RestartRelations() to reset relation subscript (#548)

docs/RELATIONS.md

@@ -41,6 +41,8 @@ Now that you've accepted the relations, they will be available from `way_functio
       print ("Part of route "..way:FindInRelation("ref"))
     end
 
+(Should you need to re-read the relations, you can reset the iterator with `way:RestartRelations()`.)
+
 
 ### Writing relation geometries
 

include/osm_lua_processing.h

@@ -165,6 +165,7 @@ class OsmLuaProcessing {
 
 	// Relation scan support
 	kaguya::optional<int> NextRelation();
+	void RestartRelations();
 	std::string FindInRelation(const std::string &key);
 	void Accept();
 

src/osm_lua_processing.cpp

@@ -58,6 +58,7 @@ OsmLuaProcessing::OsmLuaProcessing(
 		.addOverloadedFunctions("ZOrder", &OsmLuaProcessing::ZOrder, &OsmLuaProcessing::ZOrderWithScale)
 		.addFunction("Accept", &OsmLuaProcessing::Accept)
 		.addFunction("NextRelation", &OsmLuaProcessing::NextRelation)
+		.addFunction("RestartRelations", &OsmLuaProcessing::RestartRelations)
 		.addFunction("FindInRelation", &OsmLuaProcessing::FindInRelation)
 	);
 	supportsRemappingShapefiles = !!luaState["attribute_function"];
@@ -525,6 +526,10 @@ kaguya::optional<int> OsmLuaProcessing::NextRelation() {
 	return relationList[relationSubscript];
 }
 
+void OsmLuaProcessing::RestartRelations() {
+	relationSubscript = -1;
+}
+
 std::string OsmLuaProcessing::FindInRelation(const std::string &key) {
 	return osmStore.get_relation_tag(relationList[relationSubscript], key);
 }