grep: do not enter PCRE2_UTF mode on fixed matching

As discussed in the last commit partially fix a bug introduced in
b65abca ("grep: use PCRE v2 for optimized fixed-string search",
2019-07-01). Because PCRE v2, unlike kwset, validates its UTF-8 input
we'd die on e.g.:

    fatal: pcre2_match failed with error code -22: UTF-8 error:
    isolated byte with 0x80 bit set

When grepping a non-ASCII fixed string. This is a more general problem
that's hard to fix, but we can at least fix the most common case of
grepping for a fixed string without "-i". I can't think of a reason
for why we'd turn on PCRE2_UTF when matching byte-for-byte like that.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

grep.c

@@ -472,7 +472,8 @@ static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt
 		}
 		options |= PCRE2_CASELESS;
 	}
-	if (!opt->ignore_locale && is_utf8_locale() && has_non_ascii(p->pattern))
+	if (!opt->ignore_locale && is_utf8_locale() && has_non_ascii(p->pattern) &&
+	    !(!opt->ignore_case && (p->fixed || p->is_fixed)))
 		options |= PCRE2_UTF;
 
 	p->pcre2_pattern = pcre2_compile((PCRE2_SPTR)p->pattern,

t/t7812-grep-icase-non-ascii.sh

@@ -68,9 +68,9 @@ test_expect_success GETTEXT_LOCALE,LIBPCRE2 'PCRE v2: grep ASCII from invalid UT
 '
 
 test_expect_success GETTEXT_LOCALE,LIBPCRE2 'PCRE v2: grep non-ASCII from invalid UTF-8 data' '
-	test_might_fail git grep -h "æ" invalid-0x80 >actual &&
+	git grep -h "æ" invalid-0x80 >actual &&
 	test_cmp expected actual &&
-	test_must_fail git grep -h "(*NO_JIT)æ" invalid-0x80 &&
+	git grep -h "(*NO_JIT)æ" invalid-0x80 &&
 	test_cmp expected actual
 '