grep/pcre: support utf-8

In the previous change in this function, we add locale support for
single-byte encodings only. It looks like pcre only supports utf-* as
multibyte encodings, the others are left in the cold (which is
fine).

We need to enable PCRE_UTF8 so pcre can find character boundary
correctly. It's needed for case folding (when --ignore-case is used)
or '*', '+' or similar syntax is used.

The "has_non_ascii()" check is to be on the conservative side. If
there's non-ascii in the pattern, the searched content could still be
in utf-8, but we can treat it just like a byte stream and everything
should work. If we force utf-8 based on locale only and pcre validates
utf-8 and the file content is in non-utf8 encoding, things break.

Noticed-by: Plamen Totev <plamen.totev@abv.bg>
Helped-by: Plamen Totev <plamen.totev@abv.bg>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

grep.c

@@ -329,6 +329,8 @@ static void compile_pcre_regexp(struct grep_pat *p, const struct grep_opt *opt)
 			p->pcre_tables = pcre_maketables();
 		options |= PCRE_CASELESS;
 	}
+	if (is_utf8_locale() && has_non_ascii(p->pattern))
+		options |= PCRE_UTF8;
 
 	p->pcre_regexp = pcre_compile(p->pattern, options, &error, &erroffset,
 				      p->pcre_tables);

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

@@ -20,6 +20,21 @@ test_expect_success REGEX_LOCALE 'grep literal string, no -F' '
 	git grep -i "TILRAUN: HALLÓ HEIMUR!"
 '
 
+test_expect_success GETTEXT_LOCALE,LIBPCRE 'grep pcre utf-8 icase' '
+	git grep --perl-regexp    "TILRAUN: H.lló Heimur!" &&
+	git grep --perl-regexp -i "TILRAUN: H.lló Heimur!" &&
+	git grep --perl-regexp -i "TILRAUN: H.LLÓ HEIMUR!"
+'
+
+test_expect_success GETTEXT_LOCALE,LIBPCRE 'grep pcre utf-8 string with "+"' '
+	test_write_lines "TILRAUN: Hallóó Heimur!" >file2 &&
+	git add file2 &&
+	git grep -l --perl-regexp "TILRAUN: H.lló+ Heimur!" >actual &&
+	echo file >expected &&
+	echo file2 >>expected &&
+	test_cmp expected actual
+'
+
 test_expect_success REGEX_LOCALE 'grep literal string, with -F' '
 	git grep --debug -i -F "TILRAUN: Halló Heimur!"  2>&1 >/dev/null |
 		 grep fixed >debug1 &&