Fix compilation with libxml2 2.12.0 (#417)

Fixes #418

Author: KNnut

NEWS.md

@@ -1,5 +1,7 @@
 # xml2 (development version)
 
+* Now compatible with limxml2 2.12.0 and later (@KNnut).
+
 * Fix format string issues detected in R-devel.
 
 * `xml_serialize()` now includes the document type so that `xml_unserialize()` works also for HTML documents (#407, @HenrikBengtsson).

src/xml2_init.cpp

@@ -10,7 +10,18 @@
 #include <string>
 #include "xml2_utils.h"
 
+/* * *
+ * Author: Nick Wellnhofer <wellnhofer@aevum.de>
+ * Date:   Tue, 24 Oct 2023 15:02:36 +0200
+ * https://github.com/GNOME/libxml2/commit/61034116d0a3c8b295c6137956adc3ae55720711
+ *
+ * error: Make more xmlError structs constant
+ */
+#if defined(LIBXML_VERSION) && (LIBXML_VERSION >= 21200)
+void handleStructuredError(void* userData, const xmlError* error) {
+#else
 void handleStructuredError(void* userData, xmlError* error) {
+#endif
 
   BEGIN_CPP
   std::string message = std::string(error->message);

src/xml2_schema.cpp

@@ -9,7 +9,18 @@
 #include "xml2_types.h"
 #include "xml2_utils.h"
 
+/* * *
+ * Author: Nick Wellnhofer <wellnhofer@aevum.de>
+ * Date:   Tue, 24 Oct 2023 15:02:36 +0200
+ * https://github.com/GNOME/libxml2/commit/61034116d0a3c8b295c6137956adc3ae55720711
+ *
+ * error: Make more xmlError structs constant
+ */
+#if defined(LIBXML_VERSION) && (LIBXML_VERSION >= 21200)
+void handleSchemaError(void* userData, const xmlError* error) {
+#else
 void handleSchemaError(void* userData, xmlError* error) {
+#endif
   std::vector<std::string> * vec = (std::vector<std::string> *) userData;
   std::string message = std::string(error->message);
   message.resize(message.size() - 1);
@@ -22,8 +33,6 @@ extern "C" SEXP doc_validate(SEXP doc_sxp, SEXP schema_sxp) {
   XPtrDoc doc(doc_sxp);
   XPtrDoc schema(schema_sxp);
 
-  xmlLineNumbersDefault(1);
-
   BEGIN_CPP
 
   std::vector<std::string> vec;