On Mon, Nov 06 2017, Jeff King jotted:
> On Sun, Nov 05, 2017 at 10:41:17AM +0100, Дилян Палаузов wrote:
>
>> I understand that the PCRE's stack can get exhausted for some files, but in
>> such cases, git grep shall proceed with the other files, and print at the
>> end/stderr for which files the pattern was not applied. Such behaviour
>> would be more usefull than the current one.
>
> Yes, I had a similar thought. It does feel a little funny for us to
> basically treat an error as "no match" for non-interactive use, but then
> the current behavior works out to be more or less the same (we return an
> error code which most shell scripts would interpret as failure).
>
> IOW, I think something like this is probably the right direction:
>
> diff --git a/grep.c b/grep.c
> index ce6a48e634..2c152e5908 100644
> --- a/grep.c
> +++ b/grep.c
> @@ -427,7 +427,7 @@ static int pcre1match(struct grep_pat *p, const char *line, const char *eol,
> }
>
> if (ret < 0 && ret != PCRE_ERROR_NOMATCH)
> - die("pcre_exec failed with error code %d", ret);
> + warning("pcre_exec failed with error code %d", ret);
> if (ret > 0) {
> ret = 0;
> match->rm_so = ovector[0];
>
> but possibly:
>
> 1. It would be nice to report the filename that we couldn't match on.
> But we don't know it at this level of the code (and it might not be
> a file at all that we are matching). So probably we'd want to pass
> the error much further up the call stack. This is tricky as there
> are multiple regex libraries we can use, and the return value gets
> normalized to 1/0 for hit/not-hit long before we get as far as
> something that knows the filename.
>
> We might need to do something invasive like adding an extra
> parameter to hold the error message, and passing it through the
> whole stack.
>
> 2. We should still try to exit with an exit code other than "1" to
> indicate we hit an error besides "no lines were found".
>
> 3. Other regex libraries might need similar treatment. Probably
> pcre2match() needs it. It doesn't look like regexec() can ever
> return an error besides REG_NOMATCH.
>
> -Peff
Some replies to the thread in general, didn't want to spread this out
into different replies.
* Yes this sucks.
* Just emitting a warning without an appropriate exit code would suck
more, would break batch jobs & whatnot that expcept certain results
from grep.
* As you point out it would be nice to print out the file name we
didn't match on, we'd need to pass the grep_source struct down
further, it goes as far as grep_source_1 but stops there and isn't
passed to e.g. look_ahead(), which calls patmatch() which calls the
engine-specific matcher and would need to report the error. We could
just do this, would slow down things a bit (probably trivally) but we
could emit better error messages in genreal.
* You can adjust these limts in PCRE in Git, although it doesn't help
in this case, you just add (*LIMIT_MATCH=NUM) or
(*LIMIT_RECURSION=NUM) (or both) to the start of the pattern. See
pcresyntax(3) or pcre2syntax(3) man pages depending on what version
you have installed.
* While regexec() won't return an error its version of dealing with
this is (at least under glibc) to balloon CPU/memory use until the
OOMkiller kills git (although not on this particular pattern).
