Re: Bug in collation functions?

[Ken Brown <kbrown@cornell.edu>]

On 10/29/2015 2:42 PM, Ken Brown wrote:
> 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.

I withdraw this suggestion.  I took a look at the glibc code, and I 
don't see any reasonable way for Cygwin to emulate it precisely.  On the 
other hand, I have an idea for a simple fallback.  I'll play with it a 
little and then submit a patch.

Ken

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