Factor the test for \0 in grep patterns into a function. Since commit
9eceddeec6 ("Use kwset in grep", 2011-08-21) any pattern containing a
\0 is considered fixed as regcomp() can't handle it.

This limitation was never documented, and other some regular
expression engines are capable of compiling a pattern containing a
\0. Factoring this out makes a subsequent change which does that
smaller.

See a previous commit in this series ("grep: add tests to fix blind
spots with \0 patterns", 2017-04-21) for further details & rationale.

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---
 grep.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/grep.c b/grep.c
index bf6c2494fd..27de615209 100644
--- a/grep.c
+++ b/grep.c

@@ -394,12 +394,6 @@ static int is_fixed(const char *s, size_t len)
 {
 	size_t i;
 
-	/* regcomp cannot accept patterns with NULs so we
-	 * consider any pattern containing a NUL fixed.
-	 */
-	if (memchr(s, 0, len))
-		return 1;
-
 	for (i = 0; i < len; i++) {
 		if (is_regex_special(s[i]))
 			return 0;

@@ -408,6 +402,17 @@ static int is_fixed(const char *s, size_t len)
 	return 1;
 }
 
+static int has_null(const char *s, size_t len)
+{
+	/* regcomp cannot accept patterns with NULs so when using it
+	 * we consider any pattern containing a NUL fixed.
+	 */

+	if (memchr(s, 0, len))
+		return 1;
+
+	return 0;
+}
+
 static void compile_fixed_regexp(struct grep_pat *p, struct grep_opt *opt)
 {
 	struct strbuf sb = STRBUF_INIT;

@@ -451,7 +456,7 @@ static void compile_regexp(struct grep_pat *p, struct grep_opt *opt)
 	 * simple string match using kws.  p->fixed tells us if we
 	 * want to use kws.
 	 */
-	if (opt->fixed || is_fixed(p->pattern, p->patternlen))
+	if (opt->fixed || has_null(p->pattern, p->patternlen) || is_fixed(p->pattern, p->patternlen))
 		p->fixed = !icase || ascii_only;
 	else
 		p->fixed = 0;

-- 
2.11.0