fix: prefer plain error collection to Nokogiri_error_raise

Related to #1610

Author: flavorjones

ext/nokogiri/xml_xpath_context.c

@@ -326,6 +326,7 @@ evaluate(int argc, VALUE *argv, VALUE self)
   xmlXPathContextPtr ctx;
   xmlXPathObjectPtr xpath;
   xmlChar *query;
+  VALUE errors = rb_ary_new();
 
   Data_Get_Struct(self, xmlXPathContext, ctx);
 
@@ -341,13 +342,7 @@ evaluate(int argc, VALUE *argv, VALUE self)
     xmlXPathRegisterFuncLookup(ctx, lookup, (void *)xpath_handler);
   }
 
-  xmlResetLastError();
-#ifdef TRUFFLERUBY_NOKOGIRI_SYSTEM_LIBRARIES
-  VALUE errors = rb_ary_new();
-  xmlSetStructuredErrorFunc(errors, Nokogiri_error_array_pusher);
-#else
-  xmlSetStructuredErrorFunc(NULL, Nokogiri_error_raise);
-#endif
+  xmlSetStructuredErrorFunc((void*)errors, Nokogiri_error_array_pusher);
 
   /* For some reason, xmlXPathEvalExpression will blow up with a generic error */
   /* when there is a non existent function. */
@@ -357,15 +352,8 @@ evaluate(int argc, VALUE *argv, VALUE self)
   xmlSetStructuredErrorFunc(NULL, NULL);
   xmlSetGenericErrorFunc(NULL, NULL);
 
-#ifdef TRUFFLERUBY_NOKOGIRI_SYSTEM_LIBRARIES
-  if (RARRAY_LEN(errors) > 0) {
-    rb_exc_raise(rb_ary_entry(errors, 0));
-  }
-#endif
-
   if (xpath == NULL) {
-    xmlErrorPtr error = xmlGetLastError();
-    rb_exc_raise(Nokogiri_wrap_xml_syntax_error(error));
+    rb_exc_raise(rb_ary_entry(errors, 0));
   }
 
   retval = xpath2ruby(xpath, ctx);

test/xml/test_document.rb

@@ -498,7 +498,10 @@ def test_namespace_should_not_exist
         end
 
         def test_non_existent_function
-          # TODO: we should not be raising different types on the different engines
+          # TODO: we should not be raising different types on the different engines. this happens
+          # because xpath_generic_exception_handler raises directly (and see #1610 for the dangers
+          # of that). we should either squash that exception (and rely on the structured errors) or
+          # we should create a SyntaxError from it and append it to the same errors array.
           e_class = Nokogiri.uses_libxml? ? RuntimeError : Nokogiri::XML::XPath::SyntaxError
 
           e = assert_raises(e_class) do