Re: [PATCH] grep: fix colouring of matches with zero length

[Junio C Hamano <gitster@pobox.com>]

René Scharfe <rene.scharfe@lsrfire.ath.cx> writes:

> The first hunk fixes match colouring if the patterns is the empty string.
> Such a pattern matches the whole line,...

Hmmm...

An empty pattern may have to produce a match with any line, but I do not
think it should match the whole line.  GNU seems to agree with me.

	echo foo | grep --color -e ''
        echo foo | grep --color -F -e ''
        echo foo | grep --color -e '.*'
        echo foo | grep --color -F -e 'foo'

The first two are uncoloured (but still show matches).

> The second hunk of the patch makes sure that grep match colouring doesn't
> get stuck in an infinite loop if the length of a match is zero.

Certainly we need to advance the match pointer, and this issue needs to be
addressed.  I think it is a good change.

> of the line is simply printed without colouring.  Even though the empty
> pattern string doesn't result in empty matches any more, this defensive
> measure catches unknown cases.
>
> Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
> ---
>  grep.c |    8 +++++++-
>  1 files changed, 7 insertions(+), 1 deletions(-)
>
> diff --git a/grep.c b/grep.c
> index cc6d5b0..745b3c0 100644
> --- a/grep.c
> +++ b/grep.c
> @@ -324,7 +324,11 @@ static int match_one_pattern(struct grep_pat *p, char *bol, char *eol,
>  	}
>  
>   again:
> -	if (p->fixed)
> +	if (p->pattern[0] == '\0') {
> +		hit = 1;
> +		pmatch[0].rm_so = 0;
> +		pmatch[0].rm_eo = eol - bol;
> +	} else if (p->fixed)
>  		hit = !fixmatch(p->pattern, bol, pmatch);
>  	else
>  		hit = !regexec(&p->regexp, bol, 1, pmatch, eflags);
> @@ -500,6 +504,8 @@ static void show_line(struct grep_opt *opt, char *bol, char *eol,
>  
>  		*eol = '\0';
>  		while (next_match(opt, bol, eol, ctx, &match, eflags)) {
> +			if (match.rm_so == match.rm_eo)
> +				break;
>  			printf("%.*s%s%.*s%s",
>  			       (int)match.rm_so, bol,
>  			       opt->color_match,
> -- 
> 1.6.3.1