create function to get OSM type (#834)

Author: etienneJr

docs/CONFIGURATION.md

@@ -160,6 +160,7 @@ To do that, you use these methods:
 * `Attribute(key,value,minzoom)`: add an attribute to the most recently written layer. Argument `minzoom` is optional, use it if you do not want to write the attribute on lower zoom levels.
 * `AttributeNumeric(key,value,minzoom)`, `AttributeInteger(key,value,minzoom)`, `AttributeBoolean(key,value,minzoom)`: for numeric (floating-point), integer and boolean columns.
 * `Id()`: get the OSM ID of the current object.
+* `OsmType()`: get the OSM type of the current object.
 * `IsClosed()`: returns true if the current object is a closed area.
 * `IsMultiPolygon()`: returns true if the current object is a multipolygon.
 * `ZOrder(number)`: Set a numeric value (default 0) used to sort features within a layer. Use this feature to ensure a proper rendering order if the rendering engine itself does not support sorting. Sorting is not supported across layers merged with `write_to`. Features with different z-order are not merged if `combine_below` or `combine_polygons_below` is used. Use this in conjunction with `feature_limit` to only write the most important (highest z-order) features within a tile. (Values can be -50,000,000 to 50,000,000 and are lossy, particularly beyond -1000 to 1000.)

include/osm_lua_processing.h

@@ -115,6 +115,9 @@ class OsmLuaProcessing {
 	// Get the ID of the current object
 	std::string Id() const;
 
+	// Get the Type of the current object
+	std::string OsmType() const;
+
 	// Gets a table of all the keys of the OSM tags
 	kaguya::LuaTable AllKeys(kaguya::State& luaState);
 

src/osm_lua_processing.cpp

@@ -141,6 +141,7 @@ kaguya::LuaTable getAllTags(kaguya::State& luaState, const boost::container::fla
 }
 
 std::string rawId() { return osmLuaProcessing->Id(); }
+std::string rawOsmType() { return osmLuaProcessing->OsmType(); }
 kaguya::LuaTable rawAllKeys() {
 	if (osmLuaProcessing->isPostScanRelation) {
 		return osmLuaProcessing->AllKeys(*g_luaState);
@@ -247,6 +248,7 @@ OsmLuaProcessing::OsmLuaProcessing(
 
 	osmLuaProcessing = this;
 	luaState["Id"] = &rawId;
+	luaState["OsmType"] = &rawOsmType;
 	luaState["AllKeys"] = &rawAllKeys;
 	luaState["AllTags"] = &rawAllTags;
 	luaState["Holds"] = &rawHolds;
@@ -360,6 +362,11 @@ string OsmLuaProcessing::Id() const {
 	return to_string(originalOsmID);
 }
 
+// Get the Type of the current object
+string OsmLuaProcessing::OsmType() const {
+	return (isRelation ? "relation" : isWay ? "way" : "node");
+}
+
 // Gets a table of all the keys of the OSM tags
 kaguya::LuaTable OsmLuaProcessing::AllKeys(kaguya::State& luaState) {
 	// NOTE: this is only called in the PostScanRelation phase -- other phases are handled in rawAllKeys