Re: Bug in collation functions?

[Ken Brown <kbrown@cornell.edu>]

On 10/29/2015 5:49 PM, Ken Brown wrote:
> 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.

The fallback I had in mind is to return the shorter string if they have 
different lengths and otherwise to revert to wcscmp.  Using this, both 
Cygwin and Linux give the following comparisons:

"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
"1 1" < "1.1" in POSIX locale
"1 1" < "1.1" in en_US.UTF-8 locale

If this seems reasonable, I'll test it more extensively and then submit 
a patch.

Ken

P.S. In case others want to test this in different locales, here's the 
patch so far, just for wcscoll:

diff --git a/winsup/cygwin/nlsfuncs.cc b/winsup/cygwin/nlsfuncs.cc
index f7031f9..c33aa24 100644
--- a/winsup/cygwin/nlsfuncs.cc
+++ b/winsup/cygwin/nlsfuncs.cc
@@ -1156,10 +1156,15 @@ wcscoll (const wchar_t *__restrict ws1, const 
wchar_t *__restrict ws2)

    if (!collate_lcid)
      return wcscmp (ws1, ws2);
-  ret = CompareStringW (collate_lcid, 0, ws1, -1, ws2, -1);
+  ret = CompareStringW (collate_lcid, NORM_IGNORESYMBOLS, ws1, -1, ws2, 
-1);
    if (!ret)
      set_errno (EINVAL);
-  return ret - CSTR_EQUAL;
+  ret -= CSTR_EQUAL;
+  if (!ret)
+    ret = wcslen (ws1) - wcslen (ws2);
+  if (!ret)
+    ret = wcscmp (ws1, ws2);
+  return ret;
  }

  extern "C" int


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