grep/pcre2: better support invalid UTF-8 haystacks

Improve the support for invalid UTF-8 haystacks given a non-ASCII
needle when using the PCREv2 backend.

This is a more complete fix for a bug I started to fix in
870eea8166 (grep: do not enter PCRE2_UTF mode on fixed matching,
2019-07-26), now that PCREv2 has the PCRE2_MATCH_INVALID_UTF mode we
can make use of it.

This fixes the sort of case described in 8a5999838e (grep: stess test
PCRE v2 on invalid UTF-8 data, 2019-07-26), i.e.:

    - The subject string is non-ASCII (e.g. "ævar")
    - We're under a is_utf8_locale(), e.g. "en_US.UTF-8", not "C"
    - We are using --ignore-case, or we're a non-fixed pattern

If those conditions were satisfied and we matched found non-valid
UTF-8 data PCREv2 might bark on it, in practice this only happened
under the JIT backend (turned on by default on most platforms).

Ultimately this fixes a "regression" in b65abcafc7 ("grep: use PCRE v2
for optimized fixed-string search", 2019-07-01), I'm putting that in
scare-quotes because before then we wouldn't properly support these
complex case-folding, locale etc. cases either, it just broke in
different ways.

There was a bug related to this the PCRE2_NO_START_OPTIMIZE flag fixed
in PCREv2 10.36. It can be worked around by setting the
PCRE2_NO_START_OPTIMIZE flag. Let's do that in those cases, and add
tests for the bug.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/grep.c b/grep.c
index efeb6dc58d..ad0af66a26 100644
--- a/grep.c
+++ b/grep.c
@@ -492,7 +492,23 @@ static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt
 	}
 	if (!opt->ignore_locale && is_utf8_locale() && has_non_ascii(p->pattern) &&
 	    !(!opt->ignore_case && (p->fixed || p->is_fixed)))
-		options |= PCRE2_UTF;
+		options |= (PCRE2_UTF | PCRE2_MATCH_INVALID_UTF);
+
+	/* Work around https://bugs.exim.org/show_bug.cgi?id=2642 fixed in 10.36 */
+	if (PCRE2_MATCH_INVALID_UTF && options & (PCRE2_UTF | PCRE2_CASELESS)) {
+		struct strbuf buf;
+		int len;
+		int err;
+
+		if ((len = pcre2_config(PCRE2_CONFIG_VERSION, NULL)) < 0)
+			BUG("pcre2_config(..., NULL) failed: %d", len);
+		strbuf_init(&buf, len + 1);
+		if ((err = pcre2_config(PCRE2_CONFIG_VERSION, buf.buf)) < 0)
+			BUG("pcre2_config(..., buf.buf) failed: %d", err);
+		if (versioncmp(buf.buf, "10.36") < 0)
+			options |= PCRE2_NO_START_OPTIMIZE;
+		strbuf_release(&buf);
+	}
 
 	p->pcre2_pattern = pcre2_compile((PCRE2_SPTR)p->pattern,
 					 p->patternlen, options, &error, &erroffset,