configure: Check for libpcre

This patch adds checks for libpcre to configure. By default libpcre is
disabled, --with-libpcre enables it (if it works).

Signed-off-by: Michał Kiedrowicz <michal.kiedrowicz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.mak.in

@@ -61,6 +61,7 @@ NO_INET_PTON=@NO_INET_PTON@
 NO_ICONV=@NO_ICONV@
 OLD_ICONV=@OLD_ICONV@
 NO_REGEX=@NO_REGEX@
+USE_LIBPCRE=@USE_LIBPCRE@
 NO_DEFLATE_BOUND=@NO_DEFLATE_BOUND@
 INLINE=@INLINE@
 SOCKLEN_T=@SOCKLEN_T@

configure.ac

@@ -220,6 +220,27 @@ AS_HELP_STRING([--with-openssl],[use OpenSSL library (default is YES)])
 AS_HELP_STRING([],              [ARG can be prefix for openssl library and headers]),\
 GIT_PARSE_WITH(openssl))
 #
+# Define USE_LIBPCRE if you have and want to use libpcre. git-grep will be
+# able to use Perl-compatible regular expressions.
+#
+# Define LIBPCREDIR=/foo/bar if your libpcre header and library files are in
+# /foo/bar/include and /foo/bar/lib directories.
+#
+AC_ARG_WITH(libpcre,
+AS_HELP_STRING([--with-libpcre],[support Perl-compatible regexes (default is NO)])
+AS_HELP_STRING([],           [ARG can be also prefix for libpcre library and headers]),
+if test "$withval" = "no"; then \
+	USE_LIBPCRE=; \
+elif test "$withval" = "yes"; then \
+	USE_LIBPCRE=YesPlease; \
+else
+	USE_LIBPCRE=YesPlease; \
+	LIBPCREDIR=$withval; \
+	AC_MSG_NOTICE([Setting LIBPCREDIR to $withval]); \
+	GIT_CONF_APPEND_LINE(LIBPCREDIR=$withval); \
+fi \
+)
+#
 # Define NO_CURL if you do not have curl installed.  git-http-pull and
 # git-http-push are not built, and you cannot use http:// and https://
 # transports.
@@ -434,6 +455,25 @@ GIT_UNSTASH_FLAGS($OPENSSLDIR)
 AC_SUBST(NEEDS_SSL_WITH_CRYPTO)
 AC_SUBST(NO_OPENSSL)
 
+#
+# Define USE_LIBPCRE if you have and want to use libpcre. git-grep will be
+# able to use Perl-compatible regular expressions.
+#
+
+if test -n "$USE_LIBPCRE"; then
+
+GIT_STASH_FLAGS($LIBPCREDIR)
+
+AC_CHECK_LIB([pcre], [pcre_version],
+[USE_LIBPCRE=YesPlease],
+[USE_LIBPCRE=])
+
+GIT_UNSTASH_FLAGS($LIBPCREDIR)
+
+AC_SUBST(USE_LIBPCRE)
+
+fi
+
 #
 # Define NO_CURL if you do not have libcurl installed.  git-http-pull and
 # git-http-push are not built, and you cannot use http:// and https://