configure.ac: find include path to libxml2 using xml2-config tool

This patch replaces the hard-coded `-I /usr/include/libxml2` used when
building clixon_util_regexp with the output from `xml2-config --cflags`.

To support cross-compiling, and preserve backwards compatibility with
the `--with-libxml2` option, we allow the user to pass the path to the
xml2-config tool as an optional argument.  Similar to what python-lxml,
and other packages, that rely on libxml2 do.  The argument is optional
to ensure that we default to use the hard-coded path from before.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

configure

@@ -638,6 +638,7 @@ YANG_STANDARD_DIR
 YANG_INSTALLDIR
 CLIXON_YANG_SCHEMA_MOUNT
 CLIXON_YANG_PATCH
+LIBXML2_CFLAGS
 with_libxml2
 HAVE_HTTP1
 HAVE_LIBNGHTTP2
@@ -1398,7 +1399,8 @@ Optional Packages:
                           Directory of generated YANG specs (default:
                           $prefix/share/mib-yangs)
   --with-configfile=FILE  Set default path to config file
-  --with-libxml2          Use gnome/libxml2 regex engine
+  --with-libxml2[=/path/to/xml2-config]
+                          Use libxml2 regex engine
   --without-sigaction     Don't use sigaction
   --with-yang-installdir=DIR
                           Install Clixon yang files here (default:
@@ -5657,6 +5659,16 @@ fi
 
 if test "${with_libxml2}"; then
    # Find libxml2 lib
+   if test -x "${with_libxml2}" 2>/dev/null; then
+      { $as_echo "$as_me:${as_lineno-$LINENO}: checking for libxml2 header files and libs" >&5
+$as_echo_n "checking for libxml2 header files and libs... " >&6; }
+      LIBXML2_CFLAGS="`${with_libxml2} --cflags`"
+      LIBS="$LIBS `${with_libxml2} --libs`"
+      { $as_echo "$as_me:${as_lineno-$LINENO}: result: $LIBXML2_CFLAGS" >&5
+$as_echo "$LIBXML2_CFLAGS" >&6; }
+   else
+      LIBXML2_CFLAGS="-I/usr/include/libxml2"
+   fi
    { $as_echo "$as_me:${as_lineno-$LINENO}: checking for xmlRegexpCompile in -lxml2" >&5
 $as_echo_n "checking for xmlRegexpCompile in -lxml2... " >&6; }
 if ${ac_cv_lib_xml2_xmlRegexpCompile+:} false; then :
@@ -5731,7 +5743,7 @@ else
 fi
 
 
-if test "x${with_sigaction}" == "xyes"; then
+if test "x${with_sigaction}" = "xyes"; then
    for ac_func in sigaction
 do :
   ac_fn_c_check_func "$LINENO" "sigaction" "ac_cv_func_sigaction"

configure.ac

@@ -119,6 +119,7 @@ AC_SUBST(enable_netsnmp) # Enable build of apps/snmp
 AC_SUBST(HAVE_LIBNGHTTP2,false) # consider using neutral constant such as with-http2
 AC_SUBST(HAVE_HTTP1,false)
 AC_SUBST(with_libxml2)
+AC_SUBST(LIBXML2_CFLAGS)
 AC_SUBST(CLIXON_YANG_PATCH)
 AC_SUBST(CLIXON_YANG_SCHEMA_MOUNT)
 # Where Clixon installs its YANG specs
@@ -344,9 +345,17 @@ AC_CHECK_LIB(dl, dlopen)
 # Note this only enables the compiling of the code. In order to actually
 # use it you need to set Clixon config option CLICON_YANG_REGEXP to libxml2
 AC_ARG_WITH([libxml2],
-	[AS_HELP_STRING([--with-libxml2],[Use gnome/libxml2 regex engine])])
+	[AS_HELP_STRING([--with-libxml2[[=/path/to/xml2-config]]],[Use libxml2 regex engine])])
 if test "${with_libxml2}"; then
    # Find libxml2 lib
+   if test -x "${with_libxml2}" 2>/dev/null; then
+      AC_MSG_CHECKING([for libxml2 header files and libs])
+      LIBXML2_CFLAGS="`${with_libxml2} --cflags`"
+      LIBS="$LIBS `${with_libxml2} --libs`"
+      AC_MSG_RESULT([$LIBXML2_CFLAGS])
+   else
+      LIBXML2_CFLAGS="-I/usr/include/libxml2"
+   fi
    AC_CHECK_LIB(xml2, xmlRegexpCompile,[], AC_MSG_ERROR([libxml2 not found]))
 fi 
 

util/Makefile.in

@@ -46,7 +46,7 @@ localstatedir	= @localstatedir@
 sysconfdir	= @sysconfdir@
 HOST_VENDOR     = @host_vendor@
 with_restconf	= @with_restconf@
-HAVE_LIBXML2	= @HAVE_LIBXML2@
+LIBXML2_CFLAGS  = @LIBXML2_CFLAGS@
 
 SH_SUFFIX	= @SH_SUFFIX@
 
@@ -150,7 +150,7 @@ clixon_util_xml_mod: clixon_util_xml_mod.c $(LIBDEPS)
 	$(CC) $(INCLUDES) $(CPPFLAGS) $(CFLAGS) -D__PROGRAM__=\"$@\" $(LDFLAGS) $^ $(LIBS) -o $@
 
 clixon_util_regexp: clixon_util_regexp.c $(LIBDEPS)
-	$(CC) $(INCLUDES) -I /usr/include/libxml2 $(CPPFLAGS) -D__PROGRAM__=\"$@\" $(CFLAGS) $(LDFLAGS) $^ $(LIBS) -o $@
+	$(CC) $(INCLUDES) $(LIBXML2_CFLAGS) $(CPPFLAGS) -D__PROGRAM__=\"$@\" $(CFLAGS) $(LDFLAGS) $^ $(LIBS) -o $@
 
 clixon_util_socket: clixon_util_socket.c $(LIBDEPS)
 	$(CC) $(INCLUDES) $(CPPFLAGS) $(CFLAGS) -D__PROGRAM__=\"$@\" $(LDFLAGS) $^ $(LIBS) -o $@