Re: [PATCH] grep: use regcomp() for icase search with non-ascii patterns

[Duy Nguyen <pclouds@gmail.com>]

On Tue, Jul 7, 2015 at 3:10 AM, René Scharfe <l.s.r@web.de> wrote:
> Am 06.07.2015 um 14:42 schrieb Nguyễn Thái Ngọc Duy:
>>
>> Noticed-by: Plamen Totev <plamen.totev@abv.bg>
>> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
>> ---
>>   grep.c | 14 +++++++++++---
>>   1 file changed, 11 insertions(+), 3 deletions(-)
>>
>> diff --git a/grep.c b/grep.c
>> index b58c7c6..48db15a 100644
>> --- a/grep.c
>> +++ b/grep.c
>> @@ -378,7 +378,7 @@ static void free_pcre_regexp(struct grep_pat *p)
>>   }
>>   #endif /* !USE_LIBPCRE */
>>
>> -static int is_fixed(const char *s, size_t len)
>> +static int is_fixed(const char *s, size_t len, int ignore_icase)
>>   {
>>         size_t i;
>>
>> @@ -391,6 +391,13 @@ static int is_fixed(const char *s, size_t len)
>>         for (i = 0; i < len; i++) {
>>                 if (is_regex_special(s[i]))
>>                         return 0;
>> +               /*
>> +                * The builtin substring search can only deal with case
>> +                * insensitivity in ascii range. If there is something
>> outside
>> +                * of that range, fall back to regcomp.
>> +                */
>> +               if (ignore_icase && (unsigned char)s[i] >= 128)
>> +                       return 0;
>
>
> How about "isascii(s[i])"?

Yes, better.

>
>>         }
>>
>>         return 1;
>> @@ -398,18 +405,19 @@ static int is_fixed(const char *s, size_t len)
>>
>>   static void compile_regexp(struct grep_pat *p, struct grep_opt *opt)
>>   {
>> +       int ignore_icase = opt->regflags & REG_ICASE || p->ignore_case;
>>         int err;
>>
>>         p->word_regexp = opt->word_regexp;
>>         p->ignore_case = opt->ignore_case;
>
>
> Using p->ignore_case before this line, as in initialization of the new
> variable ignore_icase above, changes the meaning.

Oops.

>> -       if (opt->fixed || is_fixed(p->pattern, p->patternlen))
>> +       if (opt->fixed || is_fixed(p->pattern, p->patternlen,
>> ignore_icase))
>>                 p->fixed = 1;
>>         else
>>                 p->fixed = 0;
>>
>>         if (p->fixed) {
>> -               if (opt->regflags & REG_ICASE || p->ignore_case)
>> +               if (ignore_case)
>
>
> ignore_icase instead?  ignore_case is for the config variable
> core.ignorecase.  Tricky.

Maybe we can test isascii separately and save the result in
has_non_ascii, then we can avoid ignore_(i)case

>
>>                         p->kws = kwsalloc(tolower_trans_tbl);
>>                 else
>>                         p->kws = kwsalloc(NULL);
>>
>
> So the optimization before this patch was that if a string was searched for
> without -F then it would be treated as a fixed string anyway unless it
> contained regex special characters.  Searching for fixed strings using the
> kwset functions is faster than using regcomp and regexec, which makes the
> exercise worthwhile.
>
> Your patch disables the optimization if non-ASCII characters are searched
> for because kwset handles case transformations only for ASCII chars.
>
> Another consequence of this limitation is that -Fi (explicit
> case-insensitive fixed-string search) doesn't work properly with non-ASCII
> chars neither.  How can we handle this one?  Fall back to regcomp by
> escaping all special characters?  Or at least warn?

Hehe.. I noticed it too shortly after sending the patch. I was torn
between simply documenting the limitation and waiting for the next
person to come and fix it, or quoting the regex then passing to
regcomp. GNU grep does the quoting in this case, but that code is
GPLv3 so we can't simply copy over. It could be a problem if we need
to quote a regex in a multibyte charset where ascii is not a subset.
But i guess we can just go with utf-8..

> Tests would be nice. :)

Yeah.. but we now rely on system regcomp which may behave differently
across platforms. Then we need some locale to be always there. Some
platforms (like Gentoo) even allow building glibc without i18n.. So
I'm not sure how we know when to test or skip.
-- 
Duy