Re: Patch: non-empty matches following empty ones

[Charles Levert]

Hi Stepan.

You've been MIA (missing in action) for a while
on this list!   :-)
Good to read you back.


* On Tuesday 2005-08-23 at 12:06:13 +0200, Stepan Kasal wrote:
> 
> I think that all matches should be printed, even the empty ones.
> And the same holds for --colour; if an automated system tries to
> parse the colour tags (emacs, for example), it should get all
> matches.

Do you realize that for such patterns:

   -- every line matches;

   -- every place on a line where there isn't
      already a non-empty match, there will be
      an empty match between any two adjacent
      characters;

   -- with --only-matching, that will just
      produce a _lot_ of "filename:\n" lines;

   -- with --color, this will just produce a _lot_
      of human-invisible "\33[01;31m\33[K\33[m\33[K"
      pairs, along with possibly more such
      stuff around each non-matching character
      if GREP_COLORS is so configured (and the
      concern below addressed).

Of course, it can be argued that the user who
would supply such a pattern in the first place
is really asking for it, so we would be justified
to deliver.


> Basically, I'd start with the patch below.

> @@ -799,6 +799,12 @@
>        PR_SGR_END_IF(grep_color);
>        if (only_matching)
>       fputs("\n", stdout);
> +
> +      /* Make minimal progress; there may be further non-empty matches.  */
> +      /* XXX - Could really advance by one whole multi-octet character.  */
> +      if (match_size == 0)
> +     match_size = 1;
> +
>        beg = b + match_size;
>        ibeg += match_offset + match_size;     /* XXX */
>      }

This alone won't work because we already did a
break on match_size == 0 by this point in the
loop, so this will be unreached.  If we remove
the earlier check, then we'll have the caveats
expressed above for a lot of empty matches,
but more importantly the non-matching characters
will never have been printed in the --color case
(as opposed to the --only-matching case where
it doesn't matter).