dev: introduce NOKO_WARN_DEPRECATION macro

which will use rb_category_warning if it's available, and rb_warning
if it's not

Author: flavorjones

ext/nokogiri/extconf.rb

@@ -974,6 +974,7 @@ def compile
 have_func("xmlSchemaSetValidStructuredErrors") # introduced in libxml 2.6.23
 have_func("xmlSchemaSetParserStructuredErrors") # introduced in libxml 2.6.23
 have_func("rb_gc_location") # introduced in Ruby 2.7
+have_func("rb_category_warning") # introduced in Ruby 3.0
 
 have_func("vasprintf")
 

ext/nokogiri/nokogiri.h

@@ -202,6 +202,12 @@ NOKOPUBFUN VALUE Nokogiri_wrap_xml_document(VALUE klass,
 #define DISCARD_CONST_QUAL(t, v) ((t)(uintptr_t)(v))
 #define DISCARD_CONST_QUAL_XMLCHAR(v) DISCARD_CONST_QUAL(xmlChar *, v)
 
+#if HAVE_RB_CATEGORY_WARNING
+#  define NOKO_WARN_DEPRECATION(message) rb_category_warning(RB_WARN_CATEGORY_DEPRECATED, message)
+#else
+#  define NOKO_WARN_DEPRECATION(message) rb_warning(message)
+#endif
+
 void Nokogiri_structured_error_func_save(libxmlStructuredErrorHandlerState *handler_state);
 void Nokogiri_structured_error_func_save_and_set(libxmlStructuredErrorHandlerState *handler_state, void *user_data,
     xmlStructuredErrorFunc handler);

ext/nokogiri/xml_node.c

@@ -1806,7 +1806,7 @@ rb_xml_node_new(int argc, VALUE *argv, VALUE klass)
   }
   if (!rb_obj_is_kind_of(rb_document_node, cNokogiriXmlDocument)) {
     // TODO: deprecate allowing Node
-    rb_warn("Passing a Node as the second parameter to Node.new is deprecated. Please pass a Document instead, or prefer an alternative constructor like Node#add_child. This will become an error in a future release of Nokogiri.");
+    NOKO_WARN_DEPRECATION("Passing a Node as the second parameter to Node.new is deprecated. Please pass a Document instead, or prefer an alternative constructor like Node#add_child. This will become an error in a future release of Nokogiri.");
   }
   Noko_Node_Get_Struct(rb_document_node, xmlNode, c_document_node);