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

From: René Scharfe <l.s.r@web.de>
Date: Jul 6, 2015, 20:10 UTC
Message-ID: <559AE0B9.2040704@web.de>
In-Reply-To: <1436186551-32544-1-git-send-email-pclouds@gmail.com>

Am 06.07.2015 um 14:42 schrieb Nguyễn Thái Ngọc Duy:

Show 30 quoted lines

> 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])"?

Show 12 quoted lines

>   	}
>
>   	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.

Show 10 quoted lines

>
> -	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.

>   			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?

Tests would be nice. :)

René