locale
"11" < "1 2" in en_DE.UTF-8 locale

but on Linux it is

"11" > "1.1" in POSIX locale
"11" < "1.1" in en_US.UTF-8 locale
"11" > "1 2" in POSIX locale
"11" < "1 2" in en_US.UTF-8 locale
Unable to set locale to en_DE.UTF-8

Ken

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