add preprocess_string method and use preprocessed loyal trait

src/editor/map/map_context.cpp

@@ -732,7 +732,7 @@ config map_context::to_config()
 	// [unit]s
 	config traits;
 	preproc_map traits_map;
-	read(traits, *(preprocess_file(game_config::path+"/data/core/macros/traits.cfg", &traits_map)));
+	read(traits, *(preprocess_file(game_config::path + "/data/core/macros/traits.cfg", &traits_map)));
 
 	for(const auto& unit : units_) {
 		config& u = event.add_child("unit");
@@ -756,10 +756,11 @@ config map_context::to_config()
 			u["unrenamable"] = unit.unrenamable();
 		}
 
+		config& mods = u.add_child("modifications");
 		if(unit.loyal()) {
 			config trait_loyal;
-			read(trait_loyal, traits_map["TRAIT_LOYAL"].value);
-			u.append(trait_loyal);
+			read(trait_loyal, preprocess_string("{TRAIT_LOYAL}", &traits_map, "wesnoth-editor"));
+			mods.append(trait_loyal);
 		}
 		//TODO this entire block could also be replaced by unit.write(u, true)
 		//however, the resultant config is massive and contains many attributes we don't need.

src/serialization/preprocessor.cpp

@@ -1747,6 +1747,31 @@ filesystem::scoped_istream preprocess_file(const std::string& fname, preproc_map
 	return filesystem::scoped_istream(new preprocessor_scope_helper(fname, defines));
 }
 
+std::string preprocess_string(const std::string& contents, preproc_map* defines, const std::string& textdomain)
+{
+	log_scope("preprocessing string " + contents.substr(0, 10) + " ...");
+
+	std::unique_ptr<preprocessor_streambuf> buf;
+	std::unique_ptr<preproc_map> local_defines;
+
+	//
+	// If no defines were provided, we create a new local preproc_map and assign
+	// it to defines temporarily. In this case, the map will be deleted once this
+	// object is destroyed and defines will still be subsequently null.
+	//
+	if(!defines) {
+		local_defines.reset(new preproc_map);
+		defines = local_defines.get();
+	}
+
+	buf.reset(new preprocessor_streambuf(defines));
+
+	// Begin processing.
+	buf->add_preprocessor<preprocessor_data>(
+		std::unique_ptr<std::istream>(new std::istringstream(contents)), "<string>", "", 1, game_config::path, textdomain, nullptr);
+	return formatter() << buf.get();
+}
+
 void preprocess_resource(const std::string& res_name,
 		preproc_map* defines_map,
 		bool write_cfg,

src/serialization/preprocessor.hpp

@@ -143,8 +143,24 @@ std::ostream& operator<<(std::ostream& stream, const preproc_map::value_type& de
  */
 filesystem::scoped_istream preprocess_file(const std::string& fname, preproc_map* defines = nullptr);
 
-void preprocess_resource(const std::string& res_name,
-		preproc_map* defines_map,
-		bool write_cfg = false,
-		bool write_plain_cfg = false,
-		const std::string& target_directory = "");
+/**
+ * Function to use the WML preprocessor on a string.
+ *
+ * @param defines                 A map of symbols defined.
+ * @param contents                The string to be preprocessed.
+ * @param textdomain              The textdomain to associate the contents.
+ *                                Default: wesnoth
+ *
+ * @returns                       The resulting preprocessed string.
+ */
+std::string preprocess_string(
+	const std::string& contents,
+	preproc_map* defines,
+	const std::string& textdomain = "wesnoth");
+
+void preprocess_resource(
+	const std::string& res_name,
+	preproc_map* defines_map,
+	bool write_cfg = false,
+	bool write_plain_cfg = false,
+	const std::string& target_directory = "");