grep: fix multibyte regex handling under macOS

The commit 29de20504e (Makefile: fix default regex settings on
Darwin, 2013-05-11) fixed t0070-fundamental.sh under Darwin (macOS) by
adopting Git's regex library.  However, this library is compiled with
NO_MBSUPPORT, which causes git-grep to work incorrectly on multibyte
(e.g. UTF-8) files.  Current macOS versions pass t0070-fundamental.sh
with the native macOS regex library, which also supports multibyte
characters.

Adjust the Makefile to use the native regex library, and call
setlocale(3) to set CTYPE according to the user's preference.
The setlocale call is required on all platforms, but in platforms
supporting gettext(3), setlocale was called as a side-effect of
initializing gettext.  Therefore, move the CTYPE setlocale call from
gettext.c to common-main.c and the corresponding locale.h include
into git-compat-util.h.

Thanks to the global initialization of CTYPE setlocale, the test-tool
regex command now works correctly with supported multibyte regexes, and
is used to set the MB_REGEX test prerequisite by assessing a platform's
support for them.

Signed-off-by: Diomidis Spinellis <dds@aueb.gr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -1434,7 +1434,6 @@ ifeq ($(uname_S),Darwin)
 		APPLE_COMMON_CRYPTO = YesPlease
 		COMPAT_CFLAGS += -DAPPLE_COMMON_CRYPTO
 	endif
-	NO_REGEX = YesPlease
 	PTHREAD_LIBS =
 endif
 
@@ -2979,6 +2978,7 @@ GIT-BUILD-OPTIONS: FORCE
 	@echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@+
 	@echo NO_PTHREADS=\''$(subst ','\'',$(subst ','\'',$(NO_PTHREADS)))'\' >>$@+
 	@echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@+
+	@echo NO_REGEX=\''$(subst ','\'',$(subst ','\'',$(NO_REGEX)))'\' >>$@+
 	@echo NO_UNIX_SOCKETS=\''$(subst ','\'',$(subst ','\'',$(NO_UNIX_SOCKETS)))'\' >>$@+
 	@echo PAGER_ENV=\''$(subst ','\'',$(subst ','\'',$(PAGER_ENV)))'\' >>$@+
 	@echo DC_SHA1=\''$(subst ','\'',$(subst ','\'',$(DC_SHA1)))'\' >>$@+

common-main.c

@@ -40,6 +40,7 @@ int main(int argc, const char **argv)
 
 	git_resolve_executable_dir(argv[0]);
 
+	setlocale(LC_CTYPE, "");
 	git_setup_gettext();
 
 	initialize_the_repository();

gettext.c

@@ -10,7 +10,6 @@
 #include "config.h"
 
 #ifndef NO_GETTEXT
-#	include <locale.h>
 #	include <libintl.h>
 #	ifdef GIT_WINDOWS_NATIVE
 
@@ -80,7 +79,6 @@ static int test_vsnprintf(const char *fmt, ...)
 
 static void init_gettext_charset(const char *domain)
 {
-	setlocale(LC_CTYPE, "");
 	charset = locale_charset();
 	bind_textdomain_codeset(domain, charset);
 

git-compat-util.h

@@ -215,6 +215,7 @@ struct strbuf;
 #endif
 #include <errno.h>
 #include <limits.h>
+#include <locale.h>
 #ifdef NEEDS_SYS_PARAM_H
 #include <sys/param.h>
 #endif

t/t7810-grep.sh

@@ -18,6 +18,9 @@ test_invalid_grep_expression() {
 	'
 }
 
+LC_ALL=en_US.UTF-8 test-tool regex '^.$' '¿' &&
+  test_set_prereq MB_REGEX
+
 cat >hello.c <<EOF
 #include <assert.h>
 #include <stdio.h>
@@ -88,6 +91,10 @@ test_expect_success setup '
 		echo unusual >"\"unusual\" pathname" &&
 		echo unusual >"t/nested \"unusual\" pathname"
 	fi &&
+	if test_have_prereq MB_REGEX
+	then
+		echo "¿" >reverse-question-mark
+	fi &&
 	git add . &&
 	test_tick &&
 	git commit -m initial
@@ -569,6 +576,14 @@ do
 	'
 done
 
+test_expect_success MB_REGEX 'grep exactly one char in single-char multibyte file' '
+	LC_ALL=en_US.UTF-8 git grep "^.$" reverse-question-mark
+'
+
+test_expect_success MB_REGEX 'grep two chars in single-char multibyte file' '
+	LC_ALL=en_US.UTF-8 test_expect_code 1 git grep ".." reverse-question-mark
+'
+
 cat >expected <<EOF
 file
 EOF