Implement sort-by clause parser <field-name>, [DESC | ASC] e.g "name DESC" (default to ASC)

include/mapnik/feature_style_processor_impl.hpp

@@ -427,7 +427,7 @@ void feature_style_processor<Processor>::prepare_layer(layer_rendering_material&
     auto sort_by = lay.sort_by();
     if (sort_by)
     {
-        q.add_property_name(*sort_by);
+        q.add_property_name((*sort_by).first);
     }
 
     bool cache_features = lay.cache_features() && active_styles.size() > 1;
@@ -502,7 +502,7 @@ void feature_style_processor<Processor>::render_material(layer_rendering_materia
             {
                 cache->push(feature);
             }
-            cache->sort_by(*sort_by, true);
+            cache->sort_by((*sort_by).first, (*sort_by).second);
             std::size_t i = 0;
             for (feature_type_style const* style : active_styles)
             {

include/mapnik/layer.hpp

@@ -27,10 +27,11 @@
 #include <mapnik/well_known_srs.hpp>
 #include <mapnik/geometry/box2d.hpp>
 #include <mapnik/image_compositing.hpp>
-
+#include <mapnik/util/sort_by.hpp>
 // stl
 #include <vector>
 #include <memory>
+#include <tuple>
 
 namespace mapnik {
 
@@ -194,12 +195,12 @@ class MAPNIK_DECL layer
     /*!
      * @param column Set the field rendering of this layer is sorted by.
      */
-    void set_sort_by(std::string const& column);
+    void set_sort_by(std::string const& column, bool desc = false);
 
     /*!
-     * @return optional field rendering of this layer is sorted by.
+     * @return optional field (+order) rendering of this layer is sorted by.
      */
-    std::optional<std::string> const& sort_by() const;
+    std::optional<sort_by_type> const& sort_by() const;
 
     /*!
      * @brief Attach a datasource for this layer.
@@ -242,7 +243,7 @@ class MAPNIK_DECL layer
     bool clear_label_cache_;
     bool cache_features_;
     std::string group_by_;
-    std::optional<std::string> sort_by_;
+    std::optional<sort_by_type> sort_by_;
     std::vector<std::string> styles_;
     std::vector<layer> layers_;
     datasource_ptr ds_;

include/mapnik/util/sort_by.hpp

@@ -0,0 +1,58 @@
+/*****************************************************************************
+ *
+ * This file is part of Mapnik (c++ mapping toolkit)
+ *
+ * Copyright (C) 2025 Artem Pavlenko
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ *****************************************************************************/
+
+
+#ifndef MAPNIK_SORT_BY_HPP
+#define MAPNIK_SORT_BY_HPP
+
+#include <boost/spirit/home/x3.hpp>
+#include <boost/fusion/include/std_pair.hpp>
+
+namespace mapnik {
+
+using sort_by_type = std::pair<std::string, bool>;
+
+inline bool parse_sort_by(std::string const& str, sort_by_type & result)
+{
+    namespace x3 = boost::spirit::x3;
+    auto itr = str.begin();
+    auto end = str.end();
+    auto apply_sort_by = [&](auto const& ctx) {
+        result.first = _attr(ctx);
+    };
+    auto apply_desc = [&](auto const& ctx) {
+        result.second = true;
+    };
+    if (!x3::phrase_parse(itr, end,
+                          x3::no_skip[(+x3::char_("a-zA-Z_0-9-"))][apply_sort_by]
+                          > -(x3::no_case[x3::lit("DESC")][apply_desc] | x3::no_case[x3::lit("ASC")]),
+                          // ASC is a default
+                          x3::space
+            ) || (itr != end))
+    {
+        return false;
+    }
+    return true;
+}
+
+} // namespace mapnik
+#endif //  MAPNIK_SORT_BY_HPP

src/layer.cpp

@@ -297,12 +297,12 @@ std::string const& layer::group_by() const
     return group_by_;
 }
 
-void layer::set_sort_by(std::string const& column)
+void layer::set_sort_by(std::string const& column, bool desc)
 {
-    sort_by_ = column;
+    sort_by_ = {column, desc};
 }
 
-std::optional<std::string> const& layer::sort_by() const
+std::optional<sort_by_type> const& layer::sort_by() const
 {
     return sort_by_;
 }

src/load_map.cpp

@@ -49,6 +49,7 @@
 #include <mapnik/util/dasharray_parser.hpp>
 #include <mapnik/util/conversions.hpp>
 #include <mapnik/util/trim.hpp>
+#include <mapnik/util/sort_by.hpp>
 #include <mapnik/marker_cache.hpp>
 #include <mapnik/util/noncopyable.hpp>
 #include <mapnik/util/fs.hpp>
@@ -751,10 +752,23 @@ void map_parser::parse_layer(Parent& parent, xml_node const& node)
             lyr.set_group_by(*group_by);
         }
 
-        optional<std::string> sort_by = node.get_opt_attr<std::string>("sort-by");
-        if (sort_by)
+        optional<std::string> str = node.get_opt_attr<std::string>("sort-by");
+        if (str)
         {
-            lyr.set_sort_by(*sort_by);
+            mapnik::sort_by_type result;
+            if (!mapnik::parse_sort_by(*str, result))
+            {
+                std::string s_err("failed to parse Layer sort-by clause \"" + *str + "\"");
+                if (strict_)
+                {
+                    throw config_error(s_err);
+                }
+                else
+                {
+                    MAPNIK_LOG_ERROR(load_map) << "map_parser: " << s_err;
+                }
+            }
+            lyr.set_sort_by(result.first, result.second);
         }
 
         optional<int> buffer_size = node.get_opt_attr<int>("buffer-size");

src/save_map.cpp

@@ -549,7 +549,11 @@ void serialize_layer(ptree& map_node, layer const& lyr, bool explicit_defaults)
 
     if (lyr.sort_by() || explicit_defaults)
     {
-        set_attr(layer_node, "sort-by", *lyr.sort_by());
+        auto sort_by = *lyr.sort_by();
+        std::string str = sort_by.first;
+        if (sort_by.second)
+            str += " DESC";
+        set_attr(layer_node, "sort-by", str);
     }
 
     auto&& buffer_size = lyr.buffer_size();