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 <ava...@gmail.com>
---
 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

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