(svn r21986) -Codechange: Add helper function to test whether an engine is still associated to a GRF.

src/engine.cpp

@@ -144,6 +144,15 @@ Engine::~Engine()
 	free(this->name);
 }
 
+/**
+ * Checks whether the engine spec is properly initialised.
+ * @return true if enabled
+ */
+bool Engine::IsEnabled() const
+{
+	return this->info.string_id != STR_NEWGRF_INVALID_ENGINE;
+}
+
 /**
  * Determines whether an engine can carry something.
  * A vehicle cannot carry anything if its capacity is zero, or none of the possible cargos is available in the climate.
@@ -935,7 +944,7 @@ bool IsEngineBuildable(EngineID engine, VehicleType type, CompanyID company)
 	/* check if it's available */
 	if (!HasBit(e->company_avail, company)) return false;
 
-	if (e->info.string_id == STR_NEWGRF_INVALID_ENGINE) return false;
+	if (!e->IsEnabled()) return false;
 
 	if (type == VEH_TRAIN) {
 		/* Check if the rail type is available to this company */

src/engine_base.h

@@ -61,6 +61,7 @@ struct Engine : EnginePool::PoolItem<&_engine_pool> {
 	Engine();
 	Engine(VehicleType type, EngineID base);
 	~Engine();
+	bool IsEnabled() const;
 
 	/**
 	 * Determines the default cargo type of an engine.

src/strings.cpp

@@ -1110,7 +1110,7 @@ static char *FormatString(char *buff, const char *str_arg, int64 *argv, const in
 
 				assert(e != NULL);
 
-				if (e->name != NULL && e->info.string_id != STR_NEWGRF_INVALID_ENGINE) {
+				if (e->name != NULL && e->IsEnabled()) {
 					buff = strecpy(buff, e->name, last);
 				} else {
 					buff = GetStringWithArgs(buff, e->info.string_id, NULL, NULL, last);