On Fri, Jan 10, 2025 at 01:59:18PM +0100, Andreas Schwab wrote:
> On Jan 10 2025, Jeff King wrote:
>
> > but it is weird to me that patmatch() will match "^$" to the end of the
> > buffer at all. It is just calling regexec_buf() behind the scenes, so I
> > guess this is just a weird special case there, and may even depend on
> > the regex implementation.
>
> Shouldn't the matcher be called with REG_NOTEOL in that case?
Perhaps. If regexec_buf() is assuming we are feeding lines, then without
REG_NOTEOL it thinks the end of the buffer is the end of a line. Which
makes sense, but trips up this case because we are not feeding lines,
but rather a whole buffer. So the final newline is not the start of an
empty line, but the true end of the buffer.
But what if the buffer doesn't end in a newline? In the example, the
file is something like "content\n". But what if it was just "content"?
Then the end of the buffer really is the end of a line, isn't it? And
REG_NOTEOL would not be appropriate.
So without REG_NOTEOL:
[this is wrong, per the report]
$ echo content >file.txt
$ git grep --no-index -n '^$' file.txt
file.txt:2:
[this is right]
$ printf content >file.txt
$ git grep --no-index -n '^$' file.txt
$ echo $?
1
and with it, like this patch:
diff --git a/grep.c b/grep.c
index 4e155ee9e6..7e3b6d9474 100644
--- a/grep.c
+++ b/grep.c
@@ -1467,7 +1467,7 @@ static int look_ahead(struct grep_opt *opt,
int hit;
regmatch_t m;
- hit = patmatch(p, bol, bol + *left_p, &m, 0);
+ hit = patmatch(p, bol, bol + *left_p, &m, REG_NOTEOL);
if (hit < 0)
return -1;
if (!hit || m.rm_so < 0 || m.rm_eo < 0)
we get:
[this is now right]
$ git grep --no-index -n '^$' file.txt
$ echo $?
1
[and this stays right]
$ printf content >file.txt
$ git grep --no-index -n '^$' file.txt
$ echo $?
1
but:
[without REG_NOTEOL, this matches]
$ printf content >file.txt
$ git grep --no-index -n 't$' file.txt
file.txt:1:content
[but with that flag, it no longer does]
$ printf content >file.txt
$ git grep --no-index -n 't$' file.txt
$ echo $?
1
So I do think "\n" at the end of the buffer is a special case. Perhaps
we should always omit it, and then leave REG_NOTEOL unset, making the
end of the buffer consistently the end of the final line. Like this,
which no longer matches "^$" but does match "t$":
diff --git a/grep.c b/grep.c
index 4e155ee9e6..c4bb9f1081 100644
--- a/grep.c
+++ b/grep.c
@@ -1646,6 +1646,8 @@ static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int colle
bol = gs->buf;
left = gs->size;
+ if (left && gs->buf[left-1] == '\n')
+ left--;
while (left) {
const char *eol;
int hit;
-Peff
